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Diatoms seen through a microscopeDiatoms seen through a microscope Algae are simple, plant-like protists. An alga has no proper roots, stem or leaves, although it may have a stem-like part and a leaf-like blade. It absorbs water and nutrients through its body surface, and makes its food by photosynthesis. Algae occur in freshwater or salt water (most seaweeds are algae) or on the moist surfaces of soil or rocks. Algae are divided into seven groups: red, dinoflagellates, brown, green, golden, blue-green and Bacillariophyta.

Seaweed, types of algaeSeaweed, types of algae

Spirogyra, a kind of green algaeSpirogyra, a kind of green algae

Kinds of algae

Algae range from microscopic, single-celled organisms to seaweeds many metres long. Nearly all algae live in water, although a few kinds can survive in damp places, like Pleurococcus alga which grows as a green powder on shady tree trunks. The slimy green scum often found in stagnant ponds is made up of green algae, a group of microscopic organisms that includes the hair-like spirogyra. Dinoflagellates and diatoms, a type of red algae, are kinds of marine plankton. They are food for tiny animals that live in the ocean, called zooplankton.

Algal bloom

There are more than 70,000 species of algae.

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