- Created by: debbymarkovic
- Created on: 15-12-15 22:17
STIMULI AND RESPONSE
A stimulus is a change in the external or internal envoriemnent, in whic a response is brought about via receptor. If an orgainsm is able to detect a change, they have a higher selectional pressure, amd increased likelyhood of alleles being passed on to the next generation.
Stimuli sre detceted by receptors and responses are carried out by effectors, since there is a bi distance apart, then a hormone is diffused.
Animals have a more rapid response, a cordinater and switch board effect; where each receptor is linked with an effector. The sequence of a response is as follows: Stimuli- Receptor- Coordinater- Effector- Response.
There are three ways in which an organism can respond to a stimuli.
- Taxes. This is the movement of a motile organisism, its direction os determined by the stimuli. 1. A plant grows toward light- positive phototaxes 2.A worm grows to gravity for shelter, nutreints anad warmth- positive geotaxes. 3. Bacteria move to high glucose concentration- positive chemotaxes.
- Kinese. This is an organisms rapid and random movement as a aresult of the stimulus, to try get back into desirable conditions.
- Troprism. This is a plants growth in response to the stimuli. There are a few types: 1. Positive phototroprism- to light 2. Positive geotroprism- to gravity 3. Postive hydrotroprsim- to water
The nervous system has two parts:
- The centeral nervous systme (CNS)
- The peripheral nervous system(SNS)
The SNS has got two further divisions:
- Sensory nuroene- carry impulse from receptor to CNS
- Motor nurone- carrys impulse form CNS to the effector.
The motor nurone has also got two divsions:
- The voluntary nervous system- the conscousious muscel
- The autonomic nervous system- the subconsciuos glands and muscels.