Unit 6-Organims Respond To Changes In Their Internal And External Environment Flashcards
What is a stimulus?
A detectable change in the external or internal environment of an organism that leads to a response in the organism.
What does the ability to respond to stimuli increase?
The organism’s survival chances. They will have a greater chance of raising offspring and passing their alleles on to the next generation. Therefore there is a selection pressure which favours organisms with more appropriate responses.
What detects stimuli?
Receptors which are specific to one type of stimulus.
What formulates a suitable response to a stimulus.
A co-ordinator
What is the function of an effector?
To produce a response
What sequence links the stimulus to a response?
Stimulus -> receptor -> coordinator -> effector -> response
What is a taxis?
A simple response whose direction is determined by the direction of stimulus so as a result a motile organism responds directly to the environmental changes by moving it’s whole body away from the unfavourable stimulus or towards the favourable stimulus.
What is positive taxis?
Towards the stimulus
What is negative taxis?
Away from stimulus.
What is kinesis?
A form of response in which the organism changes the speed at which it moves and the rate in which it changes the direction.
What causes an organisms rate of turning to increase?
It the organism crosses a sharp dividing line between a favourable and unfavourable environment. This raises the chance of quick return to the favourable environment.
What happens if an organism moves a considerable distance to an unfavourbake environment?
Its rate of turning slowly decreases. This response is important when a stimulus is less directional eg humidity.
What is tropism?
The growth of plants in response to a directional stimulus.
What is positive tropism?
Growth towards stimulus (light)
What is negative tropism?
Growth away from stimulus (gravity)
