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Chlorophyceae

Brief Summary

    Brief Summary
    provided by EOL staff

    The Chlorophyceae are one of the lineages of primarily freshwater green algae.

    Chlorophyceae: Brief Summary
    provided by wikipedia

    The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example, the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some algae may store food in the form of oil droplets. Green algae usually have a rigid cell wall made up of an inner layer of cellulose and outer layer of pectose.

    Brief Summary
    provided by Ecomare
    If you ever try walking close to the waterline on a sea dike, you surely have noticed how slippery it can be. This slipperiness is caused by gutweed, a green seaweed. Green seaweed gets its bright green color from the dominating chlorophyll pigment. There are more than sixty species found in the Netherlands. All 'higher plants', from eelgrass to trees, find their origin in one-celled green algae. Just like red seaweed, green seaweeds degrade more rapidly than brown seaweeds. They make a good source of nutrients for annual seablite.

Comprehensive Description

    Chlorophyceae
    provided by wikipedia

    The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example, the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some algae may store food in the form of oil droplets. Green algae usually have a rigid cell wall made up of an inner layer of cellulose and outer layer of pectose.

    General characteristics

    • Plant body may be unicellular, colonial or filamentous, or multicellular
    • They are usually green due to the dominance of chlorophyll A and B and beta carotene.
    • The pigments present in green algae are chlorophyll a, chlorophyll b, beta- carotine.
    • The chloroplast may be discoid, cup-shaped(chlamydomonas), spiral or ribbon shaped(spyrogyra) in different species.
    • Most of the members have one or more storage bodies called pyrenoids(central protentious body covered with starch sheath) that are localised around the chloroplast.
    • Cell wall is made of cellulose {inner side} and the outer layer is from pectose.
    • Asexual reproduction is by zoospores. They are flagellates produced from the parent cells by mitosis.Also by aplanospores,hepnospores,akinetes,palmella stage etc.
    • Sexual reproduction of plants is by isogamus, anisogamus or oogamus
    • Starch is deposited on small bodies called pyrenoids

    Reproduction

    Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated zoospores. And haplospore,perrination(akinate and palmellastage). Asexual reproduction by mytospore absent in spyrogyra. Sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous e.g. Chlamydomonas, Spirogyara. anisogamous e.g. Chlamydomonas, Ulothrix or Ooulothrix e.g. Chlamydomonas , Volvox, Chara. 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.[3]

    Classification

    The following orders are typically recognised:

    In older classifications, the term Chlorophyceae is sometimes used to apply to all the green algae except the Charales, and the internal division is considerably different.

    The Orders of the Chlorophyceae as listed by: in Hoek, Mann and Jahns (1995)[4]

    • Volvocales
    • Chlorococcales
    • Chaetophoroales
    • Oedogoniales

    See also

    References

    1. ^ Warming, E., 1884. Haandbog i den systematiske botanik. Anden gjennemsete udgave. 2nd ed. Kjøbenhavn, 434 pp. German translation (1890) of the 2nd Danish edition available at archive.org: [1]. English translation (1895) of the 3rd Danish edition (1892) available at archive.org: [2].
    2. ^ Guiry, M.D.; Guiry, G.M. (2007). "Class: Chlorophyceae taxonomy browser". AlgaeBase version 4.2 World-wide electronic publication, National University of Ireland, Galway. Retrieved 2007-09-23..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
    3. ^ Raven, Evert and Eichhorn. The Biology of Plants 7th edition, pg. 335. W. H. Freeman and Company, New York, 2005.
    4. ^ Hoek,C.van den, Mann, D.G. and Jahns, H.M. 1995. Algae An Introduction to Phycology. Cambridge University Press, Cambridge

Morphology

    Morphology
    provided by EOL staff

    There are a variety of thallus types among the chlorophyceans.

