Question

Explain the process of germination in seeds with the help of diagram. Also describe the importance of air, water and warmth in the process.

Answer 1

The process of seed germination includes the following five changes or steps.

Such five changes or steps occurring during seed germination are: (1) Imbibition (2) Respiration (3) Effect of Light on Seed Germination(4) Mobilization of Reserves during Seed Germination and Role of Growth Regulators and (5) Development of Embryo Axis into Seedling.

(i) Imbibition:

The first step in the seed germination is imbibition i.e. absorption of water by the dry seed. Imbibition results in swelling of the seed as the cellular constituents get rehydrated. The swelling takes place with a great force. It ruptures the seed coats and enables the radicle to come out in the form of primary root.

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Imbibition is accomplished due to the rehydration of structural and storage macromolecules, chiefly the cell wall and storage polysaccharides and proteins. Many seeds contain additional polysaccharides, not commonly found in vegetative tissues. Seeds packed dry in a bottle can crack it as they imbibe water and become swollen.

(ii) Respiration:

Imbibition of water causes the resumption of metabolic activity in the rehydrated seed. Initially their respiration may be anaerobic (due to the energy provided by glycolysis) but it soon becomes aerobic as oxygen begins entering the seed. The seeds of water plants, as also rice, can germinate under water by utilizing dissolved oxygen.

The seeds of plants adapted to life on land cannot germinate under water as they require more oxygen. Such seeds obtain the oxygen from the air contained in the soil. It is for this reason that most seeds are sown in the loose soil near the surface. Ploughing and hoeing aerate the soil and facilitate seed germination. Thus the seeds planted deeper in the soil in water-logged soils often fail to germinate due to insufficient oxygen.

(iii) Effect of Light on Seed Germination:

Plants vary greatly in response to light with respect to seed germination. The seeds which respond to light for their germination are named as photoblastic. Three categories of photoblastic seeds are recognized: Positive photoblastic, negative photoblastic and non-photoblastic. Positive photoblastic seeds (lettuce, tobacco, mistletoe, etc.) do not 

Answer 2

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• Seed germination may be defined as the fundamental process by which different plant species grow from a single seed into a plant. This process influences both crop yield and quality.
• A common example of seed germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm.

The Process of Seed Germination

The complete process of seed germination is carried out in the following steps:

• During the beginning stage of the germination, the seeds take up water rapidly and this results in swelling and softening of the seed coat at an optimum temperature. This stage is referred to as an Imbibition. It starts the growth process by activation of enzymes. The seed activates its internal physiology and starts to respire and produce proteins and metabolizes the stored food. This is a lag phase of the seed germination.

• By rupturing of the seed coat, radicle emerges to form a primary root. The seed starts absorbing underground water. After the emerging of the radicle and the plumule, shoot starts growing upwards.

• In the final stage of seed germination, the cell of the seeds become metabolically active, elongate and divide to give rise to the seedling.