Predator-prey relationships and mechanics are important tools for understanding the ecology of environments. Population cycles were first recorded in Canadian forests by fur trappers. Species interactions are important indicators of the health and economy of a natural environment. A twelve-year study of northern Canada revealed that snowshoe hares and lynxes share highly synchronized and predictable cycles. The lynx's predator populations mimic and mirrors that of their prey, the snowshoe hare. Two scientists express their views on these population patterns below.

Scientist 1

     The observed relationship is best explained by predator-prey relationships and competition for resources. Consumer-resource interactions fluctuate independently of variation within the environment.

Scientist 2

     The observed relationship is produced by environmental changes. Fluctuations in weather patterns and resources manipulate observed predator-prey relationships.

What information is needed to help Scientist 2 to prove his point?

A mycologist performed an experiment to determine the effect of methanol on the mold Neurospora crassa.

1,500 Neurospora spores were divided evenly into five groups of three large glass test tubes each. Then each test tube was filled with 5.0 mL of liquid nutrient solution and either 0 mL, 0.5 mL, 1.0 mL, 1.5 mL, or 2.0 mL of methanol. The tubes were placed in an incubator at 28^oC overnight to germinate, and then their aerial growth was marked beginning the next morning and every twelve hours thereafter for two days.

Table 1 shows the average growth data with  hours representing the morning after germination and  hours representing the end of the two-day experiment.

Based on the description of the experiment, which of the following aspects of the experimental design can you infer were not held constant?

A science class has been assigned a group project. Three different groups have been asked to plant a small pallet of grass and record growth over the course of 3 weeks. One blade of grass per trial was designated as the blade of grass to measure each week (the grass height for "Week 0" corresponds to the day the grass was planted). Every Monday (including the day it was planted) this same blade of grass is measured and its height (in inches) is recorded in a data table. The data collected by Group 1 corresponds to Table 1, Group 2 corresponds to Table 2, and Group 3 corresponds to Table 3.

Each group had two control conditions and one variable condition. The three conditions are:

• the amount of water given to the grass
• the type of soil the grass was planted in
• the amount of sunlight the grass is exposed to every day

The variables and data collected are as follows:

Group 1 variable: different amounts of water 

Trial A - one cup of water is poured on the grass every Monday after measuring

Trial B - two cups of water are poured on the grass every Monday after measuring

Trial C - three cups of water are poured on the grass every Monday after measuring

Group 2 variable: different types of soil

Trial D - standard potting soil is used

Trial E - large rocks are mixed into the standard potting soil before the grass is planted

Trial F - small stones and pebbles are mixed into the standard potting soil before the grass is planted

Group 3 variable: different sunlight exposure

Trial G - the grass is given 3 hours of sun exposure per day

Trial H - the grass is given 6 hours of sun exposure per day

Trial J - the grass is given 9 hours of sun exposure per day

Each group has a control condition for its three trials, and the control conditions are the same for each group. Given this information, determine which trial from each group serves as the control.

A scientist discovered a new type of bacteria that can be harmful to humans. The scientist decided to perform an experiment to determine which antibiotics will be able to treat human illnesses contracted from the bacteria. The scientist created four plates that each contain the necessary minerals for the bacteria to growth and placed some of the bacteria on each plate (as seen below in the initial setup). Once the bacteria were placed on the plates, she placed a piece of paper soaked in an antibiotic in the center of each treatment’s petri dish. Each piece of paper was soaked in a different antibiotic. She also constructed a control plate using a piece of paper soaked in saline solution. Three different antibiotics and one control plate without antibiotics were tested. The final results are shown in the provided figure, in which the bacteria is represented by the grey areas.

Why did the scientist create a plate without antibiotics? 

