The Xanthophyta or Heterokontae are commonly known as yellow-green algae include only one class Xanthophyceae. This division has close relationship with. Xanthophyta (yellow-green algae) A division of algae in which the chloroplasts are yellow-green and which form motile cells with 1 long, forward-directed tinsel. Xanthophyta: Xanthophyta, division or phylum of algae commonly known as yellow-green algae.
|Published (Last):||17 June 2012|
|PDF File Size:||1.99 Mb|
|ePub File Size:||6.51 Mb|
|Price:||Free* [*Free Regsitration Required]|
The Xanthophyta or Heterokontae are commonly known as yellow-green algae include only one class Xanthophyceae. This division has close relationship with the Ghlorophyta comprising both marine and fresh-water forms. Certain species grow on drying mud, on trunk of trees, on fivision walls, and similar other habitat.
There are varied forms of vegetative body ranging from unicellular coccoid, siphonaceous to filamentous condition. Each vegetative cell has diision wall composed chiefly of pectic substances which, depending on species, may be impregnated with silica. The cell contains one to several xantjophyta chromatophores. Except in the siphonaceous forms each vegetative cell is uninucleate.
Xanthopyta to the presence of excess of carotinoids, the colour of chromatophores is yellow-green. Chlorophyll a and chlorophyll e are present. But chlorophyll b is absent. The chromatophores lack pyrenoids.
The usual food reserve is oil. One of the outstanding features of the Xanthophyta is the presence of motile cells bearing two flagella of unequal length. Vegetative reproduction is by accidental breaking of the vegetative body. Asexual reproduction in most species is by zoospores with a few exceptional cases where aplanospores are formed for asexual reproduction.
Xanthoophyta zoospores are characterized for having two unequal flagella borne at the anterior end or are multi-flagellate. One line may have developed from an unicellular motile ancestry giving rise to non-motile unicells which may be solitary or colonial.
Members of this division of algae were at one time included in the Chlorophyta. Divosion an increasing number of species were examined, the separate division Xanthophyta was created for the following characters they possess: There is frequently an excess of carotinoids over chlorophylls; moreover, chlorophyll e appears to be restricted to this division. A cell wall is frequently absent and when present it generally has a higher content of pectic material than the walls of Chlorophyta.
Plant body xqnthophyta unicellular multinucleate vesicular, globose or dichotomously branched aerial portion and a colourless rhizoidal portion; discoid chromatophores; asexual reproduction by biflagellate zoospores, aplanospores or resting spores; sexual reproduction isogamous. Food reserve is oil. Asexual diivision is by zoospores or aplanospores and sexual reproduction iso- aniso- or oogamous. This family comprises divsion algae whose plant body is characterized by unicellular multinucleate vesicular, globose or dichotomously branched aerial portion xanthophjta a colourless rhizoidal portion.
It is a vesicular, coenocytic terrestrial alga growing extensively rooted either on drying damp muddy banks of streams and pools or on bare damp soil forming a dense green coating. The plant body is differentiated into a pear-shaped or lobed aerial portion, also known as assimilator, may be one to two millimetres in diameter, and a branched, root-like underground rhizoidal portion’ Fig.
The shape of the aerial portion is considerably influenced by environmental conditions. The aerial vesicular or lobed portion is covered with a relatively tough wall chiefly of cellulose, within which there is a thin, peripheral layer of cytoplasm containing many nuclei; lenticular or fusiform plastids; oil droplets; and leucosin granules.
The rhizoidal portion may be profusely or sparsely branched and has dense or vacuolated cytoplasm with many nuclei without plastids. When exposed to drought the protoplasmic contents of the vesicle migrate into the rhizoids and divide to form thick-walled globose to ellipsoid coenocysts also known as cysts, which either germinate directly or produce zoospores Fig.
In Botrydium tuberosum the protoplast of aerial divisioj migrates into the rhizoidal portion and collects at the ends of the rhizoids which become inflated and swell to develop idvision rounded thick-walled tubers or cysts Fig. The alga is incapable of vegetative division. The protoplasm divides into innumerable uninucleate protoplasts. These protoplasts become metamorphosed into pear-shaped zoospores which bear two anteriorly placed unequal flagella. The method of liberation of zoospores from the mother cell is not definitely known, but it appears that it is accomplished by a gelatinization of apical portion in the vesicular wall Fig.
Occasional formation of many biflagellate isogametes or anisogametes which fuse in pairs being liberated from the same vesicle to form zygote indicates that Xxanthophyta.
The zygote germinates immediately into eivision individual without undergoing any resting period when meiosis takes place Fig. Formation of parthenospore has also been reported in some species.
Plants are filamentous, irregularly or dichotomously branched coenocytic. Asexual reproduction is by zoospores produced singly in sporangia formed at the tips of branches. The zoospores diision multiflagellate, the flagella in pairs over the whole surface. Sexual reproduction is oogamous.
