Plant Growth And Development Notes

Introduction

Plant growth and development are fundamental topics in botany, essential for understanding how plants progress from seed to mature organism. This study note will cover all relevant aspects of plant growth and development as per the NEET Botany syllabus, breaking down complex ideas into manageable sections.

Phases of Plant Growth

1. Meristematic Phase

• Location: Found at the root and shoot apices.
• Characteristics: Cells in this phase are small, have dense cytoplasm, and thin cell walls. They are actively dividing.

2. Elongation Phase

• Location: Just behind the meristematic region.
• Characteristics: Cells elongate and enlarge, contributing to the lengthening of plant parts.

3. Maturation Phase

• Location: Behind the elongation region.
• Characteristics: Cells attain their final size and form, and they differentiate to perform specific functions.

Factors Affecting Plant Growth

Intrinsic Factors

1. Genetic Factors: Determine the potential growth and development patterns.
2. Hormonal Control: Plant hormones like auxins, gibberellins, cytokinins, ethylene, and abscisic acid play critical roles.

Extrinsic Factors

1. Light: Essential for photosynthesis and photoperiodism.
2. Water: Critical for cell turgidity and metabolic processes.
3. Nutrients: Crucial for various biochemical pathways.
4. Temperature: Affects enzymatic activities and metabolic rates.

Plant Growth Regulators (PGRs)

Auxins

• Functions: Promote cell elongation, root initiation, and differentiation.
• Example: Indole-3-acetic acid (IAA).

Gibberellins

• Functions: Promote stem elongation, seed germination, and flowering.
• Example: Gibberellic acid (GA).

Cytokinins

• Functions: Promote cell division, delay leaf senescence, and enhance nutrient mobilization.
• Example: Kinetin.

Ethylene

• Functions: Promotes fruit ripening, leaf abscission, and stress responses.
• Example: Ethylene gas.

Abscisic Acid (ABA)

• Functions: Induces dormancy, closes stomata, and promotes stress tolerance.
• Example: Abscisic acid.

Photoperiodism and Vernalization

Photoperiodism

• Definition: The response of plants to the relative lengths of light and dark periods.
• Types:
  • Short-Day Plants: Flower when the day length is shorter than a critical period.
  • Long-Day Plants: Flower when the day length is longer than a critical period.
  • Day-Neutral Plants: Flower irrespective of the day length.

Vernalization

• Definition: The induction of flowering by a period of cold temperature.
• Significance: Ensures that flowering occurs at a favorable time.

Seed Dormancy and Germination

Seed Dormancy

• Definition: A period during which seeds do not germinate despite favorable conditions.
• Causes: Hard seed coat, immature embryo, chemical inhibitors.
• Breaking Dormancy: Scarification, stratification, and exposure to light or specific chemicals.

Seed Germination

• Phases:
  1. Imbibition: Absorption of water by seeds.
  2. Enzymatic Activity: Activation of enzymes that mobilize stored food.
  3. Radicle Emergence: The radicle breaks through the seed coat.

Growth Curves

Sigmoid Growth Curve

• Phases:
  1. Lag Phase: Slow growth as the plant adapts.
  2. Log Phase: Rapid growth due to cell division and elongation.
  3. Stationary Phase: Growth rate declines as resources become limited.

Equation for Growth Rate

$$ \text{Growth Rate} = \frac{\Delta \text{Size}}{\Delta \text{Time}} $$

Conclusion

Understanding the intricacies of plant growth and development is essential for both academic purposes and practical applications in agriculture and horticulture. By mastering these concepts, students can better appreciate the dynamic processes that drive plant life.

By breaking down these complex ideas into smaller, digestible parts, you can build a solid foundation in this critical area of botany.