Alga

General description, typology

In fact the algae often were definite by defect , by simple opposition to the pluricellular terrestrial plants.

In the broadest meaning of the term, the algae thus gather, inter alia:

of the organizations Procaryotic S: “blue algas” or Cyanobactérie S;
of the Eucaryote S:

various groups with unicellular species (Euglénophyte S, Cryptophytes, Haptophytes, Glaucophyte S, etc);
of other groups with unicellular or pluricellular species (“red algas” or Rhodophyta, and Straménopiles in particular gathering the Diatom S and the “brown algas” or Phéophycées);
and finally of the plants rather close to the terrestrial plants: the “green algas” which include/understand inter alia the Ulvophycées.

The morphology thus is very diversified: there exist algae which are unicellular, possibly mobile, others form cellular filaments or simple blades, others develop complex and differentiated architectures, by cellular affixing or tangle of tubular filaments. The algae do not have however definitely individualized fabrics, as one can find some among the vascular terrestrial plants. The colors of the algae can be very varied: green, yellow, red, brown, and were useful, in the wake of Lamouroux to indicate the various groups of algae.

Although being able to belong to nonrelated groups, the algae can set up various relevant ecological groups: marine macroalgues, the phytoplankton, etc

All the watery plants are however not algae: some Spermaphyte S set out again secondarily with the conquest of fresh water (Potamogetonacées, Hydrocharitacées, Utriculaire S, etc) or even of marine water (Zostéracées, Posidoniacées). In the opposite direction, many unicellular algae conquered very diversified terrestrial habitats, provided that they are at least a little wet.

Sometimes certain algae could become parasitic or célèbrement contribute to stabilized symbiotic forms, the Lichen S and the Coraux.

Classification of the algae

Procaryotic “Algae”

Traditionally, one classified the Cyanobactérie S among the algae, referred like cyanophytes or algae blue-green , although certain treaties excluded some. They appear already in fossils of the Précambrien, going back to approximately 3,8 billion years. They would have played a great part in the production of the Oxygène of the atmosphere. Their cells have a structure typical Procaryote bacteria. Photosynthesis occurs directly in the Cytoplasme. When they are in symbiosis with a Champignon, they form a Lichen.

They are at the origin of the Chloroplaste S of the cells eucaryotes, and thus made it possible the plants to carry out the Photosynthèse, following a Endosymbiose.

Algae eucaryotes

All the other algae are Eucaryote S. At, photosynthesis occurs in particular structures, surrounded by a membrane, which one calls These structures Chloroplaste S. contains DNA and is similar to the cyanobacteries validating the Hypothèse of the endosymbiose.

Three groups of plants have “primary” chloroplasts:

the Chlorobionte S to which the house plants belong,
red algas or Rhodophytes,
the Glaucophyte S.

In these groups, the chloroplast is surrounded by 2 membranes. Those of the red algas more or less have the typical pigmentation of the cyanobacteries, whereas the green color, and that of the higher plants, is due to chlorophyl has and B . It is thought reasonably that these groups have a common ancestor, i.e. the existence of the chloroplasts would be the consequence of only one event endosymbiotic.

Two other groups, the Euglénophytes and the Chlorarachniophytes, have green chloroplasts containing of chlorophyl has and B . These chloroplasts are surrounded, respectively, of three or four membranes and were probably acquired incorporation of a green alga. Those of Chlorarachniophytes contain small a Nucléomorphe, remains core of the cell. It is supposed that the chloroplasts of Euglénophytes have only 3 membranes because they were acquired by Myzocytose rather than by Phagocytose.

The other algae have all of the chloroplasts containing of chlorophyls has and C . This last type of chlorophyl is not known less procaryote or primary education chloroplast, but of the genetic similarities suggest a relation with the red alga. These groups include/understand:

Hétérokontophytes (for example: gilded algae, diatoms, brown algas)
Haptophytes (for example: coccolithophores)
Cryptophytes
Dinoflagellés

In the three first of these groups ( Chromista ) the chloroplast has 4 membranes, retaining a nucléomorphe at Cryptophytes, and it is supposed now that they in common have a coloured ancestor. The chloroplast of Dinoflagellés typical has 3 membranes, but there is a considerable diversity in the chloroplasts of this group, some members having acquired their plastids by other sources. The Apicomplexa, a group of narrowly connected parasites, have also Plaste S degenerated called apicoplastes, various however true chloroplasts, which seem to have a common origin with those of dinoflagellés.

Membership of the algae, according to various classifications

In the system with 3 reigns, the algae are in the Vegetable kingdom, among the Thallophyte S, with the Champignon S and the Lichen S.

In the system with 5 reigns of Whittaker, the algae are distributed between the Plantae and the Protista .

In Phylogenetic classification , the algae is a group Polyphylétique. They are divided into 11 groups.

