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The green algae (singular: green alga) are a large, informal grouping of
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
consisting of the
Chlorophyta Chlorophyta or Prasinophyte, Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, i ...
and
Charophyta The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a superdivision, or an unranked clade. The terrestrial plants, the Embryophyta, most likely emerged within Charophyta, ...
/
Streptophyta Streptophyta (), informally the streptophytes (, from the Greek language, Greek ''strepto'' 'twisted', for the morphology of the sperm of some members), is a clade of plants. The composition of the clade varies considerably between authors, but t ...
, which are now placed in separate
divisions Division or divider may refer to: Mathematics *Division (mathematics) Division is one of the four basic operations of arithmetic, the ways that numbers are combined to make new numbers. The other operations are addition, subtraction, and multi ...
, together with the more basal
Mesostigma ''Mesostigma viride'' is a species of freshwater green algae. It is now considered to be one of the earliest diverging members of green plants/algae (Viridiplantae). Earlier studies were unable to resolve the position of the species, and it was o ...
tophyceae,
Chlorokybophyceae ''Chlorokybus'' is a multicellular (sarcinoid) genus of basal green algae or Streptophyte containing the sole species ''Chlorokybus atmophyticus'', a soil alga Algae (; singular alga ) is an informal term for a large and diverse group of photo ...
and
Spirotaenia ''Spirotaenia'' is a genus of basal green algae that may be sister to the Chlorokybophyceae. It was previously considered to be part of the Zygnemataceae. It is sexually conjugating, a mode of reproduction that was previously only known in the ...
. The land plants, or
embryophyte The Embryophyta (), or land plants, are the most familiar group of green plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into ...

embryophyte
s, are thought to have emerged from the
charophyte The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a superdivision, or an unranked clade. The terrestrial plants, the Embryophyta, most likely emerged within Charophyta, ...
s. Therefore,
cladistically Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...

cladistically
, embryophytes belong to green algae as well. However, because the embryophytes are traditionally classified as neither algae nor green algae, green algae are a
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—Monophyly, monophyletic subgroups. The group is said to be paraphyleti ...

paraphyletic
group. Since the realization that the embryophytes emerged from within the green algae, some authors are starting to include them. The
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
that includes both green algae and embryophytes is
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...

monophyletic
and is referred to as the clade
Viridiplantae Viridiplantae (literally "green plants") are a clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an indi ...
and as the kingdom
Plantae Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions ...
. The green algae include unicellular and colonial
flagellate 's '' Artforms of Nature'', 1904 (''Giardia lamblia'') ('' Chlamydomonas'') A flagellate is a cell or organism with one or more whip-like Appendage, appendages called flagellum, flagella. The word ''flagellate'' also describes a particular const ...
s, most with two
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...
per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular
seaweed Seaweed, or macroalgae, refers to thousands of species of , , . The term includes some types of ' (red), ' (brown) and ' (green) macroalgae. Seaweed species such as s provide essential nursery habitat for fisheries and other marine species an ...

seaweed
s. There are about 22,000 species of green algae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds. A few other organisms rely on green algae to conduct
photosynthesis Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthesis
for them. The
chloroplast A chloroplast is a type of membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structure ...

chloroplast
s in
dinoflagellate The dinoflagellates (Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 m ...
s of the genus '' Lepidodinium'',
euglenid Euglenids (euglenoids, or euglenophytes, formally Euglenida/Euglenoida, ICZN, or Euglenophyceae, ICBN) are one of the best-known groups of flagellate 's '' Artforms of Nature'', 1904 (''Giardia lamblia'') ('' Chlamydomonas'') A flagellate is ...
s and
chlorarachniophyte The chlorarachniophytes are a small group of exclusively marine alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes ...
s were acquired from ingested green algae, and in the latter retain a
nucleomorph Nucleomorphs are small, vestigial eukaryotic nuclei found between the inner and outer pairs of membranes in certain plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in th ...
(vestigial nucleus). Green algae are also found symbiotically in the ciliate ''
Paramecium '' ''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic, unicellular ciliates, commonly studied as a representative of the ciliate group. ''Paramecia'' are widespread in freshwater, brackish, and Ocean, marine environments ...

