Germination of seeds,list down and explain phases of germination and types of germination (epigeal and hypogeal
The process of germination is the initial growth of a seed into a new plant. It can be divided into several phases, each with distinct characteristics. Additionally, there are two main types of germination: epigeal and hypogeal. Let's explore them in more detail:
Phases of Germination:
1. Imbibition: During this phase, the seed takes in water through its outer covering, called the seed coat. This allows the seed to swell and become activated. Imbibition helps to rehydrate the seed tissues and reactivate the metabolic processes required for germination.
2. Activation: The dormant seed begins to prepare for germination by resuming metabolic activity. Enzymes and proteins become active again, and the stored nutrients within the seed are mobilized to fuel future growth.
3. Respiration: As the seed becomes metabolically active, it requires energy to grow. Hence, it undergoes aerobic respiration to convert stored carbohydrates into usable forms of energy, such as ATP (adenosine triphosphate). This phase releases carbon dioxide and heat as byproducts.
4. Early Growth: The radicle, which is the embryonic root, emerges from the seed and grows downward. This phase also involves the development of the hypocotyl, which connects the radicle to the cotyledons (embryonic leaves). The cotyledons may also emerge from the seed, depending on the type of germination.
5. Seedling Establishment: Once the radicle anchors the seedling into the growing medium, the shoot system begins to develop. The plumule, which harbors the embryonic shoot, emerges from the cotyledons or directly from the growing point of the seedling. The first true leaves appear, and the plant starts photosynthesizing to sustain growth.
Types of Germination:
1. Epigeal Germination: In this type, the cotyledons emerge above the ground level after the germination process. They turn green and start photosynthesizing. The plumule elongates and forms the shoot above the cotyledons. Examples of plants that exhibit epigeal germination are sunflowers, beans, and melons.
2. Hypogeal Germination: In hypogeal germination, the cotyledons remain underground or stay inside the seed coat. The epicotyl, which is the part above the cotyledons, grows and develops into a shoot system. The cotyledons usually have a white or pale yellow color, as they do not perform photosynthesis. Examples of plants with hypogeal germination are peas, potatoes, and onions.
Both epigeal and hypogeal germination are natural strategies employed by plants for survival and dispersal. The specific type of germination exhibited by a plant depends on its evolutionary adaptations and environmental conditions.