🌱 Plant Growth and Development – NEET 2025 Notes, Diagrams & MCQs

🌿 Introduction: Growth — The Defining Feature of Life

Every seed you sow holds the potential to become a magnificent plant. But what makes it grow?

Growth and development in plants are not random — they follow a well-coordinated process involving cell division, enlargement, and differentiation, all controlled by plant hormones.

For NEET aspirants, this chapter is a frequently tested section in Plant Physiology. Let’s break it down in a simple, clear, and exam-oriented way.

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🌳 Section 1: What is Plant Growth?

Growth is a permanent, irreversible increase in size, volume, or number of cells.

In plants, growth is indeterminate, meaning it continues throughout life due to the presence of meristems.

📘 Characteristics of Growth

1. Irreversible: Once a cell enlarges, it cannot return to its previous size.

2. Permanent: The increase remains stable over time.

3. Metabolically active: Requires energy from respiration.

4. Quantitative: Can be measured (length, volume, weight, etc.).

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🌿 Section 2: Phases of Growth

Growth in plants occurs in three distinct phases.

Imagine a root tip — it beautifully demonstrates all three:

1️⃣ Meristematic Phase (Region of cell division):

Located at root and shoot tips.

Cells are small, rich in cytoplasm, and actively dividing.

Example: Root apical meristem, shoot apical meristem.

2️⃣ Elongation Phase:

Cells increase in size due to vacuole enlargement.

Responsible for the lengthening of the plant organ.

3️⃣ Maturation Phase:

Cells attain permanent shape and function.

Tissues differentiate into xylem, phloem, etc.

🔹 Graphical Representation:

Growth curve is sigmoid (S-shaped) — includes lag, log (exponential), and stationary phases.

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🌺 Section 3: Growth Rate

Growth rate is the increase in growth per unit time.

Formula:

Relative Growth Rate (RGR) = 

Where W = Weight, t = Time

Types of Growth:

Arithmetic Growth: One daughter cell divides while the other differentiates.

Example: Root elongation.

Formula: 

Geometric Growth: Both cells divide continuously (as in meristematic tissues).

Formula: 

NEET Tip:

Growth rate is maximum during the log phase.

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🌾 Section 4: Conditions for Growth

Plant growth depends on intrinsic and extrinsic factors:

Intrinsic: Hormones, genes, enzyme systems.

Extrinsic: Temperature, water, oxygen, nutrients, and light.

Water: Essential for cell enlargement.

Temperature: Optimum 25–30°C.

Light: Regulates photomorphogenesis.

Minerals: Nitrogen and potassium aid growth.

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🌼 Section 5: Plant Growth Regulators (Plant Hormones)

Plants coordinate growth using chemical messengers called hormones or phytohormones.

There are five major hormones with distinct roles.

Hormone Site of Synthesis Function Example NEET Question

Auxins Shoot tip Cell elongation, apical dominance IAA promotes rooting

Gibberellins (GA) Young leaves, seeds Stem elongation, seed germination GA breaks seed dormancy

Cytokinins Root tips Cell division, delay in senescence Found in coconut milk

Abscisic Acid (ABA) Mature leaves Stress hormone, stomatal closure Causes seed dormancy

Ethylene Ripening fruits Fruit ripening, abscission Induces triple response

Easy Trick to Remember:

👉 “A Great Cook Always Eats”

(Auxin – GA – Cytokinin – ABA – Ethylene)

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🌻 Section 6: Development and Differentiation

Development = Sum total of growth + differentiation + maturation.

Differentiation: Cells become specialized (e.g., tracheids, xylem vessels).

Dedifferentiation: Mature cells regain ability to divide (e.g., interfascicular cambium).

Redifferentiation: Dedifferentiated cells again become specialized.

Example:

Parenchyma → Cambium → Secondary xylem/phloem

NEET Concept Link:

Tissue culture depends on the totipotency of cells — ability to form a whole plant from one cell.

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🌿 Section 7: Photoperiodism

Plants respond to day and night length — this is called photoperiodism.

It controls flowering and growth patterns.

Type of Plant Flowering Condition Example

Short Day Plants < 12 hours light Rice, Chrysanthemum

Long Day Plants > 12 hours light Wheat, Barley

Day Neutral Plants Independent of day length Tomato, Cucumber

Receptor: Phytochrome — a light-sensitive pigment.

Forms:

Pr absorbs red light (660 nm)

Pfr absorbs far-red light (730 nm)

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🌸 Section 8: Vernalization

Vernalization = Flowering induced by prolonged exposure to low temperature.

Example:

Wheat, cabbage, and beet require cold treatment to flower.

NEET Question Example:

“Which plant hormone replaces the need for vernalization?”

👉 Gibberellin (GA)

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🌱 Section 9: Seed Dormancy and Germination

Seeds remain dormant due to presence of ABA.

Breaking dormancy involves:

Leaching of inhibitors

Softening of seed coat

Application of Gibberellin (GA₃)

Germination Types:

1. Epigeal: Cotyledons above soil (Bean, Castor).

2. Hypogeal: Cotyledons below soil (Maize, Pea).

Condition Required for Germination: Water, oxygen, optimum temperature, and sometimes light.

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🧠 Section 10: NEET PYQs on Plant Growth and Hormones

1️⃣ NEET 2023:

Which hormone is responsible for fruit ripening?

✅ Ethylene

2️⃣ NEET 2021:

Apical dominance is caused by:

✅ Auxin

3️⃣ NEET 2020:

Which hormone promotes seed dormancy?

✅ Abscisic Acid

4️⃣ NEET 2019:

Which hormone delays senescence?

✅ Cytokinin

5️⃣ NEET 2018:

Which process converts meristematic cells to permanent cells?

✅ Differentiation

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🌿 Section 11: Summary Table for Quick Revision

Concept Keyword Example

Growth Irreversible increase Root tip elongation

Phases Meristematic → Elongation → Maturation Root apex

Hormones Auxin, GA, Cytokinin, ABA, Ethylene Different functions

Development Growth + Differentiation Totipotency

Photoperiodism Day length effect Rice, Wheat

Vernalization Cold treatment Cabbage, Beet

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🌺 Conclusion

Plant Growth and Development explains how plants grow, differentiate, and adapt.

Understanding hormones and their interactions helps NEET aspirants score high, as 3–4 questions from this chapter are almost guaranteed each year.

Keep revising the growth curve, hormone chart, and phytochrome mechanism — these are NEET favorites!