Stimuli and Responses Flashcards
Define stimulus
Any change in the internal or external env
Why do animals and plants respond to changes in their env?
- External : to inc chances of survival eg. avoid harmful env
- Internal: to make sure conditions are optimum for metabolism
Define receptors
- Detect specific stimuli
- Can be cells/proteins on cell surface membranes
- Loads of diff. types
- Communicate w/ effector
Define effector
- Cells that bring about a response to a stimulus, produce effect
- Eg. Muscles + glands
Define nervous system
Complex network of cells called neurones
Sensory neurones
Transmit electrical impulses from receptor to CNS (brain + spinal cord)
Motor neurones
Transmit electrical impulses from CNS to effectors
Relay neurones
Transmit electrical impulses btw sensory neurones + motor neurones
Outline what happens when a stimulus is detected
- Stimulus detected by receptor cells
- Electrical impulse sent along sensory
- At synapse, NT is sent
- CNS processes info + sends impulse along motor
- Impulse sent to effector
- Response occurs
CNS
Made up of brain + spinal cord
Peripheral NS
- Made up of neurones that connect CNS to rest of body
- Has 2 systems: somatic NS + autonomic NS
Somatic NS
Controls conscious activities
Autonomic NS
- Controls unconscious activities
- 2 divisions: sympathetic NS + parasympathetic NS
Parasympathetic NS
Gets body ready for action - fight or flight
Sympathetic NS
Calms body down - rest and digest
Define reflex
- Body responds to stimulus w/o conscious decision to respond
- Protect body bc rapid
What is the reflex arc?
- Stimulus
- Receptor
- Sensory
- Relay
- Motor
- Effector
- Response
Describe the nervous system communication
- Localised: NT secreted directly to target cells
- Short-lived: NT removed quickly
- Rapid : electrical impulses are really fast
Give examples to how plants respond to changes in their env to inc their chances of survival
- Sense direction of light + grow towards it to max light absorption for photosynthesis
- Sense gravity, roots + shoots grow in right direction
- Climbing plants: sense of touch, find things to climb + reach sunlight
Define tropism
Plant’s growth response to directional stimulus
How do plants respond to stimuli?
By regulating their growth
Positive tropism
Growth towards stimulus
Negative tropism
Growth away from stimulus
Phototropism
- Growth of plant in response to light
- Shoots: +ve phototropism - grow towards light
- Roots: -ve phototropism - grow away from light
Gravitropism
- Growth of plant in response to gravity
- Shoots: -ve gravitropism - grow upwards
- Roots: +ve gravitropism - grow downwards
Growth factors
- Hormone like-chemicals that speed up/slowdown plant growth eg. Indoleacetic acid (IAA)
- Produced in growing regions (tips)
- Shoots: stimulate growth by cell elongation - cell walls become loose + stretchy
- Roots: inhibit growth
How does IAA move around a plant?
- Diffusion + AT (short distance)
- Phloem (long distance)
How does IAA respond to phototropism in the shoots and roots?
- Moves to shaded area - uneven distrubution = uneven growth
- Shoots: cells elongate + bend towards light
- Roots: inhibits growth so bends away from light
How does IAA respond to gravitropism in the shoots and roots?
- IAA moves underside - uneven distrubution = uneven growth
- Shoots: cells elongate + grow upwards
- Roots: growth inhibited so grow downwards
How do mobile organisms respond to keep in favourable env?
- Tactic response (taxes)
- Kinetic response (kineses)
Tactic response (taxes)
Organism move towards or away from directional stimulus eg. light
Kinetic response (kineses)
Organisms’ movement is affected by non-directional stimulus eg. humidity
Give one similarity and one difference between a taxis and a tropism (2)
- Similarity: directional response to stimulus
- Difference:
- Taxi organism moves AND tropism growth response
- Taxi occurs w/ animals AND tropism occurs in plants
Outline what a choice chamber is
Container w/ diff compartments in which you can create diff environmental conditions
Outline how you can use a choice chamber to investigate animal response to diff conditions
- Light intensity: cover half of lid w/ black paper - one side of chamber will be dark. Put damp filter paper on both sides
- Place woodlice on mesh + cover w/ lid
- After 10mins record no. woodlice on each side - most will end up in dark side (tactic response to light)
- Humidity: damp filter paper in one side + desiccating drying agent in other side
What are pacinian corpuscles?
- Mechanoreceptors - detect mechanical stimuli eg. pressure + vibrations
- Found in skin
- Contain sensory nerve ending which is wrapped in loads of layers of connective tissue called lamellae
What happens when a pacinian corpuscle is stimulated?
