Stimuli and Response Flashcards
What is kinesis?
Kinesis is the random non-directional movement of a whole organism in response to a stimulus. If the organism is in unfavourable conditions, it moves fast and turns rarely (to move away from the area). If the organism is in favourable conditions, it moves slowly and turns a lot (to stay in the same place).
What is taxis?
Taxis is a directional response where a whole organism moves either towards (positive taxis) or away from (negative taxis) a stimulus.
What is a reflex?
An involuntary response which follows a specific pattern in response to a stimulus.
What is a tropism?
A directional response that involves an organism either growing towards (positive) or away from (negative) a stimulus, such as light or gravity (in plants)
What are auxins?
Auxins are a group of hormones in plants that control many processes, such as growth. They are sometimes refereed to as growth factors because they directly affect growth and are made my cells all over the plant, rather than only being made in particular organs. Unlike animal hormones, some growth factors can directly affect the tissues that released them, as opposed to a target organ.
What is a phototropism?
A response in which parts of a plant grow towards or away the direction in which light is coming.
What is geotropism/gravitropism?
A response in which parts of a plant grow towards/away from gravity.
What is indoleacetic acid (IAA)?
IAA is an auxin produced in shoot tips which causes cell elongation is the shoot tips. IAA inhibits cell elongation in the roots. Gravity causes IAA to diffuse down from the shoot tips to other parts of the plant.
How does phototropism occur in shoots?
IAA accumulates on the shady side of the plant, causing cell elongation. This causes the shoot tip to bend towards the sunlight (as the shady side is growing faster than the brighter side). This is positive phototropism.
How does phototropism occur in roots?
IAA accumulates on the shady side of the roots, causing the inhibition of cell elongation. This means that the shaded side of the plant grows slower than the brighter side, so the root grows away from the light. This is negative phototropism.
How does gravitropism occur in shoots?
IAA accumulates on the lower side of the shoot, which causes cell elongation. This means that the shoot bends upwards (against gravity), as the lower side is growing faster than the upper side. This is negative geotropism.
How does gravitropism occur in roots?
Gravity pulls IAA to the lower side of the root, which inhibits cell elongation. This causes the root to bend downwards (with gravity). This is positive geotropism.
What is the acid growth hypothesis?
IAA increases plasticity of the plant cell wall by actively transporting H+ from the cytoplasm into spaces in the cell wall. This allows the cell to elongate by expansion. This is easier in younger cell walls, rigidity develops with maturity so roots and shoots become less responsive.
What are the benefits of positive phototropism in plants?
Leaves exposed to more sunlight and so carry out more photosynthesis. Flowers can be seen by insects for pollination. Plants get higher for better seed dispersal.
What are the benefits of positive gravitropism in plants?
By growing deeply into the soil, the root fixes the plant into the ground firmly. Roots are able to reach more water and roots have a larger surface area for more diffusion and osmosis.
Describe the method for the choice chamber practical (CP10).
Place a wet paper towel over half of a choice chamber and put a thin mesh on top. Place the lid on the choice chamber and put a set number (e.g. 20) of the organism you are studying (e.g. woodlice, maggots) into the chamber. Place a dark paper covering on half of the choice chamber, such that the four sections each have different conditions (dark and damp, dark and dry, light and damp and light and dry). Observe the movements of the organisms and after 5 minutes, count how many individuals are in each section. Repeat the experiment to obtain a total of 3 trials.
What are the expected results for the choice chamber practical?
You would expect the organisms to show a tactic or kinetic response to the stimulus and move towards the dark and damp conditions, as these are the most favourable (to avoid being spotted by predators and to avoid drying out). You would therefore expect to find more individuals in the darker and darker sections of the choice chamber.
Why might you not obtain the results you expect in the choice chamber practical?
The organisms are likely to be distressed by the situation, so may not act as they naturally would. If you don’t wash the mesh between trials, they may do the same thing every time, as they leave scent trails which they are more likely to follow than to go to other parts of the mesh. There may also be not enough organisms (to small a sample size) or not enough trials.
What is the central nervous system?
The CNS consists of the brain and spinal cord and contains relay neurones which connect sensory neurones to relevant effectors.
What is the peripheral nervous system?
