(i) USEFUL ASPECTS :
# (a) Nitrogen fixation : Some fifty species of blue-green algae are capable of fixing atmospheric nitrogen in the soil e.g., Anabaena, Aulosira, Cylindrospermum, Calothrix, Gleotrichia, Nostoc, Scytonema, Stigonema, Tolypothrix etc. Under aerobic conditions, nitrogen is fixed by heterocysts only. The fixation is brought about by the enzyme nitrogenase. Under anaerobic condition the vegetative cells also show nitrogenase activity.
# (b) Algae as food : Many green algae such as Chlorella, Ulva, Caulerpa, Enteromorpha, etc. are used as food. Chlorella, a unicellular green alga, possesses a high quality of food value. It has about 50% protein and 20% of lipid and carbohydrates. The Chlorella protein contains all the amino acids essential for human nutrition. Besides, it contains vitamins A, B, C, K and various other essential elements. Ulva is collected and processed as food product. Ulva lactuca has formerly used in salad and soup in Scotland.
# (c) Green algae in space research : In recent years biologists have realized that unicellular green algae (e.g., Chlorella) could be used to provide O2 during space flight trips. The alga can reuse CO2 during the process of photosynthesis and release O2 for the use by Astronauts.
# (d) Antibiotics : The genus Chlorella yields an antibiotic chlorellin, which is used against Gram +ve and Gram –ve bacteria, especially Escherichia coli, Shigella dysenteriae and Staphylococcus aureus. The genus Caulerpa also yields antibiotics.
# (e) Alginates : Alginic acid is a polymer of carbohydrate. It occurs in the cell wall and middle lamella. The alginates particularly ammonium, Fe, Na and K, salts are water soluble. They are obtained from Laminaria, Ascophyllum, Fucuc, Nereocystis, Turbinaria etc. They are viscous, gel-forming and non-toxic. Hence they are used in pharmaceuticals as emulsifiers and stabilizers as well as for making pills, antibiotic capsules etc. They are also used in the preparation of soups, jellies, cosmetics, toothpastes, polishes, hair dyes, compact powders, lotions, shampoos etc.
# (f) Carrageenin : It is a polysaccharide colloid (phycocolloid) obtained from the red algae Chondrus crispus and Gigartinia stellata. It is widely used in soups, sauces, milk shakes, cheese, jellies, cream and fruit juices. It is also used in painting and printing.
# (g) Kieselguhr or Diatomite : The fossil deposits of unicelled alga, diatoms are formed due to their highly siliceous cell wall (frustules). This is called as diatomite or diatomaceous earth. It is used in making sound proof buildings, lining furnaces and boilers, as insulating material and also as a filter.
# (h) Agar-agar : It is a non-nitrogenous carbohydrate consisting of two polysaccharides namely agarose and agaropectin. It is obtained from several red algae e.g., Gracilaria, Gelidium, Gigartinia, Pterocladia, Chondrus, Furcellaria, Phyllophora etc. It is insoluble in cold water but soluble in hot. It is used as a base for a variety of culture media.
# (i) Source of minerals and elements : The members of brown algae called 'kelps' have been the source for obtaining iodine e.g., Laminaria, Macrocystis, Fucus. About 25% of total iodine is extracted from kelps. Besides iodine, the kelp also contain Bromine, Boron, Copper, Cobalt, Chromium, Iron, Manganese, Molybdenum and Zinc.
# (j) Sewage disposal : Green unicellular algae such as Chlorella and Chlamydomonas are used in sewage disposal ponds. They remove CO2 and restore O2 by the process of photosynthesis and makes the sewage water habitable for many fishes and aerobic bacteria.
(ii) HARMFUL ASPECTS
# (a) Algal toxicity : Some dinoflagellates like Prymnesium, Gymnodinium are extremely poisonous to fishes. The blue-green alga Microcystis secretes hydroxylamine which not only kills aquatic life but also the birds and cattles who care to drink that water. While Lyngbya and Chlorella may cause skin allergies in human beings.
# (b) Algal parasitism : The red alga Cephaleuros virescens causes red rust of tea thus destroying the tea leaves. Similar disease are caused by the species of Cephaleuros to coffee plant, Piper and Citrus sp.
# (c) Fouling of marine vessels : Some brown and red algae grow on the metallic and wooden submerged parts of naval vessels. As a result, their surfaces are corroded. This creates problems in their navigation.
# (d) Spoilage of drinking water : Forms like Anabaena, Microcystis not only spoil the taste of drinking water but also produces toxic effect. The water filters are blocked due to growth of diatoms, Spirogyra, Oscillatoria etc. Forms like Chaetophora, Anacystis grow inside the water pipes and boilers, and thus corrode their surface by their secretion. The growth of algae is controlled by using algicides such as dichlorophen, sodium perborate, phygon XI, exalgae, delrad, cuson etc. Besides, cyanophages (LPP-1) are also used for the destruction of Lyngbya, Phormidium and Plectonema.
# (e) Water blooms : Algae grow abundantly in water reservoirs where excess of nutrients are available to them. This algal growth floats on the water surface and look like foam or soap lather. It is called water bloom. e.g., Member of cyanophyceae (Microcystis, Anabaena, Oscillatoria etc.) are common. Water bloom deplete oxygen of water reservoirs and therefore, aquatic animals die of deoxygenation.
