taxis and kinesis

how do organisms increase their chance of survival?

by responding to stimuli via diff response mechanisms

what is a taxis? in what organisms may it occur?

• directional response to a stimulus, leading to movement towards or away from a stimulus

• occurs in motile organisms

give an example of taxis:

• earthworms and woodlice show -ve phototaxis

• to avoid dehydration/predators and find food

what is kinesis? in what organisms can it occur?

• non-directional response to a stimulus 

• occurs in motile organisms

for kinesis, what affects the speed/rate of movement/turning?

intensity of the stimulus

give an example of kinesis:

• woodlice - respond to humidity

• dry conditions but close to moist - move faster, turning increases (increasing the likelihood that moist conditions will be reached)

• dry conditions but far from moist - move faster, turning decreases until close to moist conditions

• moist conditions - slow down, turning constant so stay in favourable conditions

• this helps them survive - keeps them in/helps them to reach environments better suited to their needs i.e. avoid dessication

give 3 differences between taxis and kinesis:

• taxis = directional, kinesis = non directional

• taxis - stimulus determines direction, kinesis - stimulus affects movement speed

• taxis - +ve/-ve response, kinesis - response dependent on intensity of stimulus

give 4 similarities between taxis and kinesis:

• both are responses to stimuli

• both involve movement

• both increase survival

• both are involuntary

in each experiment, the biologist exposed the surfaces to light that was dim and even, so that he could see where the worms went.

apart from seeing where the worms went, suggest 2 reasons why it was important that the light was dim and even (2)

the movement of the woodlice in low relative humidity is an advantage to their survival - explain how (2)