1. survival and response Flashcards
stimulus definition
Any change in the internal or external environment e.g. change in temperature, light intensity or pressure
receptors definition
organs that detect stimuli
response
reaction to a stimuli
effectors response
Muscles and glands respond to stimuli to bring about a change
responding to the environment
Animals = physically move away from harmful environments such as places that are too hot or too cold.
Plants = can’t actually move themselves, but they can change the way they grow in an attempt to find better environmental conditions.
responding to internal environments
Organisms also respond to changes in their internal environment to make sure the conditions are always optimal for their metabolism (all the reactions).
simple responses
these responses are automatic responses - organisms have no choice
Simple mobile (moving) organisms, e.g. woodlice have simple responses to keep them in a favourable environment.
tactic response (taxis)
if an organism moves towards a stimulus it’s a positive taxis
if it moves away from a stimulus it’s a negative taxis
This is directional movement in response to a stimulus. The organism will move directly towards or away from a stimulus.
The direction of the stimulus affects the response.
tactic response + euglena
Euglena is a single-celled organism that has chloroplasts and lives in ponds.
It responds to light by swimming towards it has an eye spot to detect light, and a flagellum to swim.
This movement towards light is called a positive phototaxis.
word before taxi
light = photo
chemicals = chemo
earth/gravity = geo
water = hydro
sound = phono
kinetic response (kinesis)
This is non-directional (random) movement in response to a stimulus.
The intensity of the stimulus affects the response.
kinetic response + woodlice
Woodlice show a kinetic response to humidity.
In high humidity they move slowly and turn less often, so that they stay where they are.
As air becomes drier, they move faster and more randomly, until they move into favourable areas.
This response helps woodlice move from drier to more humid air and then stay put. This improves survival chances – reducing water loss and keeps them concealed.
