Plant Physiology Previous Year Questions with Solutions

1.0Introduction

Plant Physiology is the branch of botany that deals with the functions and processes occurring in plants. It covers essential topics such as photosynthesis, respiration, water transport, nutrient uptake, growth regulation, and plant hormones.

Solving questions from Plant Physiology from previous years helps aspirants understand the trend of questions on this topic. NEET follows a specific pattern in asking questions about Plant Physiology. The listed questions and solutions from past years' papers help identify frequently asked topics like photosynthesis, respiration, transport in plants, and plant hormones.

2.0Key Concepts to Remember

Photosynthesis

Definition: Process by which plants convert light energy into chemical energy (glucose).
Occurs in: Chloroplasts
Phases: Light Reaction (Photochemical phase): In thylakoids, involves PS I & PS II, ATP & NADPH synthesis, and O₂ release.

Dark Reaction (Calvin Cycle): In stroma, uses ATP & NADPH to fix CO₂ into glucose.
Types:
C₃ plants: (Wheat, rice) Photorespiration occurs
C₄ plants: (Maize, sugarcane) No photorespiration, high efficiency
CAM plants: (Cactus, pineapple) CO₂ fixed at night to prevent water loss

Respiration 

• Breakdown of glucose to release ATP
  Types:
  Aerobic respiration: In mitochondria, complete oxidation of glucose (C₆H₁₂O₆ → CO₂ + H₂O + ATP).
  Anaerobic respiration (Fermentation): In cytoplasm, partial breakdown to ethanol/lactic acid.

Water & Mineral Transport 

• Absorption of water & minerals by roots
• Xylem: Transports water through transpiration pull & root pressure.
• Phloem: Translocates food (sugars) through pressure-flow hypothesis.
• Transpiration: Loss of water vapor from stomata, helps in cooling & nutrient transport.

Plant Growth Regulators (Phytohormones) 

• Auxins (IAA): Promote cell elongation, apical dominance, root initiation.
• Gibberellins (GA): Stimulate seed germination, flowering, and stem elongation.
• Cytokinins: Promote cell division, delay leaf senescence.
• Abscisic Acid (ABA): Induces dormancy, closes stomata during stress.
• Ethylene: Ripening hormone, promotes fruit ripening & leaf abscission.

Photoperiodism & Vernalization 

• Photoperiodism: Flowering response to light duration (Short-day, Long-day, Day-neutral plants).
• Vernalization: Cold treatment required for flowering in some plants (Wheat, Mustard).

3.0Past Year Questions with Solutions on Plant Physiology: NEET (UG)

Q-1. Which of the following simple tissues are commonly found in the fruit walls of nuts and pulp of pear ? 

(1) Sclereids                                        (2) Fibres 

(3) Parenchyma                                    (4) Collenchyma

Solution: The correct answer is: (1) Sclereids 

Explanation: Sclereids are a type of sclerenchyma (a simple permanent tissue) characterized by their thick, lignified cell walls and irregular shapes. They provide mechanical support and hardness. Sclereids are commonly found in the hard walls of nuts and the gritty texture of pear pulp.

Q-2.Which of the following are required for the light reaction of Photosynthesis ? 

A. CO₂ 

B. O₂ 

C. H₂O 

D. Chlorophyll 

E. Light 

Choose the correct answer from the options given below : 

(1) A, C, D and E only                            (2) C, D and E only 

(3) A and B only                                     (4) A, C and E only 

Solution: The correct answer is (2) C, D and E only

Explanation - The light reaction of photosynthesis (also called the photochemical phase) requires:

• H₂O (Water): Acts as the source of electrons and protons. Water undergoes photolysis, releasing oxygen.
• Chlorophyll: The pigment that absorbs light energy.
• Light: Provides the energy needed to drive the reactions.

Q-3.Observe the given figure. Identify the different stages labelled with alphabets by selecting the correct option.

