Tonya used a microscope to observe five kinds of organisms in a sample of pond water. She wants to identify each organism using the dichotomous key below.

A method of deducing the correct species assignment of a living thing is known as dichotomous key, which is also called identification key. It works by requiring a user to choose two alternatives at each step and the choice of one alternatives give the name of the organism or direct further down in the key. However, a common error in using dichotomous key is the assumption that the correct name or identification of the organism is even included in the set of key. Therefore, this method alone is not reliable to identify specific species.