The Chlorophyceae are one of the classes of

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

e, distinguished mainly on the basis of ultrastructural morphology. They are usually green due to the dominance of pigments chlorophyll a and

chlorophyll b } Chlorophyll ''b'' is a form of chlorophyll. Chlorophyll ''b'' helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll ''a'' in polar solvents because of its carbonyl group. Its color is green, and it primarily a ...

. The

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

may be

discoid Discoid may refer to: * Disk (mathematics), the region in a plane enclosed by a circle Medicine * Furosemide, a medication sold under the trade name Discoid * Discoid meniscus, a human anatomical variant * Discoid lupus erythematosus, a chroni ...

, plate-like,

reticulate Reticulation is a net-like pattern, arrangement, or structure. Reticulation or Reticulated may refer to: * Reticulation (single-access key), a structure of an identification tree, where there are several possible routes to a correct identificati ...

, cup-shaped,

spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are:ribbon shaped in different species. Most of the members have one or more storage bodies called

pyrenoid Pyrenoids are sub-cellular micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. Annu. Rev. Plant Bio ...

s located in the chloroplast. Pyrenoids contain protein besides

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

. Some green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

and outer layer of pectose.

General characteristics

* the body may be unicellular, colonial, filamentous or multicellular. * They are usually green due to the presence of chlorophyll a, chlorophyll b and beta-carotene. * The chloroplast may be discoid, cup-shaped (e.g. ''Chlamydomonas''), spiral or ribbon shaped * Most chlorophytes have one or more storage bodies called pyrenoids (central proteinaceous body covered with a starch sheath) that are localised around the chloroplast. * The inner cell wall layer is made of cellulose and the outer layer of pectose. *

Asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...

is by zoospores. They are flagellates produced from the parent cells by mitosis. Also by aplanospores, hypnospores, akinetes, Palmella stage, etc. *

Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

of Chlorophyceae is isogamous, anisogamous or oogamous. * The chlorophycean CW

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

, and chlorophycean DO clade, are defined by the arrangement of their

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g.

Chlamydomonadales Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae.See the NCBIbr>webpage on Chlamydomonadales Data extracted from the Chlamydomonadales can form planar or ...

. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g.

Sphaeropleales Sphaeropleales is an order of green algae that used to be called Chlorococcales. The order includes some of the most common freshwater planktonic algae such as ''Scenedesmus'' and ''Pediastrum''. The Spaeropleales includes vegetatively non-motile ...

Reproduction

Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated

zoospores A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

. And haplospore, perrination (akinate and palmellastage). Asexual reproduction by mitospore absent in spyrogyra. Sexual reproduction shows considerable variation in the type and formation of sex cells and it may be

isogamous Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or fe ...

e.g. ''Chlamydomonas, Ulothrix'',

anisogamous Different forms of anisogamy: A) anisogamy of motile cells, B) egg_cell.html"_;"title="oogamy_(egg_cell">oogamy_(egg_cell_and_sperm_cell),_C)_anisogamy_of_non-motile_cells_(egg_cell_and_spermatia)..html" ;"title="egg_cell_and_sperm_cell.html" ;" ...

e.g. ''Chlamydomonas, Eudorina'' or

Oogamous 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 ovum) is immobile, while the small male gamete (also known as sperm) is mobile. Oogamy is a common form of an ...

e.g. ''Chlamydomonas, Volvox''. ''Chlamydomonas'' has all three types of sexual reproduction. They share many similarities with the higher plants, including the presence of asymmetrical flagellated cells, the breakdown of the nuclear envelope at mitosis, and the presence of phytochromes, flavonoids, and the chemical precursors to the cuticle.Raven, Evert and Eichhorn. ''The Biology of Plants'' 7th edition, pg. 335. W. H. Freeman and Company, New York, 2005. The sole method of reproduction in ''Chlorella'' is asexual and azosporic. The content of the cell divides into 2,4 (B), 8(C) sometimes daughter protoplasts. Each daughter protoplast rounds off to form a non-motile spore. These autospores (spores having the same distinctive shape as the parent cell) are liberated by the rupture of the parent cell wall (D). On release each autospore grows to become a new individual. The presence of sulphur in the culture medium is considered essential for cell division. It takes place even in the dark with sulphur alone as the source material but under light conditions nitrogen also required in addition. Pearsal and Loose (1937) reported the occurrence of motile cells in ''Chlorella''. Bendix (1964) also observed that ''Chlorella'' produces motile cells which might be gametes. These observations have an important bearing on the concept of the life cycle of ''Chlorella,'' which at present is considered to be strictly asexual in character. Asexual reproduction in ''Chlorella ellipsoides'' has been studied in detail and the following four phases have been observed during the asexual reproduction. (i) Growth Phase - During this phase the cells grow in size by utilizing the photosynthetic products. (ii) Ripening phase - In this phase the cells mature and prepare themselves for division. (iii) Post ripening phase - During this phase, each mature cell divides twice either in dark or in light. The cells formed in dark are known as dark to light phase, cells again grow in size. (iv) Division Phase - During this phase the parent cell wall ruptures and unicells are released.

Orders

AlgaeBase AlgaeBase is a global species database of information on all groups of algae, both marine and freshwater, as well as sea-grass. History AlgaeBase began in March 1996, founded by Michael Guiry. Text was copied from this source, which is avai ...

accepted the following orders in the class Chlorophyceae: * Chaetopeltidales C.J.O'Kelly, Shin Watanabe, & G.L.Floyd – 15 species * Chaetophorales Wille – 216 species *

F.E.Fritsch – 1752 species * Oedogoniales Heering – 733 species * Palaeosiphonocladales – 2 species *

Luerssen – 909 species Other orders that have been recognized include: * Dunaliellales – ''

Dunaliella ''Dunaliella'' is a single-celled, photosynthetic green alga, that is characteristic for its ability to outcompete other organisms and thrive in hypersaline environments. It is mostly a marine organism, though there are a few freshwater species ...

'' and Dunaliellaceae are placed in Chlamydomonadales by AlgaeBase * Chlorococcales – '' Chlorococcum'' and

Chlorococcaceae Chlorococcaceae is a family of green algae, in the order Chlamydomonadales. List of genera * '' Apodochloris'' * '' Bracteacoccus'' * '' Chlorococcopsis'' * ''Chlorococcum ''Chlorococcum'' is a genus of green algae, in the family Chlorococca ...

are placed in Chlamydomonadales by AlgaeBase * Microsporales – '' Microspora'' and Microsporaceae are placed in Sphaeropleales by AlgaeBase * Tetrasporales – ''

Tetraspora ''Tetraspora'' is a genus of green algae in the family Tetrasporaceae of the order Chlamydomonadales, division Chlorophyta. Species of ''Tetraspora'' are unicellular green algae that exist in arrangements of four and consist of cells being packa ...

'' and

Tetrasporaceae The Tetrasporaceae are a family of green algae, specifically of the Chlamydomonadales.See the NCBIbr>webpage on Tetrasporaceae Data extracted from the Genera , AlgaeBase AlgaeBase is a global species database of information on all groups ...

are placed in Chlamydomonadales by AlgaeBase In older classifications, the term Chlorophyceae is sometimes used to apply to all the green algae except the

Charales Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Depending on the treatment of the genus '' Nitellopsis'', living (extant) species are placed into either one family (Ch ...

, and the internal division is considerably different.

References

External links

AlgaeBase
{{Taxonbar, from=Q132609 Green algae classes

General characteristics

Reproduction

Orders

See also

References

External links