The peripheral nervous system contains all the other nerves in the body including sensory neurones and motor neurones. The PNS contains the sensory nervous system and motor nervous system (which contains voluntary and autonomic parts (the autonomic part contains the sympathetic and parasympathetic nervous system)).
What are dendrites?
Dendrites are fine extensions of the dendrons, which are larger extensions of the cytoplasm of the neurone. They carry electrical impulses towards the cell body from neighbouring neurones.
What is the axon?
Long thread-like extension of the cell membrane and cytoplasm. Transmits the nerve impulse from the cell body down to an effector.
What are the myelin sheath?
A sheath of lipid wrapped around the axon, with gaps (Nodes of Ranvier). Insulates the neurone and allows saltatory condition (this speeds up electrical transmission).
What are branched axon terminals?
Branched extensions of the axon at the end of the neurone. This carries an impulse to an effector such as a gland or muscle, or to other neurones at synapses.
What are Schwann cells?
Schwann cells surround the axon and protect it, provide electrical insulation, carry out phagocytosis and play a role in nerve cell regeneration. The membranes of Schwann cells from the myelin sheath, which is rich in lipid.
What is a neurone?
Specialised nerve cells that are adapted to carrying rapid electrochemical changes called nerve impulses from one part of the body to another.
What are sensory (afferent) neurones?
Transmit electrical impulses from receptors to the CNS. The cell body is located the the middle of the neurone on a side branch while there is a long dendron and a shorter axon than usual.
What are relay (association) neurones?
Found within the CNS, transmits electrical impulses between sensory neurones and motor neurones. Relay neurones are very short compared to other neurones and they don’t have long dendrons or axons.
What is a motor (efferent) neurone?
Transmits electrical impulses from the CNS to effectors (usually muscles or glands). Has dendrites and a long axon, but very short dendrons leading to the cell body.
What are some important features of reflexes that help survival?
Reflexes are involuntary actions which are automatic and faster than voluntary actions as they require no processing. They are sent to the spinal cord or unconscious areas of the brain, involving short neuronal pathways. This reduces damage to tissues (e.g. from burning), allow organisms to escape from predators and form a part of homeostasis.
What is the reflex arc?
The path information takes from receptor to effector in a reflex response.
Describe the reflex arc.
There is a detectable change in the surroundings which acts as a stimulus. Recepotirs detect this and an electrical impulse is sent from the receptor along a sensory neurone to a relay neurone in the CNS via diffusion of neurotransmitter across a synapse. The electrical impulse is transmitted to the relevant motor neurone, which transmits the impulse to an effect or. This effector brings about a response (e.g. contracting a muscle to move your hand away from a hot object).
What are the differences between the endocrine and nervous systems?
E- communication by hormones that travel in the blood plasma
N - communication by electrical impulses down neurones
E - the response is slow
N- the response happens instantly
E - response is long-lasting
N - response n is short-lasting
E - hormones can have a widespread effect on many cells or organs
N - the impulse acts on one or a few calls only
E- effect may be permanent
N - effect is not permanent
What is a nerve impulse?
The change in electrical charge that moves along a neurone in response to a stimulus.
What is the resting potential?
The electrical potential across the plasma membrane of a cell that is not conducting an impulse. (-70 mV)
What is the sodium-potassium pump?
An intrinsic protein found in neurone cell membranes which uses ATP to actively transport 2 K+ into the axon and 3 Na+ out of the axon. This helps to contribute to the resting potential and is used to maintain resting potential faster depolarisation.
How is the resting potential generated in a neurone?
Ions are charged, so cannot diffuse directly across the phospholipid bilayer. There are sodium-gated channels and potassium-gated channels which allow sodium ions to leak into the axon and K+ to leak out of the axon down their concentration gradients (even when the channels are closed). The bilayer is 100x more permeable to K+ than Na+, giving an overall negative charge inside the axon (resting potential). The Na+/K+ pump also contributes to the resting potential.
Describe the formation of an action potential.
