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In April of 2004, d dogs and c cats lived in an animal shelter. If 4 cats arrived at the shelter in May of 2004 and the ratio of dogs to cats remained unchanged, in terms of c and d, how many dogs arrived at the shelter in May of 2004?
(D) d^2 - 4d
(E) (2cd + 4d)/c
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Traditionally, oral drugs in pill or capsule form have been designed to release the dose of medicine in the upper gastrointestinal tract, where drugs are more readily dissolved and absorbed. New research has targeted the colon as an ideal environment for drug absorption to treat certain illnesses. To reach the colon, the drug must first pass through the stomach and small intestine. Table 1 details several drug-delivery systems.
The following experiments test two of the drug-delivery systems:
Bacteria-dependent delivery. This experiment measured the average time it took a coated tablet to travel from the stomach (gastric emptying) through the small intestine (small intestine transit) to arrive in the colon. Twelve healthy men aged 23 to 25 years old and weighing between 55 and 70 kilograms (kg) who had fasted overnight were divided into 3 groups. They each swallowed 1 tablet, which contained a tracer (A or B) and 1 of 2 natural coatings (1 or 2). The location of the tracer was measured every half-hour for 12 hours. The average times are recorded in Table 2.
Time-dependent delivery. The methods were the same as those used in Experiment 1, except that the tablets all contained the same tracer and 1 of 2 outer coatings (A or B) and one of two inner coatings (1 or 2). The average times are recorded in Table 3.
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Several scientists considered some different environmental factors and their influence on the growth of certain bacteria. The following experiments used Salmonella bacteria to measure the effect of pH levels, nutrients, and temperature on the number of bacteria produced within a given time period.
1. According to Table 1, what might best contribute to the growth of Salmonella bacteria?
A. A pH level above 9
B. A pH level below 5
C. A pH level near 7
D. A pH level near 5
2. According to the results of the three experiments, which combination of the three factors studied would be expected to produce the highest percent growth?
F. pH level of 5, organic compound in Dish 2, temperature of 40◦C
G. pH level of 7, organic compound in Dish 2, temper- ature of 10◦C
H. pH level of 5, organic compound in Dish 1, temper- ature of 40◦C
J. pH level of 9, organic compound in Dish 1, temper- ature of 90◦C
3. Which of the following conclusions is strengthened by the results of Experiment 1?
A. Salmonella bacteria reproduce most efficiently in an acidic environment.
B. Salmonella bacteria reproduce most efficiently in a neutral environment.
C. Salmonella bacteria cannot reproduce in a basic environment.
D. Salmonella bacteria cannot reproduce in an acidic environment.
4. Bacteria will generally reproduce until all of the nutrients available have been depleted. How could the experiment be altered to maximize the length of time that bacteria will reproduce?
F. Change the observation time from 6 hours to 12 hours.
G. Regularly re-supply each group of bacteria with unlimited nutrients.
H. Increase the rate of growth by decreasing the pH levels.
J. Do not test the effect of different nutrient combinations on growth.
5. Which of the following was the independent variable in Experiment 3?
A. pH level
C. organic compound
D. percent growth
6. The experiments recorded the percent growth that occurred over a 6-hour period. Bacteria often repro- duce at a rate that drastically varies from one stage to the next. The best way to study the different stages of growth would be to record the percent growth:
F. after 2 hours only.
G. after 4 hours, then again after 6 hours.
H. after 8 hours only.
J. every 15 minutes for 3 hours.
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Dopamines serve as enhancers or catalysts (a substance that initiates or increases the rate of impulses during a chemical reaction, but is not depleted during the process) to certain reactions involved in the activity of human thought. The dopamine intropin is involved in the stimulation of the neurotransmitters in the brain when thought is initiated. A student investigated the effects of dopamine activity on a specific neurotransmitter.
To each of 10 test tubes, 7 milliliters (mL) of a peptide (a neurotransmitter) solution was added. Two mL of an intropin solution was added to each of Tubes 1–9. Tube 10 received 2 mL of water without intropin. The tubes were then stirred at a constant rate in water baths at various temperatures and incubated (heated) from 0 to 15 minutes (min). At the end of the incubation period, 0.3 mL of NaCl solution was added to each tube. The NaCl stopped the reaction between the intropin and the peptide. The precipitates, solids formed in a solution during a chemical reaction, which in this case were caused by the reaction of NaCl and the pep- tide, were removed from the tubes and dried. The masses of the precipitates, in milligrams (mg), were measured to determine the relative amount of enhancer that remained in the tube. The results are shown in Table 1.
Peptide solution (8 mL) was added to an additional 8 test tubes to which 2 mL of intropin solution was then added. The tubes were incubated at 10 degrees Celsius and stirred at a constant rate for 15 min. The effect of acidity on the neurotransmitter was observed by varying the acidity levels (using the pH scale). The relative amount of neurotransmitter present in each tube was determined in the same manner as Experiment 1, by adding NaCl solution to each test tube. The results are in shown in Table 2.