response to stimuli Flashcards
what is a stimulus
a detectable change in the internal or external environment that leads to a response in the organism
what are stimuli detected by
receptors which are specific to one type of stimulus
role of an effector
produces a response
the nervous system sequence of event
stimulus - receptor - coordinator - effector - response
what is a taxes
a simple response whose direction is determined by the direction if the stimulus
what is a positive taxes
movement towards a stimulus
what is a negative stimulus
movement away form a stimulus
what is positive phototaxis
movement towards light (single celled algae)
what is negative phototaxis
movement away form light (earthworms)
what is positive chemotaxis
movement towards high concentrations of glucose
what is kineses
an organism changes the speed at which it moves and the rate at which it changes direction
kineses in woodlice
when they enter a dry ares their movement becomes more rapid and they change direction often, increasing the chance of moving back into the damp area, once in the damp ares their movement slops and change direction less
what is a tropism
the growth of a part of a plant in response to a directional stimulus
example of positive photothropism
plant shoots grow towards light
example of negative phototropism
plant roots grow away form light
example of positive gravitropism
plant roots grow towards gravity
example of negative gravitropism
plant shoot grow away form gravity
example of a plant growth factor
indoleacetic acid (IAA)
belongs to the group of auxins
controls plant elongation
process of phototropism in flowering plants
- cells in the tip of the shoot produce IAA which is transported down the shoot
- light causes the movement of IAA from the light side to the shaded side of the shoot
- a greater conc of IAA builds up on the shaded side
- the cells on the shades side elongates more causing the shoot tip to bend towards the light
effect of IAA in root cells
inhibits cell elongation
IAA in roots
more IAA in light light so more cell elongation so more bending away form the light
process of gravitropism in flowering plants roots
- cells in the tip of the root produces IAA which is transported along the root
- a greater conc of IAA builds up on the lower side as gravity influences the movement of IAA form the upper to the lower side
- lower side elongates more causeing the root to bend towards the force of gravity
process of gravitropism in flowering plants shoots
the greater conc of IAA on the lower side increases cell elongation causing it to grow upwards away form the force of gravity
what are the divisions of the nervous system
- central nervous system (CNS) made up of the brain and spinal cord
- peripheral nervous system (PNS)
what is the peripheral nervous system divided into
- nervous system which carries nerve impulses form receptors towards the central nervous system
- motor neurones which carries nerve impulses away form the central nervous system to effectors
what is the motor nervous system divided into
- voluntary nervous system which carries nerve impulses to body muscles
- autonomic nervous system which carries nerve impulses to glands, smooth muscle and cardic muscle
what is the spinal cord
a columm of nervous tissue that runs along the back and lies inside the vertebral column for protection
what are the stages of a reflex arc
- the stimulus ( heat from the hot object)
- a receptor (temperature receptors in the skin)
- sensory neurone (passes nerve impulses to the spinal cord)
- a coordinator (links the sensory neurone to the motor neurone in the spinal cord)
- motor neurone (carries nerve impulses form the spinal cord to a muscle in the upper arm)
- an effector (the muscle in the arm which is stimulated to contract)
- the response (pulling hand away from the hot object )
what is the importance of reflex arc
- involuntary so do not require the decision making power of the brain so can carry out more complex response
- protect the body form harm, do not have to be learnt
- fast as the neuron pathway id short
- absence of decision making means the action is rapid