At resting potential (-70mV) Na+ voltage-gated channels are closed. A stimulus causes the membrane at one part of the neurone to increase permeability to Na+ (sodium channels open and Na+ enters the axon down their electrochemical gradient by diffusion. The membrane is depolarised and when the potential reaches -30mV (threshold), more Na+ channels open and the inside of the cell becomes more positively charged (positive feedback). At around +40mV, the Na+ channels close and the K+ channels open. K+ rush out down their electrochemical gradient, making the cell more negative (repolarisation). There is an undershoot meaning the axon becomes more negative than usual (hyperpolarisation). The K+ channels close and this triggers a wave of depolarisation in the next part of the neurone. The Na+/K+ pump restores resting potential.
How is the action potential propagated along the axon?
Na+ ions enter the axon by diffusion when the Na+ channels open after a stimulus. The Na+ are attracted sideways to the negative parts of the axon (at resting potential). This sets up a localised current, which causes the opening of adjacent voltage-gated Na+ channels further along the axon. As these regions depolarise, the regions before then repolarise as K+ leaves the axon through potassium-gated channels.
Why do myelinated neurones conduct impulses faster than unmyelinated neurones?
There are gaps in the myelin sheath called Nodes of Ranvier. Action potentials only occur at the nodes, so the nerve impulse jumps from node to node (saltatory conduction). Therefore, the action potential does not need to depolarise the whole neurone (only the Nodes of Ranvier), this speeds up conduction.
How does the diameter of the axon influence speed of conduction?
The greater the diameter of the axon, the faster the speed of conductance. This is because there is less leakage, so the strength of the action potential is maintained across the whole axon.
How does temperature affect the speed of impulse conduction?
At higher temperatures, the faster the rate of diffusion of ions, so action potentials occur faster (the speed of nerve impulses increases). Respiration provides the ATP required for active transport of ions (if temp is too high, respiratory enzymes may be denatured, so the Na+/K+ pump will stop working and resting potential will not be maintained). The Na+/K+ pump/ion channels could be denatured which would prevent action potentials. Therefore a very high temperature would slow down conduction.
What is the all or nothing principle?
An action potential is only generated if the threshold value is met for a given stimulus. The strength of the stimulus cannot be determined by the size of the action potential (as this is the same every time), but the frequency of impulses can be used (larger stimulus has higher frequency). Some neurones also have different threshold values, which the brain can interpret.
What is the absolute refractory period?
When the sodium channels open, the neurone is not able to respond to any other stimulus (i.e. one neurone cannot respond to multiple stimuli at once).
What is the relative refractory period?
No action potential can start in a section of a neurone until resting potential is reached again.
What are the benefits of having refractory periods in impulse conduction?
Impulses are seen as separate (discrete), which makes it easier for the brain to interpret. You can limit how many impulses you can send, which also helps interpret information. Also ensures single-direction propagation of the impulse.
What are receptors?
Receptors are cells which respond to a single specific stimulus, at a certain intensity. They act as transducers (they convert a type of stimulus into an electrical signal (generator potential then action potential))
Where are Pacinian corpuscles found?
Deep in the skin - most abundant on fingers, soles of feet, external genitalia, joints, ligaments and tendons.
How do Pacinian corpuscles work?
The ending of a sensory neurone has stretch-mediated sodium ion channels in its plasma membrane. In a resting state, these stretch-mediated channels are too narrow to allow sodium ions to pass through. The nerve has a ‘resting’ potential. When pressure is applied to the corpuscle, it deforms the lamellae which deforms the sodium ion channels, widening them. The sodium channels open and sodium ions diffuse in, causing the neurone to become depolarised, generating a generator potential which will lead to an action potential if threshold is reached.
What are the parts of the eye and what are their functions?
• Cornea – front portion of the eye that refracts light as it enters and protects the eye.
• Iris – muscle that controls how much light enters pupil (coloured part of the eye)
• Lens – focuses light onto retina
• Retina – layer of tissue at the back of the eye containing light receptors cells (rods and cones)
• Optic nerve – bundle of sensory neurones that carry impulses to brain
• Pupil - opening to the eye, allowing light to enter
• Blind spot – region at the base of the optic nerve, with no light receptors
• Fovea – the central part of the retina - contains highest concentration of cones cells to provide sharp vision.
