Which of the following stomatal movements is primarily controlled by turgor pressure changes in guard cells?
Answer: C
Stomatal opening and closing are mainly controlled by hydroactive movements, which involve osmotic changes in guard cells due to potassium ion accumulation.
Q.222Medium
The phenomenon where plants exhibit different photosynthetic rates at different light intensities until a plateau is reached is called:
Answer: A
The light saturation point is the light intensity beyond which photosynthesis does not increase, indicating maximum rate of photosynthesis has been achieved.
Q.223Easy
Which element is essential for the synthesis of chlorophyll and is present at the center of the chlorophyll molecule?
Answer: B
Magnesium is the central atom in the porphyrin ring of chlorophyll molecules, making it essential for photosynthetic light absorption.
Q.224Medium
During active transport, which of the following statements is NOT correct?
Answer: D
Active transport is entirely dependent on metabolic activities and ATP availability. It requires energy to move substances against their concentration gradient.
Q.225Easy
Which of the following hormones primarily promotes stomatal closure in response to water stress?
Answer: B
Abscisic acid is the stress hormone that promotes stomatal closure during drought by reducing guard cell turgor pressure, thereby reducing water loss.
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Q.226Hard
The process of photorespiration in C3 plants is initiated when:
Answer: C
Photorespiration occurs when RuBisCO catalyzes oxygenation of RuBP instead of carboxylation, which happens under high O2 and low CO2 conditions.
Q.227Medium
Which of the following best explains why the guttation process occurs in plants during early morning?
Answer: B
Guttation occurs due to root pressure being high at night (stomata closed), causing water exudation through hydathodes at leaf tips.
Q.228Hard
The Km value of an enzyme indicates:
Answer: B
Km (Michaelis constant) is the substrate concentration at half Vmax, and it inversely represents enzyme affinity for substrate. Lower Km means higher affinity.
Q.229Hard
During the Z-scheme of photosynthesis, electrons move from PSII to PSI. What happens to electrons after they leave PSI?
Answer: B
In the Z-scheme, electrons from PSI reduce NADP+ to NADPH with the help of ferredoxin and NADP reductase enzyme.
Q.230Medium
Which of the following processes does NOT contribute to water transport in xylem?
Answer: C
Turgor pressure in sieve tubes is involved in phloem transport, not xylem transport. Water transport in xylem is driven by root pressure, capillarity, and transpirational pull.
Q.231Medium
A plant shows wilting despite soil having adequate water. This could be due to:
Answer: A
Wilting occurs when transpiration rate exceeds the water absorption rate by roots, even with adequate soil water, due to environmental stress or damaged vascular tissue.
Q.232Medium
The phenomenon where a plant loses its leaves in response to water shortage is controlled by which hormone?
Answer: A
Ethylene accumulates in leaf petioles during water stress, promoting abscission layer formation, leading to leaf shedding. ABA increases ethylene production.
Q.233Hard
In the electron transport chain of photosynthesis, the role of cytochrome b6f complex is to:
Answer: B
The cytochrome b6f complex transfers electrons between PSII and PSI while simultaneously pumping H+ ions into thylakoid lumen for chemiosmosis.
Q.234Hard
Which of the following C3 plants can show characteristics similar to CAM plants under water stress?
Answer: C
Some C3 plants show facultative CAM characteristics under severe drought stress, temporarily shifting to CAM metabolism to conserve water.
Q.235Medium
The phenomenon where stomata open partially to balance water loss and photosynthesis is called:
Answer: A
Stomatal oscillation refers to the dynamic opening and closing of stomata in response to changing environmental conditions to maintain optimal gas exchange while reducing water loss.
Q.236Easy
In phloem transport, the source is typically the:
Answer: B
The source in phloem transport is any photosynthetically active tissue, primarily mature leaves, which produce and load photosynthates into sieve tubes.
Q.237Medium
Which of the following best describes the role of plasmodesmata in plant physiology?
Answer: B
Plasmodesmata are cytoplasmic bridges allowing symplastic movement of water, minerals, and even macromolecules like proteins and RNA between adjacent cells.
Q.238Hard
A researcher observes that a plant's net photosynthesis decreases with increase in temperature above 35°C. This is primarily because:
Answer: B
At high temperatures, Rubisco and other enzymes denature reducing their activity. Additionally, stomata close to prevent excessive water loss, reducing CO2 availability and thus net photosynthesis.
Q.239Easy
Which of the following is the primary pigment involved in capturing light energy during photosynthesis?
Answer: A
Chlorophyll a is the primary pigment that directly participates in the photochemical reactions of both PSI and PSII, while other pigments act as accessory pigments.
Q.240Easy
The rate of transpiration is LEAST affected by which of the following factors?
Answer: B
Soil pH has minimal direct effect on transpiration rate. Primary factors affecting transpiration are light, humidity, temperature, and wind velocity.