    • Unicells:
      • Flagellated
        • individuals or
        • colonies
      • unflagellated except in reproductive state
      • with unflagellated asexual reproductive cells
    • Sarcinoid aggregations of nonmotile cells in which daughter cells fail to separate after division
    • Coenobium, a colony in which the number and arrangement of cells can be constant
    • Filaments:
      • unbranched or
      • branched
    • Multinucleate siphonous

    (Graham & Wilcox, 2000)

Diagnostic Description

    Diagnostic Description
    provided by EOL staff
    • Motile cells with radial or near-radial external symmetry
    • Flagella attached at the anterior end of the cell
    • The possibility of a rhizoplast
    • No multilayered structure
    • Eyespots common
    • Glycolate breaddown by glycolate dehydrogenase
    • Urea breakdown by urea amidolyase
    • Theca covering the cells (some of the flagellates have lost this characteristic)
    • Collapsing telophase spindle that brings daughter cells close together, followed by cell-division by a phycoplast*
    • Flagellar root system cruciate

    *”type of cell division in which the mitotic spindle disperses after nuclear division with the two daughter nuclei coming close together, another set of microtubules arising perpendicular to the former position of the microtubules of the mitotic spindle, and the new cell wall forming along these microtubules.”

    (Lee, 1999)

Habitat

    Habitat
    provided by EOL staff

    Primarily freshwater or terrestrial (soils, tree bark, etc.) some in brackish or marine water (Graham & Wilcox, 2000).

Life Cycle

    Life Cycle
    provided by EOL staff

    Meiosis occurs when the zygote germinates, so that most of the lifecycle is haploid (Lee, 1999).

Reproduction

    Reproduction
    provided by EOL staff

    Those taxa for which the sexual reproductive process is known produce a dormant zygote, with meiosis usually occurring when the zygote germinates (Lee, 1999).

Evolution

    Systematics and Taxonomy
    provided by EOL staff

    Under the old five kingdom system of classification, all the algae were placed within the Kingdom Protista. However, the molecular research of the last decades has resulted in major reclassifications, and at least for now, some uncertainty and disagreement. There is no debate about the placement of the algae in the Domain Eukarya – they have eukaryote cells. And, for the most part, there seems to be agreement that the green algae are members of the plant kingdom. However, classification into lower taxa is less clear.

    For example, Lee (1999) defines Chlorophyceae as a taxon within the class(?) Chlorophyta and with the following orders:

    • Volvocales – can be unicellular or multicellular; the vegetative cells are flagellated & motile
    • Tetrasporales – non-filamentous colonies with immobile vegetative cells capable of cell division; pseudocilia may be present
    • Schizogoniales – foliose marine algae with stellate choroplasts
    • Chlorococcales – unicellular or non-filamentous colonial algae; if colonial, daughter colonies formed as coenobia; vegetative cells non-motile
    • Sphaerophleales – unbranched filaments with new walls formed inside the old filament walls, resulting in H-shaped wall pieces
    • Chlorosarcinales – daughter cells retained within parent cell wall; no plasmodesmata present
    • Chaetophorales – branched or unbranched filaments; plasmodesmata present
    • Oedogoniales – uninucleate filamentous freshwater algae with a unique type of cell division; motile spores and gametes with a whorl of flagella at one pole

    In Graham and Wilcox (2000), the Chlorophyceans are a lineage of green algae, encompassing the following clades:

    • DO (flagellar basal bodies are directly opposed)
      • Sphaeropleales
    • CW (flagellar basal bodies are displaced in a clockwise direction)
      • Volvocales
      • Tetracystis
      • Dunaliella
      • Chaetophorales
      • Oedogoniales

Benefits

    Uses
    provided by EOL staff

    “Chlamydomonas and Volvox are important laboratory model systems, Selensastrum capricornutum is widely recognized for its utility as a bioassay organism, and Dunaliella and Botryococcus can be valuable in production of industrially useful materials.” (Graham & Wilcox, 2000)