The rate of photosynthesis is maximum at which wavelength of light?
Answer: B
Red light (600-700 nm) is most effectively used in photosynthesis, followed by blue light. Green light is poorly absorbed.
Q.2Medium
Which pigment is responsible for absorbing light energy in photosystem II?
Answer: C
P680 is a special chlorophyll a molecule in the reaction center of PSII that absorbs light at 680 nm wavelength.
Q.3Medium
In C4 plants, the first stable compound formed during photosynthesis is:
Answer: B
In C4 plants, CO2 combines with PEP to form oxaloacetate (4-carbon compound) in the mesophyll cells, unlike C3 plants where 3-PGA is formed.
Q.4Medium
Which of the following statements about transpiration is correct?
Answer: C
Transpiration increases with decrease in humidity as the vapor pressure gradient between leaf and atmosphere increases.
Q.5Medium
The opening and closing of stomata is primarily regulated by:
Answer: B
Turgor pressure changes in guard cells due to osmotic changes regulate stomatal opening. ABA plays a secondary regulatory role.
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Q.6Medium
Which of the following is a consequence of excessive transpiration?
Answer: A
Excessive transpiration leads to water loss exceeding water uptake, causing wilting due to loss of turgor pressure in cells.
Q.7Medium
The Casparian strip is found in which region of the root?
Answer: B
The Casparian strip is a waxy impermeable band in the endodermis that blocks apoplastic water movement and ensures selective uptake.
Q.8Medium
Root pressure is primarily responsible for:
Answer: B
Root pressure is a positive pressure that pushes water upwards in xylem due to active uptake of minerals by root cells.
Q.9Medium
The compensation point of a plant is the light intensity at which:
Answer: A
At compensation point, the rate of photosynthesis equals the rate of respiration, resulting in no net gas exchange.
Q.10Medium
CAM plants open their stomata primarily at:
Answer: B
CAM plants open stomata at night to minimize water loss and fix CO2 into malic acid, which is released during the day for photosynthesis.
Q.11Medium
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.12Medium
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.13Medium
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.14Medium
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.15Medium
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.16Medium
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.17Medium
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.18Medium
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.19Medium
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.20Medium
The compensation point in photosynthesis is defined as the light intensity at which:
Answer: B
At compensation point, the rate of CO2 fixation in photosynthesis equals the rate of CO2 release in respiration, resulting in net zero gas exchange.
