Respiration

Abstract

Energy requirement for growth and functions in all living beings is met through ATP generated during respiration. Additionally in plants, light energy is conserved as ATP and NADPH, which are subsequently utilized for CO₂ assimilation. Besides, carbohydrates thus synthesized are consumed by animals as the primary source of energy. Though in animals lipids may also be consumed, in plants carbohydrates remain the main energy source. Plants store carbohydrates mainly as starch since it is osmotically inactive. All carbon accumulation in plants is the result of photosynthesis, which remains the source of energy as well as for biosynthesis of various other biomolecules. In cells hexose monophosphate pool constitutes an important component of carbohydrate metabolism. Hexose monophosphate pool maintained in cells consists of glucose 6-phosphate, glucose 1-phosphate, and fructose 6-phosphate. At the sinks, sucrose translocated from source is consumed during respiration. Respiration is an exergonic redox reaction with ΔG^0′ value −5760 kJ.mol⁻¹ of sucrose. Sucrose is oxidized to CO₂ coupled with the reduction of O₂ to water as follows:

Multiple-Choice Questions

• 1. While studying glycolysis, adding iodoacetate to the medium leads to accumulation of:

  • (a) Fructose 6-phosphate

  • (b) 3-Phosphoglyceraldehyde

  • (c) 1,3-Bisphosphoglycerate

  • (d) Fructose 1,6-bisphosphate

• 2. Net gain of energy during conversion of one glucose molecule to two molecules of pyruvate in glycolysis is:

  • (a) 2 ATP + 2 NADH

  • (b) 4 ATP

  • (c) 2 NADH

  • (d) 2 ATP

• 3. Which of the following reaction in glycolysis is not reversible?

  • (a) Glucose 6-phosphate to fructose 6-phosphate

  • (b) Glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate

  • (c) 2-Phosphoglycerate to 2-phosphoenolpyruvate

  • (d) Fructose 6-phosphate to fructose 1,6-bisphosphate

• 4. Under anaerobic conditions in the cell, fermentation is necessary because:

  • (a) Lactate is produced.

  • (b) Ethanol produced leaches out of the cell.

  • (c) NADH is oxidized to NAD⁺.

  • (d) ATP is produced.

• 5. Pyruvate dehydrogenase is active when the enzyme is:

  • (a) Dephosphorylated

  • (b) Phosphorylated

  • (c) Reduced

  • (d) Oxidized

• 6. TCA has got amphibolic role in cell metabolism because:

  • (a) Both ATP and NADH are produced in the cycle.

  • (b) It is the main pathway for generation of metabolic form of energy.

  • (c) It is responsible for oxidative as well as reductive reactions.

  • (d) Precursors of various pathways are also produced during the cycle besides their oxidation.

• 7. Glycolysis in plants differs from that of in animals in the presence of:

  • (a) Fermentation in animals

  • (b) PP_i-dependent phosphofructokinase

  • (c) Transport of glycolytic NADH to mitochondria

  • (d) Synthesis of pyruvate from PEP in animal cells

• 8. Antimycin A inhibits electron transport at the:

  • (a) UQ-binding site of Complex I

  • (b) UQ-binding site of Complex III

  • (c) O₂-binding site of Complex IV

  • (d) With Complex II

• 9. The inhibitor for cyanide respiration is:

  • (a) Rotenone

  • (b) Antimycin A

  • (c) Salicylhydroxamin

  • (d) Cyanide

• 10. The number of ATP equivalents produced during complete oxidation of one glucose molecule is:

  • (a) 30–32

  • (b) 32–34

  • (c) 34–36

  • (d) None of the above

Answers

1. d	2. a	3. d	4. c	5. a	6. d	7. b
8. b	9. c	10. a