Quick answer: A plant growth and development NEET PYQ analysis shows that NTA asks about two questions a year from this chapter, and most of them test plant growth regulators: the functions of auxins, gibberellins, cytokinins, ethylene and ABA, how each was discovered, and their uses in farming. The rest come from growth rates (arithmetic vs geometric, the sigmoid curve), differentiation, dedifferentiation and redifferentiation, and plasticity. The 2024, 2025 and 2026 papers all asked PGR questions.
This guide breaks down what NTA repeats, the tables to memorise and PYQ-pattern questions with answers. For the full plant physiology plan, see our plant physiology guide for NEET.
Want to test yourself first? Solve the Plant Growth and Development PYQs for free, then use this guide to fix the gaps.
Table of Contents
Why This Chapter Is Easy Marks
With about 85 past questions, Plant Growth and Development has a large PYQ bank, and most of it is one table: which hormone does what. Learn that table and the discovery experiments, and the chapter becomes almost guaranteed marks. For chapter notes, use our Plant Growth and Development notes, and to see where it sits among other chapters, check the NEET 2027 chapter weightage.
It closes the plant physiology unit, after our Photosynthesis PYQ analysis and Respiration in Plants PYQ analysis. For a quick warm-up, try these five quick plant physiology questions.
Plant Growth and Development NEET PYQ Analysis: What NTA Repeats
When you sort the past NEET biology PYQs from this chapter, four question types cover nearly everything.
| Question type | Frequency | What it tests |
|---|---|---|
| Plant growth regulators | Most frequent | Functions and uses of auxins, gibberellins, cytokinins, ethylene and ABA |
| Discovery of PGRs | Very frequent | Darwin, Went, Kurosawa, Skoog and the ethylene and ABA experiments |
| Growth and growth rates | Regular | Phases of growth, arithmetic vs geometric growth, the sigmoid curve |
| Differentiation and plasticity | Regular | Dedifferentiation, redifferentiation, heterophylly, phenotypic plasticity |
Growth and Its Phases
Growth is an irreversible, permanent increase in the size of an organ, its parts or a single cell. It is measured as fresh weight, dry weight, length, area, volume or cell number.
NCERT examples that are asked as facts:
- A single maize root apical meristem can produce more than 17,500 new cells an hour.
- Cells in a watermelon can increase in size up to 3,50,000 times.
| Phase of growth | Where in the root or shoot tip |
|---|---|
| Meristematic | At the apex; cells divide constantly, with large nuclei and thin walls |
| Elongation | Just behind the meristem; cells enlarge, vacuolate and lay down new walls |
| Maturation | Further back; cells reach their final size and shape |
Conditions for growth: water, oxygen, nutrients, an optimum temperature, and environmental signals such as light and gravity.
Arithmetic vs Geometric Growth
| Feature | Arithmetic growth | Geometric growth |
|---|---|---|
| What happens | Only one daughter cell keeps dividing; the other differentiates | Both daughter cells keep dividing |
| Equation | Lₜ = L₀ + rt | W₁ = W₀eʳᵗ |
| Curve | Linear | Sigmoid (S-shaped) |
| Example | A root elongating at a constant rate | Growth of cells, organs or a whole plant |
The sigmoid growth curve has three phases: a slow lag phase, a fast exponential (log) phase and a stationary phase, when growth slows because nutrients become limited.
Absolute vs relative growth rate: absolute growth rate is the total growth per unit time, while relative growth rate is growth per unit time per unit initial size. Two leaves can grow by the same area (same absolute rate) but at very different relative rates if one started much smaller.
Differentiation, Dedifferentiation and Redifferentiation
| Process | What happens | Example |
|---|---|---|
| Differentiation | Cells from meristems mature to perform specific functions | Tracheary elements lose their protoplasm and develop strong, lignified walls |
| Dedifferentiation | Differentiated living cells regain the ability to divide | Interfascicular cambium and cork cambium forming from fully differentiated parenchyma |
| Redifferentiation | Cells formed by dedifferentiated tissue mature again | Secondary xylem and secondary phloem formed by the cambium |
Growth in plants is open: cells from the same meristem give different structures depending on where they end up. For example, root apical meristem cells pushed to the tip become the root cap, while those pushed to the periphery mature as epidermis.
Development and Plasticity
Plants follow different pathways in response to the environment or the phase of life to form different structures. This ability is called plasticity.
- Heterophylly in cotton, coriander and larkspur: juvenile leaves differ in shape from mature leaves. This is plasticity linked to the stage of life.
- In buttercup, leaves produced in water differ from those produced in air. This is plasticity caused by the environment.
Phenotypic plasticity was asked in 2026 and several times before.
Plant Growth Regulators: The Overview
Plant growth regulators (PGRs) are small, simple molecules of diverse chemical nature.
| Chemical nature | PGR |
|---|---|
| Indole compounds | Indole-3-acetic acid (IAA), an auxin |
| Adenine derivatives | Kinetin (N⁶-furfurylamino purine), a cytokinin |
| Carotenoid derivatives | Abscisic acid (ABA) |
| Terpenes | Gibberellic acid (GA₃) |
| Gases | Ethylene |
| Type | PGRs | Role |
|---|---|---|
| Promoters | Auxins, gibberellins, cytokinins | Cell division, enlargement, flowering, fruiting, seed formation |
| Inhibitors | ABA (and ethylene, which can act either way but mostly inhibits) | Dormancy, abscission, responses to stress |
Discovery of PGRs
| Scientist or observation | PGR discovered |
|---|---|
| Charles and Francis Darwin: the coleoptile of canary grass bent towards light | Led to auxin |
| F.W. Went: isolated auxin from the coleoptile tips of oat (Avena) seedlings | Auxin |
| E. Kurosawa: “bakanae” (foolish seedling) disease of rice, caused by the fungus Gibberella fujikuroi | Gibberellic acid |
| F. Skoog and co-workers: tobacco callus divided only when the medium had vascular tissue extract, yeast extract, coconut milk or DNA; Skoog and Miller crystallised the active substance | Kinetin (cytokinin) |
| Cousins: a volatile substance from ripened oranges hastened the ripening of stored bananas | Ethylene |
| Three inhibitors (inhibitor-B, abscission II and dormin) found to be chemically identical in the mid-1960s | ABA |
NCERT also notes that auxin was first isolated from human urine. The discovery of cytokinins through Skoog’s experiments was asked in the 2024 Re-NEET.
