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Biomolecules

CBSE · Class 12 · Chemistry

NCERT Solutions for Biomolecules — CBSE Class 12 Chemistry.

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Exercises

10.1What are monosaccharides?Show solution
A monosaccharide is the simplest carbohydrate unit. It cannot be hydrolysed further to give a simpler carbohydrate. It is a polyhydroxy aldehyde or polyhydroxy ketone.

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10.2What are reducing sugars?Show solution
Reducing sugars are those carbohydrates which can reduce Fehling’s solution and Tollens’ reagent. All monosaccharides are reducing sugars, whether they are aldoses or ketoses.

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10.3Write two main functions of carbohydrates in plants.Show solution
Carbohydrates perform two main functions in plants:

1. They act as food storage molecules, mainly as starch.
2. They provide structural support, as in cellulose of the cell wall.

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10.4Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose and lactose.Show solution
- Monosaccharides: ribose, 2-deoxyribose, galactose, fructose
- Disaccharides: maltose, lactose

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10.5What do you understand by the term glycosidic linkage?Show solution
A glycosidic linkage is the oxygen bridge formed between two monosaccharide units when a molecule of water is lost. It joins the two sugar units together.

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10.6What is glycogen? How is it different from starch?Show solution
Glycogen is the storage polysaccharide in animals, also called animal starch. It is stored mainly in the liver, muscles and brain.

Difference from starch:
- Starch is the main storage polysaccharide of plants.
- Glycogen is the storage polysaccharide of animals.
- Glycogen is more highly branched than starch (its structure is similar to amylopectin but more branched).

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10.7What are the hydrolysis products of (i) sucrose and (ii) lactose?Show solution
On hydrolysis:
- Sucrose gives D-(+)-glucose and D-(-)-fructose.
- Lactose gives D-glucose and D-galactose.

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10.8What is the basic structural difference between starch and cellulose?Show solution
The basic structural difference is that:
- Starch is made of **alphaalpha-D-glucose units.
- Cellulose is made of betabeta-D-glucose units.

So, starch and cellulose differ in the kind of glucose unit and the linkage pattern** between them.

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10.9What happens when D-glucose is treated with the following reagents?Show solution
When D-glucose is treated with:

1. HI: It gets reduced to n-hexane.
2. Bromine water: It is oxidised to gluconic acid.
3. **HNO3_3: It is oxidised to the dicarboxylic acid saccharic acid**.

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10.10Enumerate the reactions of D-glucose which cannot be explained by its open chain structure.Show solution
The following reactions of D-glucose cannot be explained by its open-chain structure:

1. It does not give Schiff’s test and does not form the hydrogensulphite addition product with **NaHSO3_3, although it has an aldehyde group in the open-chain formula.
2. Its pentaacetate does not react with hydroxylamine, showing the absence of a free –CHO group.
3. It exists in two crystalline forms, alphaalpha-glucose and betabeta-glucose**.

These facts led to the cyclic hemiacetal structure of glucose.

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10.11What are essential and non-essential amino acids? Give two examples of each type.Show solution
Essential amino acids are those which cannot be synthesised in the body and must be supplied through diet. Non-essential amino acids can be synthesised by the body.

Examples:
- Essential: valine, lysine
- Non-essential: glycine, alanine

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10.12Define the following as related to proteinsShow solution
Related to proteins:

1. Peptide linkage: An amide bond, **−CO−NH−-CO-NH-, formed between the −COOH-COOH group of one amino acid and the −NH2-NH_2 group of another.
2. Primary structure: The specific sequence of amino acids in a polypeptide chain.
3. Denaturation: The process in which a protein loses its native structure and biological activity due to change in temperature or pH**; secondary and tertiary structures are destroyed while primary structure remains intact.

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10.13What are the common types of secondary structure of proteins?Show solution
The two common secondary structures of proteins are:
- **alphaalpha-helix
- betabeta-pleated sheet**

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10.14What type of bonding helps in stabilising the α\alpha-helix structure of proteins?
10.15Differentiate between globular and fibrous proteins.
10.16How do you explain the amphoteric behaviour of amino acids?
10.17What are enzymes?
10.18What is the effect of denaturation on the structure of proteins?
10.19How are vitamins classified? Name the vitamin responsible for the coagulation of blood.
10.20Why are vitamin A and vitamin C essential to us? Give their important sources.
10.21What are nucleic acids? Mention their two important functions.
10.22What is the difference between a nucleoside and a nucleotide?
10.23The two strands in DNA are not identical but are complementary. Explain.
10.24Write the important structural and functional differences between DNA and RNA.
10.25What are the different types of RNA found in the cell?

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Frequently Asked Questions

What are the important topics in Biomolecules for CBSE Class 12 Chemistry?
Biomolecules covers several key topics that are frequently asked in CBSE Class 12 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Biomolecules — CBSE Class 12 Chemistry?
Understand the core concepts first, then work through the 52 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.
Where can I get free NCERT Solutions for Biomolecules Class 12 Chemistry?
This page has free step-by-step NCERT Solutions for every exercise question in Biomolecules (CBSE Class 12 Chemistry) — written the way examiners award marks: given, formula, working, answer.

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