Paramecium
'', and in '' Hydra viridissima'' and in
flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a count ...

flatworm
s. Some species of green algae, particularly of genera ''
Trebouxia ''Trebouxia'' is a unicellular green alga.Silverside, A. J. (2009). Retrieved from http://www.bioref.lastdragon.org/Chlorophyta/''Trebouxia''.html It is a photosynthesis, photosynthetic organism that can exist in almost all habitats found in Polar ...
'' of the class ''
Trebouxiophyceae The Trebouxiophyceae are a class of green algae, in the division Chlorophyta Image:Taiwan 2009 East Coast ShihTiPing Giant Stone Steps Algae FRD 6581.jpg, Green algae on coastal rocks at :zh:石梯坪, Shihtiping in Taiwan Chlorophyta or Pras ...
'' and '' Trentepohlia'' (class
Ulvophyceae The Ulvophyceae or ulvophytes are a class of green algae, distinguished mainly on the basis of ultrastructural morphology, life cycle and molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, here ...
), can be found in symbiotic associations with
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
to form
lichen A lichen ( , ) is a composite organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecu ...

lichen
s. 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. ''Trentepohlia'' is a filamentous green alga that can live independently on humid soil, rocks or tree bark or form the photosymbiont in lichens of the family Graphidaceae. Also the macroalga '''' (Trebouxiophyceae) is terrestrial, and '''', which live in the
supralittoral zone The supralittoral zone, also known as the splash zone, spray zone or the supratidal zone, sometimes also referred to as the white zone, is the area above the spring high tide (U.S.), low tide occurs roughly at moonrise and high tide with a high ...
, is terrestrial and can in the Antarctic form large carpets on humid soil, especially near bird colonies.


Cellular structure

Green algae have chloroplasts that contain and , giving them a bright green color, as well as the accessory pigments (red-orange) and
xanthophyll indicates the presence of a xanthophyll pigment, and is the typical color of lutein or zeaxanthin of the xanthophylls, a division of the carotenoids group. Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and ...
s (yellow) in stacked
thylakoid Thylakoids are membrane-bound compartments inside chloroplast Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy ...

thylakoid
s.Burrows 1991. ''Seaweeds of the British Isles.'' Volume 2 Natural History Museum, London. The
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
s of green algae usually contain
cellulose Cellulose is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

cellulose
, and they store carbohydrate in the form of
starch Starch or amylum is a polymeric A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance ...
. All green algae have
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
with flat
cristae A crista (; plural cristae) is a fold in the inner membrane of a mitochondrion A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it al ...
. When present, paired
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...
are used to move the cell. They are anchored by a cross-shaped system of
microtubule Microtubules are polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, rep ...

microtubule
s and fibrous strands. Flagella are only present in the motile male gametes of
charophytes The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a superdivision, or an unranked clade. The terrestrial plants, the Embryophyta most likely emerged within Charophyta, p ...
bryophytes, pteridophytes, cycads and ''
Ginkgo ''Ginkgo'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circums ...

Ginkgo
'', but are absent from the gametes of
Pinophyta Conifers are a group of cone-bearing seed plants The spermatophytes (; ), also known as phanerogams (taxon Phanerogamae) or phaenogams (taxon Phaenogamae), comprise those plant Plants are predominantly photosynthetic eukaryotes of the Kin ...

Pinophyta
and
flowering plants The flowering plants, also known as Angiospermae (), or Magnoliophyta (), are the most diverse group of land plants The Embryophyta () or land plants are the most familiar group of green plants that form vegetation on earth. Embryophyta is a c ...

flowering plants
. Members of the class
Chlorophyceae The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example, the chlorophycean CW clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic gr ...
undergo closed mitosis in the most common form of cell division among the green algae, which occurs via a . By contrast,
charophyte The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a superdivision, or an unranked clade. The terrestrial plants, the Embryophyta, most likely emerged within Charophyta, ...
green algae and land plants (embryophytes) undergo open
mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proce ...

mitosis
without
centriole In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...

centriole
s. Instead, a 'raft' of microtubules, the
phragmoplast image:Phragmoplast.png, 300px, Phragmoplast and cell plate formation in a plant cell during cytokinesis. Left side: Phragmoplast forms and cell plate starts to assemble in the center of the cell. Towards the right: Phragmoplast enlarges in a donut-s ...

phragmoplast
, is formed from the
mitotic spindle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
and cell division involves the use of this
phragmoplast image:Phragmoplast.png, 300px, Phragmoplast and cell plate formation in a plant cell during cytokinesis. Left side: Phragmoplast forms and cell plate starts to assemble in the center of the cell. Towards the right: Phragmoplast enlarges in a donut-s ...

phragmoplast
in the production of a
cell plate image:Phragmoplast.png, 300px, Phragmoplast and cell plate formation in a plant cell during cytokinesis. Left side: Phragmoplast forms and cell plate starts to assemble in the center of the cell. Towards the right: Phragmoplast enlarges in a donut- ...
.P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): ''Biology of Plants'', 7th Edition, W.H. Freeman and Company Publishers, New York,


Origins

Photosynthetic eukaryotes originated following a primary
endosymbiotic An endosymbiont or endobiont is any organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synony ...

endosymbiotic
event, where a heterotrophic eukaryotic cell engulfed a photosynthetic
cyanobacterium Cyanobacteria , also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical ca ...

