Summary IGCSE / GCSE Notes on the Plant Coordination and Response Topic

Plant Coordination and Response

Tropisms:
- Plants must respond to their environment in order to survive
• These responses are much slower than in animals
- A growth towards or away from a stimulus is called a tropism
• Phototropism: Movement towards or away from light
• Geotropism: Movement towards or away from gravity
• Hydrotropism: Movement towards or away from water
- Tropisms can either be positive or negative
• Positive: If growth is toward the stimulus
• Negative: If growth is away from the stimulus


Examples of different plant tropisms:
- Shoots
• Shoots grow upwards to maximize their ability to photosynthesize
• Example of POSITIVE PHOTOTROPISM – Growth towards sunlight
• Example of NEGATIVE GEOTROPISM – Growth upwards, against gravity
- Roots
• Roots grow downwards into the soil for nutrients
• Example of NEGATIVE PHOTOTROPISM – Growth away from sunlight
• Example of POSITIVE GEOTROPISM – Growth downwards, towards gravity


Auxins:
- Are a type of plant hormone
- Control the growth rate of plant cells
- Are made in the tip of growing stems
- Cause cells to stretch out


How does auxin work?
- When the plant is illuminated on all sides, auxin causes the cells in the shoot to
grow at the same rate.
• The shoot will grow upwards