(1) A-Carboxylation, B-Regeneration, C-Reduction 

(2) A- Reduction, B-Decarboxylation C-Regeneration 

(3) A-Carboxylation, B-Reduction, C-Regeneration 

(4) A-Reduction, B-Carboxylation, C-Regeneration

Solution: The correct answer is: (3) A-Carboxylation, B-Reduction, C-Regeneration 

The figure described seems to represent the Calvin cycle (C3 cycle) of photosynthesis, which consists of three main stages:

1. Carboxylation – CO₂ is fixed by RuBP to form 3-PGA.
2. Reduction – ATP and NADPH reduce 3-PGA to form G3P.
3. Regeneration – RuBP is regenerated from G3P using ATP.

Q-4. The reaction centre in PS II has an absorption maxima at 

(1) 700 nm                                                  (2) 660 nm 

(3) 780 nm                                                  (4) 680 nm

Solution: The correct answer is: (4) 680 nm

Explanation: The reaction centre of Photosystem II (PS II) is known as P680. It has an absorption maxima at 680 nm, meaning it most efficiently absorbs light at this wavelength, which is in the red region of the spectrum.

Q-5. Which of the following statements is incorrect? 

(1) Both ATP and NADPH + H+ are synthesized during non-cyclic photophosphorylation. (2) Stroma lamellae have PS I only and lack NADP reductase. 

(3) Grana lamellae have both PS I and PS II. 

(4) Cyclic photophosphorylation involves both PS I and PS II. 

Solution: The incorrect statement is: (4) Cyclic photophosphorylation involves both PS I and PS II.

Explanation: Cyclic photophosphorylation involves only Photosystem I (PS I). Electrons cycle back to PS I after passing through the electron transport chain, producing ATP only (no NADPH, no oxygen evolution).

Q-6. Given below are two statements : 

Statement I : RuBisCO is the most abundant enzyme in the world. 

Statement II : Photorespiration does not occur in C4 plant 

the above statements, choose the most appropriate answer from the options given below : 

(1) Statement I is correct but Statement II is incorrect 

(2) Statement I is incorrect but Statement II is correct 

(3) Both Statement I and Statement II are correct 

(4) Both Statement I and Statement II are incorrect

Solution:  The correct answer is: (3) Both Statement I and Statement II are correct.

Explanation:  Statement I= RuBisCO It is the most abundant enzyme on Earth because of its widespread presence in plants, algae, and some bacteria.
Statement II: Photorespiration does not occur in C4 plants → Correct C4 plants (e.g., maize, sugarcane) have a special mechanism to avoid photorespiration. They use a spatial separation of carbon fixation:

Q-7. Match List I with List II :

Choose the correct answer from the options given below: 

(1) A-II, B-IV, C-I, D-III 

(2) A-III, B-I, C-II, D-IV 

(3) A-II, B-IV, C-III, D-I 

(4) A-III, B-IV, C-II, D-I

Solution:  The correct answer is (3) A-II, B-IV, C-III, D-I

Explanation:

Q-8. What amount of energy is released from glucose during lactic acid fermentation? 

(1) More than 18%                                       (2) About 10% 

(3) Less than 7%                                        (4) Approximately 15%

Solution: The correct answer is: (3) Less than 7%

Explanation:

1. Total energy in glucose - One molecule of glucose (C₆H₁₂O₆) contains about 686 kcal of potential energy.
2. Energy yield in lactic acid fermentation - Glycolysis produces 2 ATP molecules per glucose, yielding about 14.6 kcal (since 1 ATP ≈ 7.3 kcal).
3. Percentage of energy released 14.6/686×100≈2.1%

This is less than 7%, meaning most of the energy remains in lactic acid.

Q-9. Spraying which of the following phytohormone on juvenile conifers helps in hastening the maturity period, that leads to early seed production ? 

(1) Gibberellic Acid                                   (2) Zeatin 

(3) Abscisic Acid                                       (4) Indole-3-butyric Acid

Solution: The correct answer is: (1) Gibberellic Acid (GA) - Gibberellic Acid (GA) is a plant hormone that promotes stem elongation, flowering, and seed development.n juvenile conifers, spraying GA helps in hastening the maturity period, leading to early seed production.

