diff --git a/.gitpod.yml b/.gitpod.yml index 2b3561585..94441afa2 100644 --- a/.gitpod.yml +++ b/.gitpod.yml @@ -1,4 +1,7 @@ +ports: +- port: 27149 + visibility: public vscode: extensions: - - openstax.editor - - redhat.vscode-xml + - openstax.editor + - redhat.vscode-xml diff --git a/modules/m45417/index.cnxml b/modules/m45417/index.cnxml index 30c1045e0..3b43aa5ca 100644 --- a/modules/m45417/index.cnxml +++ b/modules/m45417/index.cnxml @@ -40,7 +40,7 @@ The age of remains that contain carbon and are less than about 50,000 years old, such as this pygmy mammoth, can be determined using carbon dating. (credit: Bill Faulkner/NPS) -To learn more about atoms and isotopes, and how you can tell one isotope from another, visit this site and run the simulation. +To learn more about atoms and isotopes, and how you can tell one isotope from another, visit this site and run the simulation.
Chemical Bonds diff --git a/modules/m45419/index.cnxml b/modules/m45419/index.cnxml index a8c5b4813..aee727a56 100644 --- a/modules/m45419/index.cnxml +++ b/modules/m45419/index.cnxml @@ -32,7 +32,7 @@ The leaves of this sensitive plant (Mimosa pudica) will instantly droop and fold when touched. After a few minutes, the plant returns to its normal state. (credit: Alex Lomas) - Watch this video to see how the sensitive plant responds to a touch stimulus.
+ Watch this video to see how the sensitive plant responds to a touch stimulus.
Reproduction @@ -75,7 +75,7 @@ The diversity of life on Earth is a result of mutations, or random changes in he A molecule, like this large DNA molecule, is composed of atoms. (credit: "Brian0918"/Wikimedia Commons) - To see an animation of this DNA molecule, click here.Some cells contain aggregates of macromolecules surrounded by membranes; these are called organelles. Organelles are small structures that exist within cells and perform specialized functions. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. (This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack a living cell; only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes are single-celled organisms that lack organelles surrounded by a membrane and do not have nuclei surrounded by nuclear membranes; in contrast, the cells of eukaryotes do have membrane-bound organelles and nuclei. + To see an animation of this DNA molecule, click here.Some cells contain aggregates of macromolecules surrounded by membranes; these are called organelles. Organelles are small structures that exist within cells and perform specialized functions. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. (This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack a living cell; only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes are single-celled organisms that lack organelles surrounded by a membrane and do not have nuclei surrounded by nuclear membranes; in contrast, the cells of eukaryotes do have membrane-bound organelles and nuclei. In most multicellular organisms, cells combine to make tissues, which are groups of similar cells carrying out the same function. Organs are collections of tissues grouped together based on a common function. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. For example vertebrate animals have many organ systems, such as the circulatory system that transports blood throughout the body and to and from the lungs; it includes organs such as the heart and blood vessels. Organisms are individual living entities. For example, each tree in a forest is an organism. Single-celled prokaryotes and single-celled eukaryotes are also considered organisms and are typically referred to as microorganisms. diff --git a/modules/m45425/index.cnxml b/modules/m45425/index.cnxml index 908f573e5..e189e26c8 100644 --- a/modules/m45425/index.cnxml +++ b/modules/m45425/index.cnxml @@ -27,7 +27,7 @@ (a) The lattice structure of ice makes it less dense than the freely flowing molecules of liquid water. Ice's lower density enables it to (b) float on water. (credit a: modification of work by Jane Whitney; credit b: modification of work by Carlos Ponte) -Click here to see a 3-D animation of the structure of an ice lattice.
+Click here to see a 3-D animation of the structure of an ice lattice.
Water Is an Excellent Solvent Because water is polar, with slight positive and negative charges, ionic compounds and polar molecules can readily dissolve in it. Water is, therefore, what is referred to as a solvent—a substance capable of dissolving another substance. The charged particles will form hydrogen bonds with a surrounding layer of water molecules. This is referred to as a sphere of hydration and serves to keep the particles separated or dispersed in the water. In the case of table salt (NaCl) mixed in water (), the sodium and chloride ions separate, or dissociate, in the water, and spheres of hydration are formed around the ions. A positively charged sodium ion is surrounded by the partially negative charges of oxygen atoms in water molecules. A negatively charged chloride ion is surrounded by the partially positive charges of hydrogen atoms in water molecules. These spheres of hydration are also referred to as hydration shells. The polarity of the water molecule makes it an effective solvent and is important in its many roles in living systems. @@ -43,7 +43,7 @@ Cohesive and adhesive forces are important for sustaining life. For example, because of these forces, water can flow up from the roots to the tops of plants to feed the plant. -To learn more about water, visit the U.S. Geological Survey Water Science for Schools: All About Water! website.
+To learn more about water, visit the U.S. Geological Survey Water Science for Schools: All About Water! website.
Buffers, pH, Acids, and Bases The pH of a solution is a measure of its acidity or bascicity. You have probably used litmus paper, paper that has been treated with a natural water-soluble dye so it can be used as a pH indicator, to test how much acid or base (basicity) exists in a solution. You might have even used some to make sure the water in an outdoor swimming pool is properly treated. In both cases, this pH test measures the amount of hydrogen ions that exists in a given solution. High concentrations of hydrogen ions yield a low pH, whereas low levels of hydrogen ions result in a high pH. The overall concentration of hydrogen ions is inversely related to its pH and can be measured on the pH scale (). Therefore, the more hydrogen ions present, the lower the pH; conversely, the fewer hydrogen ions, the higher the pH.The pH scale ranges from 0 to 14. A change of one unit on the pH scale represents a change in the concentration of hydrogen ions by a factor of 10, a change in two units represents a change in the concentration of hydrogen ions by a factor of 100. Thus, small changes in pH represent large changes in the concentrations of hydrogen ions. Pure water is neutral. It is neither acidic nor basic, and has a pH of 7.0. Anything below 7.0 (ranging from 0.0 to 6.9) is acidic, and anything above 7.0 (from 7.1 to 14.0) is alkaline. The blood in your veins is slightly alkaline (pH = 7.4). The environment in your stomach is highly acidic (pH = 1 to 2). Orange juice is mildly acidic (pH = approximately 3.5), whereas baking soda is basic (pH = 9.0).
diff --git a/modules/m45426/index.cnxml b/modules/m45426/index.cnxml index d113fc0c8..e1d8661e0 100644 --- a/modules/m45426/index.cnxml +++ b/modules/m45426/index.cnxml @@ -87,7 +87,7 @@ A fat molecule, such as a triglyceride, consists of Cholesterol is a steroid. Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol. It is also the precursor of vitamins E and K. Cholesterol is the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. It is a key component of the plasma membranes of animal cells. Waxes are made up of a hydrocarbon chain with an alcohol (–OH) group and a fatty acid. Examples of animal waxes include beeswax and lanolin. Plants also have waxes, such as the coating on their leaves, that helps prevent them from drying out. -For an additional perspective on lipids, watch this video about types of fat.
+For an additional perspective on lipids, watch this video about types of fat.
Proteins Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes. Each cell in a living system may contain thousands of different proteins, each with a unique function. Their structures, like their functions, vary greatly. They are all, however, polymers of amino acids, arranged in a linear sequence. @@ -120,7 +120,7 @@ The chemical nature of the R group determines the chemical nature of the amino a The four levels of protein structure can be observed in these illustrations. (credit: modification of work by National Human Genome Research Institute)Each protein has its own unique sequence and shape held together by chemical interactions. If the protein is subject to changes in temperature, pH, or exposure to chemicals, the protein structure may change, losing its shape in what is known as denaturation as discussed earlier. Denaturation is often reversible because the primary structure is preserved if the denaturing agent is removed, allowing the protein to resume its function. Sometimes denaturation is irreversible, leading to a loss of function. One example of protein denaturation can be seen when an egg is fried or boiled. The albumin protein in the liquid egg white is denatured when placed in a hot pan, changing from a clear substance to an opaque white substance. Not all proteins are denatured at high temperatures; for instance, bacteria that survive in hot springs have proteins that are adapted to function at those temperatures. -For an additional perspective on proteins, explore “Biomolecules: The Proteins” through this interactive animation.
+For an additional perspective on proteins, explore “Biomolecules: The Proteins” through this interactive animation.
Nucleic Acids diff --git a/modules/m45428/index.cnxml b/modules/m45428/index.cnxml index e07f325b7..4fa09009e 100644 --- a/modules/m45428/index.cnxml +++ b/modules/m45428/index.cnxml @@ -27,7 +27,7 @@ Light microscopes commonly used in the undergraduate college laboratory magnify up to approximately 400 times. Two parameters that are important in microscopy are magnification and resolving power. Magnification is the degree of enlargement of an object. Resolving power is the ability of a microscope to allow the eye to distinguish two adjacent structures as separate; the higher the resolution, the closer those two objects can be, and the better the clarity and detail of the image. When oil immersion lenses are used, magnification is usually increased to 1,000 times for the study of smaller cells, like most prokaryotic cells. Because light entering a specimen from below is focused onto the eye of an observer, the specimen can be viewed using light microscopy. For this reason, for light to pass through a specimen, the sample must be thin or translucent. -For another perspective on cell size, try the HowBig interactive. +For another perspective on cell size, try the HowBig interactive. A second type of microscope used in laboratories is the dissecting microscope (b). These microscopes have a lower magnification (20 to 80 times the object size) than light microscopes and can provide a three-dimensional view of the specimen. Thick objects can be examined with many components in focus at the same time. These microscopes are designed to give a magnified and clear view of tissue structure as well as the anatomy of the whole organism. Like light microscopes, most modern dissecting microscopes are also binocular, meaning that they have two separate lens systems, one for each eye. The lens systems are separated by a certain distance, and therefore provide a sense of depth in the view of their subject to make manipulations by hand easier. Dissecting microscopes also have optics that correct the image so that it appears as if being seen by the naked eye and not as an inverted image. The light illuminating a sample under a dissecting microscope typically comes from above the sample, but may also be directed from below.
diff --git a/modules/m45434/index.cnxml b/modules/m45434/index.cnxml index b9183bbe3..3edf55b42 100644 --- a/modules/m45434/index.cnxml +++ b/modules/m45434/index.cnxml @@ -37,7 +37,7 @@ -For an animation of the diffusion process in action, view this short video on cell membrane transport. +For an animation of the diffusion process in action, view this short video on cell membrane transport.
Facilitated transport @@ -54,7 +54,7 @@ A principle of diffusion is that the molecules move around and will spread evenly throughout the medium if they can. However, only the material capable of getting through the membrane will diffuse through it. In this example, the solute cannot diffuse through the membrane, but the water can. Water has a concentration gradient in this system. Therefore, water will diffuse down its concentration gradient, crossing the membrane to the side where it is less concentrated. This diffusion of water through the membrane—osmosis—will continue until the concentration gradient of water goes to zero. Osmosis proceeds constantly in living systems. -Watch this video that illustrates diffusion in hot versus cold solutions. +Watch this video that illustrates diffusion in hot versus cold solutions.
Tonicity diff --git a/modules/m45437/index.cnxml b/modules/m45437/index.cnxml index 6e982aaa4..2aee6c85c 100644 --- a/modules/m45437/index.cnxml +++ b/modules/m45437/index.cnxml @@ -64,7 +64,7 @@ Still water has potential energy; moving water, such as in a waterfall or a rapidly flowing river, has kinetic energy. (credit "dam": modification of work by "Pascal"/Flickr; credit "waterfall": modification of work by Frank Gualtieri)Potential energy is not only associated with the location of matter, but also with the structure of matter. Even a spring on the ground has potential energy if it is compressed; so does a rubber band that is pulled taut. On a molecular level, the bonds that hold the atoms of molecules together exist in a particular structure that has potential energy. Remember that anabolic cellular pathways require energy to synthesize complex molecules from simpler ones and catabolic pathways release energy when complex molecules are broken down. The fact that energy can be released by the breakdown of certain chemical bonds implies that those bonds have potential energy. In fact, there is potential energy stored within the bonds of all the food molecules we eat, which is eventually harnessed for use. This is because these bonds can release energy when broken. The type of potential energy that exists within chemical bonds, and is released when those bonds are broken, is called chemical energy. Chemical energy is responsible for providing living cells with energy from food. The release of energy occurs when the molecular bonds within food molecules are broken. -Visit the site and select “Pendulum” from the “Work and Energy” menu to see the shifting kinetic and potential energy of a pendulum in motion. +Visit the site and select “Pendulum” from the “Work and Energy” menu to see the shifting kinetic and potential energy of a pendulum in motion.
Free and Activation Energy @@ -80,7 +80,7 @@ -Watch an animation of the move from free energy to transition state of the reaction. +Watch an animation of the move from free energy to transition state of the reaction.
Enzymes @@ -93,7 +93,7 @@ For many years, scientists thought that enzyme-substrate binding took place in a simple “lock and key” fashion. This model asserted that the enzyme and substrate fit together perfectly in one instantaneous step. However, current research supports a model called induced fit (). The induced-fit model expands on the lock-and-key model by describing a more dynamic binding between enzyme and substrate. As the enzyme and substrate come together, their interaction causes a mild shift in the enzyme’s structure that forms an ideal binding arrangement between enzyme and substrate. -View an animation of induced fit. +View an animation of induced fit. When an enzyme binds its substrate, an enzyme-substrate complex is formed. This complex lowers the activation energy of the reaction and promotes its rapid progression in one of multiple possible ways. On a basic level, enzymes promote chemical reactions that involve more than one substrate by bringing the substrates together in an optimal orientation for reaction. Another way in which enzymes promote the reaction of their substrates is by creating an optimal environment within the active site for the reaction to occur. The chemical properties that emerge from the particular arrangement of amino acid R groups within an active site create the perfect environment for an enzyme’s specific substrates to react. The enzyme-substrate complex can also lower activation energy by compromising the bond structure so that it is easier to break. Finally, enzymes can also lower activation energies by taking part in the chemical reaction itself. In these cases, it is important to remember that the enzyme will always return to its original state by the completion of the reaction. One of the hallmark properties of enzymes is that they remain ultimately unchanged by the reactions they catalyze. After an enzyme has catalyzed a reaction, it releases its product(s) and can catalyze a new reaction.
diff --git a/modules/m45440/index.cnxml b/modules/m45440/index.cnxml index ffd431f59..5b99c01c8 100644 --- a/modules/m45440/index.cnxml +++ b/modules/m45440/index.cnxml @@ -16,7 +16,7 @@ In aerobic respiration, the final electron acceptor is an oxygen molecule, O2. If aerobic respiration occurs, then ATP will be produced using the energy of the high-energy electrons carried by NADH or FADH2 to the electron transport chain. If aerobic respiration does not occur, NADH must be reoxidized to NAD+ for reuse as an electron carrier for glycolysis to continue. How is this done? In some living systems the electron transport chain (ETC) use an organic molecule as the final electron acceptor. Processes that use an organic molecule to regenerate NAD+ from NADH are collectively referred to as fermentation. In contrast, in some living systems, the electron transport chain (ETC) uses an inorganic molecule (other than oxygen) as a final electron acceptor to regenerate NAD+ which is called anaerobic (do not require oxygen) to achieve NAD+ regeneration. Both processes allow organisms to convert energy for their use in the absence of oxygen. - Watch this video to see fermentation in action. + Watch this video to see fermentation in action.
Lactic Acid Fermentation diff --git a/modules/m45448/index.cnxml b/modules/m45448/index.cnxml index e0647766c..c95b851f9 100644 --- a/modules/m45448/index.cnxml +++ b/modules/m45448/index.cnxml @@ -20,7 +20,7 @@ Photosynthesis also results in the release of oxygen into the atmosphere. In short, to eat and breathe, humans depend almost entirely on the organisms that carry out photosynthesis. -Click the following link to learn more about photosynthesis. +Click the following link to learn more about photosynthesis.
