Question

Agar is obtained from which of the following alga?
(a)Sargassum
(b)Spirogyra
(c)Gelidium
(d)Chondrus crispus

Answer 1

Hint: Agar is a jelly-like material formed from thalloid red (Rhodophyta) algae. Those algae are referred to as agarophytes. These species typically prefer steeply sloped rocky areas and are rarely found on muddy or sandy bottoms.

Complete answer:
Agar is derived from polysaccharide agarose, which forms the supporting structure of some algae species mainly from the genera Gelidium and Gracilaria in the cell walls and is released on boiling. Agar is the resulting mix of two components: linear polysaccharide agarose, and agaropectin, a heterogeneous mixture of smaller molecules. Chemically, agar is a polymer made up of the sugar galactose subunits. For trade purposes, agar is mainly extracted from Gelidium amansii.

Additional Information: Sargassum is a genus in the order Fucales of the brown (class Phaeophyceae) macroalgae (seaweed). Many species are distributed in the world's temperate and tropical oceans, where they inhabit shallow water and coral reefs in general, and the genus is commonly recognized for its planktonic (free-floating) species.
Irish moss or carrageen moss is usually called the Chondrus crispus. It is a red algae species that grows abundantly along with the rocky parts of the European and North American Atlantic coast.
A green alga Spirogyra is also known as water-silk.
So, the correct answer is, ‘Gelidium’.

Note: The species of Gelidium grows best where water flow is rapid majorly in the eulittoral and sublittoral zones. It can be found in water, depending on the species, from 2 to 20 m in depth. It prefers partial shade and in tropical latitudes, it can be bleached by maximum intensity light. It normally grows best at 15-20° C, but higher temperatures can be tolerated. It can live under low nutrient conditions and some species can adapt to low or high salinity.