📑 Topics on this page (Jump to Topic):
📌 1. Photosynthesis, Transpiration & Plant Hormones
- Photosynthesis: 6CO₂ + 12H₂O → (light, chlorophyll) → C₆H₁₂O₆ + 6O₂ + 6H₂O. In chloroplasts; the O₂ released comes from splitting of water (not CO₂).
- Chlorophyll has magnesium at its centre. Light reaction — in grana (thylakoids); dark reaction (Calvin cycle) — in stroma. Photosynthesis is maximum in red light, minimum in green.
- Transpiration — loss of water vapour through leaf stomata; helps pull water up ("transpiration pull"). Stomata open and close by guard cells. Water droplets at leaf margins — guttation.
- Phototropism — stem towards light; geotropism — root downwards; folding of touch-me-not (Mimosa pudica) leaves on touch — thigmonasty (non-growth movement).
- The crescograph (measuring plant growth) — Jagadish Chandra Bose, who showed plants respond to stimuli.
| Hormone | Main function |
|---|---|
| Auxin | Cell elongation, apical dominance, rooting; first plant hormone discovered |
| Gibberellin | Stem elongation, makes dwarf plants tall, seed germination |
| Cytokinin | Cell division, delays senescence |
| Ethylene | Fruit ripening (gaseous hormone) |
| Abscisic acid (ABA) | "Stress hormone"; closes stomata, seed dormancy, leaf fall |
📌 2. Plant Parts & Reproduction
| Edible part | Examples |
|---|---|
| Modified root | Carrot, radish, turnip, sweet potato, beetroot |
| Modified stem | Potato (tuber), ginger, turmeric (rhizome), onion-garlic (bulb), colocasia |
| Inflorescence/flower | Cauliflower, clove (flower bud), saffron (stigma) |
| Seed | Gram, pea, wheat; coconut's edible part — endosperm |
- Male part of a flower — stamen (anther + filament); female part — pistil (stigma, style, ovary). After fertilisation, ovary → fruit, ovule → seed.
- Angiosperms show double fertilisation — one male gamete + egg = zygote; the other + secondary nucleus = endosperm (3n).
- Wind pollination — maize, grasses; water pollination — Vallisneria; insect pollination — bright, scented flowers. Vegetative propagation — potato (eyes), Bryophyllum (leaf buds), sugarcane (stem cuttings).
- Fruit formed without fertilisation — parthenocarpy, e.g. seedless banana, grapes. Nitrogen fixation — Rhizobium bacteria in root nodules of legumes.
⚠️ Exam Traps:
- Potato is a stem (tuber), not a root; sweet potato is a root.
- In photosynthesis O₂ comes from water.
- Ethylene ripens fruit; ABA closes stomata.
📌 3. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. In photosynthesis, the oxygen released comes from: Practice
Correct answer: (B)
From photolysis of water.
From photolysis of water.
Q2. Which metal is present in chlorophyll? Practice
Correct answer: (B)
Haemoglobin contains iron.
Haemoglobin contains iron.
Q3. Photosynthesis takes place in the: Practice
Correct answer: (D)
The food factory of the plant cell.
The food factory of the plant cell.
Q4. Photosynthesis is minimum in which colour of light? Practice
Correct answer: (B)
Green light is reflected.
Green light is reflected.
Q5. Loss of water vapour from leaves is called: Practice
Correct answer: (D)
Mainly through stomata.
Mainly through stomata.
Q6. Opening and closing of stomata is controlled by: Practice
Correct answer: (A)
Through changes in turgor.
Through changes in turgor.
Q7. The plant hormone that ripens fruits is: Practice
Correct answer: (A)
The only gaseous plant hormone.
The only gaseous plant hormone.
Q8. The "stress hormone" of plants is: Practice
Correct answer: (D)
Closes stomata.
Closes stomata.
Q9. The hormone that makes dwarf plants tall is: Practice
Correct answer: (C)
Stem elongation.
Stem elongation.
Q10. Which hormone promotes cell division and delays senescence? Practice
Correct answer: (D)
Keeps leaves green longer.
Keeps leaves green longer.
Q11. Potato is which part of the plant? Practice
Correct answer: (A)
Its "eyes" are buds.
Its "eyes" are buds.
Q12. Sweet potato is a: Practice
Correct answer: (C)
Potato is a stem.
Potato is a stem.
Q13. Clove is which part of the plant? Practice
Correct answer: (C)
Dried unopened buds.
Dried unopened buds.
Q14. Saffron is obtained from which part of the flower? Practice
Correct answer: (A)
Of Crocus sativus.
Of Crocus sativus.
Q15. After fertilisation, the ovary develops into the: Practice
Correct answer: (C)
Ovule → seed.
Ovule → seed.
Q16. Double fertilisation is a feature of: Practice
Correct answer: (B)
Forms triploid endosperm.
Forms triploid endosperm.
Q17. The nitrogen-fixing bacterium in legume root nodules is: Practice
Correct answer: (A)
Symbiotic nitrogen fixation.
Symbiotic nitrogen fixation.
Q18. Formation of seedless fruit without fertilisation is: Practice
Correct answer: (B)
E.g. seedless banana.
E.g. seedless banana.
Q19. The crescograph was invented by: Practice
Correct answer: (D)
To measure plant growth.
To measure plant growth.
Q20. Folding of touch-me-not leaves on touch is: Practice
Correct answer: (C)
A non-growth movement.
A non-growth movement.