Solar Dependence and Food Production Some organisms can carry out photosynthesis, whereas others cannot. An autotroph is an organism that can produce its own food. The Greek roots of the word autotroph mean “self” (auto) “feeder” (troph). Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae (). Oceanic algae contribute enormous quantities of food and oxygen to global food chains. Plants are also photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. All organisms carrying out photosynthesis require sunlight. diff --git a/modules/m45452/index.cnxml b/modules/m45452/index.cnxml index fa8857e95..d3777b3a1 100644 --- a/modules/m45452/index.cnxml +++ b/modules/m45452/index.cnxml @@ -20,7 +20,7 @@ Autotrophs can capture light energy from the sun, converting it into chemical energy used to build food molecules. (credit: modification of work by Gerry Atwell, U.S. Fish and Wildlife Service)
-Watch the process of photosynthesis within a leaf in this video.
+Watch the process of photosynthesis within a leaf in this video.
What Is Light Energy? The sun emits an enormous amount of electromagnetic radiation (solar energy). Humans can see only a fraction of this energy, which is referred to as “visible light.” The manner in which solar energy travels can be described and measured as waves. Scientists can determine the amount of energy of a wave by measuring its wavelength, the distance between two consecutive, similar points in a series of waves, such as from crest to crest or trough to trough ().
diff --git a/modules/m45453/index.cnxml b/modules/m45453/index.cnxml index 2b9cd7463..59315ab80 100644 --- a/modules/m45453/index.cnxml +++ b/modules/m45453/index.cnxml @@ -28,7 +28,7 @@ The Calvin cycle has three stages. In stage 1, the enzyme RuBisCO incorporates carbon dioxide into an organic molecule. In stage 2, the organic molecule is reduced. In stage 3, RuBP, the molecule that starts the cycle, is regenerated so that the cycle can continue.
In summary, it takes six turns of the Calvin cycle to fix six carbon atoms from CO2. These six turns require energy input from 12 ATP molecules and 12 NADPH molecules in the reduction step and 6 ATP molecules in the regeneration step. -The following is a link to an animation of the Calvin cycle. Click Stage 1, Stage 2, and then Stage 3 to see G3P and ATP regenerate to form RuBP. +The following is a link to an animation of the Calvin cycle. Click Stage 1, Stage 2, and then Stage 3 to see G3P and ATP regenerate to form RuBP. Photosynthesis The shared evolutionary history of all photosynthetic organisms is conspicuous, as the basic process has changed little over eras of time. Even between the giant tropical leaves in the rainforest and tiny cyanobacteria, the process and components of photosynthesis that use water as an electron donor remain largely the same. Photosystems function to absorb light and use electron transport chains to convert energy. The Calvin cycle reactions assemble carbohydrate molecules with this energy. diff --git a/modules/m45461/index.cnxml b/modules/m45461/index.cnxml index 3b3e59438..99452a27e 100644 --- a/modules/m45461/index.cnxml +++ b/modules/m45461/index.cnxml @@ -17,7 +17,7 @@ The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produce two genetically identical cells. The cell cycle has two major phases: interphase and the mitotic phase (). During interphase, the cell grows and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated and the cell divides. -Watch this video about the cell cycle: http://openstax.org/l/biocellcyc
+Watch this video about the cell cycle: https://openstax.org/l/biocellcyc
@@ -68,7 +68,7 @@ Watch this video about the cell cycle: -This page of movies illustrates different aspects of mitosis. Watch the movie entitled “DIC microscopy of cell division in a newt lung cell” and identify the phases of mitosis. +This page of movies illustrates different aspects of mitosis. Watch the movie entitled “DIC microscopy of cell division in a newt lung cell” and identify the phases of mitosis.
Cytokinesis Cytokinesis is the second part of the mitotic phase during which cell division is completed by the physical separation of the cytoplasmic components into two daughter cells. Although the stages of mitosis are similar for most eukaryotes, the process of cytokinesis is quite different for eukaryotes that have cell walls, such as plant cells. diff --git a/modules/m45462/index.cnxml b/modules/m45462/index.cnxml index cf906cfeb..d0b26b4a6 100644 --- a/modules/m45462/index.cnxml +++ b/modules/m45462/index.cnxml @@ -31,7 +31,7 @@ (a) The role of p53 is to monitor DNA. If damage is detected, p53 triggers repair mechanisms. If repairs are unsuccessful, p53 signals apoptosis. (b) A cell with an abnormal p53 protein cannot repair damaged DNA and cannot signal apoptosis. Cells with abnormal p53 can become cancerous. (credit: modification of work by Thierry Soussi) -Go to this website to watch an animation of how cancer results from errors in the cell cycle. +Go to this website to watch an animation of how cancer results from errors in the cell cycle. Since cancer is defined by uncontrolled cell growth, cancer treatments aim to interrupt the cell cycle. One of the first treatments involved folic acid, a substance discovered by Lucy Wills while she was researching pregnancy anemia (blood disorder). Several scientists showed that inhibiting folic acid uptake by tumor cells resulted in reduced growth. Jane C. Wright identified the drug now known as methotrexate as an effective treatment for breast and skin cancers. The same drug was applied to other cancers, such as placental, uterine, and lung cancers. Methotrexate is known as the first chemotherapy drug, and Wright's additional work to establish dosage protocols and sequences—both to maximize the effect and manage side effects—laid the foundation for contemporary chemotherapy treatments.
diff --git a/modules/m45466/index.cnxml b/modules/m45466/index.cnxml index 3fd3f9b74..3882ad526 100644 --- a/modules/m45466/index.cnxml +++ b/modules/m45466/index.cnxml @@ -44,7 +44,7 @@ Cytokinesis, the physical separation of the cytoplasmic components into two daughter cells, occurs without reformation of the nuclei in other organisms. In nearly all species, cytokinesis separates the cell contents by either a cleavage furrow (in animals and some fungi), or a cell plate that will ultimately lead to formation of cell walls that separate the two daughter cells (in plants). At each pole, there is just one member of each pair of the homologous chromosomes, so only one full set of the chromosomes is present. This is why the cells are considered haploid—there is only one chromosome set, even though there are duplicate copies of the set because each homolog still consists of two sister chromatids that are still attached to each other. However, although the sister chromatids were once duplicates of the same chromosome, they are no longer identical at this stage because of crossovers. -Review the process of meiosis, observing how chromosomes align and migrate, at this site. +Review the process of meiosis, observing how chromosomes align and migrate, at this site.
Meiosis II @@ -67,7 +67,7 @@ Meiosis and mitosis are both preceded by one round of DNA replication; however, meiosis includes two nuclear divisions. The four daughter cells resulting from meiosis are haploid and genetically distinct. The daughter cells resulting from mitosis are diploid and identical to the parent cell. -For an animation comparing mitosis and meiosis, go to this website. +For an animation comparing mitosis and meiosis, go to this website.
Section SummarySexual reproduction requires that diploid organisms produce haploid cells that can fuse during fertilization to form diploid offspring. The process that results in haploid cells is called meiosis. Meiosis is a series of events that arrange and separate chromosomes into daughter cells. During the interphase of meiosis, each chromosome is duplicated. In meiosis, there are two rounds of nuclear division resulting in four nuclei and usually four haploid daughter cells, each with half the number of chromosomes as the parent cell. During meiosis, variation in the daughter nuclei is introduced because of crossover in prophase I and random alignment at metaphase I. The cells that are produced by meiosis are genetically unique. diff --git a/modules/m45471/index.cnxml b/modules/m45471/index.cnxml index bb51ef4c9..9bd272680 100644 --- a/modules/m45471/index.cnxml +++ b/modules/m45471/index.cnxml @@ -67,7 +67,7 @@ Discoveries in fruit fly genetics can be applied to human genetics. When a female parent is homozygous for a recessive X-linked trait, the parent will pass the trait on to 100 percent of the male offspring, because the males will receive the Y chromosome from the male parent. In humans, the alleles for certain conditions (some color-blindness, hemophilia, and muscular dystrophy) are X-linked. Females who are heterozygous for these diseases are said to be carriers and may not exhibit any phenotypic effects. These females will pass the disease to half of their male offspring and will pass carrier status to half of their female offspring; therefore, X-linked traits appear more frequently in males than females. In some groups of organisms with sex chromosomes, the sex with the non-homologous sex chromosomes is the female rather than the male. This is the case for all birds. In this case, sex-linked traits will be more likely to appear in the female, in whom they are hemizygous. - Watch this video to learn more about sex-linked traits.
+ Watch this video to learn more about sex-linked traits.
Linked Genes Violate the Law of Independent Assortment @@ -82,7 +82,7 @@ Mendel’s studies in pea plants implied that the sum of an individual’s phenotype was controlled by genes (or as he called them, unit factors), such that every characteristic was distinctly and completely controlled by a single gene. In fact, single observable characteristics are almost always under the influence of multiple genes (each with two or more alleles) acting in unison. For example, at least eight genes contribute to eye color in humans. - Eye color in humans is determined by multiple alleles. Use the Eye Color Calculator to predict the eye color of children from parental eye color. + Eye color in humans is determined by multiple alleles. Use the Eye Color Calculator to predict the eye color of children from parental eye color. In some cases, several genes can contribute to aspects of a common phenotype without their gene products ever directly interacting. In the case of organ development, for instance, genes may be expressed sequentially, with each gene adding to the complexity and specificity of the organ. Genes may function in complementary or synergistic fashions, such that two or more genes expressed simultaneously affect a phenotype. An apparent example of this occurs with human skin color, which appears to involve the action of at least three (and probably more) genes. Cases in which inheritance for a characteristic like skin color or human height depend on the combined effects of numerous genes are called polygenic inheritance. Genes may also oppose each other, with one gene suppressing the expression of another. In epistasis, the interaction between genes is antagonistic, such that one gene masks or interferes with the expression of another. “Epistasis” is a word composed of Greek roots meaning “standing upon.” The alleles that are being masked or silenced are said to be hypostatic to the epistatic alleles that are doing the masking. Often the biochemical basis of epistasis is a gene pathway in which expression of one gene is dependent on the function of a gene that precedes or follows it in the pathway. An example of epistasis is pigmentation in mice. The wild-type coat color, agouti (AA) is dominant to solid-colored fur (aa). However, a separate gene C, when present as the recessive homozygote (cc), negates any expression of pigment from the A gene and results in an albino mouse (). Therefore, the genotypes AAcc, Aacc, and aacc all produce the same albino phenotype. A cross between heterozygotes for both genes (AaCc x AaCc) would generate offspring with a phenotypic ratio of 9 agouti:3 black:4 albino (). In this case, the C gene is epistatic to the A gene.
diff --git a/modules/m45473/index.cnxml b/modules/m45473/index.cnxml index d33658e79..09961cc0c 100644 --- a/modules/m45473/index.cnxml +++ b/modules/m45473/index.cnxml @@ -66,7 +66,7 @@
-Watch this animation of DNA packaging. +Watch this animation of DNA packaging.
Section SummaryThe model of the double-helix structure of DNA was proposed by Watson and Crick. The DNA molecule is a polymer of nucleotides. Each nucleotide is composed of a nitrogenous base, a five-carbon sugar (deoxyribose), and a phosphate group. There are four nitrogenous bases in DNA, two purines (adenine and guanine) and two pyrimidines (cytosine and thymine). A DNA molecule is composed of two strands. Each strand is composed of nucleotides bonded together covalently between the phosphate group of one and the deoxyribose sugar of the next. From this backbone extend the bases. The bases of one strand bond to the bases of the second strand with hydrogen bonds. Adenine always bonds with thymine, and cytosine always bonds with guanine. The bonding causes the two strands to spiral around each other in a shape called a double helix. Ribonucleic acid (RNA) is a second nucleic acid found in cells. RNA is a single-stranded polymer of nucleotides. It also differs from DNA in that it contains the sugar ribose, rather than deoxyribose, and the nucleotide uracil rather than thymine. Various RNA molecules function in the process of forming proteins from the genetic code in DNA. diff --git a/modules/m45475/index.cnxml b/modules/m45475/index.cnxml index 9d5365b7d..ab7973c88 100644 --- a/modules/m45475/index.cnxml +++ b/modules/m45475/index.cnxml @@ -105,7 +105,7 @@ -Click through a tutorial on DNA replication. +Click through a tutorial on DNA replication.
diff --git a/modules/m45479/index.cnxml b/modules/m45479/index.cnxml index c287e5278..4ca321926 100644 --- a/modules/m45479/index.cnxml +++ b/modules/m45479/index.cnxml @@ -54,7 +54,7 @@ Termination of translation occurs when a stop codon (UAA, UAG, or UGA) is encountered. When the ribosome encounters the stop codon, the growing polypeptide is released and the ribosome subunits dissociate and leave the mRNA. After many ribosomes have completed translation, the mRNA is degraded so the nucleotides can be reused in another transcription reaction. -Transcribe a gene and translate it to protein using complementary pairing and the genetic code at this site. +Transcribe a gene and translate it to protein using complementary pairing and the genetic code at this site.
Section SummaryThe central dogma describes the flow of genetic information in the cell from genes to mRNA to proteins. Genes are used to make mRNA by the process of transcription; mRNA is used to synthesize proteins by the process of translation. The genetic code is the correspondence between the three-nucleotide mRNA codon and an amino acid. The genetic code is “translated” by the tRNA molecules, which associate a specific codon with a specific amino acid. The genetic code is degenerate because 64 triplet codons in mRNA specify only 20 amino acids and three stop codons. This means that more than one codon corresponds to an amino acid. Almost every species on the planet uses the same genetic code. diff --git a/modules/m45482/index.cnxml b/modules/m45482/index.cnxml index 2aa38a87a..93bee3fa2 100644 --- a/modules/m45482/index.cnxml +++ b/modules/m45482/index.cnxml @@ -92,7 +92,7 @@ Using recombinant DNA technology to modify an organism’s DNA to achieve desirable traits is called genetic engineering. Addition of foreign DNA in the form of recombinant DNA vectors that are generated by molecular cloning is the most common method of genetic engineering. An organism that receives the recombinant DNA is called a genetically modified organism (GMO). If the foreign DNA that is introduced comes from a different species, the host organism is called transgenic. Bacteria, plants, and animals have been genetically modified since the early 1970s for academic, medical, agricultural, and industrial purposes. These applications will be examined in more detail in the next module. -Watch this short video explaining how scientists create a transgenic animal. +Watch this short video explaining how scientists create a transgenic animal. Although the classic methods of studying the function of genes began with a given phenotype and determined the genetic basis of that phenotype, modern techniques allow researchers to start at the DNA sequence level and ask: "What does this gene or DNA element do?" This technique, called reverse genetics, has resulted in reversing the classical genetic methodology. One example of this method is analogous to damaging a body part to determine its function. An insect that loses a wing cannot fly, which means that the wing’s function is flight. The classic genetic method compares insects that cannot fly with insects that can fly, and observes that the non-flying insects have lost wings. Similarly in a reverse genetics approach, mutating or deleting genes provides researchers with clues about gene function. Alternately, reverse genetics can be used to cause a gene to overexpress itself to determine what phenotypic effects may occur.