• Sclera – tough, white outer layer of the eye that muscles moving it attach to
• Aqueous humour – maintains the pressure in the eye and nourishes the cornea
• Vitreous humour – liquid cavity behind the lens that gives the eyeball shape and attaches to the retina
• Choroid - Dark layer of tissue below sclera that contains blood vessels and pigment cells
• Suspensory ligaments – fibres between the ciliary muscles and the lens, that help to hold the lens in position
• Ciliary muscle – ring of muscle around the lens that alters the shape of the lens during ‘accommodation’
• Conjunctiva – thin membrane that protects the front of the eye
Describe rod cells.
Rod cells are photoreceptors found in the retina of the eye, which are rod shaped. There are many more rod cells than cone cells in the eye. Rod cells cannot distinguish between wavelengths of light, so produce images on black and white.
Why do multiple rod cells attach to one bipolar neurone and what does this lead to?
Many rod cells attach to one bipolar cell (retinal convergence), so it is easier to exceed threshold value. This leads to poor visual acuity (stimulation of multiple rods only produces a single impulse). This means that if separate sources of light stimulate the same bipolar neurone, they cannot be distinguished, so two close dots appear as one.
What pigment do rods contain?
Rods contain rhodopsin which must be broken down/bleached to create a generator potential. Low light intensity is sufficient to do this. However, rhodopsin takes a long time to reform so rod cells are not very useful for bright light vision.
Describe cone cells.
Cone shaped. Fewer numbers than rod cells. 3 types of cones; each have peak light absorption at a different wavelength - blue-sensitive, green-sensitive and red-sensitive. Many wavelengths are absorbed by more than one type of cone cell, so perceived colour depends on proportion of cones stimulated.
Why do cone cells only attach to one bipolar neurone and what does this lead to?
Good visual acuity - cones produce separate impulses which can be distinguished by the brain, so two close dots can be seen as separate. However, this means that it is more difficult to exceed threshold values for each bipolar neurone, so stronger stimuli are required.
What pigment do cone cells contain?
Cone cells contain iodopsin which needs a higher light intensity to break down/bleach it. Cones therefore do not work well in low light conditions. However, iodopsin reforms quickly, so cones remain responsive during bright light vision.
What does myogenic mean?
The heart cells initiate their own excitatory impulse, rather than coming from a nerve
How is heart rate controlled by electrical impulses?
Waves of electrical excitation from the sinoatrial node (SAN - ‘pacemaker’) spread along the muscle cells across the walls of both atria, causing the muscles to contract and push blood into the ventricles (atrial systole). The impulses do not travel directly to the ventricles because there is a layer of non-conducting tissue between the atria and ventricles. Impulses reach the atrioventricular node (AVN), which delays the impulses, giving the ventricles time to fill up before contraction. AVN sends impulses down specialised muscle tissue in wall of septum called the Purkyne fibres, arranged into Bundles of His. Electrical impulse reaches the muscle at the apex of the heart then travels up the wall of the ventricles in the Purkyne fibres, causing contraction upwards from the base (ventricular systole). Blood is pumped through the semi-lunar valves to finish the heart beat.
What is the sympathetic nervous system?
A part of the autonomic nervous system which stimulates effectors, speeds up activity and controls activities in stressful situations e.g. fight or flight response.
What is the parasympathetic nervous system?
A part of the autonomic nervous system which works antagonistically to the sympathetic nervous system. Inhibits effectors, slows down activity, controls activities under normal resting conditions. Conserves energy and replenishes body reserves.
How do baroreceptors work?
When blood pressure is higher than normal, baroreceptors increase the frequency of impulses to the medulla. The medulla oblongata sends impulses along parasympathetic neurones, which secrete acetylcholine. This binds to the receptors on the SAN and causes heart rate to slow down, reducing blood pressure. When blood pressure is too low, uses sympathetic neurones, which secrete noradrenaline, which increases heart rate and therefore blood pressure.
Where are baroreceptors found?
In the walls of the aorta and carotid arteries
What happens if the blood O2 is too high, CO2 is too low or pH is too high?
Chemoreceptors detect chemical changes in the blood and send impulses along parasympathetic neurones which secrete acetylcholine, which binds to receptors on the SAN, this causes heart rate to decrease, which restores homeostasis.
What happens if blood O2 is too low, CO2 too high or pH too low?
