Coordination and Response in Plants - Summary Notes

Tropic Responses: Plant growth responses to environmental stimuli.
- Positive Phototropism:
- Shoots grow towards light, optimizing leaf positioning for photosynthesis.
- Flowers positioned for maximum visibility to pollinators.
Negative Gravitropism:
- Shoots grow upwards, enhancing competition for light and CO2.
- Flowers are elevated for better pollination.
- Example: Seed dispersal is more effective from vertically positioned fruits.
Experiment Interpretation:
- Young shoots display positive phototropism, demonstrating growth towards light.
- Caution: Results from a single plant can't be generalized across all species.
- A wider variety of plant species is required for thorough investigation.
Practical Work Questions:
- Importance of a clinostat in experiments involves preventing the effect of gravity on plant orientation.
- If seedlings are placed in a dark box, they would exhibit elongation due to lack of light, potentially leading to weak growth.
Rhizomes:
- Some stems (rhizomes) grow horizontally underground and are not negatively gravitropic; their shoots grow upwards.
Positive Gravitropism:
- Roots show positive gravitropism, growing downwards, anchoring the plant and sourcing water/mineral ions.
Plant Growth Substances:
- Controlled by chemical substances (e.g., hormones in animals, growth substances in plants).
- Auxin: A primary growth substance, produced in actively growing plant tips.