In an experiment to determine the effect of exercise on pulse rate, a student checks his pulse rate before
and after exercising for several minutes. the purpose of checking his pulse rate before exercising is that it
(1) serves as the conclusion for the experiment
(2) is needed to justify the sample size
(3) serves as a control for the experiment
(4) is needed to formulate a hypothesis

The correct answer is option 3.

Explanation:

In the mentioned experiment, the pulse rate prior to performing exercise functions as a control of the experiment. Before doing exercise, the pulse rate would be under normal conditions, that is, without changing any variable, and thus is considered as the control for the experiment.  

In order to find a change witnessed in the pulse rate post performing exercise, the pulse rate post-exercise would be compared with the control pulse rate.  

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

explanation: