Plant Physiology for NEET: photosynthesis, respiration and growth

Plant Physiology questions in NEET focus on a small set of processes. Here is what to revise in photosynthesis, respiration and plant growth, with the facts that get asked.

Paper Predict Notes · 13 Jan 2026

Plant Physiology is a Class 11 unit that students often find dry, but its questions follow clear patterns. They focus on the steps of photosynthesis and respiration, where each step happens, and what plant growth regulators do. This guide covers what to revise.

Photosynthesis in Higher Plants

Light reactions

• Happen in the thylakoid membranes of the chloroplast.
• Involve photosystems I and II, photolysis of water, and the release of oxygen.
• Produce ATP and NADPH.
• Know the difference between cyclic and non-cyclic photophosphorylation.

Calvin cycle (C3 pathway)

• Happens in the stroma.
• Three stages: carboxylation, reduction and regeneration.
• RuBisCO fixes CO₂ to RuBP, forming 3-PGA.
• For each CO₂ fixed, 3 ATP and 2 NADPH are used. Six turns of the cycle produce one glucose.

C4 pathway

• Seen in plants like maize and sorghum.
• Kranz anatomy, with bundle sheath cells around vascular bundles.
• The first stable product is a four-carbon compound, oxaloacetic acid.
• C4 plants largely avoid photorespiration.

Photorespiration

• Happens in C3 plants when RuBisCO binds oxygen instead of CO₂.
• It wastes energy and produces no ATP or sugar.

Questions often compare C3 and C4 plants. Make a two-column table covering site, first product, enzymes and photorespiration.

Factors affecting photosynthesis

Light, CO₂ concentration, temperature and water, along with Blackman's law of limiting factors.

Respiration in Plants

• Glycolysis: happens in the cytoplasm and converts glucose to pyruvate.
• Fermentation: anaerobic, producing ethanol or lactic acid.
• Link reaction and Krebs cycle: in the mitochondrial matrix.
• Electron transport system and oxidative phosphorylation: on the inner mitochondrial membrane.
• Respiratory quotient (RQ): about 1 for carbohydrates, less than 1 for fats (about 0.7 for tripalmitin), and about 0.9 for proteins.

Plant Growth and Development

Plant growth regulators

• Auxins: apical dominance, rooting of stem cuttings, and preventing early fruit and leaf drop.
• Gibberellins: stem elongation, bolting, and increasing the length of grape stalks.
• Cytokinins: cell division and delaying leaf senescence.
• Ethylene: fruit ripening, and breaking seed and bud dormancy in some cases.
• Abscisic acid: stomatal closure, seed dormancy and stress responses.

Questions often describe an effect and ask which regulator causes it.

Growth

Know the phases of growth, growth rates (arithmetic and geometric), and differentiation, dedifferentiation and redifferentiation.

How to revise Plant Physiology

1. Draw the Calvin cycle and the Krebs cycle from memory.
2. Make a C3 versus C4 table.
3. Make a table of plant growth regulators and their effects.
4. Learn where each process happens in the cell.
5. Solve PYQs chapter by chapter.

Frequently asked questions

Which Plant Physiology chapter is most important?

Photosynthesis and plant growth regulators are tested most often, with respiration close behind.

Do I need to learn every intermediate of the Krebs cycle?

Know the sequence and the key steps. A mnemonic helps.

Is this unit only Class 11?

Yes, but it links to Class 12 topics such as ecology and plant reproduction.

The short version

Revise where each step of photosynthesis and respiration happens, compare C3 and C4 plants, learn the RQ values, and make a table of plant growth regulators. Solve PYQs to see how each fact is tested.

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