Question

33 read the description of a laboratory investigation below and then answer the following questions. an experiment was designed to investigate the effect of caffeine on the heart rate of water fleas. two populations of water fleas were cultured. both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20°c. every two hours, water fleas from both populations were selected and their heart rates were monitored. the fleas of population a had caffeine administered five minutes before their heart rate was checked. the fleas of population b were given nothing. a. what is the independent variable in this experiment? (1 pt) b. what is the dependent variable in this experiment? (1 pt) c. write a hypothesis (if... then...) for this experiment. (2 pts) d. what is the control group in this experiment? (1 pt) e. what is the experimental group(s) in this experiment? (1 pt) f. list two constants or controls in this experiment. (2 pts)

Explanation:

• a: The independent variable is what is changed in the experiment. Here, it's whether caffeine is given (only population A gets caffeine).
• b: The dependent variable is what is measured. Heart rate is measured to see the effect of caffeine.
• c: A hypothesis predicts the relationship between the independent and dependent variable. In an "If...Then..." format, it links caffeine (independent) to heart rate (dependent).
• d: The control group is the one not exposed to the independent variable. Population B has no caffeine.
• e: The experimental group is exposed to the independent variable. Population A has caffeine.
• f: Constants/controls are factors kept the same. The description lists several (e.g., water mineral content, food amount, light amount, temperature). Any two of these are valid.

Answer:

a. Caffeine
b. Heart rate
c. If water fleas are given caffeine, then their heart rate will increase.
d. Population B
e. Population A
f. Water with the same mineral content, identical amounts of bacteria as food, same amount of light, temperature maintained at 20°C (any two)