9.6 Growth and Development in Plants

What is Growth?

Growth is defined as an irreversible, permanent increase in the size, volume, or dry weight of an organism or its parts. It is accompanied by metabolic processes — both anabolism (building up) and catabolism (breaking down).

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What is Development?

Development is the sum total of all changes an organism undergoes during its entire life cycle — from germination of the seed to senescence (ageing and death). It includes:

• Growth — increase in size
• Differentiation — cells becoming specialised
• Morphogenesis — formation of body shape and structure

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Phases of Plant Growth

Plant growth occurs in three sequential phases:

1. Phase of Cell Division (Formative Phase)

• Occurs in meristematic zones (regions of actively dividing cells)
• Cells undergo rapid mitosis
• Cells are small, have thin walls, dense cytoplasm, and large nuclei
• No vacuole or very small vacuole present

2. Phase of Cell Elongation

• Cells produced by division increase in size
• Water uptake increases turgor pressure
• Cell wall becomes plastic (extensible) and stretches
• Central vacuole enlarges significantly
• This phase is responsible for the visible increase in plant length

3. Phase of Cell Maturation (Differentiation)

• Cells acquire their final specialised structure and function
• Cell wall may thicken and become rigid
• Cells differentiate into xylem, phloem, epidermis, etc.
• Metabolic activity stabilises

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Meristems and Types of Growth

Growth in plants is localised in regions called meristems — zones of actively dividing, undifferentiated cells.

Primary Growth (Increase in Length)

• Produced by Apical Meristems located at the tips of roots and shoots
• Results in elongation of the plant body
• Occurs in all plants (herbaceous and woody)

Secondary Growth (Increase in Girth)

• Produced by Lateral Meristems — found in woody dicots and gymnosperms
• Results in increase in diameter (thickness) of stems and roots
• Two types of lateral meristems:

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Summary Table