Summarizing Prokaryotic Cells

Summary of lessons so far

A cell is the smallest unit of life. Most cells are so tiny that we cannot see them with the naked eye. Therefore, scientists use microscopes to study cells. Electron microscopes provide higher magnification, higher resolution, and more detail than light microscopes. The unified cell theory states that all organisms are composed of one or more cells, the cell is the basic unit of life, and new cells arise from existing cells.

Prokaryotes are predominantly single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, and DNA that is not membrane-bound. Most have peptidoglycan cell walls and many have polysaccharide capsules. Prokaryotic cells range in diameter from 0.1 to 5.0 μm.

As a cell increases in size, its surface area-to-volume ratio decreases. If the cell grows too large, the plasma membrane will not have sufficient surface area to support the rate of diffusion required for the increased volume.

Glossary of Words

Cell theory

see unified cell theory

Electron microscope

an instrument that magnifies an object using a beam of electrons passed and bent through a lens system to visualize a specimen

Light microscope

an instrument that magnifies an object using a beam of visible light passed and bent through a lens system to visualize a specimen

Microscope

an instrument that magnifies an object

Nucleoid

central part of a prokaryotic cell in which the chromosome is found

Prokaryote

unicellular organism that lacks a nucleus or any other membrane-bound organelle

Unified cell theory

a biological concept that states that all organisms are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells