What a seed needs
The following factors are essential for seed germination. If any one of them is missing, nothing happens.
- The viability of the seed
- Air (oxygen)
- Water
- Temperature
What water actually does
In seed germination, water activates the enzymes present within the seed leaves, and these digest the complex food stored there into simple food. By means of that food, the radicle and the plumule grow.
The other three follow from that one sentence. Digesting the store and building new tissue takes energy, which comes from respiration — so oxygen is needed. Enzymes only work within a range of temperature. And all of it is useless unless the embryo is still alive, which is what viability means.
Light is not on the list
A germinating seed needs no light — it is living on a packed lunch, not photosynthesising. That is exactly why seeds can germinate buried in soil, and why light becomes necessary only once the first leaves are above ground and the food store has run out.
Activity 14.5
Plan a suitable activity in order to test the external factors needed for seed germination.