cyanobacterium
-like prokaryote that became stably integrated and eventually evolved into a membrane-bound
organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
: the
plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ' ...
. This primary endosymbiosis event gave rise to three
autotroph An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bo ...
ic clades with primary plastids: the (green) plants (with
chloroplast A chloroplast is a type of membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structure ...

chloroplast
s) the
red algae Red algae, or Rhodophyta ( , ; ), are one of the oldest groups of eukaryotic algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organism ...

red algae
(with rhodoplasts) and the
glaucophyte The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater unicellular algae, less common today than they were during the Proterozoic. Only 15 species have been described, but more species are likely to exi ...

glaucophyte
s (with muroplasts).


Evolution and classification

Green algae are often classified with their embryophyte descendants in the green plant
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
Viridiplantae Viridiplantae (literally "green plants") are a clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an indi ...
(or Chlorobionta). Viridiplantae, together with red algae and
glaucophyte The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater unicellular algae, less common today than they were during the Proterozoic. Only 15 species have been described, but more species are likely to exi ...

glaucophyte
algae, form the supergroup Primoplantae, also known as
Archaeplastida The Archaeplastida (or kingdom ') are a major group of s, comprising the (Rhodophyta), the , and the s, and some smaller groups such as the s. All of the lineages of Archaeplastida have become ic, except for the lineage , sister to the Rhodoph ...
or Plantae ''sensu lato''. The ancestral green alga was a unicellular flagellate. The Viridiplantae diverged into two clades. The
Chlorophyta Chlorophyta or Prasinophyte, Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, i ...
include the early diverging
prasinophyte The Prasinophytes (incl. Tetraphytina) or chlorophyta Image:Taiwan 2009 East Coast ShihTiPing Giant Stone Steps Algae FRD 6581.jpg, Green algae on coastal rocks at :zh:石梯坪, Shihtiping in Taiwan Chlorophyta or Prasinophyte, Prasinophyta ...
lineages and the core Chlorophyta, which contain the majority of described species of green algae. The
Streptophyta Streptophyta (), informally the streptophytes (, from the Greek language, Greek ''strepto'' 'twisted', for the morphology of the sperm of some members), is a clade of plants. The composition of the clade varies considerably between authors, but t ...
include
charophytes The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a superdivision, or an unranked clade. The terrestrial plants, the Embryophyta most likely emerged within Charophyta, p ...
and land plants. Below is a consensus reconstruction of green algal relationships, mainly based on molecular data. The basal character of the Mesostigmatophyceae, Chlorokybophyceae and ''spirotaenia'' are only more conventionally basal Streptophytes. The algae of this paraphyletic group "Charophyta" were previously included in Chlorophyta, so green algae and Chlorophyta in this definition were synonyms. As the green algae clades get further resolved, the embryophytes, which are a deep charophyte branch, are included in "
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Co ...

algae
", "green algae" and "
Charophytes The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a superdivision, or an unranked clade. The terrestrial plants, the Embryophyta most likely emerged within Charophyta, p ...
", or these terms are replaced by cladistic terminology such as
Archaeplastida The Archaeplastida (or kingdom ') are a major group of s, comprising the (Rhodophyta), the , and the s, and some smaller groups such as the s. All of the lineages of Archaeplastida have become ic, except for the lineage , sister to the Rhodoph ...
,
Plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

Plant
ae/
Viridiplantae Viridiplantae (literally "green plants") are a clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an indi ...
, and streptophytes, respectively.


Reproduction

Green algae are a group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as ''
Ulva Ulva ( gd, Ulbha) is a small island in the Inner Hebrides of Scotland, off the west coast of Isle of Mull, Mull. It is separated from Mull by a narrow strait, and connected to the neighbouring island of Gometra by a bridge. Much of the island is ...
'', follow a reproductive cycle called
alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the type of life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism unde ...

alternation of generations
in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic (having the same morphology). In haplobiontic species only the haploid generation, the
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert ...
is multicellular. The fertilized egg cell, the diploid
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
, undergoes
meiosis Meiosis (; , because it is a reductional division) is a special type of of in organisms used to produce the , such as or . It involves two rounds of division that ultimately result in four cells with only one copy of each (). Additionall ...

meiosis
, giving rise to haploid cells which will become new gametophytes. The diplobiontic forms, which evolved from haplobiontic ancestors, have both a multicellular haploid generation and a multicellular diploid generation. Here the zygote divides repeatedly by
mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proce ...

mitosis
and grows into a multicellular diploid
sporophyte A sporophyte () is the diploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chr ...
. The sporophyte produces haploid spores by meiosis that germinate to produce a multicellular gametophyte. All
land plants The Embryophyta (), or land plants, are the most familiar group of green plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into ...

