Germination & Factors Affecting Germination | Biology for JAMB PDF Download

Germination

• Germination is the process by which a seed develops into a new plant.
• It involves the activation of the embryo within the seed, leading to the growth of the seedling.
• The key steps in germination include water absorption, activation of enzymes, and emergence of the radicle (embryonic root).

Factors Affecting Germination

• Water: Adequate water availability is crucial for seed germination. It softens the seed coat and triggers the release of growth-promoting substances.
  Example: Lettuce seeds require sufficient water for germination.
• Temperature: Seeds have specific temperature requirements for germination. Each species has an optimum temperature range for successful germination.
  Example: Tomato seeds germinate well at temperatures between 20°C and 30°C.
• Oxygen: Germination requires oxygen for the breakdown of stored food reserves and for energy production in the growing embryo.
  Example: Rice seeds need access to oxygen for germination.
• Light: Some seeds require light for germination, while others need darkness. Light may stimulate the synthesis of growth regulators or influence the behavior of the seed coat.
  Example: Petunia seeds need exposure to light for optimal germination.
• Seed Dormancy: Dormancy is a period of inhibited germination. It ensures that seeds only germinate under favorable conditions. Dormancy can be caused by factors such as seed coat impermeability, chemical inhibitors, or physiological dormancy.
  Example: Apple seeds have a hard seed coat, and they require a cold stratification period to break dormancy.

Types of Germination

• Hypogeal Germination: In this type, the cotyledons remain below the soil surface after germination.
  Example: Pea plants exhibit hypogeal germination.
• Epigeal Germination: Here, the cotyledons emerge above the soil surface during germination.
  Example: Bean plants display epigeal germination.
• Viviparous Germination: This type occurs when seeds germinate while still attached to the parent plant.
  Example: Some mangrove tree species exhibit viviparous germination.
• Intermediate Germination: Intermediate germination is a combination of hypogeal and epigeal germination, where the cotyledons partially emerge from the soil.
  Example: Squash plants demonstrate intermediate germination.