Biomolecules: Class 12 Important Questions with Answers

Practice set: test yourself

Try every question before looking at the answers below. 64 or more out of 80 means you are ready for the board.

C. Very short answer (1 mark each)

1. Define a monosaccharide.
2. Name the products of hydrolysis of maltose.
3. What is a zwitter ion?
4. Name a fibrous protein.
5. What is invert sugar?
6. Give the disease caused by lack of vitamin B₁.
7. Which bases pair with three H-bonds?
8. What is a nucleoside?
9. What is the anomeric carbon of fructose?
10. Name the three types of RNA.

D. Short answer I (2 marks each)

1. Write the reactions of glucose with Br₂ water and HNO₃.
2. Give two observations the open chain of glucose cannot explain.
3. Distinguish amylose and amylopectin.
4. Explain the amphoteric nature of amino acids.
5. Write two differences between DNA and RNA.
6. What is denaturation? Give an example.
7. Name two water-soluble vitamins and their deficiency diseases.
8. What are essential amino acids? Give two examples.

Rough work

E. Short answer II (3 marks each)

1. How was the open-chain structure of glucose established? (three reactions)
2. Explain the four levels of protein structure.
3. Write the structures of a nucleoside and a nucleotide in words, with the link positions.
4. Explain why sucrose is called invert sugar.
5. Classify carbohydrates with examples.
6. Explain the complementary base pairing in DNA.

F. Long answer (5 marks each)

1. (a) Draw the Haworth structures of α- and β-D-glucopyranose. (b) What are anomers? (c) Why does glucose not give Schiff's test?
2. (a) Write the deficiency diseases of vitamins A, B₁, C, D, E and K. (b) Why must water-soluble vitamins be taken regularly? (c) Why can vitamin A be stored?

G. HOTS (higher-order thinking)

1. Why is cellulose not digested by humans though it is made of glucose?
2. Why are amino acids high-melting solids?
3. Why does a boiled egg become hard?
4. What happens to the optical rotation when sucrose is hydrolysed?

20 MCQs

1. Glucose + HI (heat)
   (a) gluconic acid (b) saccharic acid (c) n-hexane (d) sorbitol
2. Non-reducing sugar
   (a) sucrose (b) maltose (c) lactose (d) glucose
3. Glucose + Br₂ water
   (a) saccharic acid (b) oxime (c) hexane (d) gluconic acid
4. Hydrolysis of lactose
   (a) glucose only (b) glucose + galactose (c) glucose + fructose (d) galactose only
5. Cellulose units
   (a) α-glucose (b) β-glucose (c) fructose (d) galactose
6. Optically inactive amino acid
   (a) alanine (b) lysine (c) valine (d) glycine
7. Primary structure means
   (a) amino-acid sequence (b) helix (c) folding (d) subunits
8. Vitamin for blood clotting
   (a) A (b) C (c) K (d) D
9. Scurvy is due to lack of
   (a) vitamin A (b) vitamin E (c) vitamin D (d) vitamin C
10. Base only in RNA
    (a) thymine (b) uracil (c) adenine (d) guanine
11. Nucleotides are linked by
    (a) peptide (b) glycosidic (c) phosphodiester (d) ionic bonds
12. Bond stabilising the α-helix
    (a) hydrogen (b) disulphide (c) ionic (d) peptide
13. Glucose pentaacetate shows
    (a) –CHO (b) five –OH (c) straight chain (d) ring
14. Pyranose ring forms between
    (a) C1–C4 (b) C2–C5 (c) C1–C5 (d) C1–C6
15. Fat-soluble vitamin
    (a) C (b) B₁₂ (c) B₁ (d) D
16. Denaturation leaves intact the
    (a) primary (b) tertiary (c) secondary (d) quaternary structure
17. DNA sugar
    (a) 2-deoxyribose (b) ribose (c) glucose (d) fructose
18. Invert sugar is
    (a) glucose + galactose (b) starch (c) maltose (d) glucose + fructose
19. Animal starch
    (a) cellulose (b) glycogen (c) amylose (d) sucrose
20. Vitamin B₆
    (a) thiamine (b) riboflavin (c) pyridoxine (d) ascorbic acid

1 (c) · 2 (a) · 3 (d) · 4 (b) · 5 (b) · 6 (d) · 7 (a) · 8 (c) · 9 (d) · 10 (b) · 11 (c) · 12 (a) · 13 (b) · 14 (c) · 15 (d) · 16 (a) · 17 (a) · 18 (d) · 19 (b) · 20 (c)

Assertion–Reason (6)

(a) Both true, R explains A. (b) Both true, R does not explain A. (c) A true, R false. (d) A false, R true.

1. A: Sucrose is non-reducing. R: Its glycosidic link uses both anomeric carbons.
2. A: Glucose does not give Schiff's test. R: Glucose exists mainly in the cyclic form.
3. A: Vitamin C must be taken regularly. R: It is fat-soluble.
4. A: DNA strands are complementary. R: A pairs with T and G with C.
5. A: Amino acids are amphoteric. R: They exist as zwitter ions.
6. A: Cellulose is digested by humans. R: It contains β-glucose units.

Key: 1 (a) · 2 (a) · 3 (c) · 4 (a) · 5 (a) · 6 (d)

Answers to the practice set