Scientists want to see how any athlete's heart health is different from others. The scientists monitor four individual's (A, B, C and D) heart rates during sleep, rest and intense exercise. Only one athlete was tested and the data was recorded in the table below in heart beats per minute.

Which individual has the best overall fitness? 

Botulism is a rare disease caused by the botulinum toxin produced and secreted by Clostridium botulinum. Botulism causes muscle weakness and in severe cases can inhibit the muscles of respiration and lead to respiratory failure and even death. The exotoxin produced by Clostridium botulinum causes damage to its host by inhibiting of the release of the chemical messenger acetylcholine. Acetylcholine is a neurotransmitter, meaning it is responsible for enabling communication between a nerve cell and other cells. 

Experiment A

Scientists conducting a study on the lethality of the botulinum toxin are looking at the effect of acidification on the toxin’s potency. They design a study in mice to identify the minimal lethal dose of botulinum toxin. The scientists believe acidification will reduce the minimal lethal dose. The findings from their study are below:

Experiment B

Scientists also assessed the relationship between acidification and the incubation period. The incubation period was defined as the time between exposure to the toxin and the onset of symptoms. 

Data and concepts from: Bronfenbrenner, J. & Schlesinger M.J. (1922). Some of the factors contributing to toxicity of botulinus toxin by mouth. JAMA, 78(20), 1519-1521.

Which of the following is best summarizes the scientists' hypothesis for Experiment A?

A mycologist, a scientist specializing in the study of mushrooms, wants to compare the growth of three types of mushroom (A, B, and C) on varying growth substrates. He is also curious how light will affect the growth of each of the samples. He designs an experiment where each variety of mushroom will be grown on manure, wood chips, or rice flour and includes identical trials with and without light. He records the mass of the mushrooms produced after 14 days of fruiting and finds the following results:

Based on this data, describe the growth conditions for Mushroom strain A that would lead to the largest mushrooms produced.

A botanist is trying to see the effects of temperature on a certain plant species. She prepares four identical plots of soil and runs a heating element through the soil so she can vary the temperature of each plot. After one month she harvests all of the plant biomass and records the temperature of each plot along with the biomass collected. The data are given in the table below.

Based on the data in the table, which of the following best describes the preferred climate for this plant?

A botanist is trying to see the effects of temperature on a certain plant species. She prepares four identical plots of soil and runs a heating element through the soil so she can vary the temperature of each plot. After one month she harvests all of the plant biomass and records the temperature of each plot along with the biomass collected. The data are given in the table below.

The botanist then consults the following information that lists the range of temperatures at which the species may be found growing in the wild. 

Based on the data above, which of the following is most likely to be the species studied by the experimenter?

The Millikin oil drop experiment is among the most important experiments in the history of science. It was used to determine one of the fundamental constants of the universe, the charge on the electron. For his work, Robert Millikin won the Nobel Prize in Physics in 1923.

Millikin used an experimental setup as follows in Figure 1. He opened a chamber of oil into an adjacent uniform electric field. The oil droplets sank into the electric field once the trap door opened, but were then immediately suspended by the forces of electricity present in the field.

Figure 1:

By determining how much force was needed to exactly counteract the gravity pulling the oil droplet down, Millikin was able to determine the force of electricity. This is depicted in Figure 2.

Using this information, he was able to calculate the exact charge on an electron. By changing some conditions, such as creating a vacuum in the apparatus, the experiment can be modified. 

Figure 2:

When the drop is suspended perfectly, the total forces up equal the total forces down. Because Millikin knew the electric field in the apparatus, the force of air resistance, the mass of the drop, and the acceleration due to gravity, he was able to solve the following equation: 

Table 1 summarizes the electric charge found on oil drops in suspension. Millikin correctly concluded that the calculated charges must all be multiples of the fundamental charge of the electron. A hypothetical oil drop contains some net charge due to lost electrons, and this net charge cannot be smaller than the charge on a single electron.

Table 1: 

For an electron in suspension within a vacuum, under the influence of an electric field:

In the 1980’s, an epidemic of bovine spongiform encephalopathy, or mad cow disease, swept through cattle herds in the United Kingdom. Scientists and veterinarians were troubled and had a difficult time managing the disease because it spread from one animal to another, and behaved differently than other diseases in the past. 

When infectious material from affected animals was treated with high levels of radiation, for example, the material remained infectious. All known bacteria or viruses that carry disease would have been killed by such a treatment. Additionally, some animals developed the disease without first being exposed to sick animals. Perhaps most frustratingly, among those animals that are exposed before becoming sick, it can take many years after exposure for illness to appear.

There quickly emerged two distinct explanations for the disease. 

Scientist 1:

Mad cow disease is unlike any disease we have handled before. It is increasingly clear that the best explanation for the disease’s dynamics involve proteins, called the protein-only hypothesis. These protein molecules are likely causative of the disease, and they lack any DNA or RNA. It is damage to these DNA or RNA molecules that kills bacteria or viruses when exposed to high levels of radiation. The most important observations that made scientists consider a unique, protein-only model for this disease involved its resistance to radiation. Remarkably, this would be the first example of an infectious agent copying itself without DNA or RNA to mediate the process.

Moreover, some animals develop the disease spontaneously, without physically being infected by another animal. This suggests that internal disorder among protein molecules is a potential route to developing disease, and may be accelerated by exposure to other sick animals.

In fact, this is consistent with the proposed mechanism. It is likely that proteins fold incorrectly, and then influence proteins around them to take on this errant conformation. Some proteins may fold incorrectly by chance, which explains spontaneous disease development. It also explains the long course of disease, as it takes many years for enough proteins to fold incorrectly and result in observable disease.