diff --git a/modules/m45483/index.cnxml b/modules/m45483/index.cnxml index f2329fabd..7ee99bc68 100644 --- a/modules/m45483/index.cnxml +++ b/modules/m45483/index.cnxml @@ -19,7 +19,7 @@ The process of testing for suspected genetic defects before administering treatment is called genetic diagnosis by genetic testing. In some cases in which a genetic disease is present in an individual’s family, family members may be advised to undergo genetic testing. For example, mutations in the BRCA genes may increase the likelihood of developing breast, ovarian, and some other cancers. A person with breast cancer can be screened for these mutations. If one of the high-risk mutations is found, relatives may also wish to be screened for that particular mutation, or simply be more vigilant for the occurrence of cancers. Genetic testing is also offered for fetuses (or embryos with in vitro fertilization) to determine the presence or absence of disease-causing genes in families with specific debilitating diseases. -See how human DNA is extracted for uses such as genetic testing.Gene therapy is a genetic engineering technique that may one day be used to cure certain genetic diseases. In its simplest form, it involves the introduction of a non-mutated gene at a random location in the genome to cure a disease by replacing a protein that may be absent in these individuals because of a genetic mutation. The non-mutated gene is usually introduced into diseased cells as part of a vector transmitted by a virus, such as an adenovirus, that can infect the host cell and deliver the foreign DNA into the genome of the targeted cell (). To date, gene therapies have been primarily experimental procedures in humans. A few of these experimental treatments have been successful, but the methods may be important in the future as the factors limiting its success are resolved. +See how human DNA is extracted for uses such as genetic testing.Gene therapy is a genetic engineering technique that may one day be used to cure certain genetic diseases. In its simplest form, it involves the introduction of a non-mutated gene at a random location in the genome to cure a disease by replacing a protein that may be absent in these individuals because of a genetic mutation. The non-mutated gene is usually introduced into diseased cells as part of a vector transmitted by a virus, such as an adenovirus, that can infect the host cell and deliver the foreign DNA into the genome of the targeted cell (). To date, gene therapies have been primarily experimental procedures in humans. A few of these experimental treatments have been successful, but the methods may be important in the future as the factors limiting its success are resolved.
diff --git a/modules/m45485/index.cnxml b/modules/m45485/index.cnxml index 62ed362a7..5b4811fdf 100644 --- a/modules/m45485/index.cnxml +++ b/modules/m45485/index.cnxml @@ -26,7 +26,7 @@ This is a physical map of the human X chromosome. (credit: modification of work by NCBI, NIH)
Genetic maps provide the outline, and physical maps provide the details. It is easy to understand why both types of genome-mapping techniques are important to show the big picture. Information obtained from each technique is used in combination to study the genome. Genomic mapping is used with different model organisms that are used for research. Genome mapping is still an ongoing process, and as more advanced techniques are developed, more advances are expected. Genome mapping is similar to completing a complicated puzzle using every piece of available data. Mapping information generated in laboratories all over the world is entered into central databases, such as the National Center for Biotechnology Information (NCBI). Efforts are made to make the information more easily accessible to researchers and the general public. Just as we use global positioning systems instead of paper maps to navigate through roadways, NCBI allows us to use a genome viewer tool to simplify the data mining process. -Online Mendelian Inheritance in Man (OMIM) is a searchable online catalog of human genes and genetic disorders. This website shows genome mapping, and also details the history and research of each trait and disorder. Click the link to search for traits (such as handedness) and genetic disorders (such as diabetes). +Online Mendelian Inheritance in Man (OMIM) is a searchable online catalog of human genes and genetic disorders. This website shows genome mapping, and also details the history and research of each trait and disorder. Click the link to search for traits (such as handedness) and genetic disorders (such as diabetes).
Whole Genome Sequencing diff --git a/modules/m45489/index.cnxml b/modules/m45489/index.cnxml index 38a47160c..0c76cd16e 100644 --- a/modules/m45489/index.cnxml +++ b/modules/m45489/index.cnxml @@ -37,7 +37,7 @@ A chance event or catastrophe can reduce the genetic variability within a population.Another scenario in which populations might experience a strong influence of genetic drift is if some portion of the population leaves to start a new population in a new location, or if a population gets divided by a physical barrier of some kind. In this situation, those individuals are unlikely to be representative of the entire population which results in the founder effect. The founder effect occurs when the genetic structure matches that of the new population’s founding fathers and mothers. The founder effect is believed to have been a key factor in the genetic history of the Afrikaner population of Dutch settlers in South Africa, as evidenced by mutations that are common in Afrikaners but rare in most other populations. This is likely due to a higher-than-normal proportion of the founding colonists, which were a small sample of the original population, carried these mutations. As a result, the population expresses unusually high incidences of Huntington’s disease (HD) and Fanconi anemia (FA), a genetic disorder known to cause bone marrow and congenital abnormalities, and even cancer.A. J. Tipping et al., “Molecular and Genealogical Evidence for a Founder Effect in Fanconi Anemia Families of the Afrikaner Population of South Africa,” PNAS 98, no. 10 (2001): 5734-5739, doi: 10.1073/pnas.091402398. -Visit this site to learn more about genetic drift and to run simulations of allele changes caused by drift. +Visit this site to learn more about genetic drift and to run simulations of allele changes caused by drift.
Gene Flow Another important evolutionary force is gene flow, or the flow of alleles in and out of a population resulting from the migration of individuals or gametes (). While some populations are fairly stable, others experience more flux. Many plants, for example, send their seeds far and wide, by wind or in the guts of animals; these seeds may introduce alleles common in the source population to a new population in which they are rare. diff --git a/modules/m45491/index.cnxml b/modules/m45491/index.cnxml index ec6bef5d8..6d28f6924 100644 --- a/modules/m45491/index.cnxml +++ b/modules/m45491/index.cnxml @@ -27,7 +27,7 @@ The similar construction of these appendages indicates that these organisms share a common ancestor. -Click through the activities at this interactive site to guess which bone structures are homologous and which are analogous, and to see examples of all kinds of evolutionary adaptations that illustrate these concepts. +Click through the activities at this interactive site to guess which bone structures are homologous and which are analogous, and to see examples of all kinds of evolutionary adaptations that illustrate these concepts. Another piece of evidence of evolution is the convergence of form in organisms that share similar environments. For example, species of unrelated animals, such as the arctic fox and ptarmigan (a bird), living in the arctic region have temporary white coverings during winter to blend with the snow and ice (). The similarity occurs not because of common ancestry, indeed one covering is of fur and the other of feathers, but because of similar selection pressures—the benefits of not being seen by predators.
diff --git a/modules/m45493/index.cnxml b/modules/m45493/index.cnxml index dc8cd6b5f..2ac8c32db 100644 --- a/modules/m45493/index.cnxml +++ b/modules/m45493/index.cnxml @@ -37,7 +37,7 @@ The honeycreeper birds illustrate adaptive radiation. From one original species of bird, multiple others evolved, each with its own distinctive characteristics.
Notice the differences in the species’ beaks in . Change in the genetic variation for beaks in response to natural selection based on specific food sources in each new habitat led to evolution of a different beak suited to the specific food source. The fruit and seed-eating birds have thicker, stronger beaks which are suited to break hard nuts. The nectar-eating birds have long beaks to dip into flowers to reach their nectar. The insect-eating birds have beaks like swords, appropriate for stabbing and impaling insects. Darwin’s finches are another well-studied example of adaptive radiation in an archipelago. -Click through this interactive site to see how island birds evolved; click to see images of each species in evolutionary increments from five million years ago to today. +Click through this interactive site to see how island birds evolved; click to see images of each species in evolutionary increments from five million years ago to today.
Speciation without Geographic Separation diff --git a/modules/m45505/index.cnxml b/modules/m45505/index.cnxml index 1a230a60c..83e473b01 100644 --- a/modules/m45505/index.cnxml +++ b/modules/m45505/index.cnxml @@ -16,7 +16,7 @@ Although the theory of evolution initially generated some controversy, by 20 years after the publication of On the Origin of Species it was almost universally accepted by biologists, particularly younger biologists. Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound. In addition, there are those that reject it as an explanation for the diversity of life. -This website addresses some of the main misconceptions associated with the theory of evolution. +This website addresses some of the main misconceptions associated with the theory of evolution.
Evolution Is Just a Theory Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word “theory” with the way scientists use the word. In science, a “theory” is understood to be a concept that has been extensively tested and supported over time. We have a theory of the atom, a theory of gravity, and the theory of relativity, each of which describes what scientists understand to be facts about the world. In the same way, the theory of evolution describes facts about the living world. As such, a theory in science has survived significant efforts to discredit it by scientists, who are naturally skeptical. While theories can sometimes be overturned or revised, this does not lessen their weight but simply reflects the constantly evolving state of scientific knowledge. In contrast, a “theory” in common vernacular means a guess or suggested explanation for something. This meaning is more akin to the concept of a “hypothesis” used by scientists, which is a tentative explanation for something that is proposed to either be supported or disproved. When critics of evolution say evolution is “just a theory,” they are implying that there is little evidence supporting it and that it is still in the process of being rigorously tested. This is a mischaracterization. If this were the case, geneticist Theodosius Dobzhansky would not have said that “nothing in biology makes sense, except in the light of evolution.”Theodosius Dobzhansky. “Biology, Molecular and Organismic.” American Zoologist 4, no. 4 (1964): 449. diff --git a/modules/m45507/index.cnxml b/modules/m45507/index.cnxml index abcbb18a9..2f4b30120 100644 --- a/modules/m45507/index.cnxml +++ b/modules/m45507/index.cnxml @@ -52,7 +52,7 @@ This phylogenetic tree is rooted by an organism that lacked a vertebral column. At each branch point, organisms with different characters are placed in different groups. -This interactive exercise allows you to explore the evolutionary relationships among species. +This interactive exercise allows you to explore the evolutionary relationships among species.
Limitations of Phylogenetic Trees diff --git a/modules/m45509/index.cnxml b/modules/m45509/index.cnxml index cb7d65797..d1603cb36 100644 --- a/modules/m45509/index.cnxml +++ b/modules/m45509/index.cnxml @@ -62,7 +62,7 @@ To aid in the tremendous task of choosing the best tree, scientists often use a concept called maximum parsimony, which means that events occurred in the simplest, most obvious way. This means that the “best” tree is the one with the fewest number of character reversals, the fewest number of independent character changes, and the fewest number of character changes throughout the tree. Computer programs search through all of the possible trees to find the small number of trees with the simplest evolutionary pathways. Starting with all of the homologous traits in a group of organisms, scientists can determine the order of evolutionary events of which those traits occurred that is the most obvious and simple. -Practice Parsimony: Go to this website to learn how maximum parsimony is used to create phylogenetic trees (be sure to continue to the second page). +Practice Parsimony: Go to this website to learn how maximum parsimony is used to create phylogenetic trees (be sure to continue to the second page). These tools and concepts are only a few of the strategies scientists use to tackle the task of revealing the evolutionary history of life on Earth. Recently, newer technologies have uncovered surprising discoveries with unexpected relationships, such as the fact that people seem to be more closely related to fungi than fungi are to plants. Sound unbelievable? As the information about DNA sequences grows, scientists will become closer to mapping the evolutionary history of all life on Earth.
diff --git a/modules/m45512/index.cnxml b/modules/m45512/index.cnxml index 32f215b33..71639039d 100644 --- a/modules/m45512/index.cnxml +++ b/modules/m45512/index.cnxml @@ -86,7 +86,7 @@ One of the most devastating pandemics was the Black Death (1346 to 1361), which is believed to have been another outbreak of bubonic plague caused by the bacterium Yersinia pestis. This bacterium is carried by fleas living on black rats. The Black Death reduced the world’s population from an estimated 450 million to about 350 to 375 million. Bubonic plague struck London hard again in the mid-1600s. There are still approximately 1,000 to 3,000 cases of plague globally each year. Although contracting bubonic plague before antibiotics meant almost certain death, the bacterium responds to several types of modern antibiotics, and mortality rates from plague are now very low. - Watch a video on the modern understanding of the Black Death (bubonic plague) in Europe during the fourteenth century. + Watch a video on the modern understanding of the Black Death (bubonic plague) in Europe during the fourteenth century. Over the centuries, Europeans developed resistance to many infectious diseases. However, European conquerors brought disease-causing bacteria and viruses with them when they reached the Western hemisphere, triggering epidemics that completely devastated populations of Native Americans (who had no natural resistance to many European diseases).
@@ -95,7 +95,7 @@ Another problem is the excessive use of antibiotics in livestock. The routine use of antibiotics in animal feed promotes bacterial resistance as well. In the United States, 70 percent of the antibiotics produced are fed to animals. The antibiotics are not used to prevent disease, but to enhance production of their products. - Watch an overview report on the problem of routine antibiotic administration to livestock and antibiotic-resistant bacteria.Staphylococcus aureus, often called “staph,” is a common bacterium that can live in and on the human body, which usually is easily treatable with antibiotics. A very dangerous strain, however, has made the news over the past few years (). This strain, methicillin-resistant Staphylococcus aureus (MRSA), is resistant to many commonly used antibiotics, including methicillin, amoxicillin, penicillin, and oxacillin. While MRSA infections have been common among people in healthcare facilities, it is appearing more commonly in healthy people who live or work in dense groups (like military personnel and prisoners). The Journal of the American Medical Association reported that, among MRSA-afflicted persons in healthcare facilities, the average age is 68 years, while people with “community-associated MRSA” (CA-MRSA) have an average age of 23 years.Naimi, T. S., LeDell, K. H., Como-Sabetti, K., et al., “Comparison of community- and health care-associated methicillin-resistant Staphylococcus aureus infection,” JAMA 290 (2003): 2976-2984, doi: 10.1001/jama.290.22.2976.
+ Watch an overview report on the problem of routine antibiotic administration to livestock and antibiotic-resistant bacteria.Staphylococcus aureus, often called “staph,” is a common bacterium that can live in and on the human body, which usually is easily treatable with antibiotics. A very dangerous strain, however, has made the news over the past few years (). This strain, methicillin-resistant Staphylococcus aureus (MRSA), is resistant to many commonly used antibiotics, including methicillin, amoxicillin, penicillin, and oxacillin. While MRSA infections have been common among people in healthcare facilities, it is appearing more commonly in healthy people who live or work in dense groups (like military personnel and prisoners). The Journal of the American Medical Association reported that, among MRSA-afflicted persons in healthcare facilities, the average age is 68 years, while people with “community-associated MRSA” (CA-MRSA) have an average age of 23 years.Naimi, T. S., LeDell, K. H., Como-Sabetti, K., et al., “Comparison of community- and health care-associated methicillin-resistant Staphylococcus aureus infection,” JAMA 290 (2003): 2976-2984, doi: 10.1001/jama.290.22.2976.
diff --git a/modules/m45519/index.cnxml b/modules/m45519/index.cnxml index 59d82589d..dcd0d9498 100644 --- a/modules/m45519/index.cnxml +++ b/modules/m45519/index.cnxml @@ -39,7 +39,7 @@ -Watch this video to see the process of seed production in gymnosperms. +Watch this video to see the process of seed production in gymnosperms.
@@ -74,7 +74,7 @@ Ephedra viridis, known by the common name Mormon tea, grows in the western United States. (credit: US National Park Service, USDA-NRCS PLANTS Database) -Watch this BBC video describing the amazing strangeness of Welwitschia. +Watch this BBC video describing the amazing strangeness of Welwitschia.
diff --git a/modules/m45520/index.cnxml b/modules/m45520/index.cnxml index b22cd9e5c..27d098ede 100644 --- a/modules/m45520/index.cnxml +++ b/modules/m45520/index.cnxml @@ -120,7 +120,7 @@ -Explore this website for more information on pollinators.
+Explore this website for more information on pollinators.