Chemoreceptors detect chemical changes in the blood and send impulses along sensory neurones to the medulla, which sends impulses along sympathetic neurones. These secrete noradrenaline, which binds to receptors on the SAN, increasing heart rate and maintaining homeostasis.
What is a synapse?
A synapse is the junction between two neurones.
What is temporal summation?
When a single presynaptic neurone releases neurotransmitter many times over a short period of time, eventually surpassing threshold.
What is spatial summation?
Multiple presynaptic neurones release enough neurotransmitter to exceed threshold in postsynaptic neurone to trigger action potential.
How are nerve impulses transmitted across a cholinergic synapse?
An action potential arrives at the axon terminal, leading to depolarisation of the presynaptic membrane. Voltage-gated calcium channels open and calcium ions enter the axon terminal. Calcium ions cause synaptic vesicles to fuse with the pre-synaptic membrane and release neurotransmitter by exocytosis. The neurotransmitter (acetylcholine) diffuses across the synaptic cleft, and binds to receptors on the postsynaptic membrane. Receptors on the postsynaptic membrane are located on sodium ion channels, which open when the acetylcholine binds. This allows Na+ to enter the postsynaptic neurone, leading to depolarisation. This must be above threshold to generate an action potential. Acetylcholine storage is an enzyme which breaks down acetylcholine into acetyl and choline, which move across the cleft into the presynaptic neurone (this prevents continued action potentials in the postsynaptic neurone). ATP released by mitochondria helps recombine acetyl and choline which is stored in vesicles for future use. Sodium ion channels close at receptor sites.
How is unidirectionality ensured by synapses?
Neurotransmitter can only be released from the presynaptic neurone but the receptors are only found on the postsynaptic neurone, which sets up a concentration gradient, making sure impulses only travel in one direction.
Why are there lots of mitochondria and endoplasmic reticulum in the presynaptic neurone?
Lots of mitochondria means lots of ATP can be produced in aerobic respiration. This is needed to actively transport calcium ions out of the synaptic knob faster an impulse, to repackage acetylcholine into vesicles by active transport, providing ATP for the Na+/K+ pump to restore resting potential. Endoplasmic reticulum are involved in the production, storage and transport of protein (neurotransmitters are protein, so lots is required).
What are some adaptations of a synapse for fast transmission?
Large number of synaptic connections to each neurone provides large surface area for diffusion of neurotransmitter. Concentration gradient is set up with neurotransmitter only present on one side of the synapse. Short diffusion distance as the synaptic cleft is very small.
How do stimulant drugs (e.g. caffeine, ecstasy) work?
They mimic the effect of a neurotransmitter, binding to receptors on the postsynaptic membrane, triggering action potentials, so impulses are sent faster and in greater frequency.
How do depressant drugs (e.g. alcohol, heroin) work?
They block the receptor sites on the postsynaptic membrane, so impulses are slowed down and fewer action potentials are generated. This effect includes nerves which supply the heart and intercostal muscles, so strong depressant drugs can cause an inability to breathe or may cause your heart to stop, which may lead to death.
How do inhibitory synapses work?
Some presynaptic neurones release neurotransmitter that binds to chloride ion protein channels on the postsynaptic membrane. The channels open and there is an influx of Cl- ions into the postsynaptic neurone by facilitated diffusion. This triggers the K+ channels to open, so lots of K+ get released out into the synaptic cleft. This makes the inside of the postsynaptic neurone more negative (hyperpolarisation). This makes it more difficult to reach threshold and generate an action potential, thus the effect is inhibitory.
What is smooth muscle?
Smooth muscle contracts without conscious control and is found in the walls of internal organs (apart form the heart), and blood vessels.
What is cardiac muscle?
Cardiac muscle is found only in the heart and it contracts involuntarily. It is very thick.
What is skeletal muscle?
Skeletal muscles are found in most of the body and are attached to bones by tendons (ligaments attach bones together). The movement of these muscles is voluntary and are often found around joints. They are usually found in pairs which work antagonistically to each other (contracting muscle is the agonist, relaxing muscle is the antagonist) and contract differently to the other types of muscle.
What are muscle fibres?
Cells that make up skeletal muscle which have fused together and share nuclei and cytoplasm.
What are fascicles?
Bundles of muscle fibres
What are myofibrils?
