Life Processes in Plants Part 2: MCQs (Q26–Q50)
Part 2 — Plant Growth (continued) & Photosynthesis Basics (Q26–Q50)
26. Which pigment is essential for photosynthesis?
A. Hemoglobin
B. Chlorophyll ← Correct answer: B
C. Melanin
D. Carotene only
Explanations:
A/C) Animal pigments — incorrect.
B) Correct. Chlorophyll captures light energy for photosynthesis.
D) Carotenoids (carotene) assist in light capture but chlorophyll is primary — incomplete.
27. Photosynthesis occurs mainly in which part of the leaf?
A. Epidermis
B. Mesophyll (palisade parenchyma) ← Correct answer: B
C. Xylem
D. Stomatal pore only
Explanations:
A) Epidermis covers leaf but has few chloroplasts — incorrect.
B) Correct. Palisade mesophyll cells are rich in chloroplasts and are primary photosynthetic site.
C) Xylem conducts water — not main photosynthesis site — incorrect.
D) Stomata are pores for gas exchange — not photosynthetic tissue — incorrect.
28. Equation for photosynthesis (generalized) is:
A. CO₂ + H₂O → O₂ + Glucose only (with light)
B. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in presence of light and chlorophyll) ← Correct answer: B
C. O₂ + Glucose → CO₂ + H₂O + energy
D. CO₂ + O₂ → H₂O
Explanations:
A) Incomplete stoichiometry — incorrect.
B) Correct. Balanced equation for photosynthesis (simplified).
C) That is cellular (aerobic) respiration — incorrect.
D) Chemically incorrect — incorrect.
29. Which gas is released as a byproduct of photosynthesis?
A. Carbon dioxide
B. Nitrogen
C. Oxygen ← Correct answer: C
D. Methane
Explanations:
A) CO₂ is a reactant in photosynthesis — incorrect.
B/D) Not photosynthesis byproducts — incorrect.
C) Correct. O₂ is evolved from splitting water during light reactions.
30. Which of the following is NOT required for photosynthesis?
A. Carbon dioxide
B. Light
C. Nitrogen gas (N₂) ← Correct answer: C
D. Water
Explanations:
A/B/D) Essential raw materials/energy — incorrect to choose.
C) Correct. Nitrogen in gaseous form isn’t a direct input for photosynthesis (though plants need nitrogen for proteins).
31. Stomata help in:
A. Transport of sugars only
B. Absorption of nutrients from soil
C. Gas exchange and transpiration ← Correct answer: C
D. Water uptake by roots
Explanations:
A/B/D) Not stomata’s primary function — incorrect.
C) Correct. Stomata permit CO₂ intake, O₂ release, and water vapor loss (transpiration).
32. Which environmental factor affects the rate of photosynthesis?
A. Light intensity
B. Carbon dioxide concentration
C. Temperature
D. All of the above ← Correct answer: D
Explanations:
A–C) Each influences photosynthesis rate; together they determine the limiting factor — Correct.
33. In which organelle does photosynthesis occur?
A. Mitochondria
B. Nucleus
C. Chloroplast ← Correct answer: C
D. Ribosome
Explanations:
A) Mitochondria are site of respiration — incorrect.
B/D) Not photosynthesis organelles — incorrect.
C) Correct. Chloroplasts contain chlorophyll and perform photosynthesis.
34. The opening and closing of stomata are mainly regulated by:
A. Guard cells through change in turgor pressure
B. Xylem vessels only
C. Root hairs only
D. Phloem pressure only
Correct answer: A
Explanations:
A) Correct. Guard cells control stomatal aperture by taking up/losing water (turgor changes).
B–D) Not the controlling structures — incorrect.
35. Transpiration is:
A. Absorption of minerals only
B. Loss of water vapor from aerial plant parts ← Correct answer: B
C. Uptake of CO₂ only
D. Uptake of oxygen only
Explanations:
A/C/D) Not definitions of transpiration — incorrect.
B) Correct. Transpiration helps in water movement and cooling.
36. Which statement is TRUE about phloem?
A. Transports water only
B. Transports organic food (sugars) from leaves to other parts ← Correct answer: B
C. Is made of dead cells only
D. Transports oxygen to roots
Explanations:
A) Xylem chiefly transports water — incorrect.
B) Correct. Phloem conducts photosynthates (sucrose) bidirectionally (source to sink).
C) Phloem sieve elements are living (though companion cells assist) — incorrect.
D) Blood/air carry oxygen in animals; phloem doesn’t transport O₂ — incorrect.
37. The pressure-flow hypothesis explains:
A. Water movement in xylem only
B. Movement of sugars in phloem from source to sink
C. Phloem translocation due to pressure gradients between source and sink ← Correct answer: B
D. How stomata open
Explanations:
A/D) Not correct topics — incorrect.
B) Correct. Movement of solutes creates osmotic pressure driving mass flow in phloem.
38. During daytime, rate of transpiration is generally:
A. Lower than at night
B. Higher than at night (due to light and open stomata) ← Correct answer: B
C. Always zero
D. Independent of light
Explanations:
A/C/D) Incorrect.
B) Correct. Light opens stomata for photosynthesis, increasing transpiration.
