6A Stimuli and Responses Flashcards
How do animals responding to their environment help them?
They increase their chances of survival
They also respond to changes in their internal environment
What do receptors do?
They detect stimuli
What do effectors do?
They produce a response
Give some examples of receptors in humans
They can be cells or proteins on cell surface membranes
Loads of different types of receptors detect different stimuli
What can effectors be?
They can be muscle cells & cells found in glands
e.g. the pancreas
How does the nervous system send info?
As electrical impulses
What is the nervous system made up of?
It is a complex network of cells called neurones
What are the 3 main types of neurones?
- Sensory neurones
- Motor neurones
- Relay neurones
What do sensory neurones do?
They transmit electrical impulses from receptors to CNS - the brain & spinal cord
What do motor neurones do?
They transmit electrical impulses from the CNS to effectors
What do relay neurones do?
They transmit electrical impulses between sensory neurones & motor neurones
What can electrical impulses also be called?
- Nerve impulses
- Action potential
What sorts of stimuli do plants respond to?
They respond to changes in their environment:
- Light
- Gravity
Why do plants grow towards light?
To maximise light absorption for photosynthesis
Why do plants grow according to gravity?
They can sense gravity, their roots & shoots then grown in the right direction
How do climbing plants respond to stimuli?
They have a sense of touch, so they can find things to climb up & reach the sunlight
What is a tropism?
A plant’s growth response to an external (directional) stimulus
How do plants respond to stimuli in general?
By regulating their growth
What is a positive tropism?
Growth of the plant towards the stimulus
What is a negative tropism?
Growth of the plant away from the stimulus
What is phototropism?
The growth of a plant in response to light
How do shoots respond in phototropism?
Shoots are positively phototropic & grow towards light
How do roots respond to phototropism?
They are negatively phototropic & grow away from light
What is gravitropism?
The growth of a plant in response to gravity
How do shoots respond to gravitropism?
Shoots are negatively gravitropic & grow upwards
How do roots respond to gravitropism?
Roots are positively gravitropic & grow downwards
How do plant responses occur?
They are brought around by growth factors
What are growth factors?
They are hormone-like chemicals that speed up or slow down plant growth
Where are growth factors produced?
They are produced in the growing regions of the plant (e.g. shoot tips, leaves) & they move to where they’re needed in the other parts of the plant
Give an example of a growth factor in plants
Auxins
What do auxins do?
They stimulate the growth of shoots by cell elongation
This is where cell walls become loose & stretchy, so the cells get longer
How do high concentrations of auxins affect the roots?
These auxins inhibit growth in roots
What is IAA?
Indoleacetic Acid - it is an important auxin
Where is IAA produced?
In the tips & shoots in flowering plants
Why and how is IAA moved around a plant?
It is moved around the plant to control tropisms
It moves by diffusion & active transport over short distances, via the phloem over long distances
What happens if the concentrations of IAA are uneven in the plant?
Growth is uneven
How does an uneven distribution of IAA occur?
The movement of it through the plant means there are varying concentrations around the plant
In phototropism, how does IAA move?
IAA moves to the more shaded parts of the shoots and roots , so theres uneven growth
In gravitropism, how does IAA move?
IAA moves to the underside of shoots & roots, so there’s uneven growth
How does IAA act in shoots for photoropism?
IAA concentration increases on the shaded side - cells elongate & the shoot bends towards the light
How does IAA act in roots for phototropism?
IAA conc. increases on the shaded side - growth is inhibited so the root bends away from the light
How does IAA act in the shoots for gravitropism?
IAA conc. increases on the lower side - cells elongate so the shoot grows upwards
How does IAA act in the roots for gravitropism?
IAA increases on lower side, growth is inhibited so the root grows downwards
How do simple organisms respond?
They use simple responses to keep simple organismsin a favourable environment
Give two examples of simple mobile organisms?
Woodlice and earthworms
What are the two types of simple responses?
- Tactic (taxes)
- Kinetic (kineses)
What are tactic responses?
The organism moves towards or away from a directional stimulus
e.g. light
What are kinetic responses?
The organisms’ movement is affected by a non-directional stimulus
e.g. humidity
Give an example of a tactic response
Woodlice - they show a tactic response to light (phototaxis)
They move away from a light source
What is phototaxies?
A tactic response to light
How does a phototactic response help woodlice?
Concealed under stones during the day = safe from predators
Damp conditions = reduces water loss
What muscles control the regular beating of the heart?
The cardiac muscles
The cardiac muscle is ‘myogenic’ - what does this mean?
It can contract and relax without receiving signals from nerves
This patter of contractions controls the regular heartbeat
What are the key areas of the heart in the control of heart rate?