The Role of Seed Plants Without seed plants, life as we know it would not be possible. Plants play a key role in the maintenance of terrestrial ecosystems through the stabilization of soils, cycling of carbon, and climate moderation. Large tropical forests release oxygen and act as carbon dioxide “sinks.” Seed plants provide shelter to many life forms, as well as food for herbivores, thereby indirectly feeding carnivores. Plant secondary metabolites are used for medicinal purposes and industrial production. Virtually all animal life is dependent on plants for survival. diff --git a/modules/m45523/index.cnxml b/modules/m45523/index.cnxml index 28bd4fd7c..b12ad7da9 100644 --- a/modules/m45523/index.cnxml +++ b/modules/m45523/index.cnxml @@ -24,7 +24,7 @@ A hallmark trait of animals is specialized structures that are differentiated to perform unique functions. As multicellular organisms, most animals develop specialized cells that group together into tissues with specialized functions. A tissue is a collection of similar cells that had a common embryonic origin. There are four main types of animal tissues: nervous, muscle, connective, and epithelial. Nervous tissue contains neurons, or nerve cells, which transmit nerve impulses. Muscle tissue contracts to cause all types of body movement from locomotion of the organism to movements within the body itself. Animals also have specialized connective tissues that provide many functions, including transport and structural support. Examples of connective tissues include blood and bone. Connective tissue is comprised of cells separated by extracellular material made of organic and inorganic materials, such as the protein and mineral deposits of bone. Epithelial tissue covers the internal and external surfaces of organs inside the animal body and the external surface of the body of the organism. -View this video to watch a presentation by biologist E.O. Wilson on the importance of animal diversity. +View this video to watch a presentation by biologist E.O. Wilson on the importance of animal diversity.
Animal Reproduction and Development @@ -63,7 +63,7 @@ Bilateral symmetry is illustrated in c using a goat. The goat also has upper and lower sides to it, but they are not symmetrical. A vertical plane cut from front to back separates the animal into roughly mirror-image right and left sides. Animals with bilateral symmetry also have a “head” and “tail” (anterior versus posterior) and a back and underside (dorsal versus ventral). - Watch this video to see a quick sketch of the different types of body symmetry. + Watch this video to see a quick sketch of the different types of body symmetry.
Layers of Tissues Most animal species undergo a layering of early tissues during embryonic development. These layers are called germ layers. Each layer develops into a specific set of tissues and organs. Animals develop either two or three embryonic germs layers (). The animals that display radial symmetry develop two germ layers, an inner layer (endoderm) and an outer layer (ectoderm). These animals are called diploblasts. Animals with bilateral symmetry develop three germ layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). Animals with three germ layers are called triploblasts. diff --git a/modules/m45524/index.cnxml b/modules/m45524/index.cnxml index 88064437e..bdc22c927 100644 --- a/modules/m45524/index.cnxml +++ b/modules/m45524/index.cnxml @@ -34,7 +34,7 @@ Sponges are monoecious (or hermaphroditic), meaning one individual can produce both eggs and sperm. Sponges may be sequentially hermaphroditic, producing eggs first and sperm later. Eggs arise from amoebocytes and are retained within the spongocoel, whereas sperm arise from choanocytes and are ejected through the osculum. Sperm carried by water currents fertilize the eggs of other sponges. Early larval development occurs within the sponge, and free-swimming larvae are then released through the osculum. This is the only time that sponges exhibit mobility. Sponges are sessile as adults and spend their lives attached to a fixed substrate. - Watch this video that demonstrates the feeding of sponges.
+ Watch this video that demonstrates the feeding of sponges.
Cnidarians @@ -68,7 +68,7 @@ Use this video to identify the life cycle stages of jellies.The class Cubozoa includes jellies that are square in cross-section and so are known as “box jellyfish.” These species may achieve sizes of 15–25 cm. Cubozoans are anatomically similar to the jellyfish. A prominent difference between the two classes is the arrangement of tentacles. Cubozoans have muscular pads called pedalia at the corners of the square bell canopy, with one or more tentacles attached to each pedalium. In some cases, the digestive system may extend into the pedalia. Cubozoans typically exist in a polyp form that develops from a larva. The polyps may bud to form more polyps and then transform into the medusoid forms. - Watch this video to learn more about the deadly toxins of the box jellyfish. + Watch this video to learn more about the deadly toxins of the box jellyfish. Hydrozoa includes nearly 3,500 species,“The Hydrozoa Directory,” Peter Schuchert, Muséum Genève, last updated November 2012, http://www.ville-ge.ch/mhng/hydrozoa/hydrozoa-directory.htm. most of which are marine. Most species in this class have both polyp and medusa forms in their life cycle. Many hydrozoans form colonies composed of branches of specialized polyps that share a gastrovascular cavity. Colonies may also be free-floating and contain both medusa and polyp individuals in the colony, as in the Portuguese Man O’War (Physalia) or By-the-Wind Sailor (Velella). Other species are solitary polyps or solitary medusae. The characteristic shared by all of these species is that their gonads are derived from epidermal tissue, whereas in all other cnidarians, they are derived from gastrodermal tissue (ab).
diff --git a/modules/m45525/index.cnxml b/modules/m45525/index.cnxml index fa5d7f71a..dc28df2de 100644 --- a/modules/m45525/index.cnxml +++ b/modules/m45525/index.cnxml @@ -50,7 +50,7 @@ Most nematodes have four nerve cords that run along the length of the body on the top, bottom, and sides. The nerve cords fuse in a ring around the pharynx, to form a head ganglion or “brain” of the worm, as well as at the posterior end to form the tail ganglion. Beneath the epidermis lies a layer of longitudinal muscles that permits only side-to-side, wave-like undulation of the body. - View this video to see nematodes move about and feed on bacteria. + View this video to see nematodes move about and feed on bacteria. Nematodes employ a diversity of sexual reproductive strategies depending on the species; they may be monoecious, dioecious (separate sexes), or may reproduce asexually by parthenogenesis. Caenorhabditis elegans is nearly unique among animals in having both self-fertilizing hermaphrodites and a male sex that can mate with the hermaphrodite.
@@ -87,7 +87,7 @@ (a) The chelicerae (first set of appendages, circled) are well developed in the Chelicerata, which includes scorpions (a) and spiders (b). (credit a: modification of work by Kevin Walsh; credit b: modification of work by Marshal Hedin) - Click through this lesson on arthropods to explore interactive habitat maps and more. + Click through this lesson on arthropods to explore interactive habitat maps and more.
Section SummaryFlatworms are acoelomate, triploblastic animals. They lack circulatory and respiratory systems, and have a rudimentary excretory system. The digestive system is incomplete in most species. There are four traditional classes of flatworms, the largely free-living turbellarians, the ectoparasitic monogeneans, and the endoparasitic trematodes and cestodes. Trematodes have complex life cycles involving a secondary mollusk host and a primary host in which sexual reproduction takes place. Cestodes, or tapeworms, infect the digestive systems of primary vertebrate hosts. diff --git a/modules/m45526/index.cnxml b/modules/m45526/index.cnxml index fec003c83..a81b87548 100644 --- a/modules/m45526/index.cnxml +++ b/modules/m45526/index.cnxml @@ -44,7 +44,7 @@ Class Bivalvia (“two shells”) includes clams, oysters, mussels, scallops, and geoducks. They are found in marine and freshwater habitats. As the name suggests, bivalves are enclosed in a pair of shells (or valves) that are hinged at the dorsal side. The body is flattened on the sides. They feed by filtering particles from water and a radula is absent. They exchange gases using a pair of ctenidia, and excretion and osmoregulation are carried out by a pair of nephridia. In some species, the posterior edges of the mantle may fuse to form two siphons that inhale and exhale water. Some bivalves like oysters and mussels have the unique ability to secrete and deposit a calcareous nacre or “mother of pearl” around foreign particles that enter the mantle cavity. This property is commercially exploited to produce pearls. - Watch animations of clams and mussels feeding to understand more about bivalves. + Watch animations of clams and mussels feeding to understand more about bivalves. Gastropods (“stomach foot”) include well-known mollusks like snails, slugs, conchs, sea hares, and sea butterflies. Gastropods include shell-bearing species as well as species with a reduced shell. These animals are asymmetrical and usually present a coiled shell ().
@@ -76,7 +76,7 @@ Annelids may be either monoecious with permanent gonads (as in earthworms and leeches) or dioecious with temporary or seasonal gonads (as in polychaetes). - This video and animation provides a close-up look at annelid anatomy. + This video and animation provides a close-up look at annelid anatomy.
Annelid Diversity diff --git a/modules/m45531/index.cnxml b/modules/m45531/index.cnxml index 3f8fcce41..696e74a29 100644 --- a/modules/m45531/index.cnxml +++ b/modules/m45531/index.cnxml @@ -31,7 +31,7 @@ This phylum is divided into five classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers) ().Perhaps the best-known echinoderms are members of the class Asteroidea, or sea stars. They come in a large variety of shapes, colors, and sizes, with more than 1,800 species known. The characteristics of sea stars that set them apart from other echinoderm classes include thick arms that extend from a central disk where organs penetrate into the arms. Sea stars use their tube feet not only for gripping surfaces but also for grasping prey. Sea stars have two stomachs, one of which they can evert through their mouths to secrete digestive juices into or onto prey before ingestion. This process can essentially liquefy the prey and make digestion easier. - View this video to explore a sea star’s body plan up close, watch one move across the sea floor, and see it devour a mussel. + View this video to explore a sea star’s body plan up close, watch one move across the sea floor, and see it devour a mussel. Brittle stars have long, thin arms that do not contain any organs. Sea urchins and sand dollars do not have arms but are hemispherical or flattened with five rows of tube feet, which help them in slow movement. Sea lilies and feather stars are stalked suspension feeders. Sea cucumbers are soft-bodied and elongate with five rows of tube feet and a series of tube feet around the mouth that are modified into tentacles used in feeding.
diff --git a/modules/m45534/index.cnxml b/modules/m45534/index.cnxml index 1e8ae1be2..2367190ed 100644 --- a/modules/m45534/index.cnxml +++ b/modules/m45534/index.cnxml @@ -26,7 +26,7 @@ An animal that maintains a constant body temperature in the face of environmental changes is called an endotherm. These animals are able to maintain a level of activity that an ectothermic animal cannot because they generate internal heat that keeps their cellular processes operating optimally even when the environment is cold. - Watch this Discovery Channel video on thermoregulation to see illustrations of the process in a variety of animals. + Watch this Discovery Channel video on thermoregulation to see illustrations of the process in a variety of animals. Animals conserve or dissipate heat in a variety of ways. Endothermic animals have some form of insulation. They have fur, fat, or feathers. Animals with thick fur or feathers create an insulating layer of air between their skin and internal organs. Polar bears and seals live and swim in a subfreezing environment and yet maintain a constant, warm, body temperature. The arctic fox, for example, uses its fluffy tail as extra insulation when it curls up to sleep in cold weather. Mammals can increase body heat production by shivering, which is an involuntary increase in muscle activity. In addition, arrector pili muscles can contract causing individual hairs to stand up when the individual is cold. This increases the insulating effect of the hair. Humans retain this reaction, which does not have the intended effect on our relatively hairless bodies; it causes “goose bumps” instead. Mammals use layers of fat as insulation also. Loss of significant amounts of body fat will compromise an individual’s ability to conserve heat. Ectotherms and endotherms use their circulatory systems to help maintain body temperature. Vasodilation, the opening up of arteries to the skin by relaxation of their smooth muscles, brings more blood and heat to the body surface, facilitating radiation and evaporative heat loss, cooling the body. Vasoconstriction, the narrowing of blood vessels to the skin by contraction of their smooth muscles, reduces blood flow in peripheral blood vessels, forcing blood toward the core and vital organs, conserving heat. Some animals have adaptions to their circulatory system that enable them to transfer heat from arteries to veins that are flowing next to each other, warming blood returning to the heart. This is called a countercurrent heat exchange; it prevents the cold venous blood from cooling the heart and other internal organs. The countercurrent adaptation is found in dolphins, sharks, bony fish, bees, and hummingbirds. Some ectothermic animals use changes in their behavior to help regulate body temperature. They simply seek cooler areas during the hottest part of the day in the desert to keep from getting too warm. The same animals may climb onto rocks in the evening to capture heat on a cold desert night before entering their burrows. diff --git a/modules/m45535/index.cnxml b/modules/m45535/index.cnxml index 4d9fa5387..5c2a6dd71 100644 --- a/modules/m45535/index.cnxml +++ b/modules/m45535/index.cnxml @@ -83,7 +83,7 @@ For humans, a balanced diet includes fruits, vegetables, grains, protein, and dairy. (credit: USDA)
- Explore this interactive United States Department of Agriculture website to learn more about each food group and the recommended daily amounts.The organic molecules required for building cellular material and tissues must come from food. During digestion, digestible carbohydrates are ultimately broken down into glucose and used to provide energy within the cells of the body. Complex carbohydrates, including polysaccharides, can be broken down into glucose through biochemical modification; however, humans do not produce the enzyme necessary to digest cellulose (fiber). The intestinal flora in the human gut are able to extract some nutrition from these plant fibers. These plant fibers are known as dietary fiber and are an important component of the diet. The excess sugars in the body are converted into glycogen and stored for later use in the liver and muscle tissue. Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide energy during food shortage. Fats are stored under the skin of mammals for insulation and energy reserves. + Explore this interactive United States Department of Agriculture website to learn more about each food group and the recommended daily amounts.The organic molecules required for building cellular material and tissues must come from food. During digestion, digestible carbohydrates are ultimately broken down into glucose and used to provide energy within the cells of the body. Complex carbohydrates, including polysaccharides, can be broken down into glucose through biochemical modification; however, humans do not produce the enzyme necessary to digest cellulose (fiber). The intestinal flora in the human gut are able to extract some nutrition from these plant fibers. These plant fibers are known as dietary fiber and are an important component of the diet. The excess sugars in the body are converted into glycogen and stored for later use in the liver and muscle tissue. Glycogen stores are used to fuel prolonged exertions, such as long-distance running, and to provide energy during food shortage. Fats are stored under the skin of mammals for insulation and energy reserves. Proteins in food are broken down during digestion and the resulting amino acids are absorbed. All of the proteins in the body must be formed from these amino-acid constituents; no proteins are obtained directly from food. Fats add flavor to food and promote a sense of satiety or fullness. Fatty foods are also significant sources of energy, and fatty acids are required for the construction of lipid membranes. Fats are also required in the diet to aid the absorption of fat-soluble vitamins and the production of fat-soluble hormones. While the animal body can synthesize many of the molecules required for function from precursors, there are some nutrients that must be obtained from food. These nutrients are termed essential nutrients, meaning they must be eaten, because the body cannot produce them. diff --git a/modules/m45536/index.cnxml b/modules/m45536/index.cnxml index 198ff031d..12032b75e 100644 --- a/modules/m45536/index.cnxml +++ b/modules/m45536/index.cnxml @@ -40,7 +40,7 @@ - Watch this video for a review of the respiratory system. + Watch this video for a review of the respiratory system.
The Circulatory System @@ -74,7 +74,7 @@ The electrical impulses in the heart produce electrical currents that flow through the body and can be measured on the skin using electrodes. This information can be observed as an electrocardiogram (ECG) a recording of the electrical impulses of the cardiac muscle. - Visit this site and select the dropdown “Your Heart’s Electrical System” to see the heart’s pacemaker, or electrocardiogram system, in action.
+ Visit this site and select the dropdown “Your Heart’s Electrical System” to see the heart’s pacemaker, or electrocardiogram system, in action.
Blood Vessels The blood from the heart is carried through the body by a complex network of blood vessels (). Arteries take blood away from the heart. The main artery of the systemic circulation is the aorta; it branches into major arteries that take blood to different limbs and organs. The aorta and arteries near the heart have heavy but elastic walls that respond to and smooth out the pressure differences caused by the beating heart. Arteries farther away from the heart have more muscle tissue in their walls that can constrict to affect flow rates of blood. The major arteries diverge into minor arteries, and then smaller vessels called arterioles, to reach more deeply into the muscles and organs of the body. diff --git a/modules/m45538/index.cnxml b/modules/m45538/index.cnxml index 284651e73..a48324617 100644 --- a/modules/m45538/index.cnxml +++ b/modules/m45538/index.cnxml @@ -22,7 +22,7 @@ The human skeleton is an endoskeleton that consists of 206 bones in the adult. An endoskeleton develops within the body rather than outside like the exoskeleton of insects. The skeleton has five main functions: providing support to the body, storing minerals and lipids, producing blood cells, protecting internal organs, and allowing for movement. The skeletal system in vertebrates is divided into the axial skeleton (which consists of the skull, vertebral column, and rib cage), and the appendicular skeleton (which consists of limb bones, the pectoral or shoulder girdle, and the pelvic girdle). - Explore the human skeleton by viewing the following video with digital 3D sculpturing. + Explore the human skeleton by viewing the following video with digital 3D sculpturing. The axial skeleton forms the central axis of the body and includes the bones of the skull, ossicles of the middle ear, hyoid bone of the throat, vertebral column, and the thoracic cage (rib cage) ().
