(Hypothetical) In order to assess the effectiveness of a new fertilizer, researchers applied the fertilizer to the tomato plants
on the west side of a garden but did not fertilize the plants on the east side of the garden. They later measured the weights of the tomatoes produced by each plant and found that the fertilized plants grew larger tomatoes than did the nonfertilized plants. They concluded that the fertilizer works. (a) Was this an experiment or an observational study
Explanation: An experiment can be defined as an examination under inhibited conditions made to examine the validity of a hypothesis, demonstrate a known truth, or determine the efficacy of something that has not been tried before.
In this question, the researchers applied the fertilizer to some parts while they didn't apply to some other parts. This act, is a quality of an experiment in the sense that the test was done under inhibited conditions. If the fertilizer was applied everywhere, it can be an observational study.
Explanation: Experiment is done when we apply anything to a samples or conditions in other to study another sample or conditions.
Observation is done when, we study samples or conditions in it's natural way, without application of anything that may alter it's result.
Because the researcher has applied fertilizer to one side and did not apply to the other side, that means he has performed an experiment. Since he wasn't observing the two sample in it's natural way without any external application.
