Introduction
Plant growth and development are crucial chapters in both NEET and CBSE Class 11 Biology. Understanding how plants grow and how hormones regulate this process is important not just for exams, but also for grasping key concepts in plant physiology.
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🌿 What is Plant Growth?
Growth in plants refers to an irreversible increase in size, usually accompanied by an increase in dry mass. It involves cell division (mitosis), cell elongation, and cell differentiation.
Plant growth is indeterminate, meaning it continues throughout their life due to the presence of meristems (actively dividing tissues).
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🔍 Phases of Growth
1. Meristematic Phase – cells are actively dividing.
2. Elongation Phase – cells elongate and expand in size.
3. Maturation Phase – cells differentiate and mature into specific tissues.
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📈 Growth Curve
Follows a sigmoid curve (S-shaped).
Has four phases:
1. Lag Phase (slow growth),
2. Log Phase (rapid growth),
3. Declining Phase (slowdown),
4. Stationary Phase (growth stops).
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☀️ Conditions for Growth
Water – for cell elongation and enzyme activity.
Oxygen – for respiration to release energy.
Temperature – optimal range for enzyme activity.
Light – influences seed germination, flowering.
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🌿 Plant Growth Regulators (Hormones)
These are chemical messengers that control various growth processes. There are five major types:
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1. Auxins
First discovered hormone.
Promote cell elongation, apical dominance, root initiation, and fruit development.
Examples: IAA (Indole-3-acetic acid), NAA.
Uses in agriculture: Weed killers, rooting hormones.
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2. Gibberellins
Stimulate stem elongation, seed germination, flowering, and fruit growth.
Break seed dormancy.
Example: GA₃ (Gibberellic acid).
Uses in agriculture: Elongation of sugarcane internodes, increasing fruit size in grapes.
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3. Cytokinins
Promote cell division, delay leaf senescence, and work with auxins to promote organogenesis.
Synthesized in roots.
Examples: Kinetin, Zeatin.
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4. Abscisic Acid (ABA)
Also called stress hormone.
Promotes dormancy, abscission (falling of leaves/fruits), and closes stomata during drought.
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5. Ethylene
A gaseous hormone.
Promotes fruit ripening, senescence, and leaf abscission.
Inhibits stem elongation but promotes horizontal growth.
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📘 Importance for NEET & CBSE
Frequently asked in NEET: Matching hormones with function.
Diagram-based MCQs on growth curve and hormone interactions.
Understanding application-based questions is crucial for scoring well.
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🌾 Application in Agriculture
Artificial ripening of fruits (Ethylene).
Tissue culture and cloning (Auxins + Cytokinins).
Increasing yield and controlling flowering (Gibberellins).
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🎯 NEET-Style MCQs
1. Which hormone is primarily responsible for apical dominance?
A. Gibberellin
B. Auxin
C. Cytokinin
D. Ethylene
✔️ Answer: B. Auxin
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2. Gibberellins are used in agriculture to:
A. Promote leaf fall
B. Break seed dormancy
C. Delay flowering
D. Promote senescence
✔️ Answer: B. Break seed dormancy
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3. Which plant hormone is gaseous in nature?
A. Ethylene
B. Auxin
C. Cytokinin
D. ABA
✔️ Answer: A. Ethylene
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4. Which of the following promotes seed dormancy?
A. Auxin
B. ABA
C. Cytokinin
D. Gibberellin
✔️ Answer: B. ABA
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5. A sigmoid growth curve is divided into how many phases?
A. Two
B. Three
C. Four
D. Five
✔️ Answer: C. Four
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🌿 Final Words
Understanding plant growth and the role of hormones is key to mastering NEET and CBSE Biology. Always relate theory to real-life examples in agriculture and biotechnology. Practice MCQs regularly and revise the functions of each hormone thoroughly.