@@ -79,7 +79,7 @@ Rheumatologists are medical doctors who specialize in the diagnosis and treatmen The thick and thin filaments alternate with each other in a structure called a sarcomere. The sarcomere is the unit of contraction in a muscle cell. Contraction is stimulated by an electrochemical signal from a nerve cell associated with the muscle fiber. For a muscle cell to contract, the sarcomere must shorten. However, thick and thin filaments do not shorten. Instead, they slide by one another, causing the sarcomere to shorten while the filaments remain the same length. The sliding is accomplished when a molecular extension of myosin, called the myosin head, temporarily binds to an actin filament next to it and through a change in conformation, bends, dragging the two filaments in opposite directions. The myosin head then releases its actin filament, relaxes, and then repeats the process, dragging the two filaments further along each other. The combined activity of many binding sites and repeated movements within the sarcomere causes it to contract. The coordinated contractions of many sarcomeres in a myofibril leads to contraction of the entire muscle cell and ultimately the muscle itself. The movement of the myosin head requires ATP, which provides the energy for the contraction. - View this animation to see how muscle fibers are organized. + View this animation to see how muscle fibers are organized.
Section SummaryThe human skeleton is an endoskeleton that is composed of the axial and appendicular skeleton. The axial skeleton is composed of the bones of the skull, ossicles of the ear, hyoid bone, vertebral column, and ribcage. The skull consists of eight cranial bones and 14 facial bones. Six bones make up the ossicles of the middle ear, while the hyoid bone is located in the neck under the mandible. The vertebral column contains 26 bones and surrounds and protects the spinal cord. The thoracic cage consists of the sternum, ribs, thoracic vertebrae, and costal cartilages. The appendicular skeleton is made up of the upper and lower limbs. The pectoral girdle is composed of the clavicles and the scapulae. The upper limb contains 30 bones in the arm, the forearm, and the hand. The pelvic girdle attaches the lower limbs to the axial skeleton. The lower limb includes the bones of the thigh, the leg, and the foot. diff --git a/modules/m45539/index.cnxml b/modules/m45539/index.cnxml index b6378906d..b0f078f21 100644 --- a/modules/m45539/index.cnxml +++ b/modules/m45539/index.cnxml @@ -45,7 +45,7 @@ At one time, scientists believed that people were born with all the neurons they This image shows new neurons in a rat hippocampus. New neurons tagged with BrdU glow red in this micrograph. (credit: modification of work by Dr. Maryam Faiz, University of Barcelona) - Visit this link interactive lab to see more information about neurogenesis, including an interactive laboratory simulation and a video that explains how BrdU labels new cells. + Visit this link interactive lab to see more information about neurogenesis, including an interactive laboratory simulation and a video that explains how BrdU labels new cells. While glial cells are often thought of as the supporting cast of the nervous system, the number of glial cells in the brain actually outnumbers the number of neurons by a factor of 10. Neurons would be unable to function without the vital roles that are fulfilled by these glial cells. Glia guide developing neurons to their destinations, buffer ions and chemicals that would otherwise harm neurons, and provide myelin sheaths around axons. When glia do not function properly, the result can be disastrous—most brain tumors are caused by mutations in glia.
@@ -65,7 +65,7 @@ At one time, scientists believed that people were born with all the neurons they In other surgeries to treat severe epilepsy, the corpus callosum is cut instead of removing an entire hemisphere. This causes a condition called split-brain, which gives insights into unique functions of the two hemispheres. For example, when an object is presented to patients’ left visual field, they may be unable to verbally name the object (and may claim to not have seen an object at all). This is because the visual input from the left visual field crosses and enters the right hemisphere and cannot then signal to the speech center, which generally is found in the left side of the brain. Remarkably, if a split-brain patient is asked to pick up a specific object out of a group of objects with the left hand, the patient will be able to do so but will still be unable to verbally identify it. - Visit the following website to learn more about split-brain patients and to play a game where you can model split-brain experiments yourself. + Visit the following website to learn more about split-brain patients and to play a game where you can model split-brain experiments yourself. Each hemisphere contains regions called lobes that are involved in different functions. Each hemisphere of the mammalian cerebral cortex can be broken down into four functionally and spatially defined lobes: frontal, parietal, temporal, and occipital ().
diff --git a/modules/m45541/index.cnxml b/modules/m45541/index.cnxml index 476a9f788..59ae00217 100644 --- a/modules/m45541/index.cnxml +++ b/modules/m45541/index.cnxml @@ -59,7 +59,7 @@ A virus attaches to a specific receptor site on the host-cell membrane through attachment proteins in the capsid or proteins embedded in its envelope. The attachment is specific, and typically a virus will only attach to cells of one or a few species and only certain cell types within those species with the appropriate receptors. - View this video for a visual explanation of how influenza attacks the body. + View this video for a visual explanation of how influenza attacks the body. Unlike animal viruses, the nucleic acid of bacteriophages is injected into the host cell naked, leaving the capsid outside the cell. Plant and animal viruses can enter their cells through endocytosis, in which the cell membrane surrounds and engulfs the entire virus. Some enveloped viruses enter the cell when the viral envelope fuses directly with the cell membrane. Once inside the cell, the viral capsid is degraded and the viral nucleic acid is released, which then becomes available for replication and transcription. The replication mechanism depends on the viral genome. DNA viruses usually use host cell proteins and enzymes to make additional DNA that is used to copy the genome or be transcribed to messenger RNA (mRNA), which is then used in protein synthesis. RNA viruses, such as the influenza virus, usually use the RNA core as a template for synthesis of viral genomic RNA and mRNA. The viral mRNA is translated into viral enzymes and capsid proteins to assemble new virions (). Of course, there are exceptions to this pattern. If a host cell does not provide the enzymes necessary for viral replication, viral genes supply the information to direct synthesis of the missing proteins. Retroviruses, such as HIV, have an RNA genome that must be reverse transcribed to make DNA, which then is inserted into the host’s DNA. To convert RNA into DNA, retroviruses contain genes that encode the virus-specific enzyme reverse transcriptase that transcribes an RNA template to DNA. The fact that HIV produces some of its own enzymes, which are not found in the host, has allowed researchers to develop drugs that inhibit these enzymes. These drugs, including the reverse transcriptase inhibitor AZT, inhibit HIV replication by reducing the activity of the enzyme without affecting the host’s metabolism. The last stage of viral replication is the release of the new virions into the host organism, where they are able to infect adjacent cells and repeat the replication cycle. Some viruses are released when the host cell dies and other viruses can leave infected cells by budding through the membrane without directly killing the cell. @@ -72,7 +72,7 @@ - Click through this tutorial on viruses to identify structures, modes of transmission, replication, and more. + Click through this tutorial on viruses to identify structures, modes of transmission, replication, and more.
Viruses and Disease diff --git a/modules/m45543/index.cnxml b/modules/m45543/index.cnxml index 254395c46..1e514a55c 100644 --- a/modules/m45543/index.cnxml +++ b/modules/m45543/index.cnxml @@ -48,7 +48,7 @@ An antigen-presenting cell (APC), such as a macrophage, engulfs a foreign antigen, partially digests it in a lysosome, and then embeds it in an MHC class II molecule for presentation at the cell surface. Lymphocytes of the adaptive immune response must interact with antigen-embedded MHC class II molecules to mature into functional immune cells. - View this animation from Rockefeller University to see how dendritic cells act as sentinels in the body’s immune system. + View this animation from Rockefeller University to see how dendritic cells act as sentinels in the body’s immune system. T cells have many functions. Some respond to APCs of the innate immune system and indirectly induce immune responses by releasing cytokines. Others stimulate B cells to start the humoral response as described previously. Another type of T cell detects APC signals and directly kills the infected cells, while some are involved in suppressing inappropriate immune reactions to harmless or “self” antigens. There are two main types of T cells: helper T lymphocytes (TH) and the cytotoxic T lymphocytes (TC). The TH lymphocytes function indirectly to tell other immune cells about potential pathogens. TH lymphocytes recognize specific antigens presented by the MHC class II complexes of APCs. There are two populations of TH cells: TH1 and TH2. TH1 cells secrete cytokines to enhance the activities of macrophages and other T cells. TH2 cells stimulate naïve B cells to secrete antibodies. Whether a TH1 or a TH2 immune response develops depends on the specific types of cytokines secreted by cells of the innate immune system, which in turn depends on the nature of the invading pathogen. Cytotoxic T cells (TC) are the key component of the cell-mediated part of the adaptive immune system and attack and destroy infected cells. TC cells are particularly important in protecting against viral infections; this is because viruses replicate within cells where they are shielded from extracellular contact with circulating antibodies. Once activated, the TC creates a large clone of cells with one specific set of cell-surface receptors, as in the case with proliferation of activated B cells. As with B cells, the clone includes active TC cells and inactive memory TC cells. The resulting active TC cells then identify infected host cells. Because of the time required to generate a population of clonal T and B cells, there is a delay in the adaptive immune response compared to the innate immune response. diff --git a/modules/m45545/index.cnxml b/modules/m45545/index.cnxml index b40a83c61..e5d02b8b9 100644 --- a/modules/m45545/index.cnxml +++ b/modules/m45545/index.cnxml @@ -34,7 +34,7 @@ On first exposure to an allergen, an antibody is synthesized by plasma cells in response to a harmless antigen. The antibodies bind to mast cells, and on secondary exposure, the mast cells release histamines and other modulators that cause the symptoms of allergy. (credit: modification of work by NIH)Delayed hypersensitivity is a cell-mediated immune response that takes approximately one to two days after secondary exposure for a maximal reaction. This type of hypersensitivity involves the TH1 cytokine-mediated inflammatory response and may cause local tissue lesions or contact dermatitis (rash or skin irritation). Delayed hypersensitivity occurs in some individuals in response to contact with certain types of jewelry or cosmetics. Delayed hypersensitivity facilitates the immune response to poison ivy and is also the reason why the skin test for tuberculosis results in a small region of inflammation on individuals who were previously exposed to Mycobacterium tuberculosis, the organism that causes tuberculosis. - Try your hand at diagnosing an allergic reaction by selecting one of the interactive case studies at the World Allergy Organization website. + Try your hand at diagnosing an allergic reaction by selecting one of the interactive case studies at the World Allergy Organization website.
Autoimmunity diff --git a/modules/m45547/index.cnxml b/modules/m45547/index.cnxml index 467d96beb..8fa07a8fc 100644 --- a/modules/m45547/index.cnxml +++ b/modules/m45547/index.cnxml @@ -35,7 +35,7 @@ (a) Hydra reproduce asexually through budding: a bud forms on the tubular body of an adult hydra, develops a mouth and tentacles, and then detaches from its parent. The new hydra is fully developed and will find its own location for attachment. (b) Some coral, such as the Lophelia pertusa shown here, can reproduce through budding. (credit b: modification of work by Ed Bowlby, NOAA/Olympic Coast NMS; NOAA/OAR/Office of Ocean Exploration) - View this video to see a hydra budding. + View this video to see a hydra budding.
Fragmentation diff --git a/modules/m45549/index.cnxml b/modules/m45549/index.cnxml index 17ea4b955..3dafbe6ff 100644 --- a/modules/m45549/index.cnxml +++ b/modules/m45549/index.cnxml @@ -186,7 +186,7 @@ During spermatogenesis, four sperm result from each primary spermatocyte. The process also maps onto the physical structure of the wall of the seminiferous tubule, with the spermatogonia on the outer side of the tubule, and the sperm with their developing tails extended into the lumen of the tubule. - Visit this site to see the process of spermatogenesis. + Visit this site to see the process of spermatogenesis.
Oogenesis @@ -251,7 +251,7 @@ (a) Fetal development is shown at nine weeks gestation. (b) This fetus is just entering the second trimester, when the placenta takes over more of the functions performed as the baby develops. (c) There is rapid fetal growth during the third trimester. (credit a: modification of work by Ed Uthman; credit b: modification of work by National Museum of Health and Medicine; credit c: modification of work by Gray’s Anatomy)During the second trimester, the fetus grows to about 30 cm (about 12 inches) (b). It becomes active and the pregnant person usually feels the first movements. All organs and structures continue to develop. The placenta has taken over the functions of nutrition and waste elimination and the production of estrogen and progesterone from the corpus luteum, which has degenerated. The placenta will continue functioning up through the delivery of the baby. During the third trimester, the fetus grows to 3 to 4 kg (6.5–8.5 lbs.) and about 50 cm (19–20 inches) long (c). This is the period of the most rapid growth during the pregnancy as all organ systems continue to grow and develop. - Visit this website to see the stages of human fetal development.Labor is the muscular contractions to expel the fetus and placenta from the uterus. Toward the end of the third trimester, estrogen causes receptors on the uterine wall to develop and bind the hormone oxytocin. At this time, the baby reorients, facing forward and down with the back or crown of the head engaging the cervix (uterine opening). This causes the cervix to stretch and nerve impulses are sent to the hypothalamus, which signals the release of oxytocin from the posterior pituitary. Oxytocin causes smooth muscle in the uterine wall to contract. At the same time, the placenta releases prostaglandins into the uterus, increasing the contractions. A positive feedback relay occurs between the uterus, hypothalamus, and the posterior pituitary to assure an adequate supply of oxytocin. As more smooth muscle cells are recruited, the contractions increase in intensity and force. + Visit this website to see the stages of human fetal development.Labor is the muscular contractions to expel the fetus and placenta from the uterus. Toward the end of the third trimester, estrogen causes receptors on the uterine wall to develop and bind the hormone oxytocin. At this time, the baby reorients, facing forward and down with the back or crown of the head engaging the cervix (uterine opening). This causes the cervix to stretch and nerve impulses are sent to the hypothalamus, which signals the release of oxytocin from the posterior pituitary. Oxytocin causes smooth muscle in the uterine wall to contract. At the same time, the placenta releases prostaglandins into the uterus, increasing the contractions. A positive feedback relay occurs between the uterus, hypothalamus, and the posterior pituitary to assure an adequate supply of oxytocin. As more smooth muscle cells are recruited, the contractions increase in intensity and force. There are three stages to labor. During stage one, the cervix thins and dilates. This is necessary for the baby and placenta to be expelled during birth. The cervix will eventually dilate to about 10 cm. During stage two, the baby is expelled from the uterus. The uterus contracts and, in most cases, the person giving birth pushes as they compress the abdominal muscles to aid the delivery. The last stage is the passage of the placenta after the baby has been born and the organ has completely disengaged from the uterine wall. If labor should stop before stage two is reached, synthetic oxytocin, known as Pitocin, can be administered to restart and maintain labor.
diff --git a/modules/m45550/index.cnxml b/modules/m45550/index.cnxml index b40658fbc..d827f5728 100644 --- a/modules/m45550/index.cnxml +++ b/modules/m45550/index.cnxml @@ -29,7 +29,7 @@ (a) During cleavage, the zygote rapidly divides into multiple cells. (b) The cells rearrange themselves to form a hollow ball called the blastula. (credit a: modification of work by Gray's Anatomy; credit b: modification of work by Pearson Scott Foresman; donated to the Wikimedia Foundation)In mammals, the blastula forms the blastocyst in the next stage of development. Here the cells in the blastula arrange themselves in two layers: the inner cell mass, and an outer layer called the trophoblast. The inner cell mass will go on to form the embryo. The trophoblast secretes enzymes that allow implantation of the blastocyst into the endometrium of the uterus. The trophoblast will contribute to the placenta and nourish the embryo. - Visit the Virtual Human Embryo project at the Endowment for Human Development site to click through an interactive of the stages of embryo development, including micrographs and rotating 3-D images. + Visit the Virtual Human Embryo project at the Endowment for Human Development site to click through an interactive of the stages of embryo development, including micrographs and rotating 3-D images. The cells in the blastula then rearrange themselves spatially to form three layers of cells. This process is called gastrulation. During gastrulation, the blastula folds in on itself and cells migrate to form the three layers of cells () in a structure, the gastrula, with a hollow space that will become the digestive tract. Each of the layers of cells is called a germ layer and will differentiate into different organ systems.
diff --git a/modules/m45554/index.cnxml b/modules/m45554/index.cnxml index 06763d6e3..f0b84d482 100644 --- a/modules/m45554/index.cnxml +++ b/modules/m45554/index.cnxml @@ -27,7 +27,7 @@ The time between the addition of each billion human beings to Earth decreases over time. (credit: modification of work by Ryan T. Cragun)
-Click through this video of how human populations have changed over time.