- Lamellae are deformed + press on sensory nerve ending
- Causes sensory neurone’ cell membrane to stretch, deforming stretch mediated sodium ion channels
- Channels open + sodium ions diffuse into cell, causing generator potential
- If GP reaches threshold, triggers action potential
How does light enter the eyes?
Through pupil
The amount of light that enter the eyes is controlled by what?
Muscles of the iris
What is the role of the retina?
- Fovea, area in retina, contains photoreceptor cells - detect light
- Nerve impulses are carried from retina to brain by optic nerve - bundle of neurones
What is the role of the lens?
Focuses light rays onto retina
What is the blind spot?
- Where optic nerve leaves
- No photoreceptor cells so not sensitive to light
What happens when light enter the eye?
- Hits photoreceptors + absorbed by light sensitive optical pigments
- Light bleaches pigments, causing chemical change, altering membrane permeability to sodium ions
- Generator potential created if threshold reached, nerve impulse sent along bipolar neurone
- BP connects photoreceptors to optic nerve, takes impulse to brain
What are the types of photoreceptors?
- Rods
- Cones
What are the differences btw rods and cones?
- R: found in peripheral part of retina, C: packed together in fovea
- Different optical pigments so sensitive to diff wavelengths of light
- R: black + white, C: colour (3 types of cones: red, green, + blue)
Which photoreceptor is more sensitive to light?
- Rods (work well in dim light) : many rods join 1 neurone, many weak GP combine to reach threshold + trigger AP
- Cones less sensitive : 1 cone joins 1 neurone so takes more light to reach threshold
Which photoreceptor has a higher visual acuity?
- Cones : close together + 1 cone join 1 neurone so when light hits 2 cones, 2 AP go to brain so can distinguish 2 points as seperate points
- Rods : many rods join same neurone, light from 2 close points can’t be told apart
The heart is myogenic. What does this term mean?
Can contract + relax w/o recieving signals from nerves
The heart rate controls + coordinates the regular contraction of the atria + ventricles. Describe how (5)
- Sinoatrial node (SAN) acts as pacemaker
- Sends wave of electrical activity to atria causing atrial contraction at same time
- Non-conducting tissue
- Transferred to atrioventricular node (AVN)
- Delay at AVN ensure atria empty before ventricle contract
- AVN sends electrical impulse to bundle of His/purkyne tissue
- Causing ventricle to contract from base up
What is the function of the non-conducting collagen tissue?
Prevents waves of electrical activity from being passed directly from atria to ventricle. Instead transferred to AVN
Explain the importance of the slight delay at the AVN (2)
- Allow ventricles to fill/atria to empty
- Before ventricles contract
Outline the function of the bundle of His
- Group of muscle fibre
- Conducts electrical activity btw ventricles to apex of heart
Outline the function of the purkyne tissue
- Bundle of His splits into finer muscle fibres in right + left ventricle wall
- Carries electrical activity into muscular wall of right + left ventricle, causing them to contract at same time from bottom up
What is the role of the medulla oblongata?
Unconsiously controls rate at which SAN generates electrical impulses causing cardiac muscle to contract
Baroreceptors
- Pressure receptors
- In aorta + carotid arteries
- Stimulated by high + low BP
Chemoreceptors
- Chemical receptors
- In aorta, carotid arteries + medulla
- Moniter O<strong>2</strong> , CO<strong>2</strong> + pH level in blood
How does the heart respond to a high blood pressure?
- Baroreceptors detect high BP
- Electrical impulses sent to medulla, sends impulses along parasympathetic neurones. Secretes acetylcholine, binds receptors on SAN
- Effector: cardiac muscles
- HR slows to reduce BP
How does the heart respond to a low blood pressure?
- Baroreceptors detect low BP
- Electrical impulses sent to medulla, sends impulses along sympathetic neurones. Secretes noradrenaline, binds to receptors on SAN
- Effector: cardiac muscles
- HR speeds up to inc BP
How does the heart respond to high blood O2 , low CO2 or high pH level?
- Chemoreceptors detect chem change
- Impulse sent along medulla, sends impulses along parasympathetic neurones. Secrete acetylcholine, binds to receptors on SAN
- Effector : cardiac muscle
- HR dec
How does the heart respond to low blood O2 , high CO2 or low pH level?
- Chemoreceptors detect chem change
- Impulse sent along medulla, sends impulses along sympathetic neurones. Secrete noradrenaline, binds to receptors on SAN
- Effector : cardiac muscle
- HR inc
