Stimuli Response Flashcards
What is taxis/ a tactic response?
Mobile organism moves towards/away from a directional stimulus
What is kinesis / a kinetic response?
Mobile organisms change their movement in response to a non-directional stimulus. Organisms move/turn less to remain in favourable conditions and move/turn more to move out of unfavourable conditions
Choice chamber experiment
- Put 100 woodlice in centre of chamber
- Observe for 10 mins
- Record number of turns, rate of movement and final positions
What is a reflex?
A rapid response to a stimulus without conscious control
Reflex arc
- Exposure to stimulus (eg. Hot surface)
- Receptors in skin detect stimulus
- Sensory neurone carries impulse to the CNS
- Relay neurone in the CNS carries impulse to motor neurone
- Motor neurone carries impulse to effectors (eg. Muscle cells)
- Response is triggered (eg. Bicep muscle contracts)
Advantages of reflexes
- Help organisms avoid damage
- Very fast / don’t waste time thinking about it
- Doesn’t need to be learnt so protects infants
Auxins (IAA)
- Made in growth regions of plant
- Stimulate cell elongation in the shoots
- Inhibits cell growth in the roots
- Move short distances by diffusion + active transport
- Move long distances in the phloem
Phototropism
- IAA moves to the shaded side of the root/shoot
- IAA causes cell elongation in shoots so shoots grow towards light
- IAA inhibits cell growth in roots so roots grow away from light
Gravitropism
- IAA moves to the underside of the root/shoot
- IAA causes cell elongation in shoots so shoots grow away from gravity
- IAA inhibits cell growth in roots so roots grow towards gravity
What is a Pacinian Corpuscle?
A receptors that detects pressure, touch and vibrations in the skin
Pacinian Corpuscle activation
- Pressure causes the lamellae to stretch and deform
- Stretch mediated sodium ion channels open, causing Na+ to diffuse into neurone
- Depolarisation of the neurone (generator potential)
- If threshold is reached then an action potential is fired
What happens when light enters the eye?
- Light is focussed onto the retina by the lens
- Light is absorbed by pigments in the photoreceptors
- Causes some sodium ion channels to open (generator potential)
- If threshold is reached, action potential, bipolar neurone, optic nerve, CNS
Rod cells
- Monochromatic
- More sensitive to low light
- Low visual acuity (three rods share one bipolar neurone)
Cone cells
- Trichromatic
- Less sensitive to low light
- High visual acuity (each cone has its own bipolar neurone)
How is heart rate controlled?
- SAN initiates the heartbeat, sending an electrical impulse across the atria
- Atria contract
- Non-conductive tissue prevents the electrical impulse reaching the ventricles
- AVN delays electrical impulse, allowing the atria to contract and empty before ventricles contract
- AVN sends electrical impulse down the Bundle of His along the Purkyne fibres
- Ventricles contract from the base upwards
What happens when baroreceptors detect high blood pressure?
- Receptors send nerve impulses to the medulla oblongata in the brain
- Medulla oblongata sends nerve impulses along parasympathetic neurones
- Parasympathetic neurones secrete neurotransmitter acetylcholine
- Heart rate slows down
What happens when baroreceptors detect low blood pressure?
- Receptors send nerve impulses to the medulla oblongata in the brain
- Medulla oblongata sends nerve impulses along sympathetic neurones
- Sympathetic neurones secrete neurotransmitter noradrenaline
- Heart rate speeds up
