Plant Physiology
CAM plants open their stomata primarily at:
A
Daytime
B
Night
C
Noon
D
Continuously
CAM plants open stomata at night to minimize water loss and fix CO2 into malic acid, which is released during the day for photosynthesis.
The compensation point of a plant is the light intensity at which:
A
Photosynthesis equals respiration
B
Maximum photosynthesis occurs
C
Photosynthesis exceeds respiration
D
Respiration exceeds photosynthesis
Correct Answer:
A. Photosynthesis equals respiration
At compensation point, the rate of photosynthesis equals the rate of respiration, resulting in no net gas exchange.
Which of the following processes does NOT require energy (ATP)?
A
Active transport
B
Diffusion
C
Protein synthesis
D
Photophosphorylation
Correct Answer:
B. Diffusion
Diffusion is a passive process that does not require ATP; substances move along the concentration gradient.
The ascent of sap in tall trees is best explained by:
A
Root pressure alone
B
Capillarity alone
C
Cohesion-tension theory
D
Osmotic pressure
Correct Answer:
C. Cohesion-tension theory
The cohesion-tension theory explains water transport in tall trees through cohesive forces between water molecules and tension created by transpiration.
Root pressure is primarily responsible for:
A
Pulling water upwards in xylem
B
Pushing water upwards in xylem
C
Water transport through phloem
D
Transpiration
Correct Answer:
B. Pushing water upwards in xylem
Root pressure is a positive pressure that pushes water upwards in xylem due to active uptake of minerals by root cells.
The Casparian strip is found in which region of the root?
A
Root cap
B
Endodermis
C
Cortex
D
Xylem
Correct Answer:
B. Endodermis
The Casparian strip is a waxy impermeable band in the endodermis that blocks apoplastic water movement and ensures selective uptake.
Which of the following is a consequence of excessive transpiration?
A
Wilting of leaves
B
Increased photosynthesis
C
Enhanced nutrient absorption
D
Stomatal opening
Correct Answer:
A. Wilting of leaves
Excessive transpiration leads to water loss exceeding water uptake, causing wilting due to loss of turgor pressure in cells.
The phenomenon where plants grow towards light is called:
A
Hydrotropism
B
Phototropism
C
Geotropism
D
Thigmotropism
Correct Answer:
B. Phototropism
Phototropism is the directional growth response of plants towards light, mediated by differential distribution of auxin.
Which hormone promotes cell elongation and is responsible for apical dominance?
A
Cytokinin
B
Auxin
C
Gibberellin
D
Ethylene
Auxin promotes cell elongation and causes apical dominance by inhibiting lateral bud growth through differential distribution.
The opening and closing of stomata is primarily regulated by:
A
Abscisic acid
B
Turgor pressure changes in guard cells
C
Ethylene
D
Gibberellic acid
Correct Answer:
B. Turgor pressure changes in guard cells
Turgor pressure changes in guard cells due to osmotic changes regulate stomatal opening. ABA plays a secondary regulatory role.
