9 Response to stimuli Flashcards
EXAM QUESTION
A biologist investigated the behaviour of a species of worm that lives in soil. He cultured three samples of worms in three separate trays of soil for many days.
The biologist concluded that the worms’ behaviour demonstrated taxis. How do these results support this conclusion? (2)
Using the information provided, suggest an explanation for the worms’ behaviour on
the glass surfaces in the absence of food. (3)
- (Taxis is) movement towards/away from a
stimulus / a directional response/movement (to
a stimulus); - (Move towards) temperature they were used
to/cultured in; - Hungry, so seeking food / in absence of food
respond to temperature; - Move towards temperature they were used
to/cultured in; - Associate (this temperature) with food;
- (Then) stay in this temperature;
EXAM QUESTION
In each experiment, the biologist exposed the surfaces to light that was dim and even,
so he could see where the worms went.
Apart from seeing where the worms went, suggest two reasons why it was important
that the light was dim and even. (2)
- (Dim) worms live in soil/dark/ affected by bright
light / dim light is like normal environment/what
they are used to; - (Even) because worms might move
towards/away from bright light / to avoid
creating light gradient / prevent worms showing
phototaxis/ all parts of surface exposed to same
light; - (Dim light) ensures heat from light not a
variable/ heat from lamp could kill/dry out
worms;
EXAM QUESTION
Termite B moved towards the light directed at it.
What type of behaviour was shown by the termite from group B? (1)
Give the evidence for your answer. (1)
Taxis
Moves towards stimulus/towards light;
EXAM QUESTION
Give one similarity and one difference between a taxis and a tropism. (2)
- Similarity – directional response (to a
stimulus)/movement towards/away from
a stimulus; - Difference – taxis (whole) organism
moves and tropism a growth (response);
EXAM QUESTION
Increased intensity of exercise leads to an increased heart rate. Explain how. (3)
1. (Oxygen/carbon dioxide) detected by chemoreceptors / (pressure) detected by baroreceptors; 2. Medulla/cardiac centre involved; 3. More impulses to SAN/along sympathetic nerve;
Termite C moved off the sloping board
Suggest one advantage to the termites from group C of the behaviour shown in the
investigation. (2)
Helps them to leave the soil/ground/reach the surface;
Disperse/produce new colonies;
Avoid competition;
Define stimulus
a detectable change in the internal or external environment of an organism that produces a response.
Define selection pressure
favours?
environmental force altering the frequency of alleles in a population.
organisms with better responses
Define receptor
cell/organ that detects stimuli
Define effector
cell/organ that carries out response
Why do receptors and effectors require communication system? Hormones (2) Nervous system (3)
Describe sequence
Slow
Plants and animals
Rapid
Animals
Central coordinator = connects information from each receptor with the appropriate effector.
stimulus —> receptor —> coordinator —> effector —> response
Define taxis
positive taxis?
negative taxis?
movement towards/away from stimulus, directional response
= movement towards stimulus
= movement away from stimulus
Define kinesis
Importance?
non-directional response to a stimulus, resulting in changed rate of movement/turning
Keeps organism in/moves organism into favourable environment
Define tropism
positive tropism?
negative tropism?
growth movement of part of a plant towards/away from a stimulus, a directional response.
= growth towards stimulus
= growth away from stimulus
Nervous organisation 2 major divisions? divided into? divided into? divided into?
Central nervous system (CNS) - brain and spinal cord.
Peripheral nervous system (PNS) - pairs of nerves branching off
Sensory neurones - NI towards CNS
Motor neurones - NI away from CNS
Voluntary nervous system - NI to body muscles
Autonomic nervous system - NI to glands and smooth/cardiac muscle
Sympathetic nervous system - stimulates effectors/speeds up activity when body exercises strenuously
Parasympathetic nervous system - inhibits effectors/slows activity under normal resting conditions
Define reflex
Rapid, involuntary response to a stimulus.
Define reflex arc
Does not involve?
the nerve pathway taken by action potential that leads to reflex.
Does not involve brain
Describe reflex arc (7)
Stimulus - detected by receptor
Receptor - creates NI in sensory neurone
Sensory neurone - carries NI to spinal cord
Intermediate neurone - links sensory neurone to motor neurone in spinal cord
Motor neurone - carries NI to effector
Effector - stimulated by NI
Response - carried out by effector
3 advantages of reflex arc?
Do not have to be learned/effective from birth
Ensures brain not overloaded - free to carry out complex responses (some NI sent to inform/can override if necessary)
Fast because short neurone pathway/few synapses.
Define Medulla oblongata
2 centres (4)
Region of the brain which controls changes to the heart rate.
One increases heart rate - linked to SAN by sympathetic nervous system.
One decreases heart rate - linked to SAN by parasympathetic nervous system.
Where are chemoreceptors and pressure receptors found?
Walls of carotid arteries and aorta
Describe the effect of exercise on heart rate (4)
Carbon dioxide/oxygen detected by chemoreceptors
Chemoreceptors increase frequency of NI to Medulla oblongata (centre that increases)
Medulla oblongata increases frequency NI to SAN along sympathetic nervous system
SAN increases heart rate
Describe what happens if blood pressure too high (4)
Pressure increase detected by pressure receptors
Pressure receptors increase frequency of NI to Medulla oblongata (centre that increases)
Medulla oblongata increases frequency NI to SAN along parasympathetic nervous system
SAN decreases heart rate
Describe what happens if blood pressure too low (4)
Pressure decrease detected by pressure receptors
Pressure receptors increase frequency of NI to Medulla oblongata (centre that decreases)
Medulla oblongata increases frequency NI to SAN along sympathetic nervous system
SAN increases heart rate
Define Pacinian corpuscle
2 features?
Structure? (3)
Found where? (4)
A receptor that responds to changes in mechanical pressure.
Specific to single type of stimulus
Transducer - mechanical energy to generator potential
One sensory neurone, amongst layers of tissue, separated by gel.
Deep in skin - fingers, soles, genitalia,
Pacinian corpuscle
At resting potential?
Describe how an action potential is generated. (5)
Sretch-mediated sodium channels too narrow to allow sodium ions through
Pressure applied Stretch-mediated sodium channel widens Sodium ions diffuse into neurone = depolarisation Generator potential established Action potential generated
Rod and cone cells
For each: Shape? Amount? Bipolar cell? convergence? Visual acuity? Light sensitivity? Pigment?
Rod-shaped
Greater number
Share bipolar cell (retinal convergence)
Low visual acuity
Sensitive to low-intensity light
Pigment rhodopsin must be broken down (by exceeding threshold value)
Found at the periphery of the retina, absent at the fovea.
Cone-shaped
Fewer number
One bipolar cell each (no retinal convergence)
High visual acuity
Not sensitive to low-intensity light
Pigment iodopsin must be broken down (by exceeding threshold value)
Found at fovea, absent at periphery of retina