land plants
have a diplobiontic common ancestor, and diplobiontic forms have also evolved independently within
Ulvophyceae The Ulvophyceae or ulvophytes are a class of green algae, distinguished mainly on the basis of ultrastructural morphology, life cycle and molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, here ...
more than once (as has also occurred in the red and brown algae). Diplobiontic green algae include isomorphic and heteromorphic forms. In isomorphic algae, the morphology is identical in the haploid and diploid generations. In heteromorphic algae, the morphology and size are different in the gametophyte and sporophyte. Reproduction varies from fusion of identical cells (
isogamy Isogamy is a form of sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism ...

isogamy
) to
fertilization Fertilisation or fertilization (see American and British English spelling differences#-ise.2C -ize .28-isation.2C -ization.29, spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes ...

fertilization
of a large non-motile cell by a smaller motile one (
oogamy Oogamy is an extreme form of anisogamy where the gametes differ in both size and form. In oogamy the large female gamete (also known as Egg cell, ovum) is immobile, while the small male gamete (also known as sperm) is mobile. Oogamy is a common ...
). However, these traits show some variation, most notably among the basal green algae called
prasinophyte The Prasinophytes (incl. Tetraphytina) or chlorophyta Image:Taiwan 2009 East Coast ShihTiPing Giant Stone Steps Algae FRD 6581.jpg, Green algae on coastal rocks at :zh:石梯坪, Shihtiping in Taiwan Chlorophyta or Prasinophyte, Prasinophyta ...
s. Haploid algal 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'' and occurs for example in ''
Spirogyra ''Spirogyra'' (common names include water silk, mermaid's tresses, and blanket weed) is a filamentous charophyte The Charophyta () or charophytes () is a group of freshwater green algae, sometimes treated as a phylum, division, but also as a ...

Spirogyra
''.


Sex pheromone

Sex pheromone Sex pheromones are pheromones released by an organism to attract an individual of the same species, encourage them to mate with them, or perform some other function closely related with sexual reproduction Sexual reproduction is a type of reprod ...
production is likely a common feature of green algae, although only studied in detail in a few model organisms. ''
Volvox ''Volvox'' is a polyphyletic 300px, Cladogram of the primates, showing a monophyly (the simians, in yellow), a paraphyly">monophyly.html" ;"title="primates, showing a monophyly">primates, showing a monophyly (the simians, in yellow), a paraphy ...

Volvox
'' is a genus of chlorophytes. Different species form spherical colonies of up to 50,000 cells. One well-studied species, ''
Volvox carteri ''Volvox carteri'' is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of ...

Volvox carteri
'' (2,000 – 6,000 cells) occupies temporary pools of water that tend to dry out in the heat of late summer. As their environment dries out, asexual ''V. carteri'' quickly die. However, they are able to escape death by switching, shortly before drying is complete, to the sexual phase of their life cycle that leads to production of dormant desiccation-resistant
zygote A zygote (, ) is a eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are ...

zygote
s. Sexual development is initiated by a
glycoprotein Glycoproteins are protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. Proteins dif ...
pheromone (Hallmann et al., 1998). This pheromone is one of the most potent known biological effector molecules. It can trigger sexual development at concentrations as low as 10−16M. Kirk and Kirk showed that sex-inducing pheromone production can be triggered experimentally in
somatic Somatic may refer to: * Somatic (biology), referring to the cells of the body in contrast to the germ line cells ** Somatic cell, a non-gametic cell in a multicellular organism * Somatic nervous system, the portion of the vertebrate nervous syste ...
cells by
heat shockThe heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a normal ...
. Thus heat shock may be a condition that ordinarily triggers sex-inducing pheromone in nature. The ''Closterium peracerosum-strigosum-littorale (C. psl)'' complex is a unicellular, isogamous alga group that is the closest unicellular relative to land plants.
Heterothallic Heterothallic species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in ...
strains of different
mating type Mating types are the microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structu ...
can conjugate to form
zygosporeA zygospore is a diploid reproductive stage in the life cycle of many fungi and protists. Zygospores are created by the nuclear fusion of haploid cells. In fungi, zygospores are formed in zygosporangia after the fusion of specialized budding struct ...
s. Sex pheromones termed protoplast-release inducing proteins (glycopolypeptides) produced by mating-type (-) and mating-type (+) cells facilitate this process.


Physiology

The green algae, including the characean algae, have served as model experimental organisms to understand the mechanisms of the ionic and water permeability of membranes, osmoregulation, turgor regulation, halophyte, salt tolerance, cytoplasmic streaming, and the generation of action potentials.


References


External links


Green algae and cyanobacteria in lichens




{{Authority control Green algae, Paraphyletic groups