How does the experimental design of Experiment 2 differ from Experiment 1?

What is the researchers' primary data collection method?

The cells of multicellular organisms must be linked to each other through special structures called cellular junctions. A gap junction is a type of cellular junction, which allows for the passage of small molecules for fast coordination between cells. For example, cardiac cells in the heart and neurons in the brain rely on gap junctions. However, gap junctions are small and there is a limit to how large a molecule can be in order for it to pass through the gap junction.    

An experiment is designed to see how large molecules can be to pass through a gap junction. A single layer of cells is grown in a petri dish. A single cell is then injected with a dye labeled with a fluorescent molecule. Researchers observe the following:

Based on the experiment, which of the following molecules would most likely pass through a gap junction?

Researchers at a biotechnology company have just developed a new immortal line of mammalian cells derived from raccoon hair follicles. They dub these cells RHF and note that they appear particularly resistant to environmental stressors in initial experiments. They design a set of experiments to test the limits of the RHF cell line.

Experiment 1: The scientists inoculate 5 identical flasks containing growth media with samples of the RHF cells. The flasks are then incubated in separate incubators at varying temperatures. The flasks are sampled daily for cell density to analyze growth of the cells, yielding these results: 

Experiment 2: The scientists produce 5 separate batches of cell growth media containing various amounts of salt to raise the osmolality of the solution. They inoculate 5 flasks, each with various osmolalities, then incubate the flasks at 37 °C for seven days. The flasks are sampled daily for cell density, yielding these results: 

How does the experimental design differ from Experiment 1 to Experiment 2?

A sports physician is conducting an experiment in which a competitive bicycle rider has her heart rate, oxygen content in blood, and blood lactate measured. The measurements are taken at resting, during easy, moderate, difficult, and very difficult exercise. The results are summarized in the table below. Please note that the oxygen content was normalized to the resting oxygen content. 

What important variable should also be measured that is not included? 

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.

Suppose the experimenter discovered that weeds had been growing in the plots and were not removed from the plant species of interest during biomass collection. Based on this information, the experimenter repeated the experiment, but this time was extra careful in removing weeds from the biomass. Which of the following is most likely to be true regarding the repeated experiment?

Three different species of bacteria were grown in the laboratory. The experiment measured the effect of pH on the concentration of the three species of bacteria. The graphs below show the concentration of bacteria at different pH levels. Figure 2 shows the effect of pH on the concentration of a third bacterial strain, bacteria C.

Which statement, if true, would serve to weaken the experiment?

An undergraduate biology student working in a lab was reading about the latest health epidemic in the United States concerning obesity. He recently learned in his biology class that an enzyme called fatty acid synthase (FAS) catalyzes the formation of fatty acids. Accumulation of these fatty acids then creates the adipose fatty tissue that individuals typically see in their belly or side-regions. He hypothesizes that by decreasing the rate that this enzyme produces fatty acids by administering an inhibitor will aid in reducing the storage of fats, helping to alleviate obesity. After gaining approval from the university's clinical trials and ethics committee, he gathered a group of 20 test subjects. With the help of his research director, he measured the baseline rate of FAS activity for all test subjects and the averaged rate after oral administrators of a placebo and three types of inhibitors at a concentration of 0.6M to four equally-sized groups. The data is shown in Table 1.                      

Table 1.

The student then wonders if a mixture of different inhibitors were to increase the effect in the subject. He again measured the averaged baseline FAS level of the subjects and then attempted administering a placebo and three different combinations of inhibitors to subjects in a second trial. The results are shown in Table 2.

Table 2. 

A colleague of the researcher interpreted the results from Table 1 and 2 and suggested a third trial which would track the averaged weight change of the subjects over a 6-month period. The results are shown in Table 3.

Table 3.

The researcher noted that many of the test subjects had similar diets. Most had admitted that they regularly consumed foods high in saturated fats and sodium. How would this affect the interpretation results of the study if the purpose of this study were to create a viable treatment to prevent and treat obesity?

An undergraduate biology student working in a lab was reading about the latest health epidemic in the United States concerning obesity. He recently learned in his biology class that an enzyme called fatty acid synthase (FAS) catalyzes the formation of fatty acids. Accumulation of these fatty acids then creates the adipose fatty tissue that individuals typically see in their belly or side-regions. He hypothesizes that by decreasing the rate that this enzyme produces fatty acids by administering an inhibitor will aid in reducing the storage of fats, helping to alleviate obesity. After gaining approval from the university's clinical trials and ethics committee, he gathered a group of 20 test subjects. With the help of his research director, he measured the baseline rate of FAS activity for all test subjects and the averaged rate after oral administrators of a placebo and three types of inhibitors at a concentration of 0.6M to four equally-sized groups. The data is shown in Table 1.                      

Table 1.

The student then wonders if a mixture of different inhibitors were to increase the effect in the subject. He again measured the averaged baseline FAS level of the subjects and then attempted administering a placebo and three different combinations of inhibitors to subjects in a second trial. The results are shown in Table 2.

Table 2. 

A colleague of the researcher interpreted the results from Table 1 and 2 and suggested a third trial which would track the averaged weight change of the subjects over a 6-month period. The results are shown in Table 3.

Table 3.

How might the significance of this study be increased?

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.

Which of the following would be considered as the dependent variable in Experiment 2?