Taxes and Kinesis

What is a stimulus? (1 mark)

A detectable change in the internal or external environment of an organism.

Why is it important that organisms respond to stimuli? (1 mark)

It increases their chance of survival.

kinesis in woodlice

woodlice lose water from their bodies in dry conditions

when they move from a damp area into a dry area, they move more rapidly and change direction more often to increase their chance of moving back into the damp area. once back in the damp area they slow down and change direction less often.

What is a tactic (taxic) response? (1 mark)

A directional response where the organism moves toward favourable stimuli or away from an unfavourable stimulus. such as light or chemicals.

What is a kinetic response (kinesis)? (2 marks)

A non-directional response where the rate of movement or turning changes depending on stimulus intensity.

Why should the same organism not be reused in a maze experiment? (1 mark)

To reduce stress and avoid learned behaviours that affect results.

How does a woodlouse respond when moving from damp to dry? (2 marks)

1. It increases turning rate.

2. Increases chance of returning to damp area.

Why do organisms show simple responses like taxis and kinesis? (1 mark)

To remain in favourable environmental conditions.

How would you investigate the effect of humidity on woodlice movement? (3 marks)

• Use a choice chamber with damp and dry sections.

• Place woodlice in the centre.

• Record distribution after a set time.

Why leave woodlice to settle before recording movement? (1 mark)

To reduce stress and ensure normal behaviour.

Why use a mesh platform in a choice chamber? (1 mark)

To prevent woodlice contacting harmful substances directly.

Why use a clean maze between trials? (1 mark)

To prevent chemical cues left by previous animals affecting behaviour.

Which statistical test should be used to analyse results from a choice chamber? (1 mark)

Chi-squared test.

example of woodlice in tactic response ( negative phototaxis)

Woodlice shows a tactic response to light (photo taxis)- they move away from a light soucse.

1) This helps them survive as it keeps them concealed under stones during the day ( where there are safe from predators) and keeps them in amp conditions ( which reduces water loss) 

example of woodlice in Kinetic response. (kinesis) 

Woodlice shows kinetic response to humidity. 

1) In high humidity they move faster and turn less often so that they stay where they are. 

2) As the air gets drier, they move faster and turn often, so that they move into a new area. this response increases the chance of woodlice will move to. an area with higher humidity this improves the survival chances of the organism- it reduces their water loss and helps to keel them concealed 

Negative phototaxis in earthworms

Earthworms  will shoe negative phototaxis meaning they will move away from light, towards dark environment, such as the soil to help them avoid dehydration ( to conserve water) to avoid predators and to locate food.

Positive chemotaxis in bacteria 

bacteria show positive chemotaxis as they move towards certain chemicals to aid survival. 

Difference  between taxis and kinesis 2 marks

Taxis is a directional movement in response to a stimulus — the organism moves towards (positive) or away (negative)from the stimulus.
Kinesis is a non-directional movement where the rate of movement or turning changes with stimulus intensity, not direction.

 extra questions Mosquitos fly towards a source of carbon dioxide. What kind of simple response is this?

Positive chemotaxis

What is the advantage of taxis and kinesis to an organism?

They increase the organism’s chance of survival by keeping it in favourable environmental conditions.

Explain how woodlice use taxis and kinesis to maintain a favourable environment.

• Woodlice show negative phototaxis, moving away from light into dark, damp areas.

• In dry conditions, they show kinesis — moving faster and turning more often until they reach damp areas.

A maggot is placed in a chamber with light on one side and dark on the other.
Describe and explain the behaviour you would expect.

• Maggots show negative phototaxis — they move away from light towards darkness.

• This keeps them in a dark environment under soil or decaying matter.

• Increases survival by reducing predation and preventing desiccation.

Slaters (woodlice) are placed in the centre of a dry dish with one damp corner.
Explain how kinesis helps them find the damp area.

• In dry conditions, they move faster and turn more often (increased activity).

• When they reach damp conditions, movement slows and turning decreases.

• This keeps them in the damp region where survival chances are higher.

In an experiment, worms were placed in a tray with a light shining on one end and moisture evenly distributed.
After 10 minutes, most worms were found at the darker end.
Explain this behaviour in terms of taxis and survival.

• Worms show negative phototaxis, moving away from light towards darkness.

• This is a directional movement in response to light.

• Staying in darker areas helps maintain moisture and reduces drying out.

• Increases survival as worms rely on damp skin for gas exchange.

When the humidity around woodlice decreases, they move more quickly and change direction more often.
Explain how this behaviour increases their chances of survival. (4 marks)
A:

• This is kinesis — non-directional movement depending on humidity intensity.

• In dry conditions, increased speed and turning cause random movement.

• Increases likelihood of entering a damp microhabitat.

• Prevents desiccation → improves survival.

A student investigated the response of maggots to temperature.
The maggots moved more slowly in cooler areas and more quickly in warmer areas.
Explain what type of response this is and why it is beneficial. (4 marks)

• This is kinesis, because movement rate changes with stimulus intensity (temperature).

• In warmer areas (less favourable, may dry out), movement increases → random searching.

• In cooler, moist areas (favourable), movement slows → they remain there longer.

• Helps maintain optimal conditions for survival.