Question

Agar, the gelling agent used for tissue culture media, is obtained from

• A. Green algae
• B. Red algae (Gelidium amansii)
• C. Blue-green algae
• D. Brown algae

Hint:

Agar is extracted from the cell walls of marine red algae (Rhodophyta), primarily Gelidium and Gracilaria species.
Alginate is obtained from brown algae (Phaeophyta).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Agar-agar is a sulfur-containing polysaccharide complex utilized as a solidifying agent in microbiological and plant tissue culture media.
It is preferred because of its high gel strength, stability, and resistance to enzymatic degradation by most cultured organisms.

Step 2: Detailed Explanation:
Agar is a structural polysaccharide found in the cell walls of certain genera of marine red algae (Rhodophyta), commonly referred to as agarophytes.
The primary commercial sources of agar are species belonging to the genera Gelidium (such as {Gelidium amansii) and Gracilaria.
Structurally, agar is composed of two main fractions: agarose (a linear polymer of alternating D-galactose and 3,6-anhydro-L-galactopyranose) and agaropectin (a branched, sulfated polymer).
Let us review the other algal groups:
1. Green algae (Chlorophyta): Cell walls are composed primarily of cellulose, similar to land plants.
2. Blue-green algae (Cyanobacteria): Are prokaryotes with peptidoglycan-containing cell walls.
3. Brown algae (Phaeophyta): Serve as the source for other industrial polysaccharides like alginates.

Step 3: Final Answer:
Agar is obtained from Red algae (Gelidium amansii), which corresponds to Option (B).