- Sionoatrial node
- Atrioventricular node
- Bundle of His
- Purkyne tissue
- L&R atrium
- L&R ventricle
What are the stages in producing a heart beat?
1 - Starts w sinoatrial (SAN) node
2 - SAN is like a pacemaker - sends out waves of elec. activity to the atria walls
3 - Causes R&L atria (A) to contract at same time
4 - Band of non-conducting collagen tissue prevents waves of elec. activity from passing from A to ventricles (V)
5 - Instead waves of elec. activity passed form SAN to AVN
6 - AVN passes waves of elec. activity to bundle of His - slight delay before AVN reacts
7 - Bundle of His splits into finer muscle fibres in R&L ventricle walls called purkyne fibres
8 - Purkyne fibres carry elec. activity into muscular walls of heart, causing them to contract simultaneously from the bottom up
How does the SAN set the rhythms for the heartbeat?
Sets the rhythms by sending out regular waves of electrical activity to the atrial walls
Why is there a slight delay before the AVN reacts when controlling heart beat?
Slight delay so to make sure atria have emptied before ventricles contract
What is the bundle of His?
A group of muscle fibres responsible for conducting the waves of elec. activity between the ventricles & apex of heart
What is the apex of the heart?
The bottom of the heart
What does the control of heart rate involve?
The brain & autonomic nervous system
Why are receptors specific?
The only detect one stimulus
Where are the 2 types of receptors?
- Proteins on cell surface
- Some receptors are cells
What is a nervous system receptor like in its resting state?
- Difference in charge between inside and outside of cell
- This creates a potential difference across the membrane
What happens when the nervous system receptor detects a stimulus?
- Cell membrane becomes more permeable so more ions move in and out
- This alters the potential difference (this is called the generator potential)
What happens when there is a bigger stimulus nervous system receptor?
- Excites the membrane more
- Bigger generator potential produced
What happens when the generator potential reaches a threshold?
Action potential occurs
How is the strength of the stimulus measured?
Frequency of action potentials
What are pacinian corpuscles?
Mechanoreceptors - detect pressure and vibrations
Where are pacinian corpuscles found?
In your skin
What do pacinian corpuscles contain?
Sensory nerve endings which are wrapped in lamellae
What happens when pacinian corpuscles is stimulated?
1) Lamellae are deformed and press on sensory nerve ending
2) The sensory nerve endings stretch which deforms the stretch mediated sodium ion channels
3) This creates a generator potential where if threshold is met makes a action potential
What are photoreceptors?
Light receptors in your eye
Where does light enter the eye?
Pupil
What does iris in the eye do?
Its muscles control the amount of light that enters the pupil
What does the retina do?
- Its where light rays are focused
- Contains photoreceptors that detect light
What is the fovea?
Area of the retina where there are lots of photoreceptors
Where are nerve impulses from the photoreceptor cells carried to?
They are carried from the retina to the brain by optic nerve (bundle of neurons)
What is the blind spot?
- Part where the optic nerve leaves the eye
- Has no photoreceptors so is not sensitive to light
What do photoreceptors do?
Convert light into an electrical impulse
How do photoreceptors create an electrical impulse?
1) Light hits photoreceptors and is absorbed by light sensitive optical pigments
2) Light bleaches the pigments, causing a chemical change
3) This alters membrane permeability to sodium ions
4) Generator potential created and if threshold met nerve impulse sent along bipolar neuron
What do bipolar neurons do?
Connect photoreceptors to optic nerve
What are the 2 types of photoreceptors?
Rods and cones
Where are rods found?
Peripheral parts of the retina
Where are cones found?
Found packed together in the fovea
What are the parts of the eye?
- Pupil
- Iris
- Retina
- Fovea
- Blind spot
- Optic nerve
Why are rods and cones sensitive to different wavelengths of light?
Have different optical pigments
What do rods give information for?
Black and white
What are the 3 types cones?
- Red sensitive
- Green sensitive
- Blue sensitive
What are rods sensitivity like?
- Very sensitive to light (work best in dim light)
- Many rods join one neuron so weak generator potentials can reach the threshold
What are cones sensitivity like?
- Less sensitive than rods (work best in bright light)
- One cone joins one neuron
What is the visual acuity like in rods?
- Low visual acuity
- Many rods join same neuron (light from 2 points cant be told apart)
What is visual acuity?
Ability to tell apart points that are close together
What is the visual acuity like in cones?
- High visual acuity
- One cone joins one neuron so can tell cones apart as they have different action potentials
What can be used to investigate animal responses?
A choice chamber experiment
What is a choice chamber?
