Coordination And Response In Plants: Coordination And Response In Plants
15.1 Coordination And Response In Plants
Tropisms (Plant Responses To Stimuli)
- Phototropism → Growth response to light.
- Shoots grow towards light (positive).
- Roots usually show no response or negative phototropism.
- Gravitropism (geotropism) → Growth response to gravity.
- Roots grow towards gravity (positive).
- Shoots grow away from gravity (negative).
Role Of Auxin
- Plant hormone controlling shoot and root growth.
- Made in shoot tip, spreads downward.
- Unequally distributed in response to light or gravity.
- Stimulates cell elongation in shoots.
- In roots, higher auxin concentration inhibits growth.
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course
Investigations
- Phototropism experiment: Cover tip of shoot with opaque cap → no bending (auxin activity blocked).
- Gravitropism experiment: Place seedlings on side → roots bend downwards, shoots bend upwards.
Key Points
- Tropisms help plants survive:
- Shoots towards light → better photosynthesis.
- Roots into soil → water and minerals uptake, anchorage.
- Auxin = key hormone controlling directional growth.
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course