Question

A researcher is interested in the effects of nitrate and phosphate on plant growth and sets up an experiment in which groups of five plants are given 1, 2, and 3 grams of nitrate and 1, 2, and 3 grams of phosphate in all combinations over a period of one month. The researcher measures plant height and weight at the end of the experiment. What is missing in this experimental design?

Answer 1

a control

Step-by-step explanation:

A controlled experiment is the scientific study or test done which can be directly manipulated by the experimenter. This is done to test a single variable one at a time. The variable which is tested is independent variable and is then adjusted to see the effects on the system that is studied.

In the context, a researcher sets up an experiment and takes readings of the height and weight of the variable. But the experimenter did not included a controlled experiment.