Question Bank — Biomolecules

QUESTION BANK: Biomolecules (NCERT Class 11 Biology, Chapter 9)

Section A — MCQs (10 questions, 1 mark each)

1. Which of the following elements shows a markedly higher relative abundance in living tissue compared to the earth’s crust?
   (a) Silicon
   (b) Carbon
   (c) Sodium
   (d) Calcium

2. The acid-insoluble fraction obtained after treating living tissue with trichloroacetic acid mainly contains:
   (a) micromolecules only
   (b) proteins, nucleic acids, polysaccharides and lipids
   (c) only inorganic ions
   (d) secondary metabolites

3. Amino acids are called α-amino acids because:
   (a) the amino and carboxyl groups are attached to the same carbon atom
   (b) they contain only 20 types of R groups
   (c) they are always basic in nature
   (d) they form homopolymers

4. Which of the following is a secondary metabolite?
   (a) Glycine
   (b) Ribose
   (c) Morphine
   (d) Adenylic acid

5. Lipids appear in the macromolecular fraction because:
   (a) they are true polymers
   (b) their molecular weight exceeds 1000 Da
   (c) membrane fragments form water-insoluble vesicles
   (d) they contain nitrogen bases

6. Assertion (A): Starch gives a blue colour with iodine while cellulose does not.
   Reason (R): Starch forms helical secondary structures that can hold I₂ molecules, whereas cellulose lacks such helices.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

7. The most abundant protein in the entire biosphere is:
   (a) Collagen
   (b) RuBisCO
   (c) Haemoglobin
   (d) Trypsin

8. Assertion (A): Enzymes are highly specific and work at high temperatures (above 80 °C) even when isolated from thermophilic organisms.
   Reason (R): Thermal stability is an inherent property of enzymes obtained from organisms living in hot vents and sulphur springs.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

9. In the structure of a nucleotide, the three components are:
   (a) nitrogenous base, ribose and phosphate
   (b) amino group, carboxyl group and R group
   (c) glycerol, fatty acid and phosphate
   (d) glucose, fructose and glycosidic bond

10. The quaternary structure of a protein refers to:
    (a) the sequence of amino acids
    (b) the arrangement of multiple polypeptide subunits
    (c) the formation of right-handed α-helix
    (d) the folding into a hollow woollen-ball shape

Section B — Very Short Answer (6 questions, 2 marks each)

1. Differentiate between primary and secondary metabolites with one example of each.
2. Why are lipids classified under macromolecules even though their molecular weight is less than 800 Da?
3. What is the zwitterionic form of an amino acid? Give one example.
4. Name the reducing and non-reducing ends of a polysaccharide chain. Why is starch called a storage polysaccharide?
5. List any four functions of proteins as given in the chapter.
6. What are the three components of a nucleotide? Name any two nucleotides.

Section C — Short Answer (5 questions, 3 marks each)

1. Describe the procedure used to obtain the acid-soluble and acid-insoluble fractions from a living tissue. What does each fraction represent?
2. Distinguish between homopolymers and heteropolymers with suitable examples from the chapter.
3. Explain the four levels of protein structure (primary, secondary, tertiary and quaternary) with one example for each.
4. What are polysaccharides? How do starch, glycogen and cellulose differ in structure and function?
5. Why are enzymes called biocatalysts? State any three differences between enzyme catalysts and inorganic catalysts.

Section D — Long Answer (3 questions, 5 marks each)

1. Describe the structure of proteins. Explain the primary, secondary, tertiary and quaternary structures with the help of a labelled diagram. (Labelled diagram description required)
2. What are enzymes? Explain the mechanism of enzyme action with reference to the formation of ES complex, transition state and lowering of activation energy. Support your answer with a suitable diagram.
3. Classify enzymes into six major classes giving one example and reaction type for each class. Also explain the role of cofactors with suitable examples.

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1

A student ground a piece of liver tissue with trichloroacetic acid and obtained two fractions. The retentate (acid-insoluble) fraction was found to contain proteins, nucleic acids and polysaccharides. When the same tissue was burnt completely, only ash remained which contained inorganic elements such as calcium and magnesium.

(i) What is the approximate molecular weight range of compounds present in the acid-soluble pool?
(ii) Why do membrane lipids appear in the acid-insoluble fraction?
(iii) Name any two inorganic constituents present in living tissues as given in the chapter.
(iv) Which fraction represents the cytoplasmic composition?

Case 2

Carbonic anhydrase catalyses the reaction CO₂ + H₂O → H₂CO₃. In the absence of the enzyme only 200 molecules of H₂CO₃ are formed per hour, while in its presence 600 000 molecules are formed per second. The enzyme works optimally at a particular temperature and pH; activity declines beyond these values.

(i) By what factor does the enzyme accelerate the reaction rate?
(ii) What is the role of the active site in enzyme catalysis?
(iii) Why does enzyme activity decline above the optimum temperature?
(iv) Name the type of inhibition in which the inhibitor resembles the substrate.