Chemistry Class 12 NCERT Solutions: Chapter 14 Biomolecules Part 3

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Q: 8. What is the basic structural difference between starch and cellulose?

Answer:

Starch consists of two components − amylose and amylopectin. Amylose is a long linear chain of glucose units joined by glycosidic linkage .

Q 8 1 Basic Structural of Starch and Cellulose

Q 8 1 Basic Structural of Starch and Cellulose

Q 8 1 Basic Structural of Starch and Cellulose

Amylopectin is a branched-chain polymer of units, in which the chain is formed by glycosidic linkage and the branching occurs by glycosidic linkage.

Q 8 2 Basic Structural of Starch and Cellulose

Q 8 2 Basic Structural of Starch and Cellulose

Q 8 2 Basic Structural of Starch and Cellulose

On the other hand, cellulose is a straight-chain polysaccharide of units joined by glycosidic linkage

Q 8 3 Basic Structural of Starch and Cellulose

Q 8 3 Basic Structural of Starch and Cellulose

Q 8 3 Basic Structural of Starch and Cellulose

Q: 9. What happens when D-glucose is treated with the following reagents?

(i)

(ii) Bromine water

(iii)

Answer:

(i) When D-glucose is heated with HI for a long time, n-hexane is formed.

(ii) When D-glucose is treated with Br2 water, D- gluconic acid is produced.

(iii) On being treated with HNO3, D-glucose get oxidised to give saccharic acid.

Q: 10. Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.

Answer:

(1) Aldehydes give test, Schiff’s test, and react with to form the hydrogen sulphite addition product. However, glucose does not undergo these reactions.

(2) The pentaacetate of glucose does not react with hydroxylamine. This indicates that a free group is absent from glucose.

(3) Glucose exists in two crystalline forms . The crystallises from a concentrated solution of glucose at and the crystallises from a hot and saturated aqueous solution at . This behaviour cannot be explained by the open chain structure of glucose.

Q: 11. What are essential and non-essential amino acids? Give two examples of each type.

Answer:

Essential amino acids are required by the human body, but they cannot be synthesised in the body. They must be taken through food. For example: valine and leucine.

Non-essential amino acids are also required by the human body, but they can be synthesised in the body. For example: glycine and alanine.

Q 11 Amino Acids In Human Body

Q 11 Amino Acids in Human Body

Q 11 Amino Acids In Human Body