In at least 150 words, justify the need for a control in an experiment. Use complete sentences. Write your answer in the essay box below.

You need to include a control group that is identical to the treatment group in every way except that it does not receive the experimental treatment. Without a control group, you can't know whether it was the treatment or some other variable that caused the outcome of the experiment.

The control group consists of elements that present exactly the same characteristics of the experimental group, except for the variable applied to the latter. This group of scientific control enables the experimental study of one variable at a time, and it is an essential part of the scientific method. In a controlled experiment, two identical experiments are carried out: in one of them, the treatment or tested factor (experimental group) is applied; whereas in the other group (control), the tested factor is not applied.

An autotrophic protist - they can perform photosynthesis and mainly consist of unicellular algae. they can be divided into number of systematic group according to the shape of their cell and the type of photosynthetic pigments they use.