Algae - An illustration with General features, classification , Economic importance , Examples
Overview-
The algae belong to the sub phylum Thallophyta of the kingdom Protista in modern classification of organisms. Algae are chlorophyll-bearing, simple, thalloid, autotrophic eukaryotic organisms. During photosynthesis, they produce oxygen with help of light energy from the sun and form carbohydrates.
Economic importance of Algae-
Algae are chief producers in the marine ecosystem. They fix almost half of atmospheric carbon di oxide.
Algae are good source of carbohydrates, fats, proteins, and vitamins A, B, C, and E as well as the minerals like iron, potassium, magnesium etc. Therefore they are used as source of food. Some algae like spirullina and Chlorella is used by space travellar as food. In fishes, Algae plays a very important role because it helps in the production process. Fish used plankton and zooplankton as food. It helps in maintaining the health of the marine ecosystem because algae are naturally absorbent of carbon dioxide and also provide oxygen to the water. Algae are rich in minerals and vitamins. So they are also used as bio fertilizer which helps in increasing soil quality .Algae are very sensitive. If there is a slight change in the environment their pigments change or might get died. Water pollution is checked with the help of Algae like Euglena and Chlorella. Some algae like Gelidium and Gracilaria produce Agar that are used in making ice cream, jellies etc. Some algae produces algin and carrageen , water holding substances.
General features of Algae-
Occurrence - They are found in both freshwater and marine water. They are found in a variety of habitats like moist stones, soils and wood.
Association - Some of them make symbiotic association with fungi in the form of lichen. Algae are also reported to be found in association with the animals like sloth bears.
Size - They are unicellular and microscopic like Chlamydomonas to colonial forms like Volvox and to the filamentous forms like Ulothrix and Spirogyra. Some of the marine alga form the kelp. Kelp may be sixty meter long.
Reproduction - The algae reproduce by vegetative, asexual and sexual methods. Vegetative reproduction is by fragmentation. Each fragment develops into a thallus. Asexual reproduction is by the production of different types of spores, the most common being the zoo spores. They are flagellated and motile and on germination give rise to new plants. Sexual reproduction takes place through fusion of two gametes. In Spirogyra The gametes can be flagellated and similar in size or non-flagellated or non-motile. Such reproduction is called isogamous. Fusion of two gametes dissimilar in size, as in some species of Chlamydomonas is termed as anisogamous. If Fusion takes place between one large and non-motile female gamete and smaller motile male gamete is termed oogamous like Volvox, Fucus.
Classification of algae –
Algae are classified in to main three groups – Chlorophyceae, Phaeophyceae and Rhodophyceae
Chlorophyceae
They are green algae and the largest group in Algae. They are usually green due to the presence of pigments chlorophyll a and b. They also have little amount of β-carotenoids .The pigments are present in chloroplasts. In Algae, The shape of chloroplast may vary from species to species. The chloroplasts shows various shape ie. Spiral shape in Spirogyra, cup shaped in Chlamydomonas, star shaped in Zygnema, girdle shaped in Ulothrix .
Most of the members have one or more storage bodies called pyrenoids located in the chloroplasts. Pyrenoids contain protein besides starch.. Green algae usually have a rigid cell wall made of cellulose and pectose.
Vegetative reproduction usually takes place by fragmentation or by formation of different types of spores. Asexual reproduction is by flagellated zoospores produced in zoosporangia. The sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous, anisogamous or oogamous. For Ex- Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara Oedogonium
Pheophyeae-
Pheophyceaen Algae are commonly known as brown algae and found primarily in marine habitats. They show great variation in size. Their size varies from simple branched, filamentous forms like Ectocarpus and some algae are profusely branched to form the kelps. They possess chlorophyll a, c, carotenoids and xanthophylls. They are also found in various colours from olive green to brown depending upon the amount of the xanthophyll pigment, fucoxanthin present in them. Food is stored in the form of complex carbohydrates, like laminarin or mannitol. The vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin.. The plant body is usually attached to the substratum by a holdfast. They also have stalks and stipes. They bear a leaf-like photosynthetic organ called the frond. Vegetative reproduction takes place by fragmentation. Asexual reproduction in most brown algae is by biflagellate zoospores . Sexual reproduction may be isogamous, anisogamous or oogamous. Union of gametes may take place in water or within the oogonium. The gametes are pyriform or pear-shaped with two laterally flagella. For Ex- Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus
👌👌Remember - In this group, there are no unicellular and colonial brown algae reported so far.
Rhodophyceae- The members of Rhodophyceae are comonly known as Red algae. They have
red colored photosynthetic pigments like r-phycocyanin and r-phycoerythrin along with chlorophyll a, d, xanthophyll and β-carotene.They are aquatic and marine but like Batrachospermum some are freshwater algae are also reported. They store reserve food in the form of Floridean starch. They are unicellular like Porphyridium or multicellular like
Geotrichum. They reproduce Vegetatively by fragmentation.
Akinete, aplanospore, azygospore are non motile spore involved in asexual reproduction. The sexual reproduction is only of the Oogamous type. Some species like Batrachospermum , Polysiphonia exhibit Alternation of generations in their life cycle.
For Example -Porphyridium, Gelidium, Gracilaria Batrachospermum , Polysiphonia.
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