Variation among algae.

Account for the enormous variation among algae.

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Introduction

The word algae represents a large group of different organisms from different phylogenetic groups, representing many taxonomic divisions. In general, algae can be referred to as plant-like protists that are usually photosynthetic and aquatic, but do not have true roots, stems, leaves, vascular tissue and have simple reproductive structures. They are distributed worldwide in the sea, in freshwater and in moist situations on land. Most are microscopic, but some are quite large, for example there are some marine seaweeds that can exceed 50 m in length. The algae have chlorophyll and can manufacture their own food through the process of photosynthesis. They produce and release oxygen like plants. Algae are classified in the kingdom of protista, which comprise a variety of unicellular and some simple multinuclear and multicellular eukaryotic organisms that have cells with a membrane-bound nucleus.

Almost all the algae are eukaryotes and conduct photosynthesis within membrane bound structure called chloroplasts, which contain DNA. The exact nature of the chloroplasts is different among the different lines of algae.Cyanobacteria are organisms which were previously included among the algae, but they have a prokaryotic cell structure typical of bacteria and conduct photosynthesis directly within the cytoplasm, rather than in specialized organelles(Mader, 2001).

Algae are differentiated into eight major groups based on their apomorphic characteristics which include pigmentation and its derivation , habitat , nutrition , morphology , structure of reproductive parts , mode of reproduction and mode of locomotion. These groups are : Chlorophyta (green algae) , Pyrrophyta (dinoflagellates), Phaeophyta (brown algae) , Rhodophyta (red algae) , Chrysophyta (golden algae) , Bacillariophyta (Diatoms) , Euglenophyta (euglenoids) and Cyanophytaa(blue-green algae).

Chlorophyta (green algae)

The green algae represent a very diverse group, which includes members distributed not only in the sea, but also in freshwater and terrestrial habitats. They are of eukaryotic form and contain chlorophyll a and b. This group can be single-celled or colonial and have two flagella for locomotion. In the green seaweeds, the body of the alga shows a great range of variation of forms, but usually its morphology is quite simple. Thin filaments, either branched or not, are a common growth form and are found in Cladophora and Chaetomorpha, two wide spread genera. Sheets formed by two layers of cells are typical of Ulva. Because of their appearance, species of this genus are popularly called sea lettuce. These algae are well known for their fast growth and high capacity to absorb nutrients from seawater. A type of body organization which is unique to the green seaweeds is the siphonalean organization. Its cell walls accumulate calcium carbonate in the form of calcite. After the death of the alga, this material is released and contributes to produce the white sand typical of atoll beaches (Dawes, 1998).

Rhodophyta (red algae)

A distinctive characteristic of this group is that they are the only seaweeds lacking flagella (as well as centrioles and other structures typical of the flagella apparatus) at any stage of their life histories. Their colour, which ranges from pink to bright red, purple or sometimes dark brown, is due to the presence of pigments called phycobilins . Their sexual reproductive apparatus is a very sophisticated structure, whose arrangement has been used for a long time as the main criterion for taxonomy at ordinal level. The red algae show a great range of morphological variation. The simplest forms consist of single cells like Porphyridium or thin filaments like Bangia. The habit of expanded blades is found in many genera, including some of the most spectacular, such as Delesseria , Polyneura and Halymenia. In other red algae, the body of the alga is formed by a crust which grows attached to the rocky bottom. Many other species of red seaweeds have a branched plantlike shape and look like small bushes or trees. Species with this habit include many common genera, such as Chondrus, Gelidium . Species of Eucheuma and Kappahycus are the most important source of carrageenans (compounds widely used in the food industry). (Bold and Wynne, 1985)

Phaeophyta (brown algae)

Brown seaweeds are distributed in all seas of the world, but they are most diverse and abundant in cold seas, entirely confined to polar and cold-temperate waters. Their brown pigmentation is derived from fucoxathin. Filamentous species consisting of thin branched threads, such as Ectocarpus and Pylaiella , grow on rock or on larger seaweeds in the intertidal zone of many regions of the world. Most brown algae, however, have a bigger size and look like branched ribbons, bushes or small trees. Members of the order Fucales are algae of particular ecological importance, as they form dense belts in the intertidal zone of many rocky shores of temperate seas. The kelps are also the most complex algae from an anatomic and morphological point of view, as their tissues contain types of cells and structures with complexity comparable to those of vascular plants(Bold and Wynne, 1985)

Euglenophyta (euglenoids).