39. Which of the following is a C₄ plant adaptation to high light/intensity and temperature?
A. Stomata always closed
B. Spatial separation of initial CO₂ fixation and Calvin cycle (Kranz anatomy) ← Correct answer: B
C. No chloroplasts in mesophyll
D. Photosynthesis in roots only
Explanations:
A) Stomata not always closed — incorrect.
B) Correct. C₄ plants (maize, sugarcane) concentrate CO₂ in bundle sheath cells avoiding photorespiration.
C/D) False statements — incorrect.
40. Photorespiration results in:
A. Increased photosynthesis efficiency
B. Loss of fixed carbon and energy under high oxygen levels ← Correct answer: B
C. Production of ethanol in leaves
D. No effect on plants
Explanations:
A) Photorespiration reduces efficiency — incorrect.
B) Correct. When O₂ competes with CO₂ at Rubisco, photorespiration wastes energy.
C/D) Not true — incorrect.
41. Which pigment protects chlorophyll from photo-oxidative damage and also absorbs additional light?
A. Hemoglobin
B. Carotenoids (carotenes, xanthophylls) ← Correct answer: B
C. Melanin
D. Rubisco
Explanations:
A/C) Animal pigments — incorrect.
B) Correct. Carotenoids broaden the light spectrum and quench reactive oxygen species.
D) Rubisco is enzyme, not pigment — incorrect.
42. Which of the following best describes respiration in plants?
A. Plants do not respire
B. Plants respire (breakdown of food to release energy) day and night ← Correct answer: B
C. Plants breathe only during the day
D. Photosynthesis equals respiration always
Explanations:
A) False — plants respire continually — incorrect.
B) Correct. Cellular respiration occurs day & night to meet energy needs.
C) Respiration occurs at all times — incorrect.
D) Rates differ; they are not equal necessarily — incorrect.
43. The enzyme RuBisCO is involved in:
A. Photorespiration only
B. Carbon fixation in Calvin cycle (carboxylation of RuBP) ← Correct answer: B
C. Splitting water in light reaction
D. Transport in phloem
Explanations:
A) RuBisCO can catalyze carboxylation and oxygenation (photorespiration) but primary role is CO₂ fixation — B is better.
B) Correct. RuBisCO fixes CO₂ to RuBP in Calvin cycle.
C/D) Not roles of RuBisCO — incorrect.
44. Which layer of leaf has large intercellular spaces to facilitate gas exchange?
A. Upper epidermis
B. Spongy mesophyll ← Correct answer: B
C. Palisade parenchyma only
D. Cuticle
Explanations:
A/C/D) Epidermis/cuticle are for protection and do not have large air spaces — incorrect.
B) Correct. Spongy mesophyll has air spaces for CO₂/O₂ diffusion.
45. Which is the main pathway for water movement from roots to leaves?
A. Phloem only
B. Xylem through transpiration pull (cohesion-tension) ← Correct answer: B
C. Diffusion through stomata into phloem only
D. Active pumping by roots only
Explanations:
A) Phloem transports sugars, not main water pathway — incorrect.
B) Correct. Transpiration creates negative pressure pulling water up xylem via cohesion/adhesion.
C/D) Not accurate mechanisms per NCERT — incorrect.
46. Which process moves water across a semi-permeable membrane from low to high solute concentration?
A. Diffusion
B. Facilitated diffusion
C. Osmosis ← Correct answer: C
D. Active transport
Explanations:
A/B) Diffusion is solute movement down gradient — incorrect.
C) Correct. Osmosis is water movement toward higher solute concentration.
D) Active transport uses energy to move solutes against gradient — not water movement per se.
47. Transpiration pull is created because:
A. Stomata actively pump water out
B. Roots push water up actively
C. Evaporation of water from leaves creates negative pressure ← Correct answer: C
D. Xylem cells contract to push water
Explanations:
A/B/D) Misrepresentations of mechanisms — incorrect.
C) Correct. Evaporation from mesophyll surfaces produces tension drawing water upward.
48. Which of the following statements about xylem is TRUE?
A. Xylem is living tissue that transports sugars
B. Xylem vessels conduct water and are dead at maturity
C. Xylem transports proteins to leaves only
D. Xylem contains sieve tubes and companion cells
Correct answer: B
Explanations:
A) Xylem is mostly dead (vessels/tracheids) conducting water — incorrect wording.
B) Correct. Mature xylem vessels lack protoplasm and transport water/minerals.
C/D) Functions and components of phloem, not xylem — incorrect.
49. Which of these reduces rate of transpiration?
A. High wind speed
B. High temperature
C. Thick cuticle on leaf surface ← Correct answer: C
D. High light intensity
Explanations:
A/B/D) Generally increase transpiration by enhancing evaporation — incorrect.
C) Correct. Thick waxy cuticle reduces water loss.
50. Photorespiration increases under conditions of:
A. Low temperature and high CO₂
B. High temperature and high O₂/low CO₂ ← Correct answer: B
C. High CO₂ only
D. Low light intensity only
Explanations:
A/C/D) Conditions not favoring photorespiration — incorrect.
B) Correct. At high temps Rubisco favors O₂ binding leading to photorespiration.