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

Archeological investigators argue that homologous limb structure and physical characteristics are the most important factors in determining evolutionary ties. Homologous limb structure is defined as a structure found in the anatomy of an organism that is similiar to that of another species. Would the scientists of Study 1 and Study 2 agree with this information?

     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

What is the central theme of the two phylogenetic studies?

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.

According to Scientist 1, seres are best described by which of the following statements?

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.

What is the main difference between the viewpoints of Scientist 1 and Scientist 2?

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.

An ecological study observes plots of land that are allowed to grow for extended periods of time. There are five plots that have grown under seemingly identical conditions; however, each climax community possesses a species composition slightly different from the others. Which scientist would agree with the possibility of accurately obtaining these results?

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

If the researchers of Study 1 read the work of those involved of Study 2, they would most likely agree with which of the following conclusions?

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

A common problem present in the Russian prison system is that of antibiotic resistant tuburculosis. Scientists have traced this epidemic to the misuse of antibiotics. Within the prison system, antibiotics are costly and doctors have attempted to save money by cutting down the doses of antibiotics administered to inmates. The doctors concluded that this process only killed off weak bacteria and produced antibiotic-resistant strains. Which group of researchers would most readily agree with this conclusion?

In the 19th century, there were two competing views as to how diseases spread.

Miasma theory:

Miasma (Greek for pollution) is a poisonous vapor that comes from rotting carcasses or other diseased bodies. It carries particles of the decomposing matter in it and spreads illness. This is why the bubonic plague spread so quickly in Europe: the air itself was foul-smelling and polluted with disease which caused everyone in the locale to become sick and die. It also explains why epidemics tend to originate in a certain area and infect everyone within that area -- they are all breathing in this noxious gas and getting the same disease. In hospitals, we need to ensure that the air is fresh smelling and clean so as to avoid all patients breathing in this miasma and all getting sick.

Germ theory:

Disease is spread through small microbial organisms called germs. These germs, which can be bacteria, viruses, or other pathogens, should be able to be isolated from an infected host and then should no longer exist in the host's body when the host becomes healthy. Germs can move from one body to another through direct or indirect contact -- they can move through touching, spreading of fluids (coughing, sneezing, etc.) and potentially air, but not exclusively through the air.

In a certain hospital, a doctor found that by washing his hands, he decreased the spread of infection in pregnant women from 18% to 2%. Which theory does this best support?

In the 19th century, there were two competing views as to how diseases spread.

Miasma theory:

Miasma (Greek for pollution) is a poisonous vapor that comes from rotting carcasses or other diseased bodies. It carries particles of the decomposing matter in it and spreads illness. This is why the bubonic plague spread so quickly in Europe: the air itself was foul-smelling and polluted with disease which caused everyone in the locale to become sick and die. It also explains why epidemics tend to originate in a certain area and infect everyone within that area -- they are all breathing in this noxious gas and getting the same disease. In hospitals, we need to ensure that the air is fresh smelling and clean so as to avoid all patients breathing in this miasma and all getting sick.

Germ theory:

Disease is spread through small microbial organisms called germs. These germs, which can be bacteria, viruses, or other pathogens, should be able to be isolated from an infected host and then should no longer exist in the host's body when the host becomes healthy. Germs can move from one body to another through direct or indirect contact -- they can move through touching, spreading of fluids (coughing, sneezing, etc.) and potentially air, but not exclusively through the air.

Which of the following observations, if true, would best support miasma theory?

In the 19th century, there were two competing views as to how diseases spread.

Miasma theory:

Miasma (Greek for pollution) is a poisonous vapor that comes from rotting carcasses or other diseased bodies. It carries particles of the decomposing matter in it and spreads illness. This is why the bubonic plague spread so quickly in Europe: the air itself was foul-smelling and polluted with disease which caused everyone in the locale to become sick and die. It also explains why epidemics tend to originate in a certain area and infect everyone within that area -- they are all breathing in this noxious gas and getting the same disease. In hospitals, we need to ensure that the air is fresh smelling and clean so as to avoid all patients breathing in this miasma and all getting sick.

Germ theory:

Disease is spread through small microbial organisms called germs. These germs, which can be bacteria, viruses, or other pathogens, should be able to be isolated from an infected host and then should no longer exist in the host's body when the host becomes healthy. Germs can move from one body to another through direct or indirect contact -- they can move through touching, spreading of fluids (coughing, sneezing, etc.) and potentially air, but not exclusively through the air.

Which of these solutions would a proponent of miasma theory give to  someone who is sick?