Most of us hear "the cell is the basic unit of life" in school. Then our teachers go on to tell us about different kinds of cells. Plant cells are different from animals cells, and then there are other cells that don't fit into either the plant or animal category. How are cells categorized and what different kinds of cells are there?

Eukaryotes, prokaryotes, and archaea

Biologists divide living things into three kingdoms: eukaryotes, prokaryotes, and archaea.

An eukaryotic cell has a nucelus with a nuclear membrane.

The nucleus carries genetic material for the cell and is enclosed in a membrane. Large organisms are made from eukaryotic cells. This type of cell frequently has organelles, or "little organs." The organelles, like the nucleus, are wrapped in a membrane.

Prokaryotes are bacteria.

Prokaryotes do not have a nucleus or any other organelles with membranes. For the most part, these organisms form unicellular life. That is, lifeforms made of prokaryotes only have one cell.

Most people have heard about bacteria. We have a symbiotic relationship with bacteria inside our bodies, and sometimes, unfortunately, we encounter parasitic bacteria that make us sick. Bacteria permeate the soil, the air, water, your skin, and just about everything you encounter. Bacteria are important to the planet. Besides having symbiotic relationships with other living things, bacteria are decomposers, an important part of the food web, carbon cycle, and nitrogen cycle.

Archaea

Archaea are as small as bacteria, but they have some similarities to eukaryotes, like genes in their cells and fats in their cell membranes. Many types of archaea exist and some even form a symbiotic relationship with humans, but the kingdom is often recognized for having extremophiles in it. Extremophiles are organisms which thrive in extreme conditions like hot springs, salty lakes, extremely arid areas, high pressure and low pressure areas, and by under sea volcanoes.

Back to eukaryotes

Because eukaryotes are the type of cells most multi-cellular organisms are made of, these are the type of cells people are most familiar with. The basic kinds of eukaryotic cells are plant cells, animal cells, fungi, and protista.

Plant cells

Plantsare multicellular, produce their own energy through photosynthesis, and have cellulose in their cells. A plant cell has a wall instead of a membrane. The wall gives a plant cell a fixed shape, and the cell wall is made of cellulose. Plant cells have organelles in them.

Animal cells

Animals are organisms that have a fixed body plan (shape) once they reach adulthood. Animals can move, and animals can't make their own food. Animal cells have cell membranes instead of walls, so the shapes aren't fixed. (You can poke an animal cell and it will flex.) Animal cells have organelles in them.

Fungi

Fungi are organisms such as yeast, molds, and mushrooms. Fungi aren't plants or animals. While they have cell walls, the walls aren't made of cellulose, but of chitin.

Protista

Protista typically don't have specialized cells. (Humans have different cells for our brains, muscles, skin, etc.) Protista do, however, have organelles.

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