Phyum consisting of mostly unicellular flagellated aquatic algae. Some euglenoids contain chloroplasts with the photosynthetic pigments; others are heterotrophic and can ingest or absorb their food. In some cases, the euglenoids are autotrophic and photosynthetic during the day but become heterotrophic feeding on dead organic material when it is dark. Reproduction occurs by longitudinal cell division. Most euglenoids live in freshwater. Like what is observed in the Chlorophyta, euglenoids have a eukaryotic form and contain chlorophylls a and b.The most characteristic genus is Euglena, common in ponds and pools, especially when the water has been polluted by runoff from fields or lawns on which fertilizers have been used. Its presence can serve as an indicator of pollution in a water source (Mader, 2001).

Pyrrophyta (dinoflagellates)

Some species are heterotrophic, but many are photosynthetic organisms containing chlorophyll.Red pigmentation is derived from chlorophyll a and c and xanthophylls.Various other pigments may mask the green of these chlorophylls. Other species are endosymbionts of marine animals and protozoa, and play an important part in the biology of coral reefs. Other dinoflagellates are colourless predators on other protozoa, and a few forms are parasitic. Reproduction for most dinoflagellates is asexual, through simple division of cells following mitosis. The dinoflagellates are important constituents of plankton, and as such are primary food sources in warmer oceans. Many forms are phosphorescent; they are largely responsible for the phosphorescence visible at night in tropical seas. Dinoflagellates are spinning swimmers which store food in form of starch and oils (Dawes , 1998).

Chrysophyta (golden algae)

Large group of eukaryotes algae commonly called golden algae, found mostly in freshwater. Originally they were taken to include all such forms except the diatoms and multicellular brown algae, but since then they have been divided into several different groups based on pigmentation and cell structure. In many chrysophytes the cell walls are composed of cellulose with large quantities of silica. Formerly classified as plants, they contain the photosynthetic pigments chlorophyll a and c. Under some circumstances they will reproduce sexually, but the usual form of reproduction is cell division (Dawes , 1998).

Bacillariophyta (Diatoms)

Diatoms are unicellular organisms characterized by a silica shell of often intricate and beautiful sculpturing. Most diatoms exist singly, although some join to form colonies. They are usually yellowish or brownish, and are found in fresh- and saltwater, in moist soil, and on the moist surface of plants. Fresh-water and marine diatoms appear in greatest abundance early in the year as part of the phenomenon known as the spring bloom, which occurs as a result of the availability of both light and (winter-regenerated) nutrients. They reproduce asexually by cell division. When aquatic diatoms die they drop to the bottom, and the shells, not being subject to decay, collect in the ooze and eventually form the material known as diatomaceous earth. Diatoms can occur in a more compact form as a soft, chalky, lightweight rock, called diatomite. Diatomite is used as an insulating material against both heat and sound, in making dynamite and other explosives, and for filters, abrasives, and similar products. Diatoms have deposited most of the earth’s limestone, and much petroleum is of diatom origin. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. (Campbell and Reece, 2002)

Cyanophyta(blue-green algae)

Phylum of prokaryotic aquatic bacteria that obtain their energy through photosynthesis. They are often referred to as blue-green algae, even though it is now known that they are not related to any of the other algal groups, which are all eukaryotes. Cyanobacteria may be single-celled or colonial. Depending upon the species and environmental conditions, colonies may form filaments, sheets or even hollow balls. Some filamentous colonies show the ability to differentiate into three different cell types. Despite their name, different species can be red, brown, or yellow; blooms (dense masses on the surface of a body of water) of a red species are said to have given the Red Sea its name. There are two main sorts of pigmentation. Most cyanobacteria contain chlorophyll a, together with various proteins called phycobilins, which give the cells a typical blue-green to greyish-brown colour. A few genera, however, lack phycobilins and have chlorophyll b as well as a, giving them a bright green colour (Campbell and Reece, 2002).

Conclusion

Algae are the ancestors of Kingdom Plantae with the Charaphyceae being of closest relation. Both Nitella and Chara look like rooted, aquatic plants, but both are actually a form of algae. Control of abundant algae like Chara and Nitella is best accomplished by reducing or redirecting nutrient sources from the pond. Diversity allows for variation and ensures success of the algae as competition is reduced. Algae are a major food source and primary producers for water organisms. Other economic importance include: industrial use, in medicines and antibiotics and nitrogen fixation (Graham and Wilcox , 2000).

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