Johannes wants to know whether soil, water, or both are needed for plant growth. he chooses to conduct experiments on a willow tree for five years to answer his question. how can his experimental methods be changed to improve his experiment?

a) he needs to ask scientists what they think.
b) he needs to conduct the experiment for a longer period.
c) he needs to use a larger sample size.
d) he needs to test more factors in the environment.

The answer is C) He needs to use a larger sample size.

The results will be more accurate if there is a larger sample size. No matter the research, the larger sample size is, the more accurately will be the results and vice versa. The larger samples increase a chance of significance because they reflect the population mean more reliably. With a small sample, the chance for false conclusions is higher.

Johannes chose only one willow tree for five-year-experiment. The only one tree cannot represent a whole population. He should choose more trees in order to have better results about effects of different factors on plant growth.