Germination of seeds list down and explain phases of germination and types of germination (epigeal and hypogeal)
The germination of seeds is the process by which a seed develops into a seedling. It involves a series of phases that enable the seed to break dormancy and initiate growth. There are two primary types of germination: epigeal germination and hypogeal germination.
Phases of Germination:
1. Imbibition: This is the first phase where the seed absorbs water through its seed coat. The increased water uptake softens the protective seed coat and triggers metabolic activities within the seed.
2. Activation: Once the seed absorbs water, it activates enzyme systems essential for growth. These enzymes break down stored complex organic materials within the seed into simpler forms that can be readily utilized by the seedling.
3. Respiration: As the seed becomes metabolically active, cellular respiration increases to provide energy for growth. Oxygen is absorbed, and carbon dioxide is released during this phase.
4. Growth: After activation and respiration, the growth phase begins. The radicle, the embryonic root, emerges and starts to grow downward, anchoring the plant into the soil. Simultaneously, the shoot emerges and grows upwards towards the light.
5. Development of Cotyledons: As the shoot elongates, the cotyledons (seed leaves) unfold and emerge above the ground. Cotyledons play a crucial role in providing initial nutrients to the growing seedling.
6. Establishment of Photosynthesis: Once the cotyledons emerge, true leaves begin to develop, and photosynthesis becomes active. The plant starts producing its energy, reducing its reliance on stored nutrients from the cotyledons.
Types of Germination:
1. Epigeal Germination: In epigeal germination, the cotyledons are pushed above the ground level as the seedling grows. The cotyledons expand and turn green, performing photosynthesis. Examples of plants exhibiting epigeal germination include beans, peas, and sunflowers.
2. Hypogeal Germination: In hypogeal germination, the cotyledons remain below the ground throughout the germination process. Only the shoot emerges above the soil surface. The true leaves develop and photosynthesis starts within the shoot. Examples of plants with hypogeal germination include maize, wheat, and rice.