A scientist discovered a new type of bacteria that can be harmful to humans. The scientist decided to perform an experiment to determine which antibiotics will be able to treat human illnesses contracted from the bacteria. The scientist created four plates that each contain the necessary minerals for the bacteria to growth and placed some of the bacteria on each plate (as seen below in the initial setup). Once the bacteria were placed on the plates, she placed a piece of paper soaked in an antibiotic in the center of each treatment’s petri dish. Each piece of paper was soaked in a different antibiotic. She also constructed a control plate using a piece of paper soaked in saline solution. Three different antibiotics and one control plate without antibiotics were tested. The final results are shown in the provided figure, in which the bacteria is represented by the grey areas.

Which of the following choices would be an improvement to this experiment? 

Elena is conducting an experiment to determine the effect of a new drug, norzapam, that is meant to help diabetic patients produce insulin naturally. She has four test subjects, all with type 1 diabetes, and all of whom continued to take fast-acting insulin as needed but ceased taking long-acting insulin. Two patients received the drug and two received a placebo. Over a period of ten months Elena measured her patients’ insulin levels each day (measured in International Units) and averaged them for each month. She also asked each patient to walk for as long as they could after taking the drug before their blood sugar dropped too low to continue. Her results from the experiment are shown in the given tables.

Patient 1: Drug received

Patient 1 is a 45 year-old male who is overweight and leads a sedentary lifestyle.

Patient 2: Drug received

Patient 2 is a 23 year-old female of healthy weight who leads an active lifestyle.

Patient 3: No drug

Patient 3 is a 60 year-old female who is overweight and leads a moderately active lifestyle.

Patient 4: No Drug

Patient 4 is a 28 year-old male of healthy weight who leads very active lifestyle.

Who are the controls in the experiment?

Elena is conducting an experiment to determine the effect of a new drug, norzapam, that is meant to help diabetic patients produce insulin naturally. She has four test subjects, all with type 1 diabetes, and all of whom continued to take fast-acting insulin as needed but ceased taking long-acting insulin. Two patients received the drug and two received a placebo. Over a period of ten months Elena measured her patients’ insulin levels each day (measured in International Units) and averaged them for each month. She also asked each patient to walk for as long as they could after taking the drug before their blood sugar dropped too low to continue. Her results from the experiment are shown in the given tables.

What is the independent variable?

Elena is conducting an experiment to determine the effect of a new drug, norzapam, that is meant to help diabetic patients produce insulin naturally. She has four test subjects, all with type 1 diabetes, and all of whom continued to take fast-acting insulin as needed but ceased taking long-acting insulin. Two patients received the drug and two received a placebo. Over a period of ten months Elena measured her patients’ insulin levels each day (measured in International Units) and averaged them for each month. She also asked each patient to walk for as long as they could after taking the drug before their blood sugar dropped too low to continue. Her results from the experiment are shown in the given tables.

What is the dependent variable?

Elena is conducting an experiment to determine the effect of a new drug, norzapam, that is meant to help diabetic patients produce insulin naturally. She has four test subjects, all with type 1 diabetes, and all of whom continued to take fast-acting insulin as needed but ceased taking long-acting insulin. Two patients received the drug and two received a placebo. Over a period of ten months Elena measured her patients’ insulin levels each day (measured in International Units) and averaged them for each month. She also asked each patient to walk for as long as they could after taking the drug before their blood sugar dropped too low to continue. Her results from the experiment are shown in the given tables.

For patients who receive the drug, the relationship between length of walk and insulin levels appears to be __________.

Elena is conducting an experiment to determine the effect of a new drug, norzapam, that is meant to help diabetic patients produce insulin naturally. She has four test subjects, all with type 1 diabetes, and all of whom continued to take fast-acting insulin as needed but ceased taking long-acting insulin. Two patients received the drug and two received a placebo. Over a period of ten months Elena measured her patients’ insulin levels each day (measured in International Units) and averaged them for each month. She also asked each patient to walk for as long as they could after taking the drug before their blood sugar dropped too low to continue. Her results from the experiment are shown in the given tables.

For patients who did not receive the drug, the relationship between time and insulin levels appears to be __________.