22. Following are certain statements regarding respiratory metabolism on plants:
A. Respiratory quotient during partial breakdown of carbohydrate (alcoholic fermentation) will be infinity.
B. Respiratory quotient indirectly provides inforrnation about (i) nature of the substrate used for respiration and (ii) the relative rate of competing respiratory processes.
C. Breakdown of organic adds in mature fruit will exhibit a respiratory quotient value of more than one since organic acids are relatively oxygen-rich compared to other common substrates.
D. Anabolic metabolism can influence respiratory quotient by removing reduction equivalents for respiration leading to decrease in oxygen uptake.
Which one of the following combination of the above statement is correct?
(1) Only A (2) Only B and C
(3) Only D (4) A,B,C and D
Introduction
The respiratory quotient (RQ) is a vital parameter offering insights into the respiratory metabolism of plants. It reflects substrate utilization, competition among respiratory processes, and metabolic shifts during development and stress, impacting plant growth and productivity.
Explanation of Each Statement
(A) Respiratory quotient during partial breakdown of carbohydrate (alcoholic fermentation) will be infinity.
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Correct. Alcoholic fermentation consumes glucose but produces CO₂ without O₂ consumption, leading to an infinite RQ as oxygen uptake approaches zero.
(B) Respiratory quotient indirectly provides information about substrate nature and relative rates of competing respiratory processes.
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Correct. RQ helps deduce if carbohydrates, fats, or proteins are being metabolized and indicates prevalent respiratory pathway activity.
(C) Breakdown of organic acids in mature fruit results in RQ values more than one, as organic acids are oxygen-rich substrates.
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Correct. This occurs due to excess CO₂ production relative to O₂ consumption in organic acid catabolism.
(D) Anabolic metabolism reduces respiratory quotient by utilizing reduction equivalents, decreasing oxygen uptake.
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Correct. Anabolism diverts electrons, lowering respiration-driven oxygen consumption and thus affecting the RQ.
Why All Statements Are Correct
Each statement describes a distinct aspect of RQ in plants: its theoretical limits, biological interpretation, substrate dependency, and metabolic influence. Together, they illustrate the complexity of plant respiratory physiology.
This comprehensive understanding supports plant biologists and agricultural scientists in studying and manipulating plant metabolism.