+Click through this video of how human populations have changed over time.
Overcoming Density-Dependent Regulation Humans are unique in their ability to alter their environment in myriad ways. This ability is responsible for human population growth because it resets the carrying capacity and overcomes density-dependent growth regulation. Much of this ability is related to human intelligence, society, and communication. Humans construct shelters to protect themselves from the elements and have developed agriculture and domesticated animals to increase their food supplies. In addition, humans use language to communicate this technology to new generations, allowing them to improve upon previous accomplishments. Other factors in human population growth are migration and public health. Humans originated in Africa, but we have since migrated to nearly all inhabitable land on Earth, thus, increasing the area that we have colonized. Public health, sanitation, and the use of antibiotics and vaccines have decreased the ability of infectious disease to limit human population growth in developed countries. In the past, diseases such as the bubonic plaque of the fourteenth century killed between 30 and 60 percent of Europe’s population and reduced the overall world population by as many as one hundred million people. Infectious disease continues to have an impact on human population growth. For example, life expectancy in sub-Saharan Africa, which was increasing from 1950 to 1990, began to decline after 1985 largely as a result of HIV/AIDS mortality. The reduction in life expectancy caused by HIV/AIDS was estimated to be 7 years for 2005.Danny Dorling, Mary Shaw, and George Davey Smith, “Global Inequality of Life Expectancy due to AIDS,” BMJ 332, no. 7542 (March 2006): 662-664, doi: 10.1136/bmj.332.7542.662. @@ -56,7 +56,7 @@ Another consequence of population growth is the change and degradation of the natural environment. Many countries have attempted to reduce the human impact on climate change by limiting their emission of greenhouse gases. However, a global climate change treaty remains elusive, and many underdeveloped countries trying to improve their economic condition may be less likely to agree with such provisions without compensation if it means slowing their economic development. Furthermore, the role of human activity in causing climate change has become a hotly debated socio-political issue in some developed countries, including the United States. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment to maintain the carrying capacity for the human species. -Visit this website and select “Launch the movie” for an animation discussing the global impacts of human population growth. +Visit this website and select “Launch the movie” for an animation discussing the global impacts of human population growth.
Section SummaryEarth’s human population is growing exponentially. Humans have increased their carrying capacity through technology, urbanization, and harnessing the energy of fossil fuels. The age structure of a population allows us to predict population growth. Unchecked human population growth could have dire long-term effects on human welfare and Earth’s ecosystems. diff --git a/modules/m45555/index.cnxml b/modules/m45555/index.cnxml index 35f262a95..a04c74dc7 100644 --- a/modules/m45555/index.cnxml +++ b/modules/m45555/index.cnxml @@ -45,7 +45,7 @@ Several unpleasant-tasting Heliconius butterfly species share a similar color pattern with better-tasting varieties, an example of mimicry. (credit: Joron M, Papa R, Beltrán M, Chamberlain N, Mavárez J, et al.) -Go to this website to view stunning examples of mimicry. +Go to this website to view stunning examples of mimicry.
@@ -80,7 +80,7 @@ This diagram shows the life cycle of the tapeworm, a human worm parasite. (credit: modification of work by CDC) -To learn more about “Symbiosis in the Sea,” watch this webisode of Jonathan Bird’s Blue World.
+To learn more about “Symbiosis in the Sea,” watch this webisode of Jonathan Bird’s Blue World.
Characteristics of Communities diff --git a/modules/m45558/index.cnxml b/modules/m45558/index.cnxml index 59bd76bad..cdd77b106 100644 --- a/modules/m45558/index.cnxml +++ b/modules/m45558/index.cnxml @@ -65,7 +65,7 @@ -Head to this online interactive simulator to investigate food web function. In the Interactive Labs box, under Food Web, click Step 1. Read the instructions first, and then click Step 2 for additional instructions. When you are ready to create a simulation, in the upper-right corner of the Interactive Labs box, click OPEN SIMULATOR.Two general types of food webs are often shown interacting within a single ecosystem. A grazing food web has plants or other photosynthetic organisms at its base, followed by herbivores and various carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter (dead organisms), including decomposers (which break down dead and decaying organisms) and detritivores (which consume organic detritus). These organisms are usually bacteria, fungi, and invertebrate animals that recycle organic material back into the biotic part of the ecosystem as they themselves are consumed by other organisms. As ecosystems require a method to recycle material from dead organisms, grazing food webs have an associated detrital food web. For example, in a meadow ecosystem, plants may support a grazing food web of different organisms, primary and other levels of consumers, while at the same time supporting a detrital food web of bacteria and fungi feeding off dead plants and animals. Simultaneously, a detrital food web can contribute energy to a grazing food web, as when a robin eats an earthworm. +Head to this online interactive simulator to investigate food web function. In the Interactive Labs box, under Food Web, click Step 1. Read the instructions first, and then click Step 2 for additional instructions. When you are ready to create a simulation, in the upper-right corner of the Interactive Labs box, click OPEN SIMULATOR.Two general types of food webs are often shown interacting within a single ecosystem. A grazing food web has plants or other photosynthetic organisms at its base, followed by herbivores and various carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter (dead organisms), including decomposers (which break down dead and decaying organisms) and detritivores (which consume organic detritus). These organisms are usually bacteria, fungi, and invertebrate animals that recycle organic material back into the biotic part of the ecosystem as they themselves are consumed by other organisms. As ecosystems require a method to recycle material from dead organisms, grazing food webs have an associated detrital food web. For example, in a meadow ecosystem, plants may support a grazing food web of different organisms, primary and other levels of consumers, while at the same time supporting a detrital food web of bacteria and fungi feeding off dead plants and animals. Simultaneously, a detrital food web can contribute energy to a grazing food web, as when a robin eats an earthworm.
How Organisms Acquire Energy in a Food Web diff --git a/modules/m45559/index.cnxml b/modules/m45559/index.cnxml index 4cc14acb0..0e8b3f021 100644 --- a/modules/m45559/index.cnxml +++ b/modules/m45559/index.cnxml @@ -18,7 +18,7 @@ The cycling of these elements is interconnected. For example, the movement of water is critical for the leaching of nitrogen and phosphate into rivers, lakes, and oceans. The ocean is also a major reservoir for carbon. Thus, mineral nutrients are cycled, either rapidly or slowly, through the entire biosphere between the biotic and abiotic world and from one living organism to another. -Head to this website to learn more about biogeochemical cycles.
+Head to this website to learn more about biogeochemical cycles.
The Water Cycle Water is essential for all living processes. The human body is more than one-half water and human cells are more than 70 percent water. Thus, most land animals need a supply of fresh water to survive. Of the stores of water on Earth, 97.5 percent is salt water (). Of the remaining water, 99 percent is locked as underground water or ice. Thus, less than one percent of fresh water is present in lakes and rivers. Many living things are dependent on this small amount of surface fresh water supply, a lack of which can have important effects on ecosystem dynamics. Humans, of course, have developed technologies to increase water availability, such as digging wells to harvest groundwater, storing rainwater, and using desalination to obtain drinkable water from the ocean. Although this pursuit of drinkable water has been ongoing throughout human history, the supply of fresh water continues to be a major issue in modern times.
diff --git a/modules/m45560/index.cnxml b/modules/m45560/index.cnxml index 41f935497..88c99dea0 100644 --- a/modules/m45560/index.cnxml +++ b/modules/m45560/index.cnxml @@ -112,7 +112,7 @@
-Watch this Assignment Discovery: Biomes video for an overview of biomes. To explore further, select one of the biomes on the extended playlist: desert, savanna, temperate forest, temperate grassland, tropic, tundra. +Watch this Assignment Discovery: Biomes video for an overview of biomes. To explore further, select one of the biomes on the extended playlist: desert, savanna, temperate forest, temperate grassland, tropic, tundra.
Section SummaryEarth has terrestrial and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. The same biome can occur in different geographic locations with similar climates. Temperature and precipitation, and variations in both, are key abiotic factors that shape the composition of animal and plant communities in terrestrial biomes. Some biomes, such as temperate grasslands and temperate forests, have distinct seasons with cold and hot weather alternating throughout the year. In warm, moist biomes, such as the tropical rainforest, net primary productivity is high as warm temperatures, abundant water, and a year-round growing season fuel plant growth. Other biomes, such as deserts and tundra, have low primary productivity due to extreme temperatures and a shortage of water. diff --git a/modules/m45562/index.cnxml b/modules/m45562/index.cnxml index 153fc85eb..7ef94643f 100644 --- a/modules/m45562/index.cnxml +++ b/modules/m45562/index.cnxml @@ -54,7 +54,7 @@ Coral reefs are ocean ridges formed by marine invertebrates living in warm shallow waters within the photic zone of the ocean. They are found within 30˚ north and south of the equator. The Great Barrier Reef is a well-known reef system located several miles off the northeastern coast of Australia. Other coral reefs are fringing islands, which are directly adjacent to land, or atolls, which are circular reefs surrounding a former island that is now underwater. The coral-forming colonies of organisms (members of phylum Cnidaria) secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, thus forming the underwater reef (). Corals found in shallower waters (at a depth of approximately 60 m or about 200 ft) have a mutualistic relationship with photosynthetic unicellular protists. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor and, without this mutualism, it would not be possible for large corals to grow because there are few planktonic organisms for them to feed on. Some corals living in deeper and colder water do not have a mutualistic relationship with protists; these corals must obtain their energy exclusively by feeding on plankton using stinging cells on their tentacles. -In this National Oceanic and Atmospheric Administration (NOAA) video, marine ecologist Dr. Peter Etnoyer discusses his research on coral organisms.Coral reefs are one of the most diverse biomes. It is estimated that more than 4000 fish species inhabit coral reefs. These fishes can feed on coral, the cryptofauna (invertebrates found within the calcium carbonate structures of the coral reefs), or the seaweed and algae that are associated with the coral. These species include predators, herbivores, or planktivores. Predators are animal species that hunt and are carnivores or “flesh eaters.” Herbivores eat plant material, and planktivores eat plankton. +In this National Oceanic and Atmospheric Administration (NOAA) video, marine ecologist Dr. Peter Etnoyer discusses his research on coral organisms.Coral reefs are one of the most diverse biomes. It is estimated that more than 4000 fish species inhabit coral reefs. These fishes can feed on coral, the cryptofauna (invertebrates found within the calcium carbonate structures of the coral reefs), or the seaweed and algae that are associated with the coral. These species include predators, herbivores, or planktivores. Predators are animal species that hunt and are carnivores or “flesh eaters.” Herbivores eat plant material, and planktivores eat plankton.
diff --git a/modules/m45571/index.cnxml b/modules/m45571/index.cnxml index 00fe9b018..73126f0e2 100644 --- a/modules/m45571/index.cnxml +++ b/modules/m45571/index.cnxml @@ -181,7 +181,7 @@ Biogeography is the study of the distribution of the world’s species both in t Fishery extinctions rarely lead to complete extinction of the harvested species, but rather to a radical restructuring of the marine ecosystem in which a dominant species is so over-harvested that it becomes a minor player, ecologically. In addition to humans losing the food source, these alterations affect many other species in ways that are difficult or impossible to predict. The collapse of fisheries has dramatic and long-lasting effects on local human populations that work in the fishery. In addition, the loss of an inexpensive protein source to populations that cannot afford to replace it will increase the cost of living and limit societies in other ways. In general, the fish taken from fisheries have shifted to smaller species and the larger species are overfished. The ultimate outcome could clearly be the loss of aquatic systems as food sources. -Visit this website to view a brief video discussing a study of declining fisheries. +Visit this website to view a brief video discussing a study of declining fisheries.
Section SummaryBiodiversity exists at multiple levels of organization, and is measured in different ways depending on the goals of those taking the measurements. These include numbers of species, genetic diversity, chemical diversity, and ecosystem diversity. The number of described species is estimated to be 1.5 million with about 17,000 new species being described each year. Estimates for the total number of eukaryotic species on Earth vary but are on the order of 10 million. Biodiversity is negatively correlated with latitude for most taxa, meaning that biodiversity is higher in the tropics. The mechanism for this pattern is not known with certainty, but several plausible hypotheses have been advanced. diff --git a/modules/m45573/index.cnxml b/modules/m45573/index.cnxml index 69582aaf0..ceb6367d2 100644 --- a/modules/m45573/index.cnxml +++ b/modules/m45573/index.cnxml @@ -44,7 +44,7 @@ A typical species-area curve shows the cumulative number of species found as more and more area is sampled. The curve has also been interpreted to show the effect on species numbers of destroying habitat; a reduction in habitat of 90 percent from 100 km2 to 10 km2 reduces the number of species supported by about 50 percent. - Go to this website for an interactive exploration of endangered and extinct species, their ecosystems, and the causes of their endangerment or extinction. + Go to this website for an interactive exploration of endangered and extinct species, their ecosystems, and the causes of their endangerment or extinction.
Conservation of Biodiversity The threats to biodiversity at the genetic, species, and ecosystem levels have been recognized for some time. In the United States, the first national park with land set aside to remain in a wilderness state was Yellowstone Park in 1872. However, attempts to preserve nature for various reasons have occurred for centuries. Today, the main efforts to preserve biodiversity involve legislative approaches to regulate human and corporate behavior, setting aside protected areas, and habitat restoration. @@ -72,7 +72,7 @@ Finally, an argument can be made that conservation preserves reinforce the cultural perception that humans are separate from nature, can exist outside of it, and can only operate in ways that do damage to biodiversity. Creating preserves reduces the pressure on human activities outside the preserves to be sustainable and non-damaging to biodiversity. Ultimately, the political, economic, and human demographic pressures will degrade and reduce the size of conservation preserves if the activities outside them are not altered to be less damaging to biodiversity. - Check out this interactive global data system of protected areas. Review data about specific protected areas by location or study statistics on protected areas by country or region. + Check out this interactive global data system of protected areas. Review data about specific protected areas by location or study statistics on protected areas by country or region.
