ALGAE - From Wikipedia, the free encyclopedia

For the programming language, see algae (programming language).
For the town in Kyrgyzstan, see Alga, Kyrgyzstan.


Laurencia, a marine red alga from Hawaii.Algae (sing. alga) are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds. They are photosynthetic, like plants, and "simple" because they lack the many of the distinct organs found in land plants. Though the prokaryotic cyanobacteria (commonly referred to as blue-green algae) were traditionally included as "algae" in older textbooks, many modern sources regard this as outdated[1][2] and restrict the term algae to eukaryotic organisms.[3] All true algae therefore have a nucleus enclosed within a membrane and chloroplasts bound in one or more membranes.[1] Algae constitute a paraphyletic and polyphyletic group:[1] they do not represent a single evolutionary direction or line, but a level or grade of organization that may have developed several times in the early history of life on Earth.

Algae lack the various structures that characterize land plants, such as phyllids and rhizoids in nonvascular plants, or leaves, roots, and other organs that are found in tracheophytes. They are distinguished from protozoa in that they are photosynthetic. Many are photoautotrophic, although some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have reduced or lost their photosynthetic apparatus.

All algae have photosynthetic machinery ultimately derived from the cyanobacteria, and so produce oxygen as a byproduct of photosynthesis, unlike other photosynthetic bacteria such as purple and green sulfur bacteria.

Link to http://en.wikipedia.org/wiki/Algae for more.