Germination - SS3 Biology Lesson Note

Germination is the process by which a seed begins to develop into a new plant. It involves the resumption of metabolic activities and the emergence of the embryonic shoot and root from the seed. Germination typically occurs when the environmental conditions are favourable for the seed to grow. Here is an overview of the process of germination:

1.       Absorption of Water: The first step in germination is the imbibition, or absorption, of water by the seed. Water uptake triggers enzymatic activity and metabolic processes within the seed, leading to the activation of dormant structures and the initiation of growth.

2.       Activation of Enzymes: With the presence of water, enzymes within the seed become active. These enzymes break down stored food reserves, such as starches, proteins, and oils, into simpler forms that can be utilized by the growing embryo.

3.       Embryo Growth: As the stored nutrients are broken down, the embryo starts to grow. The embryonic shoot, known as the plumule, elongates and pushes through the seed coat, eventually emerging above the soil surface. The radicle, the embryonic root, grows downward and anchors the emerging plant into the soil.

4.       Development of Roots and Shoots: Once the radicle emerges, it develops into the primary root, which begins to grow and branch out to establish the root system. Simultaneously, the plumule elongates and forms the shoot system, giving rise to the stems, leaves, and eventually, reproductive structures.

5.       Photosynthesis: As the shoot emerges and develops leaves, photosynthesis is initiated. The leaves produce chlorophyll and utilize light energy to convert carbon dioxide and water into glucose, providing energy for the growing plant.

6.       Establishment of Seedling: With the emergence of roots and shoots and the initiation of photosynthesis, the seedling becomes established and can start to sustain itself independently. The seed coat, which served as protection, may be shed or remain attached as the plant continues to grow.

The specific requirements for germination can vary depending on the plant species. Factors such as temperature, moisture, oxygen availability, and light conditions play crucial roles in initiating and promoting germination. Adequate amounts of these factors, along with suitable soil conditions, are essential for successful seed germination and subsequent plant growth.

Germination is a critical phase in the life cycle of plants, enabling them to establish and propagate in various environments. It allows seeds to utilize their stored resources and transform into fully functional plants capable of carrying out photosynthesis and completing their life cycle.

There are several types of germination, each exhibiting unique characteristics and adaptations. The main types of germination include:

1.       Hypogeal Germination: In hypogeal germination, the cotyledons remain below the soil surface after germination. The epicotyl (embryonic shoot) elongates and raises the plumule above the ground, while the cotyledons remain within the seed or remain partially exposed. Examples of plants with hypogeal germination include beans, peas, and peanuts.

2.       Epigeal Germination: Epigeal germination is characterized by the cotyledons emerging above the soil surface after germination. The epicotyl elongates and raises the plumule, along with the cotyledons, into the air and light. The cotyledons become green and perform photosynthesis. Many dicotyledonous plants, such as sunflowers and tomatoes, exhibit epigeal germination.

Each type of germination is associated with specific ecological and physiological adaptations that enable plants to successfully establish and grow in various environments. Understanding these different types of germination helps us appreciate the diversity and resilience of plant life.