Unit 4 Plant Physiology Syllabus for NEET 2026

Plant Physiology includes the functional processes in plants that help them survive, grow, and reproduce. It explains how plants prepare food, release energy, and regulate growth through internal biochemical and hormonal mechanisms.

This unit mainly focuses on photosynthesis, respiration, and plant growth and development. It connects biochemical pathways with physiological functions such as energy production, gas exchange, and hormonal control of growth.

Plant Physiology 

Plant Physiology includes three major processes: Photosynthesis, Respiration, and Plant Growth and Development. These processes explain how plants prepare food, release energy, and regulate growth through biochemical pathways and hormones.

Photosynthesis

Photosynthesis is the process by which green plants prepare food using sunlight, carbon dioxide, and water. It occurs mainly in chloroplasts and involves light energy conversion into chemical energy.

Site and Pigments

Photosynthesis takes place in chloroplasts, mainly in mesophyll cells. Chlorophyll a, chlorophyll b, carotenoids, and xanthophylls are the main pigments involved in capturing light energy.

Phases of Photosynthesis

Light Reaction (Photochemical Phase)

Occurs in thylakoid membranes where sunlight is converted into ATP and NADPH. It involves the photolysis of water and the release of oxygen.

Dark Reaction (Biosynthetic Phase)

Occurs in the stroma where CO₂ is fixed into glucose using ATP and NADPH produced in the light reaction.

Photophosphorylation

ATP formation during the light reaction occurs through:

• Cyclic photophosphorylation → Only ATP is produced

• Non-cyclic photophosphorylation → ATP, NADPH, and oxygen are produced

Chemiosmotic hypothesis explains ATP synthesis using the proton gradient across thylakoid membrane.

C3, C4 Pathways and Photorespiration

C3 plants fix CO₂ directly into 3-carbon compounds, while C4 plants show an additional CO₂ fixation pathway that reduces photorespiration. Photorespiration is a wasteful process where oxygen is used instead of CO₂ fixation, reducing efficiency.

Factors Affecting Photosynthesis

Photosynthesis is influenced by light intensity, carbon dioxide concentration, temperature, and water availability. These factors regulate the overall rate of food production in plants.

Respiration in Plants

Respiration is the process of releasing energy from glucose molecules. It occurs in all living cells and involves the breakdown of organic compounds.

Gas Exchange and Cellular Respiration

Plants exchange gases through stomata and lenticels. Cellular respiration occurs in stages: glycolysis, Krebs cycle, and electron transport system.

• Glycolysis → Breakdown of glucose into pyruvate in cytoplasm

• Fermentation → Anaerobic breakdown producing alcohol or lactic acid

• Krebs Cycle (TCA cycle) → Complete oxidation in mitochondria

• Electron Transport System (ETS) → ATP production in mitochondria

Energy and ATP Yield

Respiration releases energy in the form of ATP molecules. Aerobic respiration produces more ATP compared to anaerobic respiration.

Amphibolic Pathway and Respiratory Quotient

Respiration is amphibolic because it involves both breakdown and synthesis of biomolecules. Respiratory quotient (RQ) is the ratio of CO₂ produced to O₂ consumed and varies with type of substrate used.

Plant Growth and Development

Plant growth involves an increase in size, number, and complexity of cells. Development includes all changes from seed germination to maturity.

Growth Processes

Seed germination marks the beginning of plant life. Growth occurs in phases: lag phase, exponential phase, and stationary phase.

Differentiation is the process by which cells become specialised. Dedifferentiation allows mature cells to divide again, while redifferentiation leads to new specialised cells.

Growth Regulators

Plant growth is controlled by hormones called growth regulators:

• Auxin → Cell elongation

• Gibberellin → Stem growth and seed germination

• Cytokinin → Cell division

• Ethylene → Fruit ripening

• Abscisic Acid (ABA) → Inhibits growth and induces dormancy

These hormones coordinate plant responses to internal and external stimuli.

How to Prepare Plant Physiology for NEET 2026?

This unit requires a clear understanding of processes, pathways, and hormonal control in plants.

• Read NCERT line by line

Focus on photosynthesis, respiration, and plant growth topics as given in NCERT without skipping diagrams or tables.

• Practice Plant Physiology PYQs regularly

PYQs help in understanding how NCERT-based processes and pathways are framed in questions.

• Solve chapter-wise MCQs

Regular practice with PW MCQs improves clarity in pathways like C3/C4 cycle, glycolysis, Krebs cycle, and ETS.

• Use mind maps for revision

PW Mind maps help connect photosynthesis, respiration, and plant hormones in a structured revision format.

• Revise all pathways and cycles

Focus on photophosphorylation, Calvin cycle, Krebs cycle, and electron transport chain with proper flow understanding.