Which of the following statements about stomatal conductance is correct?
A
It remains constant regardless of humidity
B
It increases with decreasing light intensity
C
It is directly proportional to stomatal aperture and inversely related to diffusion path length
D
It is independent of guard cell turgor pressure
Correct Answer:
C. It is directly proportional to stomatal aperture and inversely related to diffusion path length
Explanation:
Stomatal conductance (gs) is the rate of gas diffusion through stomata, dependent on aperture width and inversely on distance (g = A/L).
The Hatch-Slack cycle in C4 plants first produces which compound?
A
Oxaloacetate (4-carbon)
B
3-Phosphoglycerate (3-carbon)
C
Malate (4-carbon)
D
Pyruvate (3-carbon)
Correct Answer:
A. Oxaloacetate (4-carbon)
Explanation:
In C4 photosynthesis, CO₂ combines with phosphoenolpyruvate (PEP) to form oxaloacetate (4-carbon), catalyzed by PEP carboxylase.
The phenomenon of etiolation in plants is characterized by:
A
Increased chlorophyll synthesis in darkness
B
Elongated internodes, pale color, and reduced photosynthetic capacity
C
Increased leaf area in low light
D
Enhanced root development
Correct Answer:
B. Elongated internodes, pale color, and reduced photosynthetic capacity
Explanation:
Etiolation is the adaptation to grow in darkness: shoots elongate, leaves remain pale (no chlorophyll), and seedlings appear yellowish.
The transpiration pull mechanism in xylem transport depends on which principle?
A
Osmotic gradient
B
Cohesion-tension theory and water's high surface tension
C
Active transport of ions
D
Pressure exerted by companion cells
Correct Answer:
B. Cohesion-tension theory and water's high surface tension
Explanation:
Transpiration creates negative pressure (tension) in xylem; water cohesion allows continuous columns to be pulled upward against gravity.
Which plant hormone promotes fruit ripening and is commercially used in India for tomato and mango maturation?
A
Gibberellin
B
Ethylene
C
Cytokinin
D
Auxin
Correct Answer:
B. Ethylene
Explanation:
Ethylene (C₂H₄) is the ripening hormone that triggers color change, softening, and aroma development in climacteric fruits.
The non-cyclic photophosphorylation in photosystem II produces:
A
ATP only
B
NADPH only
C
Both ATP and NADPH, and releases O₂
D
Glucose directly
Correct Answer:
C. Both ATP and NADPH, and releases O₂
Explanation:
Non-cyclic photophosphorylation involves PSII and PSI, producing ATP, NADPH, and O₂ from water photolysis.
In the electron transport chain of chloroplasts, which complex transfers electrons from water to plastoquinone?
A
Cytochrome b₆f complex
B
Photosystem II (PSII)
C
Photosystem I (PSI)
D
ATP synthase
Correct Answer:
B. Photosystem II (PSII)
Explanation:
PSII catalyzes photolysis of water at the oxygen-evolving complex, transferring electrons to plastoquinone in the thylakoid membrane.
The double fertilization process unique to angiosperms results in the formation of:
A
Embryo and endosperm
B
Seed coat and hilum
C
Ovule and integuments
D
Pollen and stigma
Correct Answer:
A. Embryo and endosperm
Explanation:
One sperm nucleus fertilizes the egg (embryo), another fuses with polar nuclei (endosperm); this endosperm provides nutritive tissue for the developing embryo.
Which of the following is the primary pigment responsible for capturing light energy in photosynthesis?
A
Chlorophyll a
B
Chlorophyll b
C
Xanthophyll
D
Carotenoid
Correct Answer:
A. Chlorophyll a
Explanation:
Chlorophyll a is the primary pigment that directly participates in the light reactions of photosynthesis and forms the reaction centre of both photosystems.
The reduction phase of Calvin cycle produces which molecule as the final product?
A
Pyruvate
B
Glucose
C
Glyceraldehyde-3-phosphate
D
Oxaloacetate
Correct Answer:
C. Glyceraldehyde-3-phosphate
Explanation:
G3P (Glyceraldehyde-3-phosphate) is the final product of the reduction phase where 3-PG is reduced using ATP and NADPH from light reactions.
