Response to stimuli



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.


Blimi s


very clear and good! 



whoever made this has **** spelling