Q56. Identify the CORRECT statements from the following
P. Lenticels are the small pores present on the surface of the stem or branches of woody plants
Q. Glyoxysomes contain chlorophyll molecules in their thylakoid membranes
R. The enzyme ribulose 1,5 bisphosphate carboxylase is otherwise known as carboxydehydrase
S. 18 ATP and 12 NADPH molecules are utilized for fixing 6 molecules of CO2 in the dark reaction of photosynthesis
(A) P, Q
(B) P, R
(C) Q, R
(D) P, S
Lenticels facilitate gas exchange in woody stems, while statements about glyoxysomes, Rubisco naming, and Calvin cycle ATP/NADPH stoichiometry must be verified for accuracy in this multiple-choice question. The correct answer is (D) P, S.
Statement Analysis
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P (Correct): Lenticels are small, lens-shaped pores formed by loosely arranged cork cells on the periderm of stems and roots in woody plants, allowing oxygen entry for respiration and water vapor/CO2 exit.
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Q (Incorrect): Glyoxysomes are microbodies in plant cells (especially germinating seeds) containing enzymes for the glyoxylate cycle to convert fats to sugars; they lack thylakoid membranes and chlorophyll, which are exclusive to chloroplasts.
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R (Incorrect): Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) is its standard name; “carboxydehydrase” is not a recognized term for this enzyme.
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S (Correct): In the Calvin cycle (dark reaction), fixing 6 CO2 yields one glucose; this requires 18 ATP (9 for reduction, 9 for regeneration) and 12 NADPH (2 per CO2).
Introduction to Key Concepts
In plant biology for GATE Life Sciences, understanding lenticels, glyoxysomes, Rubisco (ribulose 1,5-bisphosphate carboxylase), and Calvin cycle ATP NADPH usage is crucial for photosynthesis MCQs. This article breaks down Q56 statements on lenticels in woody plants, glyoxysome contents, Rubisco naming, and dark reaction energetics to identify correct options like P and S.
Lenticels in Woody Plants (Statement P)
Lenticels are small pores on the surface of stems or branches in woody plants, formed due to phellogen activity in the periderm. They enable gaseous exchange (O2 intake for respiration) despite the bark barrier, unlike stomata on young stems.
Glyoxysomes and Chlorophyll Myth (Statement Q)
Glyoxysomes, specialized peroxisomes, house glyoxylate cycle enzymes (isocitrate lyase, malate synthase) for lipid-to-carb conversion in seeds. They contain no chlorophyll or thylakoid membranes—those define chloroplast light reactions.
Rubisco Enzyme Naming (Statement R)
Ribulose 1,5-bisphosphate carboxylase (Rubisco) catalyzes CO2 fixation in the Calvin cycle but is never termed “carboxydehydrase.” This outdated or erroneous name disqualifies the statement.
Calvin Cycle Energetics (Statement S)
For fixing 6 CO2 into one glucose in photosynthesis dark reaction: 12 NADPH reduces 3-PGA to G3P, while 18 ATP powers phosphorylation and RuBP regeneration (6 ATP for fixation, 12 more total).
| Statement | Correct? | Reason |
|---|---|---|
| P: Lenticels on woody stems | Yes | Pores for gas exchange |
| Q: Glyoxysomes have chlorophyll thylakoids | No | No thylakoids/chlorophyll |
| R: Rubisco as carboxydehydrase | No | Incorrect name |
| S: 18 ATP, 12 NADPH for 6 CO2 | Yes | Standard Calvin cost |
GATE Exam Tips
Focus on photosynthesis energetics and organelle distinctions for competitive exams. Practice PYQs matching “lenticels glyoxysomes Rubisco Calvin cycle ATP NADPH” to master options like (D) P, S.
