m/j 2006
You could say something along the lines:
- Negative geotropism - grows opposite direction to gravity. This ensures shoots grow upwards getting the leaves into sunlight.
- Positive phototropism - grows towards the light. This means leaves expose maximum sruface area to light. They can therefore absorb more light more efficiently for photosynthesis.
- Mention auxin as well.
- Talk about shoots grow because cells multiply by mitosis - leading to growth.