14.1 Response to stimuli Flashcards
What is a stimulus
A detectable change in internal or external environment of an organism that can lead to a response
Why is responding to stimulus important
Increases chance of survival for an organism.
Detecting and moving away from a harmful stimuli such as predators or extreme temperatures
The organisms that survive have a higher chance of reproducing so passing their alleles on to offspring.
So a selection pressure favours organisms who can respond to their environment
What are receptors
These detect stimuli and are specific to one type of stimulus
What happens after receptor
Then the coordination centre forms an appropriate response to stimulus.
Could involve Brain or spinal cord.
Coordinators can join the receptor to effector
Then this goes to effector eg muscle or gland that carries about a response
What is a taxis
(Plural taxes)
Simple response whose direction is determined by direction of the stimulus
So motile organism responds by moving their whole body towards favorable stimulus or away from unfavorable stimulus.
What is positive taxes and negative taxis
Positive taxis is when organism moves towards stimulus
Negative taxis is when organism moves away from stimulus
Give example of positive phototaxis
Give example of negative phototaxis
When single celled algae move towards light as they photosynthesise and it is a favorable stimulus
Earthworms move away from light which increases their chance of survival because it takes them into the soil to find food and conserve water and avoid predators
What is positive / negative chemotaxis
Chemotaxis is chemicals so if organism moves towards them it is positive and if organism moves away it is negative.
Some species of bacteria move towards region where glucose is more concentrated which increases chance of survival due to food. This is positive chemotaxis
What is a kinesis
A form of response that is non directional: organism doesn’t move towards or away a stimulus
However it changes the speed it moves at and the rate it changes direction
How can kinesis of an organism change as they go into non favourable environment
If they go far into non favorable environment, they may travel longer in a straight line to try and leave it. Its turns will be very sharp also and less frequent.
This response will hopefully bring organism to new environment with favourable conditions.
However if organism is just entering unfavorable environment they will do many turns to increase chance of quick return to favorable conditions.
What is the kinesis of an organism in a favorable environment
They move more slowly and turn but not as frequently.
What is a tropism
Growth of a part of a plant in response to directional stimulus.
Eg plant grows towards response is positive tropism, and it is negative tropism if plant grows away from stimulus.
What is phototropism
Positive and negative
Positive phototropism is growing towards the light
Negative phototropism is growing away from light
What is gravitropism
Positive and negative
Positive gravitropism is growing towards gravity, so downwards.
Negative gravitropism is growing away from gravity so upwards
How do plant shoots grow
They grow towards light (positive phototropism) and away from gravity (negative gravitropism)
