Seed Structure and Germination - International Baccalaureate Biology - Lecture Slides, Slides of Biology

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Seed Structure and Germination

Internal/External Structure, Metabolic events and Needs for Germination – Why do we have seeds?

Seed Development

Conditions for Germination

• 1. Water is needed to:
  • Activate hormones and enzymes
  • Swelling of the seeds = bursting of seed coat.
  • Transport of simple materials to the embryo – to be used for respiration and growth.
  • Metabolic and enzyme actions – occur in solution, therefore need water.
  • Conversion of storage compounds into simple components (i.e. starch to glucose)

Conditions for Germination

• 3. Suitable temperature
  • All reactions (in germination) are controlled by enzymes.
  • Optimal temperature for enzyme activity leads to faster rate of germination.
  • Freezing = inactivates enzymes
  • Very high temperatures = denatures enzymes

Metabolic Events of Germination

• 5. Gibberelline activates amylase which catalyzes the break down of starch to maltose to glucose.
• 6. Glucose is mobilized (transported) to the embryo.
• 7. Embryo absorbs glucose and uses it for respiration (oxygen needed).
• 8. Cell division, growth and elongation occurs in the embryo = radicle to root, plumule to stem.

Metabolic Events in Germination

• 9. Nutrients needed for growth all supplied by food stored in cotelydons.
• 10. As nutrients are consumed, first leaves start to appear = photosynthesis.
• 11. When photosynthesis starts, seedling absorbs water and minerals from the soil, Co from the atmosphere and sunlight.