Chapter Overview & Weightage
Plant Growth and Development is a NEET-favourite chapter. It is rich in plant hormones (5 major + 2 minor), photoperiodism, and vernalisation — all of which produce factual MCQs that reward memorisation.
Typical NEET weightage: questions per year.
| Year | NEET Qs | Question type |
|---|---|---|
| 2020 | 3 | Hormone functions, discoverer matching |
| 2021 | 2 | Apical dominance, photoperiodism |
| 2022 | 3 | Hormone applications |
| 2023 | 2 | Vernalisation, ABA functions |
| 2024 | 3 | Differentiation, redifferentiation, dedifferentiation |
Key Concepts You Must Know
- Phases of growth: meristematic, elongation, maturation
- Differentiation, dedifferentiation, redifferentiation
- Five major plant hormones: auxin, gibberellin, cytokinin, abscisic acid (ABA), ethylene
- Photoperiodism: long-day, short-day, day-neutral plants
- Vernalisation: low-temp requirement for flowering
- Plasticity in plants (heterophylly)
- Senescence and abscission
Important Formulas
This chapter has no formulas. Below are key matchings.
| Hormone | Discoverer | Key role |
|---|---|---|
| Auxin (IAA) | F. W. Went | Apical dominance, phototropism, root initiation |
| Gibberellin | E. Kurosawa | Stem elongation, bolting, breaking dormancy |
| Cytokinin | F. Skoog & Miller | Cell division, delaying senescence |
| ABA | Addicott | Stress hormone, stomatal closure, dormancy |
| Ethylene | H. H. Cousins | Fruit ripening, senescence, abscission |
| Type | Critical day length | Examples |
|---|---|---|
| Short-day | Below critical | Chrysanthemum, soybean |
| Long-day | Above critical | Wheat, spinach, henbane |
| Day-neutral | Insensitive | Tomato, cucumber |
Solved Previous Year Questions
PYQ 1 (NEET 2024)
Match the hormone with its commercial use: (a) Auxin → (i) Promote fruit ripening (b) Gibberellin → (ii) Inducing parthenocarpy (c) Cytokinin → (iii) Tissue culture (d) Ethylene → (iv) Increasing sugar yield
(a)→(ii), (b)→(iv), (c)→(iii), (d)→(i).
Auxin induces parthenocarpy (seedless fruit). Gibberellin in sugarcane increases internode length and sugar yield. Cytokinin in tissue culture promotes shoot initiation. Ethylene ripens fruits.
PYQ 2 (NEET 2023)
What is vernalisation?
The process by which flowering is promoted by exposure to low temperatures. Required by certain plants (e.g., winter wheat) to transition from vegetative to reproductive phase. Without cold exposure, the plant remains vegetative.
PYQ 3 (NEET 2022)
Which hormone is called the “stress hormone” of plants?
Abscisic acid (ABA). It accumulates under drought, salt, and cold stress and triggers stomatal closure, leaf abscission, and dormancy.
Difficulty Distribution
| Difficulty | % of NEET Qs | Typical type |
|---|---|---|
| Easy | Direct hormone-function matching | |
| Medium | Photoperiodism, vernalisation, applications | |
| Hard | Differentiation/dedifferentiation conceptual MCQs |
Expert Strategy
Make a hormone-discoverer-function-application table on a single A4 sheet. Revise it every two days. NEET’s hormone questions are scoreable in 30 seconds with this table memorised.
For photoperiodism, the critical “perception” organ is the leaf, but “response” (flowering) is in the apex. NEET examiners flip these to confuse students.
Memorise example plants for short-day (chrysanthemum, tobacco), long-day (henbane, spinach), and day-neutral (tomato). NEET often asks “which is a long-day plant?”.
Common Traps
Saying short-day plants need short DAYS. They actually need a long enough NIGHT. Interrupting the dark period with a flash of light prevents flowering.
Confusing differentiation, dedifferentiation, and redifferentiation. Differentiation: meristem → mature cell. Dedifferentiation: mature → meristem-like (e.g., callus). Redifferentiation: dedifferentiated tissue → mature again.
Saying ethylene is a liquid. It’s a gaseous hormone — only one of the five.
Assuming all hormones promote growth. ABA is the inhibitor — it triggers dormancy and stomatal closure.