Explain phases of germination
Germination is the process by which a seed grows into a new plant. It involves several distinct phases, each with its own specific characteristics. These phases are:
1. Imbibition: In this initial phase, the seed absorbs water, typically through the seed coat. This triggers hydration, causing the seed to swell and soften.
2. Activation of enzymes: As water enters the seed, it activates certain enzymes that initiate biochemical reactions. These enzymes break down complex substances stored in the seed, such as starch and proteins, into simpler forms that can be used by the growing embryo.
3. Respiration: During germination, the embryo requires energy to sustain its growth. This is achieved through respiration, where stored nutrients are converted into a usable form of energy called adenosine triphosphate (ATP).
4. Radicle emergence: The radicle is the first part of the embryo to emerge from the seed. It is the embryonic root that will anchor the plant and absorb water and nutrients from the soil. The radicle typically grows downwards, pushing through the seed coat.
5. Shoot development: Once the radicle has established itself, the shoot system begins to develop. The shoot consists of the embryonic stem and leaves. The stem elongates as it grows upwards towards the surface. The first pair of leaves, called cotyledons, will eventually emerge from the soil.
6. Photosynthesis: As the leaves emerge, they undergo photosynthesis, a process that uses sunlight to convert carbon dioxide and water into glucose and oxygen. This provides the plant with energy for growth and development.
7. Establishment: With continued growth and development, the plant establishes itself and adapts to its environment. Roots spread further into the soil, enabling the plant to access a greater supply of water and nutrients, while the shoot system continues to grow above ground.
Throughout these phases, external factors such as temperature, light, and humidity play crucial roles in the germination process, influencing the rate and success of seed germination.