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?

Many motile organisms exhibit “fight or flight” responses in order to survive and reproduce. Aggressive posturing and combative behavior are important for the reproductive success and the formation of pack hierarchies of some species. Submissive actions and retreats permit other species the ability to evade capture or danger and enhance survival capabilities. Scientists have debated about the mechanics and moderation of these behaviors within organisms. Two studies regarding this behavior were performed.

Study 1

Researchers decided to study crayfish, a type of freshwater arthropod, in an aquarium. They placed two crayfish opposing one another in an enclosed space. The crayfish were divided by an opaque screen that inhibited their ability to notice one another. The screen was lifted and the crayfish were permitted to interact with one another. The scientists observed their interactions and noted the crayfish's submissive and aggressive behaviors. The scientists noticed that more dominant and aggressive behaviors correlated with larger sized individuals. Their observations indicate that large size and aggression are traits actively selected for within the crayfish population and are necessary for survivorship and reproductive success.

Study 2

Researchers in this study suggest that aggressive behaviors are linked to chemical messengers. They attempted to alter the crayfish’s lateral giant escape reaction through chemical manipulation. They injected crayfish with serotonin, an aggression stimulant, and octopamine, a natural facilitator of the flight response. They monitored and recorded the crayfish’s response to aggressive stimuli (see Figure 1). The researchers concluded that the crayfish escape response is significantly different in the chemical trials in comparison to the control trial that observed the injection of an inert saline solution into the arthropods.

Figure 1

Which of the following types of organisms exhibit the "fight or flight" response.

Many motile organisms exhibit “fight or flight” responses in order to survive and reproduce. Aggressive posturing and combative behavior are important for the reproductive success and the formation of pack hierarchies of some species. Submissive actions and retreats permit other species the ability to evade capture or danger and enhance survival capabilities. Scientists have debated about the mechanics and moderation of these behaviors within organisms. Two studies regarding this behavior were performed.

Study 1

Researchers decided to study crayfish, a type of freshwater arthropod, in an aquarium. They placed two crayfish opposing one another in an enclosed space. The crayfish were divided by an opaque screen that inhibited their ability to notice one another. The screen was lifted and the crayfish were permitted to interact with one another. The scientists observed their interactions and noted the crayfish's submissive and aggressive behaviors. The scientists noticed that more dominant and aggressive behaviors correlated with larger sized individuals. Their observations indicate that large size and aggression are traits actively selected for within the crayfish population and are necessary for survivorship and reproductive success.

Study 2

Researchers in this study suggest that aggressive behaviors are linked to chemical messengers. They attempted to alter the crayfish’s lateral giant escape reaction through chemical manipulation. They injected crayfish with serotonin, an aggression stimulant, and octopamine, a natural facilitator of the flight response. They monitored and recorded the crayfish’s response to aggressive stimuli (see Figure 1). The researchers concluded that the crayfish escape response is significantly different in the chemical trials in comparison to the control trial that observed the injection of an inert saline solution into the arthropods.

Figure 1

Researchers have discovered fossils that suggest that a snake known as the titanoboa dominated its marsh environment due to its immense size and aggressive nature. The researchers of which study would most agree with this conclusion?

Many motile organisms exhibit “fight or flight” responses in order to survive and reproduce. Aggressive posturing and combative behavior are important for the reproductive success and the formation of pack hierarchies of some species. Submissive actions and retreats permit other species the ability to evade capture or danger and enhance survival capabilities. Scientists have debated about the mechanics and moderation of these behaviors within organisms. Two studies regarding this behavior were performed.

Study 1

Researchers decided to study crayfish, a type of freshwater arthropod, in an aquarium. They placed two crayfish opposing one another in an enclosed space. The crayfish were divided by an opaque screen that inhibited their ability to notice one another. The screen was lifted and the crayfish were permitted to interact with one another. The scientists observed their interactions and noted the crayfish's submissive and aggressive behaviors. The scientists noticed that more dominant and aggressive behaviors correlated with larger sized individuals. Their observations indicate that large size and aggression are traits actively selected for within the crayfish population and are necessary for survivorship and reproductive success.

Study 2

Researchers in this study suggest that aggressive behaviors are linked to chemical messengers. They attempted to alter the crayfish’s lateral giant escape reaction through chemical manipulation. They injected crayfish with serotonin, an aggression stimulant, and octopamine, a natural facilitator of the flight response. They monitored and recorded the crayfish’s response to aggressive stimuli (see Figure 1). The researchers concluded that the crayfish escape response is significantly different in the chemical trials in comparison to the control trial that observed the injection of an inert saline solution into the arthropods.