Scientist 2:

The suggestion that mad cow disease is caused exclusively by protein, in the absence of DNA or RNA, is such a dramatic departure from accepted biological processes that it warrants careful scrutiny. Additionally, other more conventional explanations should be thoroughly investigated before coming to such a conclusion.

Some scientists have shown that very small particles resembling viruses are visible in infectious material under powerful microscopes. Additionally, these viruses are consistent in size and shape with known, highly radiation-resistant viruses called polyomaviruses. It takes much higher-than-typical doses of radiation to cause enough DNA damage to inactivate these viruses.

The observation that mad cow disease occurs spontaneously in some animals is also explained by the viral explanation. Many viruses exist in animals and humans for years, undetected and not causing any observable disease. Sickness or stress can make these viruses reactivate, offering the illusion of spontaneous illness. All of these observations are consistent with the viral hypothesis.

Based on the passage, which of the following is most likely true about RNA & DNA?

I.  They are damaged by radiation

II.  They transmit information

III.  They are not present in polyomaviruses

If a drug is administered intravenously (i.e. injected into a vein), then the concentration of the drug in the blood will rise and then reach a plateau. After some time, the body will begin to eliminate this drug from the bloodstream. During this elimination phase, ion pumps will actively transport some drugs from the blood into the tubules of the kidneys. Organic anion transporters (OAT) transport acids into the tubules of the kidney while organic cation transporters (OCT) transport bases into the tubules of the kidney. This mechanism, known as secretion, depends entirely on transporters and allows both acidic and basic drugs to be eliminated from the body.

Another process known as reabsorption can also occur in the kidneys. During reabsorption, drugs can be transported from the tubules of the kidney back into the blood. This process depends on the pH of the fluid in kidney tubules (e.g. the urine). At a low pH (i.e. acidic environment), acidic drugs are best reabsorbed. Conversely, at high pH (i.e. basic environment), basic drugs are best reabsorbed.

Experiment 1

The same drug was administered to various individuals. After some time elapsed, the rate of renal clearance (i.e. the rate of urine elimination from the body) was measured in each of the individuals. Subsequently, the pH of the urine was measured for each individual. The rate of renal clearance versus urinary pH was then plotted in the provided figure (each black dot represents a different individual).

Experiment 2

A scientist was able to engineer a mouse kidney that lacked organic anion transporters. She administered various drugs to the mouse and measured the rates of secretion. The data collected is located in the provided table.

Suppose a third experiment were performed. In this experiment, organic cation transporters (OCT) were inhibited or blocked. Which of the following best explains how the reabsorption of basic drugs would be affected?

If a drug is administered intravenously (i.e. injected into a vein), then the concentration of the drug in the blood will rise and then reach a plateau. After some time, the body will begin to eliminate this drug from the bloodstream. During this elimination phase, ion pumps will actively transport some drugs from the blood into the tubules of the kidneys. Organic anion transporters (OAT) transport acids into the tubules of the kidney while organic cation transporters (OCT) transport bases into the tubules of the kidney. This mechanism, known as secretion, depends entirely on transporters and allows both acidic and basic drugs to be eliminated from the body.

Another process known as reabsorption can also occur in the kidneys. During reabsorption, drugs can be transported from the tubules of the kidney back into the blood. This process depends on the pH of the fluid in kidney tubules (e.g. the urine). At a low pH (i.e. acidic environment), acidic drugs are best reabsorbed. Conversely, at high pH (i.e. basic environment), basic drugs are best reabsorbed.

Experiment 1

The same drug was administered to various individuals. After some time elapsed, the rate of renal clearance (i.e. the rate of urine elimination from the body) was measured in each of the individuals. Subsequently, the pH of the urine was measured for each individual. The rate of renal clearance versus urinary pH was then plotted in the provided figure (each black dot represents a different individual).

Experiment 2

A scientist was able to engineer a mouse kidney that lacked organic anion transporters. She administered various drugs to the mouse and measured the rates of secretion. The data collected is located in the provided table.

The pKa of a substance is a measure of its acidity. The lower the pKa, then the more acidic the substance.

Drug X is a strong acid and has the following pKa:

Suppose a new drug has the following pKa:

Both of these drugs were tested under the conditions of Experiment 2. Which of the following would most likely be rate of secretion of the new drug?

If a drug is administered intravenously (i.e. injected into a vein), then the concentration of the drug in the blood will rise and then reach a plateau. After some time, the body will begin to eliminate this drug from the bloodstream. During this elimination phase, ion pumps will actively transport some drugs from the blood into the tubules of the kidneys. Organic anion transporters (OAT) transport acids into the tubules of the kidney while organic cation transporters (OCT) transport bases into the tubules of the kidney. This mechanism, known as secretion, depends entirely on transporters and allows both acidic and basic drugs to be eliminated from the body.

Another process known as reabsorption can also occur in the kidneys. During reabsorption, drugs can be transported from the tubules of the kidney back into the blood. This process depends on the pH of the fluid in kidney tubules (e.g. the urine). At a low pH (i.e. acidic environment), acidic drugs are best reabsorbed. Conversely, at high pH (i.e. basic environment), basic drugs are best reabsorbed.

Experiment 1

The same drug was administered to various individuals. After some time elapsed, the rate of renal clearance (i.e. the rate of urine elimination from the body) was measured in each of the individuals. Subsequently, the pH of the urine was measured for each individual. The rate of renal clearance versus urinary pH was then plotted in the provided figure (each black dot represents a different individual).

Experiment 2

A scientist was able to engineer a mouse kidney that lacked organic anion transporters. She administered various drugs to the mouse and measured the rates of secretion. The data collected is located in the provided table.

An individual's diet can alter urinary pH. Based on the information in the passage, consumption of foods that lower urinary pH would affect which of the following processes?