Habitat Restoration Habitat restoration holds considerable promise as a mechanism for maintaining or restoring biodiversity. Of course once a species has become extinct, its restoration is impossible. However, restoration can improve the biodiversity of degraded ecosystems. Reintroducing wolves, a top predator, to Yellowstone National Park in 1995 led to dramatic changes in the ecosystem that increased biodiversity. The wolves () function to suppress elk and coyote populations and provide more abundant resources to the guild of carrion eaters. Reducing elk populations has allowed revegetation of riparian (the areas along the banks of a stream or river) areas, which has increased the diversity of species in that habitat. Suppression of coyotes has increased the species previously suppressed by this predator. The number of species of carrion eaters has increased because of the predatory activities of the wolves. In this habitat, the wolf is a keystone species, meaning a species that is instrumental in maintaining diversity within an ecosystem. Removing a keystone species from an ecological community causes a collapse in diversity. The results from the Yellowstone experiment suggest that restoring a keystone species effectively can have the effect of restoring biodiversity in the community. Ecologists have argued for the identification of keystone species where possible and for focusing protection efforts on these species. It makes sense to return the keystone species to the ecosystems where they have been removed. diff --git a/modules/m45574/index.cnxml b/modules/m45574/index.cnxml index 6cafe4550..9e93041b2 100644 --- a/modules/m45574/index.cnxml +++ b/modules/m45574/index.cnxml @@ -33,16 +33,16 @@ Most consumers do not imagine that the home improvement products they buy might Habitat destruction can affect ecosystems other than forests. Rivers and streams are important ecosystems and are frequently the target of habitat modification through building and from damming or water removal. Damming of rivers affects flows and access to all parts of a river. Altering a flow regime can reduce or eliminate populations that are adapted to seasonal changes in flow. For example, an estimated 91 percent of river lengths in the United States have been modified with damming or bank modifications. Many fish species in the United States, especially rare species or species with restricted distributions, have seen declines caused by river damming and habitat loss. Research has confirmed that species of amphibians that must carry out parts of their life cycles in both aquatic and terrestrial habitats are at greater risk of population declines and extinction because of the increased likelihood that one of their habitats or access between them will be lost. This is of particular concern because amphibians have been declining in numbers and going extinct more rapidly than many other groups for a variety of possible reasons. Habitat destruction, even when undertaken on behalf of humans, can lead to negative effects for us as well. Excessive soil erosion after forest removal, for example, can remove fertile soil and make river water toxic. Scientists and conservationists such as Wangari Maathai, who founded the Green Belt movement in Kenya, focus on replanting trees to repair habitats and prevent damage from deforestation. Maathai was awarded a Nobel Prize for her work, but unfortunately passed away in 2011.
OverharvestingOverharvesting is a serious threat to many species, but particularly to aquatic species. There are many examples of regulated fisheries (including hunting of marine mammals and harvesting of crustaceans and other species) monitored by fisheries scientists that have nevertheless collapsed. The western Atlantic cod fishery is the most spectacular recent collapse. While it was a hugely productive fishery for 400 years, the introduction of modern factory trawlers in the 1980s and the pressure on the fishery led to it becoming unsustainable. The causes of fishery collapse are both economic and political in nature. Most fisheries are managed as a common resource, available to anyone willing to fish, even when the fishing territory lies within a country’s territorial waters. Common resources are subject to an economic pressure known as the tragedy of the commons, in which fishers have little motivation to exercise restraint in harvesting a fishery when they do not own the fishery. The general outcome of harvests of resources held in common is their overexploitation. While large fisheries are regulated to attempt to avoid this pressure, it still exists in the background. This overexploitation is exacerbated when access to the fishery is open and unregulated and when technology gives fishers the ability to overfish. In a few fisheries, the biological growth of the resource is less than the potential growth of the profits made from fishing if that time and money were invested elsewhere. In these cases—whales are an example—economic forces will drive toward fishing the population to extinction. - Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States. To begin, select “Visit the online mapper.”For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. But there are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. Also, there are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing. + Explore a U.S. Fish & Wildlife Service interactive map of critical habitat for endangered and threatened species in the United States. To begin, select “Visit the online mapper.”For the most part, fishery extinction is not equivalent to biological extinction—the last fish of a species is rarely fished out of the ocean. But there are some instances in which true extinction is a possibility. Whales have slow-growing populations and are at risk of complete extinction through hunting. Also, there are some species of sharks with restricted distributions that are at risk of extinction. The groupers are another population of generally slow-growing fishes that, in the Caribbean, includes a number of species that are at risk of extinction from overfishing. Coral reefs are extremely diverse marine ecosystems that face peril from several processes. Reefs are home to 1/3 of the world’s marine fish species—about 4000 species—despite making up only one percent of marine habitat. Most home marine aquaria house coral reef species that are wild-caught organisms—not cultured organisms. Although no marine species is known to have been driven extinct by the pet trade, there are studies showing that populations of some species have declined in response to harvesting, indicating that the harvest is not sustainable at those levels. There are also concerns about the effect of the pet trade on some terrestrial species such as turtles, amphibians, birds, plants, and even the orangutans. - View a brief video discussing the role of marine ecosystems in supporting human welfare and the decline of ocean ecosystems.Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many monkeys and the great apes living in the Congo basin. + View a brief video discussing the role of marine ecosystems in supporting human welfare and the decline of ocean ecosystems.Bush meat is the generic term used for wild animals killed for food. Hunting is practiced throughout the world, but hunting practices, particularly in equatorial Africa and parts of Asia, are believed to threaten several species with extinction. Traditionally, bush meat in Africa was hunted to feed families directly; however, recent commercialization of the practice now has bush meat available in grocery stores, which has increased harvest rates to the level of unsustainability. Additionally, human population growth has increased the need for protein foods that are not being met from agriculture. Species threatened by the bush meat trade are mostly mammals including many monkeys and the great apes living in the Congo basin.
Exotic SpeciesExotic species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. Human transportation of people and goods, including the intentional transport of organisms for trade, has dramatically increased the introduction of species into new ecosystems. These new introductions are sometimes at distances that are well beyond the capacity of the species to ever travel itself and outside the range of the species’ natural predators. Most exotic species introductions probably fail because of the low number of individuals introduced or poor adaptation to the ecosystem they enter. Some species, however, have characteristics that can make them especially successful in a new ecosystem. These exotic species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. When this happens, the exotic species also becomes an invasive species. Invasive species can threaten other species through competition for resources, predation, or disease. - Explore this interactive global database of exotic or invasive species. + Explore this interactive global database of exotic or invasive species. Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft () from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island. Several other species are still threatened. The brown tree snake is adept at exploiting human transportation as a means to migrate; one was even found on an aircraft arriving in Corpus Christi, Texas. Constant vigilance on the part of airport, military, and commercial aircraft personnel is required to prevent the snake from moving from Guam to other islands in the Pacific, especially Hawaii. Islands do not make up a large area of land on the globe, but they do contain a disproportionate number of endemic species because of their isolation from mainland ancestors.
diff --git a/modules/m62716/index.cnxml b/modules/m62716/index.cnxml index 2a05b44bc..15b8e5571 100644 --- a/modules/m62716/index.cnxml +++ b/modules/m62716/index.cnxml @@ -15,12 +15,12 @@ This NASA image is a composite of several satellite-based views of Earth. To make the whole-Earth image, NASA scientists combine observations of different parts of the planet. (credit: NASA/GSFC/NOAA/USGS)
-Viewed from space, Earth offers no clues about the diversity of life it harbors. The first forms of life on Earth are thought to be microorganisms that existed for billions of years in the ocean before plants and animals appeared. The mammals, birds, and flowers that we see in modern times are mostly “recent” species, originating 130 to 200 million years ago. In fact, only in the last 300,000 years have humans started looking like we do today.Organisms evolve in response to each other. One of the best examples is disease causing organisms, which have to adapt to overcome the defenses of the organisms they infect. One such organism that has evolved to specialize in infection in humans is Plasmodium, the organism that causes malaria. Biologists use the process of science to learn about the world and the organisms living in it. For example, people have suspected for quite some time that people with blood type O are less likely to die from severe malaria. Now, a team of scientists have been able to explain why. By examining data from several experiments, and by using both inductive and deductive reasoning, the scientists concluded that A and B type blood reacts with a protein excreted by Plasmodium. This reaction causes severe illness. However, type O blood does not react with the protein. You can read more about the response of type A and B blood groups to infection by Plasmodium. +Viewed from space, Earth offers no clues about the diversity of life it harbors. The first forms of life on Earth are thought to be microorganisms that existed for billions of years in the ocean before plants and animals appeared. The mammals, birds, and flowers that we see in modern times are mostly “recent” species, originating 130 to 200 million years ago. In fact, only in the last 300,000 years have humans started looking like we do today.Organisms evolve in response to each other. One of the best examples is disease causing organisms, which have to adapt to overcome the defenses of the organisms they infect. One such organism that has evolved to specialize in infection in humans is Plasmodium, the organism that causes malaria. Biologists use the process of science to learn about the world and the organisms living in it. For example, people have suspected for quite some time that people with blood type O are less likely to die from severe malaria. Now, a team of scientists have been able to explain why. By examining data from several experiments, and by using both inductive and deductive reasoning, the scientists concluded that A and B type blood reacts with a protein excreted by Plasmodium. This reaction causes severe illness. However, type O blood does not react with the protein. You can read more about the response of type A and B blood groups to infection by Plasmodium. Introduce the concept of unity and diversity of life. There are so many varieties of organisms and, yet, the cell is the basic unit of life. The fundamental structures and life processes of cells are similar; but, how these cells are utilized in different organisms is hugely varied and reflects adaptation of the organism to its environment. The many differences between species accumulated over long periods of time. Students are often unfamiliar with geological time scales. -The malaria example was chosen because malaria has been one of the most pervasive and widespread human disease. Therefore, through much of human history, malaria has been a strong force of natural selection on humans. Human genetics has evolved in response to this selection pressure, as with the example of resistance among O-type blood groups described in the introduction. Further examples can also be found here. +The malaria example was chosen because malaria has been one of the most pervasive and widespread human disease. Therefore, through much of human history, malaria has been a strong force of natural selection on humans. Human genetics has evolved in response to this selection pressure, as with the example of resistance among O-type blood groups described in the introduction. Further examples can also be found here. diff --git a/modules/m62717/index.cnxml b/modules/m62717/index.cnxml index 9c1c3c817..b095de1de 100644 --- a/modules/m62717/index.cnxml +++ b/modules/m62717/index.cnxml @@ -63,7 +63,7 @@ Biology is not a collection of facts to be memorized. Biological systems follow the law of physics and chemistry. Give as an example gas laws in chemistry and respiration physiology. Many students come with a 19th century view of natural sciences; each discipline is in its own sphere. Give as an example, bioinformatics which uses organism biology, chemistry, and physics to label DNA with light emitting reporter molecules (Next Generation sequencing). These molecules can then be scanned by light-sensing machinery, allowing huge amounts of information to be gathered on their DNA. Bring to their attention the fact that the analysis of these data is an application of mathematics and computer science. -For more information about next generation sequencing, check out this informative review. +For more information about next generation sequencing, check out this informative review. @@ -143,7 +143,7 @@ Tell students a similar experiment on a grand scale may have happened in the past and introduce the next activity “What killed the dinosaurs?” Some predictions can be made and later observations can support or disprove the prediction. Ask, “what killed the dinosaurs?” Explain many scientists point to a massive asteroid crashing in the Yucatan peninsula in Mexico. One of the effects was the creation of smoke clouds and debris that blocked the Sun, stamped out many plants and, consequently, brought mass extinction. As is common in the scientific community, many other researchers offer divergent explanations. -Go to this site for a good example of the complexity of scientific method and scientific debate. +Go to this site for a good example of the complexity of scientific method and scientific debate. diff --git a/modules/m62718/index.cnxml b/modules/m62718/index.cnxml index e529139a0..a84d53d1b 100644 --- a/modules/m62718/index.cnxml +++ b/modules/m62718/index.cnxml @@ -85,7 +85,7 @@ The leaves of this sensitive plant (Mimosa pudica) will instantly droop and fold when touched. After a few minutes, the plant returns to normal. (credit: Alex Lomas)Organisms respond to diverse stimuli. For example, plants can bend toward a source of light, climb on fences and walls, or respond to touch (). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response. - Watch this video to see how plants respond to a stimulus—from opening to light, to wrapping a tendril around a branch, to capturing prey. + Watch this video to see how plants respond to a stimulus—from opening to light, to wrapping a tendril around a branch, to capturing prey.
Benefits of Carbohydrates Are carbohydrates good for you? Some people believe that carbohydrates are bad for them and should be avoided. Some diets completely forbid carbohydrate consumption, claiming that a low-carbohydrate diet helps people to lose weight faster. However, carbohydrates have been an important part of the human diet for thousands of years; artifacts from ancient civilizations show the presence of wheat, rice, and corn in our ancestors’ storage areas.Carbohydrates should be supplemented with proteins, vitamins, and fats to be parts of a well-balanced diet. Calorie-wise, a gram of carbohydrate provides 4.3 Kcal. For comparison, fats provide 9 Kcal/g, a less desirable ratio. Carbohydrates contain soluble and insoluble elements; the insoluble part is known as fiber, which is mostly cellulose. Fiber has many uses; it promotes regular bowel movement by adding bulk, and it regulates the rate of consumption of blood glucose. Fiber also helps to remove excess cholesterol from the body: fiber binds to the cholesterol in the small intestine, then attaches to the cholesterol and prevents the cholesterol particles from entering the bloodstream, and then cholesterol exits the body via the feces. In addition, a meal containing whole grains and vegetables gives a feeling of fullness. As an immediate source of energy, glucose is broken down during the process of cellular respiration, which produces ATP, the energy currency of the cell. Without the consumption of carbohydrates, the availability of “instant energy” would be reduced. Eliminating carbohydrates from the diet may be necessary for some people, but such a step may not be healthy for everyone. -For an additional perspective on carbohydrates, explore “Biomolecules: the Carbohydrates” through this interactive animation. +For an additional perspective on carbohydrates, explore “Biomolecules: the Carbohydrates” through this interactive animation.
Cell Death When a cell is damaged, superfluous, or potentially dangerous to an organism, a cell can initiate a mechanism to trigger programmed cell death, or apoptosis. Apoptosis allows a cell to die in a controlled manner that prevents the release of potentially damaging molecules from inside the cell. There are many internal checkpoints that monitor a cell’s health; if abnormalities are observed, a cell can spontaneously initiate the process of apoptosis. However, in some cases, such as a viral infection or uncontrolled cell division, the cell’s normal checks and balances fail. External signaling can also initiate apoptosis. For example, most normal animal cells have receptors that interact with the extracellular matrix, a network of glycoproteins that provides structural support for cells in an organism. The binding of cellular receptors to the extracellular matrix initiates a signaling cascade within the cell. However, if the cell moves away from the extracellular matrix, the signaling ceases, and the cell undergoes apoptosis. This system keeps cells from traveling through the body and proliferating out of control. diff --git a/modules/m62801/index.cnxml b/modules/m62801/index.cnxml index 960e9da40..a8cfea31b 100644 --- a/modules/m62801/index.cnxml +++ b/modules/m62801/index.cnxml @@ -75,9 +75,9 @@ Unicellular organisms were assumed to communicate at a very primitive level, but current research reveals the existence more complex signaling systems. Examples of these forms of communication are the formation of biofilms and quorum sensing. Biofilms have received the attention of researchers only recently for several historical and technical reasons. Since the germ theory of disease was established, the interest had been to isolate and characterize pathogens, not to study microorganisms as a community. It is much easier to grow bacteria as pure cultures than replicate mixed populations biofilms, making the latter difficult to study in the laboratory setting. Such slime layers, previously considered haphazard assemblies of microorganisms, have been found to be highly organized ecosystems. The slime layer is made of extracellular polymers crisscrossed with channels for gases, nutrients, waste exchanges. Microbes attach to the solid substrate in a succession of populations. -Quorum sensing exists both within a same species and across species. It allows microbes to behave as multicellular populations and coordinate responses. One such example is the expression of genes encoding toxins in Staphylococcus aureus. Dr. Bonnie Bassler presents quorum sensing communication in Vibrio harveyi in this Ted Talk. Her enthusiasm and clear explanations make this video a thoroughly engaging experience. This is an opportunity to show a strong female role model in science. -Also available is this video clip: Quorum sensing molecules presented by Dr. Bonnie Bassler: -And an animation on quorum sensing in Vibrio harveyi can be found here. +Quorum sensing exists both within a same species and across species. It allows microbes to behave as multicellular populations and coordinate responses. One such example is the expression of genes encoding toxins in Staphylococcus aureus. Dr. Bonnie Bassler presents quorum sensing communication in Vibrio harveyi in this Ted Talk. Her enthusiasm and clear explanations make this video a thoroughly engaging experience. This is an opportunity to show a strong female role model in science. +Also available is this video clip: Quorum sensing molecules presented by Dr. Bonnie Bassler: +And an animation on quorum sensing in Vibrio harveyi can be found here. Further reading: Painter, Kimberley L. et al. (2014). What role does the quorum-sensing accessory gene regulator system play during Staphylococcus aureus bacteremia? Trends in Microbiology 22:676–685 @@ -138,7 +138,7 @@ Presumably, unicellular organisms do not need to coordinate the response of many Research on the details of quorum sensing has led to advances in growing bacteria for industrial purposes. Recent discoveries suggest that it may be possible to exploit bacterial signaling pathways to control bacterial growth; this process could replace or supplement antibiotics that are no longer effective in certain situations. -Watch geneticist Bonnie Bassler discuss her discovery of quorum sensing in biofilm bacteria in squid. +Watch geneticist Bonnie Bassler discuss her discovery of quorum sensing in biofilm bacteria in squid. -Watch this collection of interview clips with biofilm researchers in “What Are Bacterial Biofilms?” +Watch this collection of interview clips with biofilm researchers in “What Are Bacterial Biofilms?”
