Germination

There are 3 conditions needed for germination:

1. Water – is needed to activate enzymes.
2. Oxygen – is needed to allow respiration.
3. A suitable temperature is needed to allow enzyme action to proceed.

Events in Germination

• Seeds store food in the form of oils, starch, and protein.

• Germination begins when the seed absorbs water through the testa. Water activates enzymes that digest the stored food:

  • Oils are digested to fatty acids and glycerol.
  • Starch is digested to glucose.
  • Proteins are digested to amino acids.

• The products of digestion are moved to the growing embryo.

• Glucose and amino acids are used to build new structures like cell walls and enzymes.

• Fats and some glucose are used in respiration to produce energy.

• The dry weight of the seed decreases as food stores are used up in respiration.

• The weight of the embryo increases as it grows.

• The radicle (future root) bursts through the testa and grows downward, absorbing water and minerals.

• The plumule (future shoot) grows upward and emerges above the ground.

• Once the first leaves develop and start photosynthesising, the seedling begins producing its own food, and its dry weight increases again.

Types of Germination

• There are two types of germination; 4. Epigeal germination 5. Hypogeal germination
• The seed absorbs water and swells. The radicle emerges from the seed, growing downward due to gravity (geotropism), and the roots begin absorbing water and minerals from the soil.
• The hypocotyl, the part of the embryo below the cotyledons, grows rapidly, leading to one of the two types of germination.

Epigeal Germination:

• The cotyledons are pushed above the ground, where they may photosynthesise.
• Example: Sunflower seeds. _E_pigeal = above ground

E for exiting soil

Hypogeal Germination:

• The cotyledons remain below the ground and do not photosynthesise.
• Example: Beans. _H_ypogeal = below ground

H for staying hidden in the soil

6. Seed absorbs water, activating enzymes.
7. Stored food is digested:

• Oils → Fatty acids + glycerol.
• Starch → Glucose.
• Proteins → Amino acids.

8. Products fuel embryo growth:
9. Glucose + amino acids —> cell walls + enzymes
10. Glucose + fats —(respiration)—> energy
11. Dry mass falls due to foods used in respiration. The weight of the embryo increases.
12. Radicule bursts through the testa and grows down (geotropism).
13. Plumule emerges above ground and leaves are produced.
14. When the leaves begin to photosynthesise, the dry mass increases again.

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