(i) USEFUL ASPECTS :
# (a) Nitrogen fixation : Some fifty species of blue-green algae are capable of fixing atmospheric nitrogen in the soil e.g., Anabaena, Aulosira, Cylindrospermum, Calothrix, Gleotrichia, Nostoc, Scytonema, Stigonema, Tolypothrix etc. Under aerobic conditions, nitrogen is fixed by heterocysts only. The fixation is brought about by the enzyme nitrogenase. Under anaerobic condition the vegetative cells also show nitrogenase activity.
# (b) Algae as food : Many green algae such as Chlorella, Ulva, Caulerpa, Enteromorpha, etc. are used as food. Chlorella, a unicellular green alga, possesses a high quality of food value. It has about 50% protein and 20% of lipid and carbohydrates. The Chlorella protein contains all the amino acids essential for human nutrition. Besides, it contains vitamins A, B, C, K and various other essential elements. Ulva is collected and processed as food product. Ulva lactuca has formerly used in salad and soup in Scotland.
# (c) Green algae in space research : In recent years biologists have realized that unicellular green algae (e.g., Chlorella) could be used to provide O2 during space flight trips. The alga can reuse CO2 during the process of photosynthesis and release O2 for the use by Astronauts.
# (d) Antibiotics : The genus Chlorella yields an antibiotic chlorellin, which is used against Gram +ve and Gram –ve bacteria, especially Escherichia coli, Shigella dysenteriae and Staphylococcus aureus. The genus Caulerpa also yields antibiotics.
# (e) Alginates : Alginic acid is a polymer of carbohydrate. It occurs in the cell wall and middle lamella. The alginates particularly ammonium, Fe, Na and K, salts are water soluble. They are obtained from Laminaria, Ascophyllum, Fucuc, Nereocystis, Turbinaria etc. They are viscous, gel-forming and non-toxic. Hence they are used in pharmaceuticals as emulsifiers and stabilizers as well as for making pills, antibiotic capsules etc. They are also used in the preparation of soups, jellies, cosmetics, toothpastes, polishes, hair dyes, compact powders, lotions, shampoos etc.
# (f) Carrageenin : It is a polysaccharide colloid (phycocolloid) obtained from the red algae Chondrus crispus and Gigartinia stellata. It is widely used in soups, sauces, milk shakes, cheese, jellies, cream and fruit juices. It is also used in painting and printing.
# (g) Kieselguhr or Diatomite : The fossil deposits of unicelled alga, diatoms are formed due to their highly siliceous cell wall (frustules). This is called as diatomite or diatomaceous earth. It is used in making sound proof buildings, lining furnaces and boilers, as insulating material and also as a filter.
# (h) Agar-agar : It is a non-nitrogenous carbohydrate consisting of two polysaccharides namely agarose and agaropectin. It is obtained from several red algae e.g., Gracilaria, Gelidium, Gigartinia, Pterocladia, Chondrus, Furcellaria, Phyllophora etc. It is insoluble in cold water but soluble in hot. It is used as a base for a variety of culture media.
# (i) Source of minerals and elements : The members of brown algae called 'kelps' have been the source for obtaining iodine e.g., Laminaria, Macrocystis, Fucus. About 25% of total iodine is extracted from kelps. Besides iodine, the kelp also contain Bromine, Boron, Copper, Cobalt, Chromium, Iron, Manganese, Molybdenum and Zinc.
# (j) Sewage disposal : Green unicellular algae such as Chlorella and Chlamydomonas are used in sewage disposal ponds. They remove CO2 and restore O2 by the process of photosynthesis and makes the sewage water habitable for many fishes and aerobic bacteria.
(ii) HARMFUL ASPECTS
# (a) Algal toxicity : Some dinoflagellates like Prymnesium, Gymnodinium are extremely poisonous to fishes. The blue-green alga Microcystis secretes hydroxylamine which not only kills aquatic life but also the birds and cattles who care to drink that water. While Lyngbya and Chlorella may cause skin allergies in human beings.
# (b) Algal parasitism : The red alga Cephaleuros virescens causes red rust of tea thus destroying the tea leaves. Similar disease are caused by the species of Cephaleuros to coffee plant, Piper and Citrus sp.
# (c) Fouling of marine vessels : Some brown and red algae grow on the metallic and wooden submerged parts of naval vessels. As a result, their surfaces are corroded. This creates problems in their navigation.
# (d) Spoilage of drinking water : Forms like Anabaena, Microcystis not only spoil the taste of drinking water but also produces toxic effect. The water filters are blocked due to growth of diatoms, Spirogyra, Oscillatoria etc. Forms like Chaetophora, Anacystis grow inside the water pipes and boilers, and thus corrode their surface by their secretion. The growth of algae is controlled by using algicides such as dichlorophen, sodium perborate, phygon XI, exalgae, delrad, cuson etc. Besides, cyanophages (LPP-1) are also used for the destruction of Lyngbya, Phormidium and Plectonema.
# (e) Water blooms : Algae grow abundantly in water reservoirs where excess of nutrients are available to them. This algal growth floats on the water surface and look like foam or soap lather. It is called water bloom. e.g., Member of cyanophyceae (Microcystis, Anabaena, Oscillatoria etc.) are common. Water bloom deplete oxygen of water reservoirs and therefore, aquatic animals die of deoxygenation.