Symbiosis is defined as a state in which two species intimately live together. This indicates that they are in close contact with one another and can affect each other. Symbiosis has been documented in three dominant forms: commensalism, mutualism, and parasitism. Commensalism exists when one organism benefits and one, presumably the host, is affected neither negatively or positively. Mutualism is described as two organisms that both benefit from their interactions. Last, parasitism is described as an interaction that benefits an organism at the expense of the host organism.

Bacteria live in the digestive tract of humans and other mammals. The bacteria enable the the host to better digest food and in return are granted a suitable habitat and a source of food. This is an example of which type of symbiosis?

Symbiosis is defined as a state in which two species intimately live together. This indicates that they are in close contact with one another and can affect each other. Symbiosis has been documented in three dominant forms: commensalism, mutualism, and parasitism. Commensalism exists when one organism benefits and one, presumably the host, is affected neither negatively or positively. Mutualism is described as two organisms that both benefit from their interactions. Last, parasitism is described as an interaction that benefits an organism at the expense of the host organism.

A dog ingests a tapeworm. The worm feeds off of the host dog while at the same time deprives the host of much needed nutrients. This is an example of which type of symbiosis?

Symbiosis is defined as a state in which two species intimately live together. This indicates that they are in close contact with one another and can affect each other. Symbiosis has been documented in three dominant forms: commensalism, mutualism, and parasitism. Commensalism exists when one organism benefits and one, presumably the host, is affected neither negatively or positively. Mutualism is described as two organisms that both benefit from their interactions. Last, parasitism is described as an interaction that benefits an organism at the expense of the host organism.

Honey bees pollinate flowers while at the same time harvesting nectar to be made into honey. This is an example of which type of symbiosis?

     Osmoregulation is a necessary function to maintain homeostasis in organisms. Fish gills form the boundary between fish body fluid and environmental conditions. The regulation of water transport across barrier epithelial membranes in gills is assisted by membrane composition and affected by solute concentration on either side of the membrane. Fish body fluids are isotonic and have compositions of about 300 milliosmoles of solutes per liter. Freshwater environments are hypotonic and typically have compositions of about 1 milliosmole of solutes per liter. Saltwater environments are hypertonic and typically have a composition of about 1,000 milliosmoles of solutes per liter. Based on observed osmoregulation across varying concentration gradients, it is expected that gills exposed to isotonic solutions maintain steady water weight, while those exposed to hypotonic solutions increase in water weight, and those exposed to hypertonic solutions decreased in water weight.

Study 1

     Gills dissected from a fish were exposed to different ambient environments of salinity including an isotonic control solution (301.5 milliosmoles), a hypotonic solution (1.5 milliosmoles), and a hypertonic solution (601.5 milliosmoles). Percent water weight change between treatments was observed and calculated.

A homeowner purchases a fish species that can survive in either salt or freshwater environments. The homeowner has several tropical fish living in a saltwater tank. The purchased fish was placed in a bag containing an isotonic solution. The shop clerk states that the fish should be placed in a particular solution before being placed in the saltwater environment. Which solution should the fish be placed in before it is put in the tropical tank?

     Osmoregulation is a necessary function to maintain homeostasis in organisms. Fish gills form the boundary between fish body fluid and environmental conditions. The regulation of water transport across barrier epithelial membranes in gills is assisted by membrane composition and affected by solute concentration on either side of the membrane. Fish body fluids are isotonic and have compositions of about 300 milliosmoles of solutes per liter. Freshwater environments are hypotonic and typically have compositions of about 1 milliosmole of solutes per liter. Saltwater environments are hypertonic and typically have a composition of about 1,000 milliosmoles of solutes per liter. Based on observed osmoregulation across varying concentration gradients, it is expected that gills exposed to isotonic solutions maintain steady water weight, while those exposed to hypotonic solutions increase in water weight, and those exposed to hypertonic solutions decreased in water weight.

Study 1

     Gills dissected from a fish were exposed to different ambient environments of salinity including an isotonic control solution (301.5 milliosmoles), a hypotonic solution (1.5 milliosmoles), and a hypertonic solution (601.5 milliosmoles). Percent water weight change between treatments was observed and calculated.

A tropical-fish store places fish in saltwater environments. Over several months a large number of fish die in the tanks. The shop owner takes one of the fish to a research lab where its cells are analyzed. The researchers tell the owner that the fish cells burst due to the solute concentration of its environment. Compared to the fish's gills the environment was of which of the following salinities?

Carbonic anhydrase is an enzyme that is used by the human body to interconvert carbon dioxide (a gaseous compound) and bicarbonate (a compound composed of hydrogen, carbon, and oxygen), using water as a reactant. The human body needs to convert carbon dioxide to bicarbonate in the tissues to transport it in the blood to the lungs, as carbon dioxide is relatively insoluble. In the lungs, bicarbonate is converted back to carbon dioxide to be exhaled. In humans, there are two different carbonic anhydrase isomers, one that works in the lungs (isomer A) and one that works in the tissues (isomer B). Mutations in the chromosomes can prevent carbonic anhydrase from converting carbon dioxide to bicarbonate. In the following four experiments, the chromosomes of none, one, or both of the isomers were mutated per experiment.

Experiment 1

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Bicarbonate was measured in the tissues but carbon dioxide was not measured in the lungs.

Experiment 2

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be abnormally high in the tissues and no bicarbonate was measured in the lungs.

Experiment 3

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be slightly low in the tissues and bicarbonate levels were abnormally high in the lungs.