Functions of Each PGR: The Table to Memorise
| PGR | Key functions and uses |
|---|---|
| Auxins (IAA, IBA natural; NAA, 2,4-D synthetic) | Rooting of stem cuttings; flowering in pineapple; prevent early fruit and leaf drop but promote abscission of older leaves and fruits; apical dominance (removing the shoot tip, or decapitation, lets lateral buds grow, used in tea plantations and hedges); parthenocarpy in tomato; 2,4-D kills dicot weeds but not mature monocots, so it keeps lawns weed-free; xylem differentiation |
| Gibberellins (over 100, GA₁, GA₂, GA₃…; all acidic) | Increase stalk length in grapes; elongate and improve the shape of apples; delay senescence so fruits can stay on the tree longer; speed up malting in brewing; increase sugarcane yield by up to 20 tonnes per acre; hasten seed production in juvenile conifers; cause bolting (internode elongation just before flowering) in beet and cabbage |
| Cytokinins (kinetin from autoclaved herring sperm DNA; zeatin from corn kernels and coconut milk) | Cell division (cytokinesis); new leaves, chloroplasts, lateral shoot growth and adventitious shoots; overcome apical dominance; delay leaf senescence by nutrient mobilisation |
| Ethylene (gas, made by senescing tissues and ripening fruits) | Ripening of fruits (raises the respiration rate, the respiratory climacteric); senescence and abscission of leaves and flowers; breaks seed and bud dormancy (germination of peanut seeds, sprouting of potato tubers); internode elongation in deep-water rice; flowering in pineapple and mango; female flowers in cucumber. Ethephon releases ethylene slowly and is the most widely used PGR in farming |
| ABA (“stress hormone”) | General growth inhibitor; inhibits seed germination; closes stomata; increases tolerance to stress; seed maturation and dormancy; generally antagonistic to gibberellins |
Worked PYQ-Pattern Questions
Q1. Bolting in cabbage and beet is caused by: (a) Auxins (b) Gibberellins (c) Cytokinins (d) ABA
Answer: (b) Gibberellins. They cause internode elongation just before flowering in rosette plants.
Q2. Which PGR is a gas and promotes fruit ripening?
Answer: Ethylene.
Q3. Which PGR is called the stress hormone and causes stomatal closure?
Answer: Abscisic acid (ABA).
Q4. “Bakanae” or foolish seedling disease of rice led to the discovery of: (a) Auxin (b) Gibberellin (c) Cytokinin (d) Ethylene
Answer: (b) Gibberellin, produced by the fungus Gibberella fujikuroi.
Q5. The formation of interfascicular cambium from parenchyma is an example of:
Answer: Dedifferentiation. The secondary xylem it then forms is an example of redifferentiation.
Q6. Why is 2,4-D used to keep lawns weed-free?
Answer: It is a synthetic auxin that kills broad-leaved dicot weeds but does not affect mature monocots such as grass.
Common Traps in This Chapter
- Linking bolting with auxins instead of gibberellins
- Saying cytokinins promote apical dominance (they overcome it; auxins cause it)
- Calling kinetin a natural plant hormone (it was obtained from autoclaved herring sperm DNA)
- Saying ABA promotes seed germination (it inhibits it)
- Swapping dedifferentiation and redifferentiation
- Calling heterophylly in buttercup stage-related (it is caused by the environment)
Practise Every Plant Growth and Development PYQ
This plant growth and development NEET PYQ analysis shows you where the marks are. Solving real past questions makes the PGR table automatic. Every previous year question from this chapter is available chapter-wise, free:
👉 Solve all Plant Growth and Development NEET PYQs
Keep the PGR functions table beside you for the first round, then solve the second round without it.
Conclusion
Plant Growth and Development comes down to one big table and a handful of experiments. Use this plant growth and development NEET PYQ analysis to master the five PGRs, their discovery and uses, the growth curves, differentiation and plasticity. Then practise the past questions until each match comes without thinking.
❓ FAQ
Q: How many questions come from Plant Growth and Development in NEET? A: Usually about two questions a year, mostly on plant growth regulators.
Q: What is the most important topic in this chapter for NEET? A: The functions and uses of plant growth regulators, especially gibberellins, ethylene and ABA, followed by their discovery.
Q: Which PGR causes bolting? A: Gibberellins. They cause internode elongation just before flowering in rosette plants such as beet and cabbage.
Q: Why is ABA called the stress hormone? A: It increases a plant’s tolerance to stresses such as drought, partly by closing the stomata, and it promotes seed dormancy.
Q: What is the difference between dedifferentiation and redifferentiation? A: In dedifferentiation, mature living cells regain the ability to divide. In redifferentiation, the cells produced then mature to perform specific functions again.
Q: Where can I practise Plant Growth and Development NEET PYQs for free? A: You can solve every previous year question from this chapter chapter-wise for free using the practice links in this article.
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