Showing 121–130 of 207 questions
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 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.
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 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.
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 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.
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 turgor pressure in plant cells is maintained by which osmotically active substances?
A
Cellulose and starch
B
Soluble sugars, organic acids, and mineral ions
C
Proteins and lipids
D
Chlorophyll and carotenoids
Correct Answer:
B. Soluble sugars, organic acids, and mineral ions
Explanation:
Osmotically active solutes like glucose, sucrose, malate, and K⁺ ions accumulate in vacuoles to maintain turgor pressure and cell rigidity.
Guttation in plants occurs due to:
A
Transpiration
B
Root pressure and high humidity conditions
C
Photorespiration
D
Osmotic stress
Correct Answer:
B. Root pressure and high humidity conditions
Explanation:
Guttation is the exudation of xylem sap through hydathodes, caused by positive root pressure, especially in early morning when transpiration is low.
The quantum yield of photosynthesis (φ) represents:
A
The number of CO₂ molecules fixed per photon absorbed
B
The wavelength of light absorbed
C
The rate of electron transport
D
The concentration of chlorophyll
Correct Answer:
A. The number of CO₂ molecules fixed per photon absorbed
Explanation:
Quantum yield is the ratio of CO₂ fixed to photons absorbed, typically 0.05-0.1 (5-10 CO₂ per 100 photons).
