Germination of seeds.list down and explain phases of germination and types of germination (epigeal and hypogeal)
Germination of seeds is the process through which a plant emerges from a seed and begins to grow. The stages of seed germination typically involve distinct phases that concert to transition the seed from dormancy to active growth. Below are the phases of germination:
### Phases of Germination:
1. **Imbibition:**
This is the initial step wherein the dry seed absorbs water from the environment. The uptake of water leads to the seed swelling, and the seed coat may crack open. Water activates the seeds' metabolic processes required for germination.
2. **Activation of Enzymes:**
The increased hydration within the seed leads to the activation of various enzymes. These enzymes break down stored food resources within the seed, such as starches, into usable energy (sugars) to fuel growth.
3. **Radicle Emergence:**
The radicle, or embryonic root, is the first part of the seedling to emerge from the seed during germination. It grows downward in response to gravity (positive gravitropism), anchoring the plant and absorbing water and nutrients from the soil.
4. **Shoot Emergence:**
After the establishment of the radicle, the shoot (plumule) begins to grow upwards. This shoot will eventually become the stem and leaves of the plant.
5. **Seedling Growth:**
The seedling continues to grow and develops true leaves which will allow the plant to start photosynthesis. The initial leaves that appear are often called cotyledons and are part of the seed's embryo.
6. **Establishment of Seedling:**
Eventually, the seedling establishes a root system and begins to photosynthesize on its own, relying less on the food stored in the seed and more on the energy produced from photosynthesis. This establishes the seedling as an independent plant.
### Types of Seed Germination:
Seed germination can be classified into two main types based on the position of the cotyledons during seedling development: epigeal and hypogeal.
#### Epigeal Germination:
In epigeal germination, the cotyledons are pushed above ground level by the elongation of the hypocotyl (the stem of the seedling found beneath the cotyledons and above the radicle). This is commonly seen in plants like beans and sunflowers.
**Characteristics of epigeal germination:**
- The hypocotyl elongates.
- Cotyledons are raised above the soil surface and often become photosynthetic.
- The epicotyl (the portion of the stem above the cotyledons) grows and gives rise to the foliage leaves.
#### Hypogeal Germination:
In hypogeal germination, the cotyledons remain below the soil surface, and the epicotyl elongates. This is seen in plants like peas and maize.
**Characteristics of hypogeal germination:**
- The epicotyl elongates while the cotyledons stay within the seed coat, usually underground.
- The first foliage leaves develop and expand above the ground, photosynthesize, and promote further growth.
- The cotyledons may either shrink or sometimes serve as a source of nutrients for the seedling.
Both epigeal and hypogeal germination are adaptive strategies that plants have evolved in response to their environments. The type of germination can affect the early life stages of plants, including their susceptibility to factors like predation and disease.