6.1.4Organisms Respond to Changes in their Environments (A Level only)

Taxes and Kineses — AQA A Level Biology 7402 Revision Notes & Topical Questions

5 min read 8 parts Lesson 6 of 44 1 quiz

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Lesson summary

6.1.4 Taxes and Kineses — AQA A Level Biology 7402 notes: Distinguish taxes from kineses and explain how each helps simple animals to find favourable conditions.Simple animals such as woodlice, maggots and flatworms have limited nervous systems and show innate responses to stimul…

Positive phototaxis
Negative phototaxis
Chemotaxis
orthokinesis
klinokinesis
Exam-style question 1

Part 1 of 6Simple behavioural responses

Simple animals such as woodlice, maggots and flatworms have limited nervous systems and show innate responses to stimuli that keep them in favourable environments. Two types of response are taxis and kinesis. Both are inherited, automatic and require no learning, so they are quick and cost little energy.

Part 2 of 6Taxis

A taxis (plural: taxes) is a directional movement of a whole organism in response to a directional stimulus. The movement is towards (positive) or away from (negative) the source. Examples include:

Positive phototaxis

Euglena swims towards light to photosynthesise.

Negative phototaxis

Negative phototaxis fly maggots move away from light and burrow into food or soil, where they are hidden from predators.

Chemotaxis

Chemotaxis a sperm cell swims towards the egg following a chemical gradient, and bacteria move toward nutrients.

Taxis requires the animal to detect the direction of the stimulus, often by comparing signals on two sides of its body, so a gradient is needed.

Part 3 of 6Kinesis

A kinesis (plural: kineses) is a random, non-directional change in the speed of movement or rate of turning in response to the intensity of a stimulus.

Kinesis

The animal does not move toward or away from a source, but alters how much it moves.

In unfavourable conditions it moves quickly and turns frequently, which increases the chance of finding better conditions by chance.

In favourable conditions it slows down and turns less, so it stays in the area.

Woodlice illustrate thisthey lose water quickly by evaporation and need moist areas.

In dry air they move rapidly with frequent changes of direction, so they tend to leave dry places.

In humid air they move slowly and often stop, so they accumulate in damp places beneath logs or leaf litter.

This reduces water loss and protects against predators and desiccation.

Orthokinesis

This is orthokinesis if the speed changes, and klinokinesis if the rate of turning changes.

Part 4 of 6Comparison and interpretation

Feature	Taxis	Kinesis
Direction of movement	Towards or away from stimulus	Random, not directional
Depends on	Direction of stimulus	Intensity of stimulus
Change	Orientation	Speed or rate of turning
Example	Euglena phototaxis	Woodlice in humidity

In an investigation, a choice chamber with different humidity zones is used, or a trough with a light and dark side.

Comparison and interpretation

Results are given as numbers of animals in each zone after a fixed time, and the pattern is interpreted: more animals in the humid side shows a response related to humidity.

Because a kinesis changes activity, movement can also be measured as the distance travelled in a given time at different intensities.

These responses are adaptive because they place the organism in conditions that favour survival and reproduction. They are also simple to explain in terms of natural selection: individuals with these responses leave more offspring.

Part 5 of 6Linking behaviour to survival and evolution

Taxes and kineses are examples of behaviour that is controlled by genes, so they can evolve by natural selection.

Animals that find favourable environments are more likely to survive and reproduce, passing on the alleles for those responses.

For woodlice, the gains are reduced water loss, lower risk of predation by birds, and nearness to decaying material for food.

You should also be able to evaluate the limitation: kineses are inefficient, as random movement may take time to find a good area, and a taxis requires a gradient to be present.

In an exam, answer questions about the advantage of kinesis in a patchy environment by explaining that fast movement increases the chance of leaving a bad patch, while slow movement keeps the animal in a good patch, and that no sensory comparison is needed.

Test your understanding by classifying behaviours.

A maggot crawling directly away from a lamp is negative phototaxis.

Wood lice that speed up when the air becomes drier are showing kinesis.

A bacterium swimming up a glucose gradient shows positive chemotaxis.

In each case the question to ask is whether the movement is related to the direction of the stimulus or to its intensity.

Part 6 of 6Exam-style questions

Explain how a kinesis helps woodlice to survive. [3]3 marks
Distinguish between a taxis and a kinesis. [2]2 marks

Key terms

Term	Meaning
Taxis	Directional movement of an organism towards or away from a stimulus.
Kinesis	Random change in rate of movement or turning in response to stimulus intensity.
Phototaxis	Movement in response to light.
Chemotaxis	Movement in response to a chemical.
Orthokinesis	Kinesis in which speed varies with intensity.
Innate	Inherited and not learned.

Avoid these mistakes

Calling kinesis directional.

Saying that animals in a kinesis 'decide' to go to the damp area.

Confusing tropism (plants growth) with taxis (animal movement).

Describing the response as learned; they are innate.

Last updated: 18 October 2026