Species of algae

Aramé
Acetabularia , Alaria , Anabaena , Asparagopsis
Bryopsis
Carragheen, Caulerpa , Chlamydomonas , Chlorelle, Chondrus , Cladophora , Coccolithophore, Codium , Coral-red, Cystoseire
Diatom, Dictyota , Diplopore, Durvillaea
Wrack
Gelidium , Girvanelle, Goémon, Haematococcus , Laminar Himanthalia
, Lithothamnium
Macrocystis , Mougeotia
Nemalion , Nitella , Nostoc or the spittle-of-moon
Oedogonium , Oscillatoria
Pediastrum , Pleurococcus , Porphyra , Prochloron , Prochlorococcus , Protococcus
Rivularia
sargasso, Spirogyre, Spiruline, Stromatolite, Synechococcus
Tripoli
Ulothrix , Ulve
Kelp, Vauchérie, Volvox
Xanthelle
Zoochlorelle, Zooxanthelle, Zygnéma

The shapes of the algae

The majority of the simplest algae are unicellular Flagellés or Amoeboïde S, but of the colonial forms and not-mobiles developed independently in several of these groups. The most current levels of organization, of which several can intervene in the Life cycle of a species, are the following:

Colonial - ordinary small group of mobile cells.
Capsoïde - cells not-mobiles included in a Mucilage.
Coccoïde - individual cells not-mobiles with cellular walls.
Palmelloïde - cells not-mobiles included in mucilage.
Filamentous - a string of cells not-mobiles connected together, sometimes ramified.
Membranous - cells forming a thallus with a differentiation partial of fabrics.

Higher levels of organization were even reached, driving at organizations with complete differentiations of fabrics. In fact the brown algas can reach 70 m length (Varech); red algas and green algas. The most complex forms are at the green algas (see Charales), in a line which led to the higher plants. The point where these last start and where algae stop is usually marked by the presence of reproductive bodies provided with layers of protective cells, a characteristic which one does not find in the other groups of algae.

Ecology of the algae

The algae constitute a big part of watery ecology and adopt very diverse lifestyles. Although they all are equipped with chlorophyl, they can be autonomous (Autotrophe S or Saprophyte S), parasite S or live in Symbiose.

autotrophic Algae

floating Algae of the Plankton

unicellular Algae, in loose or filamentous colonies forming the Phytoplankton,
floating Algae of big size: the sargasso S, brown algas adapted to the floating life, they gave their name to the Sargasso Sea, or brown algas or reds which form balls or floating balls called Aegragopile S.

thermophilous Algues
air Algues
Algues fixed

on rocks: épilithes

They are the algae of the rock coasts fixed by robust cramps at the rocks or the rollers until a depth from 50 to 75 m, but they rarefy very quickly with the depth beyond 30 m, radiations useful for photosynthesis being absorbed by sea water. They develop more on soft inclined coasts which form wide littoral platforms. It is among these algae that one finds the species giant: the laminar ones, the Durvillea of long New Zealand 10 m, or the Nereocystis of the west coast of the North America whose slings can reach 50 m length.
NB: the Posidonie ( Posidonia oceanica ), endemic species of the Mediterranean, is not an alga, but a plant with flowers of the family of the Posidoniacée S. the Zostère is also a plant with flowers. As for the Salicorne, it is a terrestrial plant Halophile (which likes salt).

on animals: épizoïques

the Paresseux (Have or Unau) carry on their hairs a brown alga during the dry and green season during the rain season, which helps them to merge with their environment.

on plants: épiphytes
on wood: épixyles

Algae parasitic saprophytes
Algae
symbiotic Algae:

one calls zoochlorelles or zooxanthelles, the algae living in partnership with animal organizations, according to whether it is a question of green algas or brown algas. The organizations concerned are Spongiaire S, Cnidaire S, Bryozoaire S or Protozoaire S.
with mushrooms: the Lichen S. All the algae which take share with the formation of lichens are of Chlorophycées, the majority unicellular.

The largest algae, called marine algas grow especially in the not very major funds and get different habitats. Microscopic forms, called Phytoplankton, get the base of the marine food chain. The Phytoplancton can be present in strong density in particular because of the Eutrophisation. This phenomenon, called efflorescence of algae, can cause a visible change of the color of water.

The green tides which can cover certain beaches of a nauseous mattress of a few decimetres thickness and a few meters even tens of meters broad, are due to the proliferation of Green algas, primarily Ulva lactuca , in a medium enriched in Nitrate S by the streaming in the zones by intensive agriculture or by an insufficient treatment by the Waste water by urban areas.

