Q.35 Determine the correctness or otherwise of the following Assertion (a) and Reason (r).
Assertion: Plants convert fatty acids into glucose.
Reason: Plants have peroxisomes.
(A) Both (a) and (r) are true but (r) is not the correct reason for (a)
(B) Both (a) and (r) are true and (r) is the correct reason for (a)
(C) (a) is true but (r) is false
(D) (a) is false but (r) is true
Plants possess a unique metabolic capability absent in animals: converting stored fatty acids into glucose during seed germination when carbohydrate reserves deplete. This process sustains early growth until photosynthesis activates. The assertion claims this conversion occurs, while the reason cites peroxisomes, requiring evaluation of both truth and causal linkage.
Assertion and Reason Analysis
Assertion (a): Plants convert fatty acids into glucose.
False in strict biochemical terms. While plants perform β-oxidation of fatty acids to acetyl-CoA in glyoxysomes (specialized peroxisomes), the glyoxylate cycle bypasses Krebs cycle decarboxylations to yield succinate and malate, feeding gluconeogenesis. However, net conversion yields carbohydrates but not free glucose directly—glucose precursors form via gluconeogenesis from these C4 intermediates.
Reason (r): Plants have peroxisomes.
True. Peroxisomes (including glyoxysomes in germinating seeds) house β-oxidation and glyoxylate cycle enzymes like isocitrate lyase and malate synthase, enabling fat-to-sugar interconversion.
Correct Answer
Option (D) (a) is false but (r) is true.
The assertion overstates direct “glucose” production; plants synthesize glucose-6-phosphate via gluconeogenesis from glyoxylate cycle products, not direct conversion. Peroxisomes exist but do not solely explain the process—glyoxysomes specifically enable it.
| Statement | Truth Value | Biochemical Basis |
|---|---|---|
| Assertion (a) | False | Fatty acids → acetyl-CoA → glyoxylate cycle → malate → gluconeogenesis (PEP → G6P), not direct glucose |
| Reason (r) | True | Peroxisomes/glyoxysomes perform β-oxidation and glyoxylate bypass |
| Relation | No causation needed | (r) true independently; specialized glyoxysomes key for cycle |
Option Explanations
(A) Both true but (r) not correct reason: Incorrect. Assertion false; peroxisomes necessary but reason doesn’t address conversion mechanism directly.
(B) Both true and (r) correct reason: Incorrect. Assertion false; while peroxisomes host the pathway, simplistic reason ignores glyoxylate specificity.
(C) (a) true but (r) false: Incorrect. Plants do interconvert via glyoxylate cycle (e.g., castor bean seedlings), and peroxisomes undeniably present.
(D) (a) false but (r) true: Correct. Assertion imprecise—plants convert fats to sucrose/gluconeogenic precursors, not “glucose” outright; peroxisomes confirmed universal in plants.
Biochemical Mechanism
Fatty acids undergo β-oxidation in glyoxysomes, yielding acetyl-CoA. The glyoxylate cycle (isocitrate → glyoxylate + succinate via isocitrate lyase; acetyl-CoA + glyoxylate → malate via malate synthase) conserves carbons, producing malate exported to cytosol/mitochondria for gluconeogenesis: malate → OAA → PEP → glucose-6-P. This fuels seedling growth, relevant to plant biotech for oilseed engineering.
For molecular biology contexts, manipulating glyoxylate enzymes enhances lipid-to-carbohydrate conversion in microbial systems or transgenic plants.
