Unicellular
Cell Biology · Microbiology · Evolution
Say it: yoo-nih-SEL-yuh-lur
Unicellular describes an organism whose whole body is a single cell, which carries out every life process, from feeding to reproducing, on its own.
Also: single-celled, one-celled
Definition
What does unicellular mean?
Unicellular describes a living thing made of just one cell. That one cell has to do everything a larger organism shares out among many tissues: take in or make food, release energy, get rid of waste, sense its surroundings and reproduce. Most unicellular organisms are too small to see without a microscope, which is why biologists usually group them as microorganisms.
Nearly all bacteria and archaea are unicellular, although many live packed together in colonies or in slimy surface communities called biofilms. Among eukaryotes, protozoa such as amoebae and Paramecium, many algae such as diatoms, and yeasts are unicellular too. A unicellular organism reproduces when its cell divides, by binary fission in prokaryotes or by mitosis or budding in many eukaryotes, so every division produces a new individual. The opposite is multicellular, describing organisms whose cells stay together, specialize and depend on one another.
The earliest life was unicellular, and multicellular forms later evolved from single-celled ancestors on several separate occasions, including in animals, land plants, fungi and the red, green and brown algae. Green algae show what the steps may look like: Chlamydomonas is a lone cell, Gonium is a small plate of identical cells, and Volvox is a hollow ball of hundreds to thousands of cells in which only a few reproduce.
Word parts
Where does the word “unicellular” come from?
- uni-
- oneLatin unus
- cellul-
- little room, small cellLatin cellula, from cella
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Terms that go with it
- CellA cell is the smallest unit that can carry out all the processes of life, enclosed by a membrane and holding its own genetic material.
- ProkaryoteA prokaryote is a usually single-celled organism, a bacterium or an archaeon, whose cell has no nucleus or other membrane-bound organelles.
- EukaryoteA eukaryote is an organism whose cells keep their DNA inside a membrane-bound nucleus and contain other membrane-bound organelles.
- ProtozoaProtozoa are single-celled eukaryotes that do not photosynthesize, usually move on their own and feed on other organisms or organic matter.
- YeastA yeast is a single-celled fungus that usually reproduces by budding; baker's yeast ferments sugar into alcohol and carbon dioxide.
- Binary fissionBinary fission is how bacteria and archaea reproduce: a cell copies its DNA, grows, and splits in the middle into two identical daughter cells.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 1.2 Themes and Concepts of Biology
- OpenStax Microbiology, 1.3 Types of Microorganisms
- Herron, Many from one: Lessons from the volvocine algae on the evolution of multicellularity (Commun Integr Biol, 2009)
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