19. Following are certain statements with regard to plant respiration:
A. Metabolism of glucose into pyruvate through glycolysis generates NADH and not NADPH.
B. Metabolism of glucose through oxidative pentose phosphate cycle does not produce NADPH.
C. Cyanide forms a complex with haem iron of cytochromeoxidase leading to prevention of change in valency, which in turn stops electron transport in the respiratory chain.
D. Alternative oxidase is insensitive to cyanide and has higher km than that of cytochrome oxidase.
Which one of the following combination is correct?
(1) A,B and C          (2) B,C and D
(3) B and D           (4) A,C and D

Introduction

Plant respiration encompasses multiple interconnected biochemical pathways including glycolysis, oxidative phosphorylation, and alternative respiratory routes. Understanding the nuances of metabolite production and enzyme sensitivity to inhibitors is essential for grasping plant metabolic regulation.

Explanation of Each Statement

(A) Metabolism of glucose into pyruvate through glycolysis generates NADH and not NADPH.

• Correct. Glycolysis reduces NAD⁺ to NADH, supplying electrons for the mitochondrial electron transport chain.

(B) Metabolism of glucose through the oxidative pentose phosphate cycle does not produce NADPH.

• Incorrect. The oxidative pentose phosphate pathway is a major cellular source of NADPH, essential for anabolic reactions.

(C) Cyanide forms a complex with haem iron of cytochrome oxidase, preventing change in valency and stopping electron transport.

• Correct. Cyanide blocks cytochrome oxidase by binding to its heme iron center, halting electron transport and ATP synthesis.

(D) Alternative oxidase is insensitive to cyanide and has a higher Km than cytochrome oxidase.

• Correct. Alternative oxidase provides a cyanide-resistant electron transport route but requires higher substrate concentration due to higher Km.

Why Option (4) Is Correct

Statements A, C, and D correctly describe fundamental aspects of plant respiration concerning metabolite generation and enzyme inhibitor sensitivity. Statement B is factually inaccurate regarding NADPH production by the pentose phosphate pathway.

This knowledge is vital for plant physiology students preparing for exams and researchers studying cellular respiration.