Which of the following is the primary source of energy for plant cells?
Answer: A
Photosynthesis is the primary source of energy for plant cells as it converts light energy into chemical energy in the form of glucose.
Q.2Medium
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.3Medium
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.4Easy
The dark reaction of photosynthesis does not require which of the following?
Answer: C
Dark reactions (Calvin cycle) do not directly require light; they use ATP and NADPH produced from light reactions to fix CO2.
Q.5Medium
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.
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Q.6Medium
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.7Medium
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.
Q.8Easy
Which hormone promotes cell elongation and is responsible for apical dominance?
Answer: B
Auxin promotes cell elongation and causes apical dominance by inhibiting lateral bud growth through differential distribution.
Q.9Easy
The phenomenon where plants grow towards light is called:
Answer: B
Phototropism is the directional growth response of plants towards light, mediated by differential distribution of auxin.
Q.10Medium
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.11Medium
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.12Medium
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.13Hard
The ascent of sap in tall trees is best explained by:
Answer: C
The cohesion-tension theory explains water transport in tall trees through cohesive forces between water molecules and tension created by transpiration.
Q.14Easy
Which of the following processes does NOT require energy (ATP)?
Answer: B
Diffusion is a passive process that does not require ATP; substances move along the concentration gradient.
Q.15Medium
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.16Medium
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.17Hard
Which of the following is a characteristic of phloem transport?
Answer: C
Phloem transport is bidirectional and can move sugars upwards or downwards depending on source-sink relationships and requires metabolic energy.
Q.18Hard
The ratio of photosynthesis to respiration in a plant is represented by:
Answer: D
Apparent photosynthesis (net photosynthesis) represents the actual photosynthesis minus respiration measured as the gaseous exchange in the plant.
Q.19Hard
Which enzyme catalyzes the fixation of CO2 in the Calvin cycle?
Answer: B
RuBisCO catalyzes the carboxylation of RuBP with CO2 to form 3-phosphoglycerate, the first stable product of dark reactions in C3 plants.
Q.20Easy
During photosynthesis, the light-independent reactions occur in which compartment of the chloroplast?
Answer: A
The Calvin cycle (light-independent reactions) takes place in the stroma of chloroplasts, where CO2 is fixed and glucose is synthesized.
