Copyright © 2007 Dorling Kindersley
Algae are plantlike organisms that make food by photosynthesis. All algae contain chlorophyll, which is green, but many are colored brown or red by other pigments. Most algae live in water.
All seaweeds are algae, but not all algae are seaweeds. Seaweeds are easily visible, made of many cells, and grow in the sea. There are red, brown, and green forms. Many algae, such as diatoms, are microscopic and consist of a single cell.
Most species of algae live in the sea, in lakes, or in ponds. Some single-celled green algae live in moist conditions on land, such as on tree trunks, on the surface of the soil, or on damp brickwork. Others live inside lichens.
40,000 species of plantlike organisms.