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Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer. Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber. [129] [130]
Algae is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic. Marine algae can be divided into six groups: green, red and brown algae, euglenophytes, dinoflagellates and diatoms.
Some unicellular species of green algae, many golden algae, euglenids, dinoflagellates, and other algae have become heterotrophs (also called colorless or apochlorotic algae), sometimes parasitic, relying entirely on external energy sources and have limited or no photosynthetic apparatus.
The photosynthetic system of brown algae is made of a P700 complex containing chlorophyll a. Their plastids also contain chlorophyll c and carotenoids (the most widespread of those being fucoxanthin). [53] Brown algae produce a specific type of tannin called phlorotannins in higher amounts than red algae do.
Photosynthetic organisms with plastids of different origin (such as brown algae) do not belong to the Archaeplastida. The archaeplastidans fall into two main evolutionary lines. The red algae are pigmented with chlorophyll a and phycobiliproteins , like most cyanobacteria, and accumulate starch outside the chloroplasts.
Green algae are a group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as Ulva , follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic ...
Chromerids, represented by the genera Chromera and Vitrella, are photosynthetic protists, and are thus considered algae. They exist in association with corals. For most of their life cycle, they live as round brownish immobile vegetative cells called autospores, surrounded by a thick resistant cell wall.
Eukaryotic photoautotrophs include red algae, haptophytes, stramenopiles, cryptophytes, chlorophytes, and land plants. [6] These organisms perform photosynthesis through organelles called chloroplasts and are believed to have originated about 2 billion years ago. [1]