Figure 1

Which of the crayfish in Study 2 are most likely to become submissive members of a heirarchy?

Many motile organisms exhibit “fight or flight” responses in order to survive and reproduce. Aggressive posturing and combative behavior are important for the reproductive success and the formation of pack hierarchies of some species. Submissive actions and retreats permit other species the ability to evade capture or danger and enhance survival capabilities. Scientists have debated about the mechanics and moderation of these behaviors within organisms. Two studies regarding this behavior were performed.

Study 1

Researchers decided to study crayfish, a type of freshwater arthropod, in an aquarium. They placed two crayfish opposing one another in an enclosed space. The crayfish were divided by an opaque screen that inhibited their ability to notice one another. The screen was lifted and the crayfish were permitted to interact with one another. The scientists observed their interactions and noted the crayfish's submissive and aggressive behaviors. The scientists noticed that more dominant and aggressive behaviors correlated with larger sized individuals. Their observations indicate that large size and aggression are traits actively selected for within the crayfish population and are necessary for survivorship and reproductive success.

Study 2

Researchers in this study suggest that aggressive behaviors are linked to chemical messengers. They attempted to alter the crayfish’s lateral giant escape reaction through chemical manipulation. They injected crayfish with serotonin, an aggression stimulant, and octopamine, a natural facilitator of the flight response. They monitored and recorded the crayfish’s response to aggressive stimuli (see Figure 1). The researchers concluded that the crayfish escape response is significantly different in the chemical trials in comparison to the control trial that observed the injection of an inert saline solution into the arthropods.

Figure 1

Crayfish are considered to be which of the following animal types?

Bacterial resistance is a common issue encountered in various infections. Scientists have attributed this phenomenon to the overuse of anti-bacterial sanitizers and prescription antibiotics. Two groups of researchers performed studies to test bacterial resistance.

Study 1

Researchers in this study state that bacterial resistance is the result of bacterial plasmid translocation. Bacteria carry their genes on circular rings of bacterial DNA and on small, physically separate molecules known as plasmids. Plasmids are unique because they are replicons that are capable of replication autonomously within a suitable host. Researchers radioactively marked plasmids in bacterial specimens and noted that they could be easily transmitted from one bacterium to another via horizontal gene transfer. They then observed that the genes transferred from the plasmid could be incorporated into the bacteria’s genetic makeup. These genetic alterations enhanced survivorship within the environment and promoted resistance to antibiotics. They concluded that plasmids carry genes important for survival and facilitate bacterial resistance to antibiotics.

Study 2

Researchers in this study state that resistance is the result of the misuse of antibiotics. Researchers administered various antibiotics to a culture of E. coli and studied their effects over time (Figure 1). They concluded that bacterial resistance is the result of natural selection. In other words, the strongest bacteria survive antibiotics and reproduce, which produces anitbiotic-resistant offspring bacteria. 

Figure 1

According to the passage, what are small, physically separate genetic molecules that can replicate independently within a host called?

Bacterial resistance is a common issue encountered in various infections. Scientists have attributed this phenomenon to the overuse of anti-bacterial sanitizers and prescription antibiotics. Two groups of researchers performed studies to test bacterial resistance.

Study 1

Researchers in this study state that bacterial resistance is the result of bacterial plasmid translocation. Bacteria carry their genes on circular rings of bacterial DNA and on small, physically separate molecules known as plasmids. Plasmids are unique because they are replicons that are capable of replication autonomously within a suitable host. Researchers radioactively marked plasmids in bacterial specimens and noted that they could be easily transmitted from one bacterium to another via horizontal gene transfer. They then observed that the genes transferred from the plasmid could be incorporated into the bacteria’s genetic makeup. These genetic alterations enhanced survivorship within the environment and promoted resistance to antibiotics. They concluded that plasmids carry genes important for survival and facilitate bacterial resistance to antibiotics.

Study 2

Researchers in this study state that resistance is the result of the misuse of antibiotics. Researchers administered various antibiotics to a culture of E. coli and studied their effects over time (Figure 1). They concluded that bacterial resistance is the result of natural selection. In other words, the strongest bacteria survive antibiotics and reproduce, which produces anitbiotic-resistant offspring bacteria. 

Figure 1

What do the researchers in Study 2 believe is the main cause for bacterial resistance?