Plant HormonesEdexcel GCSE Biology: Revision notes
Section 1
Coordination in Plants
Plants respond via hormones causing growth changes. A tropism is directional growth to a stimulus (positive=towards, negative=away).
Section 2
Auxin and Phototropism
Auxin, made in shoot/root tips, accumulates on the shaded side with light from one direction, causing that side to elongate more — shoot bends towards light (phototropism).
Auxin accumulates on shaded side, not moving towards light itself.
Section 3
Auxin and Gravitropism
Gravitropism: in shoots, auxin builds on lower side → more growth → bends up (negative gravitropism). In roots, auxin inhibits growth on lower side → bends down (positive gravitropism).
Root on its side: auxin inhibits lower-side growth, root curves downward.
Section 4
Commercial Uses
| Hormone | Use |
|---|---|
| Auxin | Weedkillers, rooting powder |
| Gibberellins | Germination, flowering, seedless fruit |
| Ethene | Fruit ripening |
Link each use to WHY the hormone suits it.
Must Know
- Auxin: shaded/lower side accumulation; more growth in shoots, less in roots.
- Weedkillers/rooting powder = auxin.
- Gibberellins: germination, flowering, seedless fruit.
- Ethene: fruit ripening.
That's the notes covered.
Carry on to the next subtopic.