Taxis & Kinesis Simplified Revision Notes for A-Level AQA Biology

Revision notes with simplified explanations to understand Taxis & Kinesis quickly and effectively.

Learn about Response to Stimuli (A Level only) for your A-Level Biology Exam. This Revision Note includes a summary of Response to Stimuli (A Level only) for easy recall in your Biology exam

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6.1.4 Taxis & Kinesis

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Taxis

A taxis is a directional response where an organism moves towards or away from a stimulus.

Positive taxis: Movement towards the stimulus.
Negative taxis: Movement away from the stimulus. Examples:
Positive chemotaxis: Mobile bacteria moving towards a higher concentration of glucose.
Negative phototaxis: Earthworms moving away from light to avoid desiccation.

Kinesis

A kinesis is a non-directional response involving random movement.

The rate of movement and the frequency of direction change depend on the intensity of the stimulus.
This behaviour helps organisms enter more favourable conditions by increasing movement when in unfavourable environments. Example:
A woodlouse placed in a dry environment will:
- Move faster.
- Change direction more frequently.
- This increases the chance of finding a damp area, its preferred condition.

Key Differences Between Taxis and Kinesis

Taxis	Kinesis
Movement is directional.	Movement is non-directional.
Stimulus determines direction.	Stimulus affects movement rate and direction changes.
Example: Bacteria move towards glucose (chemotaxis).	Example: Woodlice move more in dry conditions.

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Exam Tip

Use examples like chemotaxis in bacteria and kinesis in woodlice to illustrate the differences between taxis and kinesis.
Be ready to interpret data or suggest experiments to investigate these responses.

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