Topic 14 - Response to Stimuli Flashcards
Stimulus
A detectable change in the internal or external environment of an organism
Receptors
Specific to one type of stimulus, with the coordinator finding an appropriate response
Taxis
A specific movement, with directed motion
Kinesis
A random movement, with undirected motion
Positive Taxis
A specific movement towards a stimulus
Negative taxis
A specific movement away from a stimulus
Tropism
The growth of a plant in relation to a directional stimulus
Growth factors
The hormone-like substances which allow plants to respond to light, water and gravity
IAA
The growth factor in plants
Gravitropism in flowering plants
1) Cells in the tip of the root produce IAA, which is then transported to all sides of the root
2) Gravity influences the movement of IAA from the upper side to the lower side of the root
3) A greater concentration of IAA builds up on the lower side of the root than on the upper side.
4) As IAA inhibits the elongation of root cells and there is a greater concentration of IAA on the lower side, the cells on this side elongate less than those on the upper side.
5) The relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity.
Phototropism in flowering plants
1) Cells in the tip of the shoot produce IAA, which is then transported down the shoot
2) The IAA is initially transported evenly throughout all the regions as it begins to move down the shoot
3) Light causes the movement of IAA from the light side to the shaded side of the shoot
4) A greater concentration of IAA builds up on the shaded side of the shoot than on the light side.
5) As IAA causes elongation of shoot cells there is a greater concentration of IAA on the shaded side of the shoot, the cells on this side elongate more.
6) The shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light.
CNS
Consists of the brain and the spinal cord in nervous organisation
Peripheral nervous system
Consists of pairs of nerves that originate from the brain or spinal chord
Sensory neurons
One division of the PNS which carry nervous impulses from receptors towards the CNS
Motor neurons
One division of the PNS which carry nervous impulses from the CNS towards effectors
Voluntary nervous system
One division of the motor nervous system which carries out nervous impulses to muscle under conscious control