IGCSE Biology / Reproduction in plants
Seed structure and germination revision notes
Edexcel International GCSE Biology (4BI1), chapter 13: Reproduction in plants, specification point 3.5, 3.6. Free lesson.
Watch the video lesson · IGCSE Biology past papers
A seed contains a young plant and stored food, and germination begins when the right conditions activate its growth. You need to know the parts of a seed, the stages of germination and how to test which conditions are needed.
What the parts of a seed do
A bean seed contains an embryo, which is the young plant, and food to help it start growing. The tough testa protects the seed from damage and drying out. Plumule: the part of the embryo that becomes the shoot. Radicle: the part that becomes the root. Cotyledons: seed leaves that store starch as food. Micropyle: a small hole where water enters the seed.
How germination starts and continues
Germination does not begin with growth. First, the seed absorbs water through the micropyle. Water activates enzymes in the cotyledons, which make the stored food available for respiration and building new cells.
Which conditions seeds need
Seeds need water, oxygen and a suitable temperature to germinate. Water activates enzymes, oxygen is needed for respiration, and warmth provides a suitable temperature for these processes. Light is not needed: the seed has no chlorophyll and uses food stored in the cotyledons until the shoot reaches the light. Water, oxygen and warmth are the three conditions to remember. Light is not a condition for germination.
How to test the conditions for germination
Use four tubes of seeds and change one condition at a time. Tube 1 is the control: it has all three conditions, so it provides a comparison for the other tubes. Leave the tubes for a week and record which seeds germinate. Tube 1: water, air and warmth. Tube 2: air and warmth, but no water. Use dry cotton wool. Tube 3: water and warmth, but no air. Boil the water first to remove dissolved oxygen, then cover it with oil. Tube 4: water and air, but cold. Keep it in a refrigerator. Only tube 1 germinates, showing that water, oxygen and a suitable temperature are all needed.