Green algae

Information about Green algae

Green algae

Scientific classification
Kingdom:Protista or Plantae
Divisions


Chlorophyta
Charophyta


Green algae are microscopic protists; found in all aquatic environments, including marine, freshwater and brackish water.

The green algae (singular: green alga) are the large group of algae from which the embryophytes (higher plants) emerged. As such, they form a paraphyletic group, variously included among the Plantae or with the Protista. The green algae include unicellular and colonial flagellates, usually but not always with two flagella per cell, as well as various colonial, coccoid, and filamentous forms. In the Charales, the closest relatives of higher plants, full differentiation of tissues occurs. There are about 6000 species of green algae. [1] Many species live most of their lives as single-cells, other species form colonies or long filaments.

A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in euglenids and chlorarachniophytes were presumably acquired from ingested green algae, and in the latter retain a vestigial nucleus (nucleomorph). Some species of green algae, particularly of genera Trebouxia or Pseudotrebouxia (Trebouxiophyceae), can be found in symbiotic associations with fungi to form lichens. In general the fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus.

Cellular structure

Almost all forms have chloroplasts. These contain chlorophylls a and b, giving them a bright green colour (as well as the accessory pigments beta carotene and xanthophylls),[2] and have stacked thylakoids.[3]

All green algae have mitochondria with flat cristae. When present, flagella are typically anchored by a cross-shaped system of microtubules, but these are absent among the higher plants and charophytes. Flagella are used to move the organism. Green algae usually have cell walls containing cellulose, and undergo open mitosis without centrioles.

Origins

The chloroplasts of green algae are bound by a double membrane, so presumably they were acquired by direct endosymbiosis of cyanobacteria. A number of cyanobacteria show similar pigmentation, but this appears to have arisen more than once, and the chloroplasts of green algae are no longer considered closely related to such forms. Instead, the green algae probably share a common origin with the red algae.

Classification

Green algae are often classified with their embryophyte descendants in the green plant clade Viridiplantae (or Chlorobionta). Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, also known as Archaeplastida or Plantae sensu lato.

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A growth of the green seaweed, Enteromorpha on rock substratum at the ocean shore. Some green seaweeds, such as Enteromorpha and Ulva, are quick to utilize inorganic nutrients from land runoff, and thus can be indicators of nutrient pollution.
The orders outside the Chlorophyta are often grouped as the division Charophyta, which is paraphyletic to higher plants, together comprising the Streptophyta. Sometimes the Charophyta is restricted to the Charales, and a division Gamophyta is introduced for the Zygnematales and Desmidiales. In older systems the Chlorophyta may be taken to include all the green algae, but taken as above they appear to form a monophyletic group.

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Green Algae conjugating

Reproduction

Green algae are eukaryotic organisms that follow a reproduction cycle called alternation of generations.

Sexual reproduction varies from fusion of identical cells (isogamy) to fertilization of a large non-motile cell by a smaller motile one (oogamy). However, these traits show some variation, most notably among the basal green algae, called prasinophytes.

Haploid algae cells (containing only one copy of their DNA) can fuse with other haploid cells to form diploid zygotes. When filamentous algae do this, they form bridges between cells, and leave empty cell walls behind that can be easily distinguished under the light microscope. This process is called conjugation.

The species of Ulva are reproductively isomorphic, the diploid vegetative phase is the site of meiosis and releases haploid zoospores which germinate and grow producing a haploid phase alternating with the vegetative phase. [1]

References

1. ^ Thomas, D. 2002. Seaweeds. The Natural History Museum, London. ISBN 0 565 09175 1
2. ^ Burrows 1991. Seaweeds of the British Isles. Volume 2 Natural History Museum, London. ISBN 0 565 00981 8
3. ^ Hoek, C. van den, Mann, D.G. and Jahns, H.M. 1995. Algae An introduction to phycology. Cambridge University Press, Cambridge. ISBN 0 521 30419 9

External links

See also

Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Eukarya
Whittaker & Margulis, 1978

Kingdom: Protista*
Haeckel, 1866

Typical phyla
  • Chromalveolata
  • Chromista

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Plantae
Haeckel, 1866[1]

