Question

Two students completed an experiment to determine if pesticide use at local farms was causing fish kills in a local pond. The steps of the experiment are listed below.
1.Select different locations to collect water samples in the pond.
2.Collect a 5-mL water sample at 8 am at a different location each day for 10 days.
3.Measure the amount of pesticide present in each sample using the same measurement tools.

After analyzing their data, the students conclude that pesticide runoff from farms is not causing the fish to die in the pond. Which of these statements best describes why their conclusion is not valid?

a. The amount of water collected each day was the independent variable.
b. The daily location for sample collection was not a controlled variable.
c. Pesticide measurements were the dependent variable.
d. The time of sample collection was not a controlled variable.

Answer 1

Answer:

D

Explanation:

The samples should not only be collected at 8am. Rather, they should be collected at different times of the day. Time is not a control variable, in this case, only the sample size is. Time of day can influence many factors that affect the pesticide levels in the samples hence the need to collect samples at different times of day too.