JAMB Biology Note- Growth

SubTopics:

a. meaning of growth
b. Germination of seeds and conditions necessary for germination of seeds.

Table of Contents

• SubTopics:
  • A. Meaning of Growth
  • B. Germination of Seeds
    • Conditions Necessary for Germination:
  • C. Types of Germination
    • 1. Epigeal Germination
    • 2. Hypogeal Germination
  • Summary

A. Meaning of Growth

• Growth refers to the increase in size and mass of an organism over time. This process involves cellular division, differentiation, and elongation.
• Growth in plants typically occurs in the meristematic regions such as the tips of roots and shoots.

B. Germination of Seeds

Germination is the process by which a seed develops into a new plant. It involves the seed absorbing water, swelling, and eventually sprouting. For successful germination, several conditions must be met:

Conditions Necessary for Germination:

1. Water:
   • Seeds need to absorb water (imbibition) to activate enzymes, which in turn start the metabolic processes necessary for growth.
2. Oxygen:
   • Oxygen is essential for cellular respiration, which provides energy for the growth of the seedling.
3. Temperature:
   • Each plant species has an optimal temperature range for germination. Extreme temperatures (either too high or too low) can prevent germination.
4. Light (for some seeds):
   • Some seeds require light to germinate, while others germinate best in darkness. Light is not essential for all seeds.
5. Suitable Soil (for certain seeds):
   • The right soil provides necessary nutrients, and it also needs to be well-drained to prevent waterlogging, which could harm the seed.

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C. Types of Germination

There are two main types of seed germination: epigeal and hypogeal.

1. Epigeal Germination

• Definition: In epigeal germination, the cotyledons (seed leaves) are brought above the ground as the seedling grows.
• Process:
  • The hypocotyl elongates and pushes the seedling and the cotyledons above the soil surface.
  • Example: Bean plants, sunflower.
• Key Features:
  • Cotyledons are exposed above the soil.
  • The primary root (radicle) emerges first, followed by the shoot (plumule).

2. Hypogeal Germination

• Definition: In hypogeal germination, the cotyledons remain underground while the shoot emerges and grows upwards.
• Process:
  • The epicotyl elongates and pushes the shoot upwards, while the cotyledons remain beneath the soil surface.
  • Example: Pea, maize.
• Key Features:
  • Cotyledons remain below the surface of the soil.
  • The first leaves appear above the soil.

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Summary

Growth in plants involves an increase in size and mass, facilitated by conditions like water, oxygen, and temperature. Germination of seeds, the first stage in a plant’s growth, requires specific conditions such as water, oxygen, and the right temperature. The two main types of germination are epigeal and hypogeal, which differ in how the seed leaves (cotyledons) behave during the process.