Experiment 4

Radiation was not used, A probe was placed into the tissues and lungs of a model animal and found normal carbon dioxide and bicarbonate levels.

Which of the following best describes the role of carbonic anhydrase in the tissues?

Carbonic anhydrase is an enzyme that is used by the human body to interconvert carbon dioxide (a gaseous compound) and bicarbonate (a compound composed of hydrogen, carbon, and oxygen), using water as a reactant. The human body needs to convert carbon dioxide to bicarbonate in the tissues to transport it in the blood to the lungs, as carbon dioxide is relatively insoluble. In the lungs, bicarbonate is converted back to carbon dioxide to be exhaled. In humans, there are two different carbonic anhydrase isomers, one that works in the lungs (isomer A) and one that works in the tissues (isomer B). Mutations in the chromosomes can prevent carbonic anhydrase from converting carbon dioxide to bicarbonate. In the following four experiments, the chromosomes of none, one, or both of the isomers were mutated per experiment.

Experiment 1

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Bicarbonate was measured in the tissues but carbon dioxide was not measured in the lungs.

Experiment 2

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be abnormally high in the tissues and no bicarbonate was measured in the lungs.

Experiment 3

Radiation was used to mutate one of the chromosomes of one or more isomers of carbonic anhydrase. A probe was placed into the tissues and lungs of a model animal. Carbon dioxide levels were found to be slightly low in the tissues and bicarbonate levels were abnormally high in the lungs.

Experiment 4

Radiation was not used, A probe was placed into the tissues and lungs of a model animal and found normal carbon dioxide and bicarbonate levels.

Carbonic anhydrase is an example of a(n) __________.

     Phylogenetics is a tool utilized by evolutionary and molecular biologists to investigate the similarities that exist in the molecular sequences of proteins in varying organisms. The amino acid sequences that build proteins are often used to construct distance matrices that aid in determining evolutionary ties. The study of these matrices helps to expose evolutionary relationships between species that may not have the same phenotypical and existential characteristics.

Study 1

     A researcher decides to compare several bat species to several bird and mammalian species in order to determine which two groups were more closely related. The study compares a ghost bat and a tomb bat with two birds, the pigeon and eagle, and two mammals, the spider monkey and macaque. The researcher compared the amino-acid sequences of beta hemoglobin molecules in order to determine whether bats were more related to birds or mammals. Percent similarities of the data were calculated for comparison purposes (Figure 1).

Figure 1

Study 2

     A researcher decides to compare a whale to a fish and to several ungulates (hoofed mammals). One set of ungulates that were studied were artiodactyls, meaning they were “even-toed” (hippopotamus and sheep).  The other set of ungulates belonged to a class of mammals known as perissodactyls meaning that they were “odd-toed” (rhinoceros and zebra). The researcher compared the amino-acid sequences of beta hemoglobin molecules in order to determine which species were more related to the Minke whale. Percent similarities of the data were calculated for comparison purposes (Figure 2).

Figure 2

A student reads the study conducted by the researchers of Study 2 and declares that it has proven that the Minke whale is most related to the sheep. Is the student correct in his logic?

Ecological succession refers to the observable change of the species composition of an ecological community over a period of time. This phenomenon is also known as forest succession. It is a process that begins with the colonization of a habitat by robust pioneer species that can survive inclement and harsh environments. Pioneer species are characterized by small size and rapid reproduction of many offspring. Over successive generations these species are replaced with increasing complexity, until the ecosystem reaches a self-perpetuating climax community that ceases to vary in composition.

Several scientists express their views on the phenomenon of ecological succession.

Scientist 1

Ecological succession can be explained as primary succession. This theory suggests that forest evolution is the product of repeatable sequences of community changes known as seres. Each sere is predictable and deterministic to particular environmental circumstances. Scientists can therefore predict the changes in an environment with accuracy and precision based on observation.

Scientist 2

Ecological succession is not defined by predictable models. Chance plays a large role in creating ecological communities, whose species respond individualistically to environmental cues and pressures. These models are more complex in nature, and less simplified, than deterministic models. In these models, communities are regarded as products of the correlations between species distributions and environmental factors independent to each community.

A plane crashes into a forest. Its wreckage is cleaned from the area. This area is stripped of all forms of plant life. What is the first step of ecological succession that will occur?

Ecological succession refers to the observable change of the species composition of an ecological community over a period of time. This phenomenon is also known as forest succession. It is a process that begins with the colonization of a habitat by robust pioneer species that can survive inclement and harsh environments. Pioneer species are characterized by small size and rapid reproduction of many offspring. Over successive generations these species are replaced with increasing complexity, until the ecosystem reaches a self-perpetuating climax community that ceases to vary in composition.

Several scientists express their views on the phenomenon of ecological succession.

Scientist 1

Ecological succession can be explained as primary succession. This theory suggests that forest evolution is the product of repeatable sequences of community changes known as seres. Each sere is predictable and deterministic to particular environmental circumstances. Scientists can therefore predict the changes in an environment with accuracy and precision based on observation.

Scientist 2

Ecological succession is not defined by predictable models. Chance plays a large role in creating ecological communities, whose species respond individualistically to environmental cues and pressures. These models are more complex in nature, and less simplified, than deterministic models. In these models, communities are regarded as products of the correlations between species distributions and environmental factors independent to each community.

Some evergreen forests are mediated by occasional fires that strip the land of overgrown foliage, enhancing the ability of new species to grow in the area. The new species would best be described as which of the following?