14 - Response to Stimuli Flashcards
stimulus
detectable change in the internal or external environment of an organism that leads to a response in the organism
receptors
detect stimuli
effectors
produces response (eg. muscle, gland)
coordinator
directs the response brought about by the effector
taxis
a response in which the organisms direction of movement is determined by the direction of the stimulus
positive taxis
towards stimulus
kinesis
a response in which the organism doesn’t move towards or away from a stimulus, but instead changes the speed at which it moves and the rate at which it changes direction
its rate of turning and movement will increase on entering an unfavourable environments as this raises its chances of quickly returning to a favourable environment
tropism
growth of a plant in response to a directional stimulus, involves plant growth factors (hormones)
tropism in plant shoots
display positive phototropism and negative gravitropism
tropism in plant roots
display negative phototropism, positive gravitropism and hydrotropism
IAA
indoleacetic acid, a plant growth factor
stimulates elongation of cells in shoots, inhibits elongation of cells in the root
process of phototropism in the shoots
cells in the tip of the shoot produce IAA, which is then transported down the shoot
IAA is initially distributed evenly through all regions of the shoot
light causes IAA to move to the shaded side of the shoot
greater concentration of IAA builds up on shaded side than the light side
IAA causes elongation of cells, so cells on shaded side elongate more quickly than cells on light side
so shoots bend towards light
CNS
central nervous system
consists of brain and spinal cord
PNS
peripheral nervous system made up of pairs of nerves which originate from either the brain or spinal cord divided into: sensory neurones motor neurones
sensory nerurones
carry nerve impulses from receptors towards CNS