sentence: Bacteria are made up of one cell, so they are a kind of 'unicellular organism'.
sentences_before: Almost all bacteria are so tiny they can only be seen through a microscope.
sentences_after: They are among the simplest single-celled organisms on Earth, and were one of the earliest forms of life. They include a number of extremophiles who live in extreme habitats.
concept_name: Bacteria
headings: Bacteria
categories: Microbiology Prokaryotes