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Plant Growth and Development
Biology · Class 11NCERT pp. 166–1782 sets × 25 questions
Key facts and formulas for Plant Growth and Development, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.
Key facts for this chapter
| Idea | Rule or fact |
|---|
| Growth | Irreversible increase in size or mass, metabolic and energy-using; swelling of dry wood is imbibition, not growth |
| Meristems | Apical, intercalary (grasses) and lateral (vascular and cork cambium, give secondary growth in dicots and gymnosperms) |
| Growth phases | Lag, log (exponential) and stationary; stationary phase comes when nutrients become limited |
| Growth formulas | Arithmetic: Lt = L0 + rt. Exponential: W = W0 e^(rt). AGR = (final − initial) / time. RGR = increase / initial size |
| Cell growth order | Division, plasmatic growth, expansion, differentiation, maturation, senescence |
| Heterophylly | Life phase: cotton, coriander, larkspur. Environment: buttercup (water vs air leaves) |
| Chemical nature | IAA indole, kinetin adenine derivative, ABA carotenoid derivative, GA3 terpene, brassinosteroid steroid |
| Discoveries | Cousins ethylene (1910), Kurosawa gibberellin (1926), Miller kinetin (1955), ABA mid 1960s, Went auxin |
| Hormone roles | Auxin: apical dominance, rooting, 2,4-D weedkiller. GA: elongation, alpha-amylase. Cytokinin: delays senescence. Ethylene: ripening. ABA: stress, dormancy, stomatal closure |
| Photoperiod and phytochrome | Pr absorbs red (about 660 nm) to become active Pfr; far-red (about 730 nm) reverses. Xanthium is short-day; vernalisation sensed by shoot apex |
Three sample questions
Q1. Consider: (i) Growth is an irreversible increase in size. (ii) Swelling of dry wood in water is growth. (iii) Growth uses energy and involves metabolism. Which are correct?
- (i) and (ii) only
- (i) and (iii) only
- (ii) and (iii) only
- (i), (ii) and (iii)
Hint and solution
Hint: Real growth is permanent and needs the cell to make new material using energy. Ask whether wood swelling in water meets both tests.
- Growth = irreversible + metabolic — Growth is a permanent increase in size or mass, and the cell must spend energy and make new material.
- (i) true; (iii) true — Statement (i) defines growth correctly. Statement (iii) is also right, because growth is a metabolic process that uses energy.
- Wood swelling = imbibition — Dry wood swells only by soaking up water, and it reverses on drying. There is no metabolism, so (ii) is false.
- Answer: (i) and (iii) — Only statements (i) and (iii) are correct. Option B.
Answer: B. Swelling of wood is a reversible, non-metabolic soaking of water, so (ii) is wrong.
Q2. Which statement about a plant meristem is correct?
- Its cells divide and renew themselves, while the cells it produces soon stop dividing
- All cells produced by it keep dividing for ever
- It is found only in the root tip
- It stops working once the plant flowers
Hint and solution
Hint: Think of meristem as a self-renewing factory. What happens to the cells it hands over to the rest of the plant?
- Meristem = self-renewing dividing tissue — A meristem keeps a pool of dividing cells. Part of each division renews the meristem itself.
- Products → differentiate — The cells cut off by the meristem enlarge and differentiate, and they soon stop dividing.
- Eliminate — Options B, C and D are false because not all products divide, meristems occur at many sites, and they continue after flowering.
- Answer: renewal plus permanent products — The correct statement is the one about self-renewal. Option A.
Answer: A. Only the meristem self-perpetuates. Its products join the permanent plant body.
Q3. Lateral meristems that cause secondary growth occur in
- all monocots only
- all plants without exception
- only the root tip
- dicotyledonous plants and gymnosperms
Hint and solution
Hint: Secondary growth adds girth through vascular cambium and cork cambium. Which plant groups have woody thickening?
- Lateral meristem = cambium — Vascular cambium and cork cambium are lateral meristems and they add girth.
- Secondary growth = woody — Secondary growth gives wood and bark, so it is seen in plants that become woody.
- Which groups — Dicots and gymnosperms have cambium. Monocots usually do not, and the root tip has only an apical meristem.
- Answer: dicots and gymnosperms — Lateral meristems occur in dicotyledonous plants and gymnosperms. Option D.
Answer: D. Vascular cambium and cork-cambium appear later in life in dicots and gymnosperms and add girth.
How to use this chapter
Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.