Question Bank — Respiration in Plants

Section A — MCQs (1 mark each)

1. The process of breakdown of complex organic molecules by oxidation within living cells to release energy is called:
   (a) Photosynthesis (b) Respiration (c) Fermentation (d) Combustion

2. In glycolysis, the enzyme that converts sucrose into glucose and fructose is:
   (a) Hexokinase (b) Invertase (c) Pyruvate decarboxylase (d) Alcohol dehydrogenase

3. Assertion (A): Plants do not have specialised organs for gaseous exchange like animals.
   Reason (R): Each plant part takes care of its own gas-exchange needs and there is very little transport of gases from one part to another.
   (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.

4. Number of ATP molecules directly synthesised during glycolysis from one glucose molecule is:
   (a) 2 (b) 4 (c) 6 (d) 8

5. Assertion (A): Respiratory pathway is considered amphibolic.
   Reason (R): It involves both breakdown (catabolism) and synthesis (anabolism) of respiratory intermediates.
   (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.

6. Pyruvic acid is converted to acetyl CoA in the mitochondrial matrix by the enzyme:
   (a) Citrate synthase (b) Pyruvate dehydrogenase (c) Lactate dehydrogenase (d) Alcohol dehydrogenase

7. In alcoholic fermentation, pyruvic acid is converted to ethanol and CO₂ by the enzymes:
   (a) Pyruvate decarboxylase and alcohol dehydrogenase (b) Hexokinase and phosphofructokinase (c) Lactate dehydrogenase only (d) Citrate synthase

8. The final hydrogen acceptor in the electron transport system is:
   (a) NAD⁺ (b) FAD (c) O₂ (d) Cytochrome c

9. Respiratory Quotient (RQ) value when tripalmitin (fat) is used as respiratory substrate is:
   (a) 1 (b) 0.7 (c) 0.9 (d) >1

10. In aerobic respiration of one glucose molecule, the theoretical net gain of ATP is:
    (a) 2 (b) 36 (c) 38 (d) 4

Section B — Very Short Answer (2 marks each)

1. Define respiration. Name the most common respiratory substrate.
2. Why do plants not require specialised respiratory organs? Give any two reasons.
3. What is glycolysis? Where does it occur in the cell?
4. Differentiate between aerobic respiration and fermentation (any two points).
5. What is the respiratory quotient? Give its value when carbohydrate is completely oxidised.
6. Name the two major components of ATP synthase. What is the role of F₀?

Section C — Short Answer (3 marks each)

1. Describe the fate of pyruvic acid under anaerobic conditions in yeast and in animal muscle cells.
2. Explain the amphibolic nature of the respiratory pathway with suitable examples.
3. Write the steps of oxidative decarboxylation of pyruvate. Where does it occur?
4. Give three assumptions made while calculating the net gain of 38 ATP molecules during aerobic respiration.
5. How does the electron transport system (ETS) lead to oxidative phosphorylation? Name the complexes involved.

Section D — Long Answer (5 marks each)

1. Describe the steps of glycolysis with the help of a schematic representation. How many ATP and NADH + H⁺ are produced in this pathway?
2. Explain the tricarboxylic acid (TCA) cycle with a labelled diagram. Mention the number of NADH + H⁺, FADH₂ and GTP/ATP generated per acetyl CoA.
3. What is fermentation? Compare alcoholic fermentation and lactic acid fermentation. Why is the energy released during fermentation much less than in aerobic respiration?

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

Case 1

During exercise, muscle cells experience temporary oxygen shortage. Under such conditions, pyruvic acid produced by glycolysis is converted to lactic acid. Yeasts, on the other hand, convert pyruvic acid to ethanol and CO₂ under anaerobic conditions. Both processes regenerate NAD⁺ from NADH + H⁺.

(i) Name the two types of fermentation mentioned above.
(ii) Write the enzymes involved in alcoholic fermentation.
(iii) Why is NAD⁺ regeneration essential in fermentation?
(iv) Calculate the net ATP gain when one glucose molecule is fermented to ethanol or lactic acid.

Case 2

In a biology practical, students measured the volumes of O₂ consumed and CO₂ released by germinating seeds using a respirometer. The RQ value obtained was approximately 0.7. When the same seeds were supplied with glucose solution, the RQ value changed to 1.

(i) Define respiratory quotient.
(ii) What does an RQ value of 0.7 indicate about the respiratory substrate?
(iii) Write the equation showing complete oxidation of tripalmitin and calculate its RQ.
(iv) Why is RQ rarely exactly 1 or 0.7 in living organisms?