Hormones in plants
Plants respond to stimuli slowly:
- Roots grow towards water.
- Shoots grow away from gravity.
- Shoots grow towards light – phototropism.
- Plant responds to unidirectional light (e.g. plant on a windowsill)
- Plant shoot bends towards light.
- Advantage of this response: - more light - more photosynthesis - more growth
How does a shoot bend towards unidirectional light?
- The shoot tip is sensitive to light and produces auxin – if the tip is covered phototropism doesn’t occur.
- Light causes the uneven distribution of auxin – it moves downwards and accumulates on the shaded side.
- Auxin causes cells on shaded side to elongate faster than on the illuminated side – this is known as differential growth.
- The stem bends towards light.