Internal and external stimuli are detected by organisms and lead to a response.
Stimulus - detectable change in the internal or external environment of an organism that produces a response in the organism.
Ability to respond to stimuli increases the chance of survival for an organism.
Organisms that survive have a greater chance of raising offspring and passing on their alleles to the next generation.
Always a selection pressure favouring organism with more appropriate resopnses.
Stimuli are detected by cells or organs known as receptors.
Receptors - transform the energy of a stimulus into some form of energy that can be processed by the organism and lead to response. Response is carried out by a range of cells, e.g. cells, tissue, organs. Known as effectors.
Measure of communication between effectors and receptors are hormones - relatively slow process found in both plants and animals.
Animals have a more rapid means of connection. Nervous system has coordinator which is linked to receptors and effectors.
stimulus --> receptor --> coordinator --> effector --> response
Taxis - simple response whose direction is determined by the direction of the stimulus.
A motile organism response directly to environmental…