A container with different compartment, in which you can create different environmental conditions
Can be used to investigate how animals (such as woodlice) respond to conditions like light intensity/humidity in the lab
What are the two different systems that the nervous system is split into?
- The central nervous system (CNS)
- The peripheral nervous system
What is the CNS made up of?
It’s made up of the brain & spinal cord
What is the peripheral nervous system?
It is made up of the neurons that connect the CNS to the rest of the body - it is made up of two different systems
What are the two systems that make up the peripheral nervous system?
- The somatic nervous system
- The autonomic nervous system
What does the somatic nervous system do?
It controls concious activities
e.g. running & playing video games
What does the autonomic nervous system do?
It controls unconcious activities (remember as it sounds like ‘automatic’)
e.g. digestion
This also has two divisions
What are the two divisions of the autonomic nervous system?
- The sypathetic nervous system
- The parasympathetic nervous system
What does the sympathetic nervous system do?
It gets the body ready for action - it’s the ‘fight or flight’ system
Remember it like a sympathetic friend who reacts to your actions
What does the parasympathetic nervous system do?
It calms the body down - the ‘rest and digest’ system
What is a reflex arc?
Where the body responds to a stimus without making a concious decision to respond
What makes a reflex arc so fast?
You don’t have to spend time deciding how to respond, info travells from receptors to effectors
Simple reflxes help organisms protect the body because they’re rapid
What would be the process of the hand-withdrawl in response to heat?
- Thermoreceptors in the skin detect the heat stimulus
- The sensory neuron carries impulses to the relay neuron
- The relay neuron connects to the motor neuron
- The motor neuron sends impulses to the effector (your biceps muscle)
- Your muscle contracts to withdraw your hand & stop it being damaged
What is nervous system communication like?
- Localised
- Short-lived
- Rapid
What makes nervous system communications localised?
When an elcetrical impulse reaches the end of a neurone, neurotransmitters are secretly directed onto target cells
This makes the nervous response loaclised
What makes nervous system communications short-lived?
Neurotansmitters are quickly removed once they’ve doen their job, so the response is short-lived
What makes nervous system communications rapid?
Electrical impulses are really fast, so the response is rapid
This allows animals to react quickly to stimuli
What do baroreceptors detect?
They detect changes in blood pressure
What do chemoreceptors detect?
They detect chemical changes in the blood
What are the receptors called that cause HR to speed up/slow down?
- Baroreceptors
- Chemoreceptors
Explain the process or receptors respondign to high blood pressure
- BARORECEPTORS detect HIGH blood pressure
- Impulses sent to medulla, send impulses along the PARASYMPATHETIC neurones - these secrete ACETYLCHOLINE, which binds to receptors on SAN
- Effector: cardiac muscles
- The heart rate SLOWS DOWN to reduce blood pressure back to normal
Explain the process or receptors respondign to low blood pressure
- BARORECEPTORS detect LOW blood pressure
- Impulses sent to medulla, send impulses along the SYMPATHETIC neurones - these secrete NORADRENALINE, which binds to receptors on SAN
- Effector: cardiac muscles
- The heart rate SPEEDS UP to reduce blood pressure back to normal
Explain the process or receptors respondign to high blood O2, low CO2 or high pH levels
- CHEMORECEPTORS detect chemical changes in blood
- Impulses are sent to medulla, send impulses along PARASYMPATHETIC neurones - these secrete ACETYLCHOLINE, which binds to receptors on SAN
- Effector: cardicac muscles
- HR DECREASES to return O2, CO2 & pH levels to normal
Explain the process or receptors respondign to low blood O2, high CO2 or low pH levels
- CHEMORECEPTORS detect chemical changes in blood
- Impulses are sent to medulla, send impulses along SYMPATHETIC neurones - these secrete NORADRENALINE, which binds to receptors on SAN
- Effector: cardicac muscles
- HR INCREASES to return O2, CO2 & pH levels to normal
What is the SAN controlled by?
The medulla oblongata
How does the SAN cause the cardiac muscles to contract?
It generates electrical impulses - this is controlled by the medulla oblongata
Why do animals alter their HR?
To respond to their internal stimuli
e.g. to prevent fainting due to low blood pressure/to make sure the heart rate is high enough to supply the body with enough oxygen
What are the (blood) pressure receptors for HR called?
They’re called baroreceptors
They’re located in the aorta & cartiod arteries - stimulated by high & low blood pressure
What are the chemical receptors for HR called?
They’re called chemoreceptors
They’re loacated in the aorta, cartiod arteries & medulla - they monitor O2 levels in the blood & also CO2 and pH levels
