The Question is from neet-botany , and it was created by the author K SURESH KUMAR

Question

Agar, a polysaccharide extracted from certain red algae, is widely used as a solidifying agent in microbiological media.  Which of the following structural features contributes most to agar's gelling properties?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Polysaccharide structure and gelling properties
 **Related Topics**: Carbohydrate chemistry, glycosidic bonds, hydrogen bonding
 **Prerequisites**: Understanding of polysaccharide structure, types of glycosidic linkages, and the role of intermolecular forces in gel formation.
## SOLUTION PATHWAY
**Given Information**:
  Agar is a polysaccharide used as a solidifying agent.
  Options describe different structural features of agar.
**Method & Steps**:
 1. Analyze each option to determine its contribution to gelling.
  Reasoning: Gelling properties arise from the ability of molecules to form a three-dimensional network through intermolecular interactions.
 2. Evaluate the importance of each structural feature in forming this network.
  Working: Option A (high branching) is characteristic of storage polysaccharides like glycogen, not gelling agents. Option B (exclusively β(1→4) linkages) describes cellulose, which forms strong fibers but not gels. Option D (highly crystalline structure) is again more typical of cellulose. Option C correctly points to the key features: sulfated galactose residues and double helix formation.  The sulfated groups contribute to increased intermolecular interactions (ionic and hydrogen bonds) and the double helix structure provides a framework for the gel formation.
 3. Select the option that best explains agar's gelling property.
  Result: Option C
  Verification: The presence of sulfated galactose and double helix formation is consistent with the known structure and gelling properties of agar.
 ## OPTION ANALYSIS
A :x: High degree of branching similar to glycogen.  Glycogen is a storage polysaccharide, not a gelling agent. Branching reduces the ability to form a rigid network.
B :x: Presence of $\beta(1ightarrow4)$ glycosidic linkages exclusively. This describes cellulose, which forms fibers, not gels.
C ✓: The presence of sulfated galactose residues and the formation of double helices. The sulfated groups increase intermolecular interactions, and the double helix provides a framework for gel formation.
D :x: Its ability to form highly crystalline structures similar to cellulose. Cellulose forms strong fibers, not gels.  Agar's gel is not highly crystalline.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the properties of different polysaccharides (e.g., glycogen, cellulose, agar).
  How to avoid: Carefully consider the function and structure of each polysaccharide.
  2.Overlooking the role of intermolecular forces in gel formation.
  How to avoid: Remember that gels form through extensive intermolecular interactions (hydrogen bonding, ionic interactions).
 **Quick Tips**:
  1.Remember that agar is a gelling agent, so look for options that explain its ability to form a three-dimensional network.
  2.Focus on the structural features that promote intermolecular interactions.

K SURESH KUMAR · Answer

High degree of branching similar to glycogen.

K SURESH KUMAR · Answer

Presence of β(1→4) glycosidic linkages exclusively.

K SURESH KUMAR · Answer

The correct Option is "The presence of sulfated galactose residues and the formation of double helices."

K SURESH KUMAR · Answer

Its ability to form highly crystalline structures similar to cellulose.

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