Uses

Useful algae

Human consumption

Certain species of algae are used for the human Alimentation, either directly, or in the form of food complements, or in the form of additive:

Like direct food, the algae are a kind of Légume, like the Laitue of sea: Ulva lactuca . Generally containing Protein S, Rock salt and Vitamin S, they however have for the moment only one marginal importance in the majority of the Western countries, except notable for certain islands or areas close to the sea: The United Kingdom (Wales), Brittany for example, but also of many countries of the Far East: China, South Korea, Japan, Vietnam.

the food complements include for example the Spiruline, micro blue alga, marketed in the form of complement particularly rich in Protéine S and Vitamine S.

the additive for the Agribusiness industry include for example the Aramé or the Bladderwrack (also known under the names of Varech or Goémon) the Algine, or acid alginic, used like binder in the pork-butcheries. The Carraghénane S extracted from Chondrus crispus are Gelling S used usually in the Flan S, pastes Dentifrice S…

By their capacity to filter water and to concentrate its components even in infinitesimal quantity, the algae are also a very useful source of Oligo-élément S, in particular the Magnésium, and the Iode which are generally lacking with the Alimentation in the industrialized countries (those which consume few Poisson in particular, and which consume salt refined stripped of its natural iodine).

But this advantage changes into disadvantage when water becomes polluted. It is the case for example with the Rejet S of radioactive water, close to the coastal nuclear plants, the centers of reprocessing of radioactive waste (Windscale in Great Britain, factory of La Hague in France for example) or to the places of experimentation of atomic bombs (the atoll of Moruroa in French Polynésie for example): the contents of Radionucléide S can then make these algae dangerous for health.

Animal feeds

One notes the old use of the goémon, manufacture of flours and Tourteau X incorporated in compound feedingstuffs, for Volaille S in particular.

Manure and amendments

The Goémon, or Kelp, is collected on the coasts, in particular in Brittany for a very long time to make Engrais of it. Formerly, it was also used to produce Soude and Potasse.

The Maërl, or Phymatolithon calcareum ( Lithothamnium calcareum ), a calcified red alga, was used for the amendment acid grounds. The funds with maërl are now protected.

Industrial uses

Certain substances drawn from the algae, in particular the algine, already quoted, are used like gelling, thickener, emulsifiers, in many industries: pharmacy, cosmetics, plastics, paintings…

The Agar-agar is used as a basis for manufacture of the bacteriological culture media.

Phymatolithon calcareum ( Lithothamnium ) provides a porous limestone used for the filtration of water.

The capacity of the algae to filter water by concentrating its components is also usable in purification plants of the Waste water (cities) or water leaving industrial facilities (Chemical industry in particular). It remains to choose what it is made of these become algae of the Déchet S, in general Toxique S.

Production of biocarburants

It is probably starting from Algue S that the Biocarburant S could be produced with the best output, making thus possible a production in significant quantity without massive Déforestation. Unicellular cultures of algae with strong content of Lipid S (50% to 80% in mass) and with fast doubling time (about 24:00) allow indeed a production of Biodiesel less polluting and incomparably more effective than the intensive agriculture of terrestrial plants: the surfaces necessary are 30 times less. Several techniques of production are studied:

Culture in pond.
Culture under greenhouse.
Culture in strongly insolated bioréacteurs, where the production of algae is accelerated by splashing of CO₂ (thus avoiding the immediate rejection of this Gaz to greenhouse effect resulting from a polluting industry like a thermal Powerplant with flame).

The lipids extracted from this biomass are then subjected to a Transesterification to produce Biodiesel. The residues can still be developed, for example by a fermentation producing of the Bioéthanol.

A limit of this die is the need for feeding the cultures of algae in strong concentrations of CO₂. As long as this CO₂ will result from the exploitation of a fossil energy, one will not be able to regard this source of biocarburant as a renewable energy. Will one be day possible to use effectively atmospheric CO₂? And this day will it come rather quickly to avoid the catastrophes promised by the Climate warming? The current data do not allow such a hope.

Toxic and harmful algae

Microscopic unicellular algae (Dinoflagellées) can make toxic for the man the Mollusque S (mould S, Huître S, Praire S, hulls, Palourde S…) and to make them unsuitable to consumption, under penalty of serious gastro-enteric disorders or, more rarely, of neuro-muscular attacks; rather recurring phenomenon in the Mytiliculture of the Basin of Thau in Languedoc and on the coasts of the Atlantic , in particular in Brittany and the Vendée.

Sargassum muticum , Brown alga introduced accidentally in Europe in 1973 with Japanese oysters, quickly colonized the Atlantic littoral of Spain in Norway as well as the Western Mediterranean to Venice. It is toxic and is not consumed by local fauna. It replaces the local flora and constitutes an important harmful effect for the Conchyliculture. It proliferates particularly in the channels attended by the ships because of its capacity of multiplication by propagation by cutting.

The “tueuse alga”, Caulerpa taxifolia , Green alga tropical escaped accidentally of the oceanographical museum of Monaco has become for a few years invading at sea the Mediterranean with the detriment of the indigenous vegetation, amongst other things the herbaria of Posidonie. It is toxic and is not consumed by local fauna.

The Goémonier S consider Saccorhiza polyschides , a laminar very robust, without economic interest, which quickly colonizes the rocks stripped by the exploitation of the Laminaria digitata , like a “bad grass”.

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