Photosynthesis

1. Photosynthesis is the process of converting light energy into chemical energy.
2. The overall equation is:
   6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O.
3. Site of photosynthesis – Chloroplast.
4. Light reaction occurs in grana; Dark reaction (Calvin cycle) occurs in stroma.
5. Hill reaction demonstrates oxygen evolution during photosynthesis.
6. Photophosphorylation is the formation of ATP using light energy.
7. C₃ plants fix CO₂ via Rubisco enzyme (Calvin cycle).
8. C₄ plants fix CO₂ via PEP carboxylase enzyme.
9. First stable product of C₃ pathway – 3-phosphoglyceric acid (3-PGA).
10. First stable product of C₄ pathway – Oxaloacetic acid (OAA).
11. CAM plants open stomata at night to fix CO₂ (e.g., Pineapple, Opuntia).
12. Optimum temperature for photosynthesis in C₃ plants: 25°C; C₄ plants: 35°C.
13. Photosynthetic quotient (PQ) = O₂ evolved / CO₂ absorbed.
14. Photorespiration occurs only in C₃ plants.
15. Photorespiration site: Chloroplast → Peroxisome → Mitochondria.

Respiration

1. Respiration is oxidation of food to release energy (ATP).
2. Site of respiration –
3. Glycolysis occurs in
4. Krebs cycle occurs in mitochondrial matrix.
5. End product of aerobic respiration – CO₂ and H₂O.
6. End product of anaerobic respiration – Alcohol / Lactic acid.
7. RQ (Respiratory Quotient) = CO₂ evolved / O₂ consumed.
8. RQ of carbohydrate = 1, fat = 7, protein = 0.8.
9. RQ of organic acids >
10. Pasteur effect – inhibition of glycolysis by

Transpiration

1. Transpiration – loss of water in vapor form through stomata.
2. Types: Stomatal, Cuticular, Lenticular.
3. Transpiration mainly occurs through
4. Transpiration ratio = Water transpired / Dry matter produced.
5. Antitranspirants reduce transpiration (e.g., PMA, Kaolin, CCC).
6. Potometer is used to measure rate of transpiration.
7. Stomata open in light and close in darkness.
8. Guard cells contain chloroplasts; surrounding epidermal cells do not.
9. Opening of stomata is due to turgor pressure in guard cells.
10. Hydathodes are involved in

Water Relations

1. Water potential (Ψw) – potential energy of water per unit volume.
2. Pure water has Ψw =
3. Osmosis – movement of water from low solute to high solute concentration.
4. Plasmolysis – shrinkage of cytoplasm due to water loss.
5. Imbibition – absorption of water by colloids (seeds, cell walls).
6. Turgor pressure – pressure exerted by cell sap on the cell wall.
7. Wilting point – when plants cannot absorb water from soil.
8. Permanent Wilting Point (PWP) – water unavailable to plants.
9. Field Capacity – maximum water soil can hold after drainage.
10. Water uptake mainly through root hairs.

Growth and Development

1. Growth – irreversible increase in size or mass.
2. Development – progression from seed to maturity.
3. Cell elongation occurs in the meristematic region.
4. Auxins promote cell elongation and apical dominance.
5. Gibberellins (GA₃) promote stem elongation and seed germination.
6. Cytokinins promote cell division and delay senescence.
7. Abscisic acid (ABA) induces dormancy and stress tolerance.
8. Ethylene promotes fruit ripening and leaf abscission.
9. Phototropism – growth towards light.
10. Geotropism – growth in response to gravity.
11. Apical dominance – suppression of lateral buds by apical bud (Auxin effect).
12. Bolting – elongation of internodes in rosette plants due to GA₃.
13. Vernalization – induction of flowering by low temperature.
14. Photoperiodism – response of plants to day length.
15. Short-day plants flower when day length < critical period (e.g., Rice).
16. Long-day plants flower when day length > critical period (e.g., Wheat).
17. Neutral plants – flowering not affected by photoperiod (e.g., Cotton).
18. Phytochrome is the photoreceptor pigment controlling photoperiodism.

Plant Stress Physiology

1. Drought stress causes closure of stomata and reduced photosynthesis.
2. Heat stress leads to protein denaturation and enzyme inactivation.
3. Cold stress reduces membrane fluidity and chlorophyll content.
4. Salt stress causes ion toxicity (Na⁺, Cl⁻) and osmotic imbalance.
5. Waterlogging causes anaerobic respiration in roots.
6. ABA increases during drought and stress.
7. Proline accumulation – an indicator of stress tolerance.