A) red algae
B) brown algae
C) cyanobacteria
D) Both (a) and (b)
Correct Answer: A
Solution :
Agar-agar is a mucilage produced by certain red algae and stored alongwith cellulose in the cell wall. The main sources of agar-agar are thalli of Gelidium, Gracilaria and Gigartina. The other red algae used for this purpose are Camphylaephora, Eucheuma, Hyphea and Furcellaria. It is a gelatinous, clear, nitrogen free extract and is used in preparation of foodstuff. It is used as a base for culture media for bacteria, fungi, algae and other tissues. It is also used in preparation of certain medicines and in cosmetics, largely used as a lexative, baked goods, meat industry and as an emulsifier in dairy products. Alginic acid is obtained from members of brown algae (Phaeophyta). Its chief sources are Ascophyllum, Laminaria, Lessonia, Ecklonia, Macrocystis and Eisenia. Alginic acid is a carbohydrate, which occurs in the middle lamella and primary wall of seaweeds. Its soluble calcium salt is algin. Blue-green algae (Cyanobacteria) furnish food for fish and other aquatic animals, they increase soil fertility by adding organic matter. Some of the blue-green algae like Oscillatoria, Anabaena, Spirulina and Nostoc increase fertility of soil by fixing atmospheric nitrogen. They also play role in soil conservation.
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