3.

A microorganism observed under a microscope is classified as unicellular because it
lacks a nucleus
is made of only one cell
consumes food for energy
is a plant

is made of only one cell

The microorganism observed under a microscope is classified as unicellular because it is made of only one cell. Unlike multicellular organisms, unicellular organisms are composed of a single cell that performs all necessary life functions, such as reproduction, obtaining nutrients, and carrying out metabolism. These organisms do not possess specialized cells and tissues like plants or animals, which have complex cellular structures and multiple cells.