Divisions

Green algae
  • Chlorophyta
  • Charophyta
Land plants (embryophytes)
  • Non-vascular land plants (bryophytes)

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Chlorophyta
Reichenbach, 1834; Pascher[1][2]

Classes[3]
  • Bryopsidophyceae
  • Chlorophyceae
  • Pedinophyceae
  • Pleurastrophyceae
  • Prasinophyceae
  • Trebouxiophyceae
  • Ulvophyceae
Chlorophyta
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Charophyta

Classes

Mesostigmatophyceae
Chlorokybophyceae
Klebsormidiophyceae
Zygnemophyceae
   Zygnematales
   Desmidiales
Charophyceae
   Coleochaetales
   Charales

The
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phytoplankton — provide the food base for most marine food chains. In very high densities (so-called algal blooms) these algae may discolor the water and outcompete or poison other life forms.
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Embryophyta

Divisions
  • Non-vascular land plants (bryophytes)
  • Marchantiophyta - liverworts
  • Anthocerotophyta - hornworts

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In phylogenetics, a group of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the group contains its most recent common ancestor, but does not contain all the descendants of that ancestor.
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Plantae
Haeckel, 1866[1]

Divisions

Green algae
  • Chlorophyta
  • Charophyta
Land plants (embryophytes)
  • Non-vascular land plants (bryophytes)

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Eukarya
Whittaker & Margulis, 1978

Kingdom: Protista*
Haeckel, 1866

Typical phyla
  • Chromalveolata
  • Chromista

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Flagellates are cells with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Higher plants and fungi do not produce flagellate cells, but the closely related green algae and chytrids do.
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For the insect anatomical structure, see .
A flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane.
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Charales

Family: Characeae

Genera

Chara
Lamprothamnium
Nitella
Tolypella

The Charales are an in the order Charales of green alga, Chlorophyta.
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Euglenoidea
Bütschli 1884

Major groups

Phototrophs
   Euglenales
   Eutreptiales
Osmotrophs
   Rhabdomonadales
Phagotrophs
   ?Heteronematales
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Chlorarachnea
Hibberd & Norris, 1984

Genera

Chlorarachnion
Gymnochlora
Lotharella
Cryptochlora
Bigelowiella
Chlorarachniophytes
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Eukarya
Whittaker & Margulis, 1978
(unranked) Opisthokonta

Kingdom: Fungi
(L., 1753) R.T. Moore, 1980[1]

Subkingdom/Phyla

Chytridiomycota
Blastocladiomycota

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Lichens (IPA: /ˈlaɪkən/)[1] are symbiotic associations of a fungus (the mycobiont) with a photosynthetic partner (the photobiont also known as the phycobiont) that can produce food for the lichen from
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Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from ancient Greek: chloros = green and phyllon = leaf.
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Carotene is responsible for the orange colour of the carrots and many other fruits and vegetables.]] The term carotene is used for several related substances having the formula C40H56.
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Xanthophylls (originally phylloxanthins) are yellow pigments from the carotenoid group. Their molecular structure is based on carotenes; contrary to the carotenes, some hydrogen atoms are substituted by hydroxyl groups and/or some pairs of hydrogen atoms are substituted by
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A Thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. The word "thylakoid" is derived from the Greek thylakos, meaning "sac".
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For the insect anatomical structure, see .
A flagellum (plural: flagella) is a long, slender projection from the cell body, composed of microtubules and surrounded by the plasma membrane.
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Microtubules are one of the components of the cytoskeleton. They have diameter of ~ 24 nm and length varying from several micrometers to possibly millimeters in axons of nerve cells.
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Cellulose is an organic compound with the formula (C6H10O5)n. It is a structural polysaccharide derived from beta-glucose.[1][2] Cellulose is the primary structural component of green plants.
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A centriole is a barrel shaped organelle[1] found in most eukaryotic cells, though absent in higher plants and fungi.[2] The walls of each centriole are usually composed of nine triplets of microtubules.
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The endosymbiotic theory concerns the origins of mitochondria and plastids (e.g. chloroplasts), which are organelles of eukaryotic cells. According to this theory, these organelles originated as separate prokaryotic organisms which were taken inside the cell as endosymbionts.
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Cyanobacteria

Orders

The taxonomy is currently under revision.[1]

Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
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