“25 Most Important MCQs on Gaseous Exchange in Plants (With Answers)”

Introduction:

Gaseous exchange in plants is an important chapter of biology and is frequently asked in MDCAT, PPSC, and other entry tests. Students often struggle to revise this topic, so practicing multiple choice questions (MCQs) is the best way to prepare. In this blog, we have compiled the 25 most important and repeated MCQs on gaseous exchange in plants along with correct answers. These questions will help you revise key concepts like stomata, lenticels, diffusion, photorespiration, and CAM pathway. Whether you are preparing for your board exams, competitive exams, or entry tests, this collection will make your revision quick and effective.

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   Why Are These MCQs Important for Exams?

• Frequently repeated in MDCAT, PPSC & entry tests

• Cover both theoretical and application-based concepts

• Help in quick revision before exams

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     Key Points to Remember

• Stomata → main site of gaseous exchange in leaves

• Lenticels → gaseous exchange in woody stems

• CAM plants open stomata at night

• Photorespiration involves chloroplast, mitochondria, and peroxisomes

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MCQs are the fastest way to test your preparation. Revise these 25 most important questions again and again before exams. Consistent practice will not only boost your confidence but also increase your chances of scoring high in biology.

1. In plants, gaseous exchange mainly takes place through:
a) Cuticle
b) Stomata
c) Lenticels
d) Root hairs
👉 Answer: b) Stomata

2. The openings in woody stems for gaseous exchange are called:
a) Trichomes
b) Lenticels
c) Stomata
d) Hydathodes
👉 Answer: b) Lenticels

3. During the daytime, stomata usually:
a) Remain closed
b) Remain open
c) Open at night only
d) Never open
👉 Answer: b) Remain open

4. Stomata are mainly found in:
a) Upper epidermis only
b) Lower epidermis only
c) Both upper and lower epidermis
d) Mesophyll cells
👉 Answer: c) Both upper and lower epidermis

5. Guard cells control:
a) Photosynthesis
b) Respiration
c) Opening and closing of stomata
d) Water transport
👉 Answer: c) Opening and closing of stomata

6. The main factor causing opening and closing of stomata is:
a) ATP production
b) Turgor changes in guard cells
c) Chlorophyll content
d) Presence of cuticle
👉 Answer: b) Turgor changes in guard cells

7. Stomata close when guard cells become:
a) Turgid
b) Flaccid
c) Elongated
d) Thickened
👉 Answer: b) Flaccid

8. Which plant tissue helps in gaseous exchange in roots?
a) Phloem
b) Xylem
c) Aerenchyma
d) Collenchyma
👉 Answer: c) Aerenchyma

9. The diffusion of gases in plants occurs mainly due to:
a) Active transport
b) Osmosis
c) Concentration gradient
d) Endocytosis
👉 Answer: c) Concentration gradient

10. In C4 plants, gaseous exchange is more efficient because of:
a) Kranz anatomy
b) Lack of stomata
c) Absence of mesophyll
d) Smaller leaf size
👉 Answer: a) Kranz anatomy

11. Lenticels are most prominent in:
a) Leaves
b) Roots
c) Stems
d) Flowers
👉 Answer: c) Stems

12. The first step in respiration is:
a) Krebs cycle
b) Electron transport chain
c) Glycolysis
d) Photorespiration
👉 Answer: c) Glycolysis

13. The closing of stomata during water stress is regulated by:
a) Ethylene
b) ABA (Abscisic acid)
c) Auxin
d) Gibberellin
👉 Answer: b) ABA (Abscisic acid)

14. Photorespiration occurs in:
a) Mitochondria only
b) Peroxisomes only
c) Chloroplast, peroxisome, mitochondria
d) Cytoplasm only
👉 Answer: c) Chloroplast, peroxisome, mitochondria

15. Gaseous exchange in plants occurs by:
a) Simple diffusion
b) Active transport
c) Osmosis
d) Facilitated transport
👉 Answer: a) Simple diffusion

16. Stomata of CAM plants open:
a) During the day
b) During the night
c) Always open
d) Never open
👉 Answer: b) During the night

17. Stomata are absent in:
a) Xerophytes
b) Hydrophytes (submerged leaves)
c) Mesophytes
d) Halophytes
👉 Answer: b) Hydrophytes (submerged leaves)

18. Which enzyme is directly involved in photorespiration?
a) ATP synthase
b) RuBisCO
c) PEP carboxylase
d) NADP reductase
👉 Answer: b) RuBisCO

19. The process of exchange of O₂ and CO₂ in plants occurs mainly through:
a) Xylem vessels
b) Phloem sieve tubes
c) Intercellular spaces
d) Guard cells only
👉 Answer: c) Intercellular spaces

20. In plants, oxygen produced during photosynthesis comes from:
a) CO₂
b) Water
c) Glucose
d) ATP
👉 Answer: b) Water

21. Pneumatophores (breathing roots) are found in:
a) Desert plants
b) Epiphytes
c) Mangroves
d) Orchids
👉 Answer: c) Mangroves

22. The opening and closing of stomata is best explained by:
a) K+ ion theory
b) ATP theory
c) Photosynthesis theory
d) Oxidation theory
👉 Answer: a) K+ ion theory

23. Guttation in plants occurs through:
a) Stomata
b) Hydathodes
c) Lenticels
d) Root hairs
👉 Answer: b) Hydathodes

24. During respiration, the maximum ATP is produced in:
a) Glycolysis
b) Krebs cycle
c) Electron Transport Chain
d) Fermentation
👉 Answer: c) Electron Transport Chain

25. The gas essential for photosynthesis is:
a) Oxygen
b) Carbon dioxide
c) Nitrogen
d) Hydrogen
👉 Answer: b) Carbon dioxide