Algae

Introduction & Top Questions
Physical and ecological features of algae
- Size range and diversity of structure
- Distribution and abundance
- Ecological and commercial importance
- Toxicity
Form and function of algae
- The algal cell
- Flagella
- Mitosis
- Cellular respiration
- Photosynthesis and light-absorbing pigments
- The effects of water on light absorption
- Nutrient storage
- Alternative methods of nutrient absorption
- Reproduction and life histories
Evolution and paleontology of algae
Classification of algae
- Diagnostic features
- Annotated classification

References & Edit History Quick Facts & Related Topics

Images & Videos

How phytoplankton function and survive in the ocean

Bright green algae blooms distort the surface of water.

Dead fish scattered along the sandy shore of Tampa Bay, Florida, with reddish and greenish water bands near the coast caused by a red tide dinoflagellate bloom.

Turning sewage into green crude oil: How does it work?

Rectangular plots of seaweed farms with workers tending algae in shallow water on Nusa Lembongan, Indonesia, with a distant mountain visible in the background.

At a Glance

algae summary

Quizzes

Mushrooms growing in forest. (vegetable; fungus; mushroom; macrofungi; epigeous)

Science at Random Quiz

Diversity among heteropterans. lace bug, termite bug, coreid bug, bat bug, toad bug, water strider, backswimmer, bedbug, stinkbug, water scorpion, plant bug, insects

All About Biology Quiz

Related Questions

How are agar and carrageenan from red algae used in foods and laboratories?
How are diatom fossils turned into diatomite deposits?
How are diatoms different from other algae?
How can algal blooms lower oxygen levels in water?
How did ancient algae contribute to crude oil and natural gas deposits?
How do Euglena species obtain food and energy?
How do algae produce oxygen through photosynthesis?
How do algae reproduce asexually by cell division, fragmentation, or spores?
How do algae support ocean animals such as fish, whales, and shellfish?
How do brown algae get their brown or olive-green color?
How do chloroplasts capture light energy for algae?
How do coralline red algae help form coral reefs and coral sands?
How do flagella help some algae move through water?
How do gas-filled bladders help some brown seaweeds float?
How do haploid and diploid stages alternate in algal life cycles?
How do zoospores differ from aplanospores and monospores?
How does Volvox form a colony of cells?
How does endosymbiosis explain the origin of algal chloroplasts?
How large can giant kelp grow?
What are diatom frustules made of?
What causes an algal bloom in a lake or ocean?
What environmental changes can trigger sexual reproduction in algae?
What parts of an algal cell carry out photosynthesis and cellular respiration?
Where are green algae commonly found?
Where do algae live besides oceans and lakes?
Which green algae are single-celled, colonial, or filamentous?
Which red algae are used to make nori, dulse, and Irish moss?
Why are algae important to aquatic food chains?
Why are algae not considered one closely related evolutionary group?
Why can Chlamydomonas turn pond water green?
Why can some red tides harm fish, waterfowl, and humans?
Why do algae lack true roots, stems, and leaves?
Why do chloroplasts and mitochondria have their own DNA?
Why do diatoms become smaller during repeated cell divisions?
Why do some freshwater algae form dormant zygospores?
Why does Chlamydomonas sometimes make snow appear red?
Why is Chlorella cultivated as a food supplement?
Why is diatomite useful for filtering beverages and water?
Are algae toxic?
Why are algae important?
How do fungi obtain nutrition?
What is a fungal spore?
Where do fungi grow?

Science Biology Fungi, Protists & Viruses

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External Websites

Engineering LibreTexts - Algae as a Source for Fuels
Smithsonian National Museum of Natural History - Algae
Pennstate College of Earth and Mineral Sciences - What are Algae?
National Center for Biotechnology Information - PubMed Central - Algae as promising organisms for environment and health
IndiaNetzone - Algae
Lenntech - Algae description and types
LiveScience - What Are Algae?

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

algae - Children's Encyclopedia (Ages 8-11)
algae - Student Encyclopedia (Ages 11 and up)

Algae

organism

Also known as: Phycophyta, alga, algas

Written by

Robert A. Andersen

Director, Provasoli-Guillard National Center for Culture of Marine Phytoplankton, Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, Maine. Coeditor of Chrysophytes: Aspects and Problems.

Robert A. AndersenAll

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 6, 2026 •History

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...

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