Section SummaryAnimals included in phylum Porifera are parazoans because they do not show the formation of true embryonically derived tissues, although they have a number of specific cell types and “functional” tissues such as pinacoderm. These organisms show very simple organization, with a rudimentary endoskeleton of spicules and spongin fibers. Glass sponge cells are connected together in a multinucleated syncytium. Although sponges are very simple in organization, they perform most of the physiological functions typical of more complex animals. diff --git a/modules/m66395/index.cnxml b/modules/m66395/index.cnxml index aec907db5..3093f4d2d 100644 --- a/modules/m66395/index.cnxml +++ b/modules/m66395/index.cnxml @@ -32,7 +32,7 @@ Obelia. The colonial sessile form of Obelia geniculata has two types of polyps: gastrozooids, which are adapted for capturing prey, and gonozooids, which asexually bud to produce medusae. -Click here to follow an Obelia life cycle animation. +Click here to follow an Obelia life cycle animation. All cnidarians are diploblastic and thus have two “epithelial” layers in the body that are derived from the endoderm and ectoderm of the embryo. The outer layer (from ectoderm) is called the epidermis and lines the outside of the animal, whereas the inner layer (from endoderm) is called the gastrodermis and lines the digestive cavity. In the planula larva, a layer of ectoderm surrounds a solid mass of endoderm, but as the polyp develops, the digestive or gastrovascular cavity opens within the endoderm. A non-living, jelly-like mesoglea lies between these two epithelial layers. In terms of cellular complexity, cnidarians show the presence of differentiated cell types in each tissue layer, such as nerve cells, contractile epithelial cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as the presence of intercellular connections. However, with a few notable exceptions such as statocysts and rhopalia (see below), the development of organs or organ systems is not advanced in this phylum. The nervous system is rudimentary, with nerve cells organized in a network scattered across the body. This nerve net may show the presence of groups of cells that form nerve plexi (singular: plexus) or nerve cords. Organization of the nervous system in the motile medusa is more complex than that of the sessile polyp, with a nerve ring around the edge of the medusa bell that controls the action of the tentacles. Cnidarian nerve cells show mixed characteristics of motor and sensory neurons. The predominant signaling molecules in these primitive nervous systems are peptides, which perform both excitatory and inhibitory functions. Despite the simplicity of the nervous system, it is remarkable that it coordinates the complicated movement of the tentacles, the drawing of captured prey to the mouth, the digestion of food, and the expulsion of waste. diff --git a/modules/m66396/index.cnxml b/modules/m66396/index.cnxml index 753e84d1c..c30c49dcd 100644 --- a/modules/m66396/index.cnxml +++ b/modules/m66396/index.cnxml @@ -67,7 +67,7 @@ Rotifers are commonly found in freshwater and some saltwater environments throughout the world. As filter feeders, they will eat dead material, algae, and other microscopic living organisms, and are therefore very important components of aquatic food webs. A rotifer's food is directed toward the mouth by the current created from the movement of the coronal cilia. The food particles enter the mouth and travel first to the mastax—a muscular pharynx with toothy jaw-like structures. Examples of the jaws of various rotifers are seen in a. Masticated food passes near digestive and salivary glands, into the stomach, and then to the intestines. Digestive and excretory wastes are collected in a cloacal bladder before being released out the anus. -Watch this video to see rotifers feeding. +Watch this video to see rotifers feeding. About 2,200 species of rotifers have been identified. shows the anatomy of a rotifer belonging to class Bdelloidea. Some rotifers are dioecious organisms and exhibit sexual dimorphism (males and females have different forms). In many dioecious species, males are short-lived and smaller with no digestive system and a single testis. Many rotifer species exhibit haplodiploidy, a method of sex determination in which a fertilized egg develops into a female and an unfertilized egg develops into a male. However, reproduction in the bdelloid rotifers is exclusively parthenogenetic and appears to have been so for millions of years: Thus, all bdelloid rotifers and their progeny are female! The bdelloids may compensate for this genetic insularity by borrowing genes from the DNA of other species. Up to 10% of a bdelloid genome comprises genes imported from related species. Some rotifer eggs are capable of extended dormancy for protection during harsh environmental conditions.
diff --git a/modules/m66397/index.cnxml b/modules/m66397/index.cnxml index 39d185187..e0a989c59 100644 --- a/modules/m66397/index.cnxml +++ b/modules/m66397/index.cnxml @@ -59,9 +59,9 @@ -Bivalves. These mussels (a), found in the intertidal zone in Cornwall, England, show the bivalve shell. The scallop Argopecten irradians (b) has a fluted shell and conspicuous eyespots. (credit (a): Mark A. Wilson. credit (b) Rachael Norris and Marina Freudzon. https://commons.wikimedia.org/w/index.php?curid=17251065)
One of the functions of the mantle is to secrete the shell. Some bivalves, like oysters and mussels, possess the unique ability to secrete and deposit a calcareous nacre or “mother of pearl” around foreign particles that may enter the mantle cavity. This property has been commercially exploited to produce pearls. +Bivalves. These mussels (a), found in the intertidal zone in Cornwall, England, show the bivalve shell. The scallop Argopecten irradians (b) has a fluted shell and conspicuous eyespots. (credit (a): Mark A. Wilson. credit (b) Rachael Norris and Marina Freudzon. https://commons.wikimedia.org/w/index.php?curid=17251065)One of the functions of the mantle is to secrete the shell. Some bivalves, like oysters and mussels, possess the unique ability to secrete and deposit a calcareous nacre or “mother of pearl” around foreign particles that may enter the mantle cavity. This property has been commercially exploited to produce pearls. -Watch the animations of bivalves feeding: View the process in clams and mussels at these sites. +Watch the animations of bivalves feeding: View the process in clams and mussels at these sites. More than half of molluscan species are in the class Gastropoda (“stomach foot”), which includes well-known mollusks like snails, slugs, conchs, cowries, limpets, and whelks. Aquatic gastropods include both marine and freshwater species, and all terrestrial mollusks are gastropods. Gastropoda includes shell-bearing species as well as species without shells. Gastropod bodies are asymmetrical and usually present a coiled shell (a). Shells may be planospiral (like a garden hose wound up), commonly seen in garden snails, or conispiral, (like a spiral staircase), commonly seen in marine conches. Cowrie shells have a polished surface because the mantle extends up over the top of the shell as it is secreted.
diff --git a/modules/m66398/index.cnxml b/modules/m66398/index.cnxml index c177f68ac..d956819e3 100644 --- a/modules/m66398/index.cnxml +++ b/modules/m66398/index.cnxml @@ -67,7 +67,7 @@ -Scanning electronmicrograph of Milnesium tardigradum. (credit: Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al. (2012) -https://commons.wikimedia.org/w/index.php?curid=22716809)
+Scanning electronmicrograph of Milnesium tardigradum. (credit: Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al. (2012) -https://commons.wikimedia.org/w/index.php?curid=22716809)
Morphology and Physiology Tardigrades have cylindrical bodies, with four pairs of legs terminating in a number of claws. The cuticle is periodically shed, including the cuticular covering of the claws. The first three pairs of legs are used for walking, and the posterior pair for clinging to the substrate. A circular mouth leads to a muscular pharynx and salivary glands. Tardigrades feed on plants, algae, or small animals. Plant cells are pierced with a chitinous stylet and the cellular contents are then sucked into the gut by the muscular pharynx. Bands of single muscle cells are attached to the various points of the epidermis and extend into the legs to provide ambulatory movement. The major body cavity is a hemocoel, but there are no specialized circulatory structures for moving the blood, nor are there specialized respiratory structures. Malpighian tubules in the hemocoel remove metabolic wastes and transport them to the gut. A dorsal brain is connected to a ventral nerve cord with segmental ganglia associated with the appendages. Sensory structures are greatly reduced, but there is a pair of simple eyespots on the head, and sensory cilia or bristles concentrated toward the head end of the animal.
diff --git a/modules/m66399/index.cnxml b/modules/m66399/index.cnxml index c2aa11ff5..9302b046a 100644 --- a/modules/m66399/index.cnxml +++ b/modules/m66399/index.cnxml @@ -119,7 +119,7 @@ Spider. The trapdoor spider, like all spiders, is a member of the subphylum Chelicerata. (credit: Marshal Hedin) The nervous system in chelicerates consists of a brain and two ventral nerve cords. Chelicerates are dioecious, meaning that the sexes are separate. These animals use external fertilization as well as internal fertilization strategies for reproduction, depending upon the species and its habitat. Parental care for the young ranges from absolutely none to relatively prolonged care. -Visit this site to click through a lesson on arthropods, including interactive habitat maps, and more. +Visit this site to click through a lesson on arthropods, including interactive habitat maps, and more.
@@ -139,7 +139,7 @@
-Crustaceans. The (a) crab and (b) shrimp krill are both aquatic crustaceans. The pill bug Armadillidium is a terrestrial crustacean. (credit a: modification of work by William Warby; credit b: modification of work by Jon Sullivan credit c: modification of work by Franco Folini. https://commons.wikimedia.org/w/index.php?curid=789616)
Crustaceans typically possess two pairs of antennae, mandibles as mouthparts, and biramous (“two branched”) appendages, which means that their legs are formed in two parts called endopods and exopods, which appear superficially distinct from the uniramous (“one branched”) legs of myriapods and hexapods (). Since biramous appendages are also seen in the trilobites, biramous appendages represent the ancestral condition in the arthropods. Currently, we describe various arthropods as having uniramous or biramous appendages, but these are descriptive only, and do not necessarily reflect evolutionary relationships other than that all jointed legs of arthropods share common ancestry. +Crustaceans. The (a) crab and (b) shrimp krill are both aquatic crustaceans. The pill bug Armadillidium is a terrestrial crustacean. (credit a: modification of work by William Warby; credit b: modification of work by Jon Sullivan credit c: modification of work by Franco Folini. https://commons.wikimedia.org/w/index.php?curid=789616)Crustaceans typically possess two pairs of antennae, mandibles as mouthparts, and biramous (“two branched”) appendages, which means that their legs are formed in two parts called endopods and exopods, which appear superficially distinct from the uniramous (“one branched”) legs of myriapods and hexapods (). Since biramous appendages are also seen in the trilobites, biramous appendages represent the ancestral condition in the arthropods. Currently, we describe various arthropods as having uniramous or biramous appendages, but these are descriptive only, and do not necessarily reflect evolutionary relationships other than that all jointed legs of arthropods share common ancestry.
diff --git a/modules/m66400/index.cnxml b/modules/m66400/index.cnxml index 6095cba36..cbc47ab3a 100644 --- a/modules/m66400/index.cnxml +++ b/modules/m66400/index.cnxml @@ -55,7 +55,7 @@ This phylum is divided into five extant classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers) (). The most well-known echinoderms are members of class Asteroidea, or sea stars. They come in a large variety of shapes, colors, and sizes, with more than 1,800 species known so far. The key characteristic of sea stars that distinguishes them from other echinoderm classes includes thick arms that extend from a central disk from which various body organs branch into the arms. At the end of each arm are simple eye spots and tentacles that serve as touch receptors. Sea stars use their rows of tube feet not only for gripping surfaces but also for grasping prey. Most sea stars are carnivores and their major prey are in the phylum Mollusca. By manipulating its tube feet, a sea star can open molluscan shells. Sea stars have two stomachs, one of which can protrude through their mouths and secrete digestive juices into or onto prey, even before ingestion. A sea star eating a clam can partially open the shell, and then evert its stomach into the shell, introducing digestive enzymes into the interior of the mollusk. This process can both weaken the strong adductor (closing) muscles of a bivalve and begin the process of digestion. -Explore the sea star’s body plan up close, watch one move across the sea floor, and see it devour a mussel. +Explore the sea star’s body plan up close, watch one move across the sea floor, and see it devour a mussel. Brittle stars belong to the class Ophiuroidea ("snake-tails"). Unlike sea stars, which have plump arms, brittle stars have long, thin, flexible arms that are sharply demarcated from the central disk. Brittle stars move by lashing out their arms or wrapping them around objects and pulling themselves forward. Their arms are also used for grasping prey. The water vascular system in ophiuroids is not used for locomotion. Sea urchins and sand dollars are examples of Echinoidea ("prickly"). These echinoderms do not have arms, but are hemispherical or flattened with five rows of tube feet that extend through five rows of pores in a continuous internal shell called a test. Their tube feet are used to keep the body surface clean. Skeletal plates around the mouth are organized into a complex multipart feeding structure called "Aristotle's lantern." Most echinoids graze on algae, but some are suspension feeders, and others may feed on small animals or organic detritus—the fragmentary remains of plants or animals. Sea lilies and feather stars are examples of Crinoidea. Sea lilies are sessile, with the body attached to a stalk, but the feather stars can actively move about using leglike cirri that emerge from the aboral surface. Both types of crinoid are suspension feeders, collecting small food organisms along the ambulacral grooves of their feather-like arms. The "feathers" consisted of branched arms lined with tube feet. The tube feet are used to move captured food toward the mouth. There are only about 600 extant species of crinoids, but they were far more numerous and abundant in ancient oceans. Many crinoids are deep-water species, but feather stars typically inhabit shallow areas, especially in substropical and tropical waters. diff --git a/modules/m66404/index.cnxml b/modules/m66404/index.cnxml index 94dcdab7c..2dd918559 100644 --- a/modules/m66404/index.cnxml +++ b/modules/m66404/index.cnxml @@ -71,7 +71,7 @@ Pain is the name given to nociception, which is the neural processing of injurious stimuli in response to tissue damage. Pain is caused by true sources of injury, such as contact with a heat source that causes a thermal burn or contact with a corrosive chemical. But pain also can be caused by harmless stimuli that mimic the action of damaging stimuli, such as contact with capsaicins, the compounds that cause peppers to taste hot and which are used in self-defense pepper sprays and certain topical medications. Peppers taste “hot” because the protein receptors that bind capsaicin open the same calcium channels that are activated by warm receptors. Nociception starts at the sensory receptors, but pain, inasmuch as it is the perception of nociception, does not start until it is communicated to the brain. There are several nociceptive pathways to and through the brain. Most axons carrying nociceptive information into the brain from the spinal cord project to the thalamus (as do other sensory neurons) and the neural signal undergoes final processing in the primary somatosensory cortex. Interestingly, one nociceptive pathway projects not to the thalamus but directly to the hypothalamus in the forebrain, which modulates the cardiovascular and neuroendocrine functions of the autonomic nervous system. Recall that threatening—or painful—stimuli stimulate the sympathetic branch of the visceral sensory system, readying a fight-or-flight response. -View this video that animates the five phases of nociceptive pain. +View this video that animates the five phases of nociceptive pain.