Question

Agar is commercially obtained from___________.
(a)Blue-green algae
(b)Brown algae
(c)Red algae
(d)Green algae

Answer 1

Hint: The main source of agar-agar is from a class of algae which mostly contains marine algae. Chlorophyll a and chlorophyll d is found in these algae and another pigment known as r-phycoerythrin is present in them.

Complete answer:
Agar is made from red algae Gelidium and Gracilaria. Agar is also known as vegetable gelatin. In India, it is produced in the coastal regions of the Bay of Bengal. The agar from Gelidium is dried, shaken, bleached, washed, and removed from foreign materials. Then, it is boiled with dilute acidified water, strained. On cooling, jelly is produced. This process has been developed for the extraction of agar from the species of Hypnea in India. Agar is insoluble in cold water but forms a gelatinous mass after cooling hot solution. It is soluble in boiling water and insoluble in organic solvents.

Additional Information:
-Agar consists of two polysaccharides: agarose and agaropectin.
-Agarose is responsible for the gel strength of agar. It is composed of D- galactose and 3,6 anhydrous L- galactose units.
-Agaropectin is responsible for the viscosity of agar solution.

So, the correct answer is, ‘Red algae.’

Note: -Agar is used as an emulsifying agent.
-It is used in the preparation of jellies.
-It is used in the treatment of chronic constipation.
Both agar and agarose find extensive use in affinity chromatography.
-It is used in the preparation of bacteriological culture.