Xanthophyta – yellow green algae – (Phylum/Division)
Plants are dioecious or monoecious. The antheridia are cylindrical, generally curved, producing many small biflagellate anterozoids. The oogonia are single or in groups, producing single egg, which is fertilized in place and develops thick walls to form an oospore. This is xanthlphyta alga which has both terrestrial as well as aquatic species. Whereas, the aquatic species occur in shallow fresh-water streams, while there are a few marine species.
Yellow-green Algae |
The thallus consists of a long, tubular, sparingly branched filament, which, in spite of its size, consists of one cell only as it lacks cross- walls. Cross-walls, however, occur only in the event of injury or in connection with the formation of reproductive organs. Attachment of the filament to the substratum is by a hapteron-like structure provided with colourless branched outgrowths known as rhizoids Fig. The central portion of the filament is occupied by a large vacuole; the cytoplasm is in a thin, peripheral layer continuous along its entire length.
Embedded in the cytoplasmic layer are numerous, small disk-shaped-or elliptical chloroplasts containing a greater proportion of xanthophyll with no pyrenoids, many nuclei, and many oil globules, oil being the reserve food.
Chlorophyll b is absent. This undivided multinucleate, single-celled filament is known as a coenocyte which may attain a length of several inches. The filament and its branches grow by terminal elongation. Vaucheria reproduces both asexually and sexually. A large number of nuclei and chloroplasts along with cytoplasm stream into swollen tip which is cut off by a cross-wall differentiating the zoosporangium from the rest of the filament Fig. The protoplasmic vacuole diminishes in size as a result of which the protoplasm appears deep green in colour.
The entire protoplast of the zoosporangium contracts to form an oval mass. The nuclei arrange themselves in the outer layer of the cytoplasm, and the chloroplasts in the central region. Opposite each nucleus arises a pair of flagella. The mature zoospore escapes through an opening formed by the gelatinization of the zoosporangial wall Fig. Since this zoospore bears numerous chloroplasts and nuclei, in addition to the many flagella, it is considered a compound zoospore and is also known as a coenozoospore.
The protoplast of the sporangium may also divide to form many small immobile thin-walled aplanospores. In some terrestrial species, if exposed to greater desiccation, the threads become septate and rows of cysts are formed giving rise to what is termed Gongrosira stage Fig. Sexual reproduction is of frequent occurrence in all species of Vaucheria but less frequent in those species growing in flowing water.
All species are oogamous. Both fresh-water and terrestrial species are homothallic, while there are quite a few hetero- thallic marine ones. Considering the simple structure of the plant body, the sexual reproduction is of fairly complicated nature. In homothallic species antheridia and oogonia are generally produced on short branches close together on the filament. The antheridium is a slender, curled hook-like tubular structure which is walled off from the rest of the filament Fig. During development of sperms, also known as antherozoids or spermatozoids, small portions of cytoplasm surround each nucleus, thus making small pear-shaped bodies which acquire a pair of flagella.
At maturity, numerous small male gametes, or antherozoids are formed.
Each antherozoid bears two laterally inserted unequal flagella one being whiplash, the other tinsel and consists of a nucleus and a small amount of cytoplasm surrounded by a membrane. When the antherodium is mature, the antherozoids are set free through a terminal pore.
The oogonium is a spherical or oval sessile or short-stalked body with a short, rounded beak which opens to receive the sperms antherozoids Fig. The contents of the oogonium form a single large spherical egg, or ovum laden with much food. The cytoplasm opposite to the beak is clear, while in the rest of the ovum chloroplasts are present.
When the oogonium is mature, the end of the beak opens slightly and the sperms by chemotaxis, cluster round, swimming in a film of water. Eventually one passes in and fuses with the nucleus of the egg resulting in the formation of oospore Fig. Actual fertilization, the fusion xanthophytta nuclei may be delayed.
Following fertilization the oospore secretes a thick wall and passes through a resting stage, having within it reserve food in the form of oil. The oospore germinates and directly forms a new plant Fig. Xanthopyhta behaviour at the reproductive stage has been insufficiently investigated. It is likely, however, that meiosis is zygotic and hence the vegetative filament is haploid Fig.
Coenocytic filamentous branched plant body attached to the substratum by specialized structure provided with rhizoids. Asexual reproduction by means of multi-flagellate zoospores whose flagella are distributed xanthopbyta the entire body—coenozoospores.
The oogonium bears single large, uninucleate oosphere, while the antheridium gives rise to numerous small biflagellate sperms bearing unequal flagella. Since long time the genus Vaucheria has been included in the Chlorophyceae. In spite of his own dislikeness, Fritsch placed Vaucheria in the family Vaucheriaceae under the order Siphonales belonging to the Chlorophyceae.
Occurrence, Structure and Affinities Xanthophyta. Occurrence and Reproduction Fungi. Economic Importance of Algae Botany.
This is a question and answer forum for students, teachers and general visitors for exchanging articles, answers and notes. Answer Now and help others.
Here’s how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top.