Biology A2 AQA Unit 5

Stimulus and Response:

Stumulus====>Detectable change in the internal or external environment

Abitlity to respond to a stimulus increases chance of survivial. E.G. moving away from harmful stimuli such as excessive heat.

Organisms that survive are more likely to pass their alleles onto offspring===> also a selection pressure. LINK TO ADAPTATION.

Stimuli are detected by receptors. Receptors transform the energy of a stimulus into some form on energy that can be processed by the organism and lead to a response.

Response is carried out by effectors. These can be a range of things such as muscle tissue, organs and systems.