Q-10.The phenomenon which is influenced by auxin and also played a major role in its discovery : 

(1) Phototropism                                        (2) Root initiation 

(3) Gravitropism                                           (4) Apical Dominance

Solution: The correct answer is: (1) Phototropism

Explanation:

• Phototropism refers to the directional growth of plants in response to light.
• Auxin (Indole-3-acetic acid, IAA) plays a key role in phototropic curvature by accumulating on the shaded side of the plant, promoting cell elongation and causing the plant to bend toward the light.

Q-11. Which out of the following statements is incorrect ? 

(1) Grana lamellae have both PS I and PS II 

(2) Cyclic photophosphorylation involves both PS I and PS II 

(3) Both ATP and NADPH + H+ are synthesised during non-cyclic photophosphorylation.

(4) Stroma lamellae lack PS II and NADP reductase 

Solution: The incorrect statement is: (2) Cyclic photophosphorylation involves both PS I and PS II

Explanation: - Cyclic photophosphorylation involves both PS I and PS II → Incorrect  Cyclic photophosphorylation only involves PS I, not PS II. In this process, electrons from PS I are cycled back to generate ATP, but NADPH is not produced and water is not split.

Q-12. Which of the following growth regulators is an adenine derivative ? 

(1) Auxin                                                        (2) Cytokinin 

(3) Ethylene                                                   (4) Abscisic acid

Solution: The correct answer is: (2) Cytokinin 

Explanation: - Cytokinins are plant growth regulators that promote cell division (cytokinesis), shoot growth, and delay senescence. They are adenine derivatives, meaning they are chemically derived from adenine (a nitrogenous base in DNA & RNA).

Q-13. Inhibitory substances in dormant seeds cannot be removed by subjecting seeds to : 

(1) Gibberellic acid                                         (2) Nitrate 

(3) Ascorbic acid                                          (4) Chilling conditions

Solution: The correct answer is: (3) Ascorbic acid  

Explanation- Ascorbic acid, also known as vitamin C, is known to induce seed dormancy, rather than break it. 

Q-14. Find out the correct match from the following table :- 

(1) (i) only                                              (2) (i) and (ii) 

(3) (iii) only                                              (4) (ii) and (iii)

Solution:  The correct answer is: (1) (i) only

Explanation:

1. (i) Photochemical phase - Photosystem II - Oxygen release  (Correct)
2. The photochemical phase (light reaction) occurs in the thylakoid membranes.
3. Photosystem II (PS II) is responsible for the photolysis of water (H₂O splitting), releasing oxygen (O₂).
4. This is a correct match.
5. (ii) Paper Chromatography - Chlorophyll 'b' - Yellow orange  (Incorrect)
6. Paper chromatography is used to separate plant pigments.
7. Chlorophyll 'b' appears yellow-green, not yellow-orange.
8. Carotenoids (carotenes) are the ones that appear yellow-orange.
9. (iii) Carotenoids - Chief pigment - Red light absorption  (Incorrect)
10. Carotenoids are accessory pigments, not the chief pigments (the chief pigment is chlorophyll a).
11. Carotenoids absorb blue and violet light, not red light.

Q-15 . The correct sequence of cell organelles during photorespiration is :- 

(1) Chloroplast-mitochondria-peroxisome 

(2) Chloroplast-vacuole-peroxisome 

(3) Chloroplast-Golgibodies-mitochondria 

(4) Chloroplast-Rough endoplasmic reticulum-Dictyosomes

Solution:  The correct answer is: (1) Chloroplast → Peroxisome → Mitochondria 

Explanation - Photorespiration (also called the C₂ cycle) is a wasteful process in C₃ plants that occurs when RuBisCO binds to O₂ instead of CO₂, leading to the production of phosphoglycolate instead of PGA.