Q.1 Which plant hormone is primarily responsible for cell elongation?
Auxin
Cytokinin
Gibberellin
Abscisic acid
Explanation - Auxins promote cell elongation by loosening cell walls, facilitating growth.
Correct answer is: Auxin
Q.2 Which process in plants converts light energy into chemical energy?
Respiration
Photosynthesis
Transpiration
Fermentation
Explanation - Photosynthesis uses chlorophyll to capture light energy and convert it into chemical energy in the form of glucose.
Correct answer is: Photosynthesis
Q.3 Which pigment is mainly responsible for capturing light energy in photosynthesis?
Chlorophyll
Carotene
Xanthophyll
Anthocyanin
Explanation - Chlorophyll absorbs light energy, primarily in the blue and red wavelengths, for photosynthesis.
Correct answer is: Chlorophyll
Q.4 The opening and closing of stomata are regulated by:
Auxin concentration
Guard cells
Phloem pressure
Xylem tension
Explanation - Guard cells control stomatal aperture by changing turgor pressure, regulating gas exchange and transpiration.
Correct answer is: Guard cells
Q.5 Transpiration pull is mainly due to:
Root pressure
Cohesion and adhesion of water
Active transport of ions
Osmotic pressure in phloem
Explanation - Water molecules stick together (cohesion) and to xylem walls (adhesion), creating a continuous column that pulls water upward.
Correct answer is: Cohesion and adhesion of water
Q.6 Which hormone is involved in breaking seed dormancy?
Gibberellin
Abscisic acid
Ethylene
Cytokinin
Explanation - Gibberellins stimulate enzymes like amylase to mobilize stored food and initiate germination.
Correct answer is: Gibberellin
Q.7 Xylem is responsible for:
Transport of water and minerals
Transport of sugars
Transport of amino acids
Transport of hormones
Explanation - Xylem conducts water and dissolved minerals from roots to other parts of the plant.
Correct answer is: Transport of water and minerals
Q.8 Which of the following is a primary site of photosynthesis in C3 plants?
Mesophyll cells
Bundle sheath cells
Phloem
Cortex
Explanation - In C3 plants, mesophyll cells contain chloroplasts where the Calvin cycle occurs.
Correct answer is: Mesophyll cells
Q.9 Which gas is released during photosynthesis?
Oxygen
Carbon dioxide
Nitrogen
Hydrogen
Explanation - During the light-dependent reactions, water is split and oxygen is released as a by-product.
Correct answer is: Oxygen
Q.10 Phloem transports:
Sugars from leaves to roots
Water from roots to leaves
Minerals from soil
Proteins from roots to leaves
Explanation - Phloem conducts organic compounds like sucrose from source (leaves) to sink (roots, fruits).
Correct answer is: Sugars from leaves to roots
Q.11 Which plant hormone is associated with leaf abscission?
Abscisic acid
Auxin
Gibberellin
Cytokinin
Explanation - Abscisic acid promotes senescence and leaf drop, especially under stress conditions.
Correct answer is: Abscisic acid
Q.12 C4 plants minimize photorespiration by:
Separating light and dark reactions in time
Spatial separation of initial CO2 fixation and Calvin cycle
Using CAM pathway
Reducing stomatal opening completely
Explanation - C4 plants fix CO2 in mesophyll cells and run the Calvin cycle in bundle sheath cells to reduce photorespiration.
Correct answer is: Spatial separation of initial CO2 fixation and Calvin cycle
Q.13 Which part of the chloroplast contains chlorophyll?
Thylakoid membrane
Stroma
Outer membrane
Intermembrane space
Explanation - Chlorophyll is embedded in the thylakoid membranes, where light-dependent reactions occur.
Correct answer is: Thylakoid membrane
Q.14 During photophosphorylation, ATP is synthesized in the presence of:
Light
Darkness
Oxygen only
CO2 only
Explanation - Photophosphorylation uses light energy to generate ATP in chloroplasts.
Correct answer is: Light
Q.15 Which plant hormone accelerates fruit ripening?
Ethylene
Cytokinin
Auxin
Abscisic acid
Explanation - Ethylene is a gaseous hormone that triggers ripening of fruits and senescence in plants.
Correct answer is: Ethylene
Q.16 Which process releases energy by breaking down glucose in plants?
Photosynthesis
Respiration
Transpiration
Germination
Explanation - Cellular respiration breaks down glucose into CO2 and water, releasing energy in the form of ATP.
Correct answer is: Respiration
Q.17 Which is the major nitrogen-assimilating enzyme in plants?
Nitrate reductase
Rubisco
ATP synthase
Amylase
Explanation - Nitrate reductase reduces nitrate to nitrite, a key step in nitrogen assimilation in plants.
Correct answer is: Nitrate reductase
Q.18 Guard cells become turgid when:
Potassium ions enter
Calcium ions leave
Water exits
Starch breaks down
Explanation - K+ influx into guard cells lowers water potential, causing water to enter by osmosis, making them turgid and opening stomata.
Correct answer is: Potassium ions enter
Q.19 CAM plants fix CO2 at night to:
Reduce water loss
Increase photorespiration
Accelerate growth
Store sugars in roots
Explanation - Crassulacean Acid Metabolism (CAM) allows stomata to open at night, conserving water in arid conditions.
Correct answer is: Reduce water loss
Q.20 Which vitamin is synthesized in plants during photosynthesis and is essential for humans?
Vitamin C
Vitamin D
Vitamin B12
Vitamin K
Explanation - Plants synthesize ascorbic acid (Vitamin C) during photosynthesis, essential for humans as an antioxidant and cofactor.
Correct answer is: Vitamin C
Q.21 Which compound acts as an energy currency in plants?
ATP
NADPH
Glucose
Chlorophyll
Explanation - ATP stores and transfers energy needed for various metabolic processes in plants.
Correct answer is: ATP
Q.22 Which is the main site for transpiration in plants?
Leaves
Roots
Stems
Flowers
Explanation - Most water loss occurs through stomata in leaves during transpiration.
Correct answer is: Leaves
Q.23 Which ion is crucial for opening and closing of stomata?
Potassium
Sodium
Calcium
Magnesium
Explanation - Potassium ion flux in guard cells regulates turgor changes that open or close stomata.
Correct answer is: Potassium
Q.24 Which hormone delays leaf senescence?
Cytokinin
Abscisic acid
Ethylene
Auxin
Explanation - Cytokinins delay aging of leaves by promoting nutrient mobilization and cell division.
Correct answer is: Cytokinin
Q.25 Which pathway in photosynthesis fixes carbon in bundle sheath cells of C4 plants?
Calvin cycle
Glycolysis
Pentose phosphate pathway
Photorespiration
Explanation - In C4 plants, CO2 is transported to bundle sheath cells where the Calvin cycle fixes carbon efficiently, reducing photorespiration.
Correct answer is: Calvin cycle