It is because of different arrangements of nucleotide bases.
<h2>Explanation</h2>
There are only five types of nucleotide basis are present in the genetic material which makes up the all the genetic information of the individuals. These nucleotides are named as Adenine, Thymine, Guanine, Cytosine and Uracil. In all the living beings on the earth, these only five nucleotides are present which decides their behaviour and functions on the earth. These five bases have features to get any arrangements according to the situation. Their different arrangement at the heredity material makes the difference in all living beings regarding their behaviour.
A mutagen changes the level of mutations that occur in the DNA either by affecting it physically or chemically. This helps researchers create different organisms with altered phenotypes according to what the research needs so that the genes can be investigated further under a controlled environment.
Remember that a cell that is surrounded by an environment with a higher osmotic pressure, will produce that the cell get some water outside to make some dilution to the salt concentration that surrounds the protozoan.