Algae are defined as a group of predominantly aquatic, photosynthetic, and nucleus-bearing organisms that lack the true roots, stems, leaves, and specialized multicellular reproductive structures of plants. Their photosynthetic pigments are also more varied than those of plants, and their cells have features not found among plants and animals.

Some species of algae produce toxins that are lethal to fish, or render shellfish and finfish unsafe for consumption. The (taxonomically contentious) dinoflagellates are responsible for red tides, which not only release toxins into the water that may be lethal to aquatic life, but also wind-sprayed toxic cells that can cause health problems for air-breathing organisms.

Algae range in size from picoplankton, which are between 0.2 to 2 micrometers (0.000008 to 0.000079 inches) in diameter, to giant kelp, which can be 60 metres (200 feet) long.

algae

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Q: What organelles do algae contain?

Algae are eukaryotic organisms and contain three types of double-membrane-bound organelles: the nucleus, the chloroplast, and the mitochondrion. In most algal cells, there is only a single nucleus, although some cells are multinucleate.

Q: Why are algae important?

Algae produce up to half of the oxygen in Earth's atmosphere, and algae help keep carbon dioxide out of the atmosphere by storing it. Algae are also the food base for almost all aquatic life, and are economically important as a source of crude oil and as sources of food and a number of pharmaceutical and industrial products for humans.

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Also known as: Phycophyta, alga, algas

Written by Robert A. Andersen, Ralph A. Lewin•All

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Dec 17, 2024 • Article History

Singular:: alga

Key People:: Ferdinand Cohn; Sylvia Earle; Sir William Jackson Hooker; Nathanael Pringsheim; Per Teodor Cleve

Related Topics:: dinoflagellate; seaweed; red algae; green algae; phytoplankton

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algae, members of a group of predominantly aquatic photosynthetic organisms of the kingdom Protista. Algae have many types of life cycles, and they range in size from microscopic Micromonas species to giant kelps that reach 60 metres (200 feet) in length. Their photosynthetic pigments are more varied than those of plants, and their cells have features not found among plants and animals. In addition to their ecological roles as oxygen producers and as the food base for almost all aquatic life, algae are economically important as a source of crude oil and as sources of food and a number of ...(100 of 8724 words)

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