Bundle of protein filaments, wrapped in endomysium.
What are transverse (T) tubules?
Folds in the sarcolemma (muscle cell membrane), which sticks into the saarcoplasm (muscle cell cytoplasm).
What is actin?
Thinner, globular protein with twisted chains. Tropomyosin forms long thin threads wound around actin filaments, with troponin proteins also present.
What is myosin?
Thicker fibre made of 2 proteins: a fibrous protein arranged into a filament , and a globular protein which forms the bulbous head which protrudes from the filament.
What is a sarcomere?
A sarcomere is a section of myofibril between two Z lines. It appears banded due to the filaments present.
What are Z-lines?
The ends of each sarcomere
What is the M-line?
The middle of the myosin filaments (and the middle of the sarcomere).
What are light (I (isotropic)) bands?
Sections of the sarcomere where only actin is present - they appear lighter in colour and are found at both ends of the sarcomere.
What is the dark (A (anisotropic)) band?
The section of the sarcomere with overlapping actin and myosin filaments, or just myosin filaments, they are in the middle of the sarcomere and appear darker in colour due to the thicker filaments.
What is the H-zone?
The H-zone in the very middle of the sarcomere contains only myosin filaments. It is darker than the I band but lighter than the sections with actin and myosin overlapping.
What happens to the different zones/bands in a sarcomere when the muscle contracts?
H-zone gets shorter and I-bands get shorter, but A-bands stay the same length. The Z-lines get closer together as the sarcomere shortens. All zones/bands return to their original length when the muscle relaxes.
What is a neuromuscular junction?
A specialised cholinergic synapse between a motor neurone and a muscle cell.
Why are there multiple neuromuscular junctions along the length of a muscle?
To allow for the rapid and powerful contraction required when simultaneously stimulated by action potentials.
What is a motor unit?
All the muscle fibres supplied by a single motor neurone. The number of units stimulated depends on the force required.
What are some features of neuromuscular junctions?
Only excitatory, uses acetylcholine as the neurotransmitter, only links neurones to muscles so only motor neurones (not relay or sensory).
What is the role of the T-tubules?
The action potential travels deep in the muscle fibre through a system of T-tubules that branch through the sarcoplasm. The tubules are in contact with the endoplasmic reticulum of the muscle fibre (sarcoplasmic reticulum) which has actively absorbed calcium ions from the sarcoplasm in the muscle fibre. The action potential opens the calcium ion channels in the sarcoplasmic reticulum and calcium ions diffuse back into the sarcoplasm down a diffusion gradient.
Describe the sliding filament theory of muscle contraction.
Ca2+ are released from the sarcolemma after stimulation from the T system. The Ca2+ bind to the troponin and change its shape. The troponin displaces the tropomyosin and exposes the myosin binding sites which had been blocked. The bulbous heads of the myosin attach to the binding sites on the actin filaments to form a cross-bridge (they have ADP attached to them which puts them in a state allowing them to do this). The myosin heads change position to achieve a lower energy state and slide the actin filaments past the stationary myosin (it pushes the actin along with a power stroke). The molecule of ADP is released. ATP is formed, which binds to the bulbous heads of myosin and causes it to become detached from actin. Calcium ions activate ATP hydrolase to hydrolyse ATP to ADP and Pi. This provides energy to ‘re-cock’ the heads back to their normal position (recovery stroke). The ADP stays attached to the myosin head, so the cycle can begin again.
How do muscles relax?
When nervous stimulation ceases, calcium ions are actively transported back into the sarcoplasmic reticulum using energy from the hydrolysis of ATP. Troponin reverts to its normal shape allowing tropomyosin to re-block the actin filament binding site. Myosin heads are now unable to bind to actin filaments and the muscle relaxes. The actin filaments slide back to their original position and the original length of the sarcomeres is restored.
What is phosphocreatine?
A chemical which is stored in muscle and acts as a reserve supply of phosphates. During exercise, phosphocreatine phosphorylates ADP to ATP, so more ATP is available for muscle contraction. At rest, ATP phosphorylates creating back to phosphocreatine.
What are the differences between slow twitch muscle fibres and fast twitch muscle fibres?
Slow fibres:
Mainly aerobic respiration, weaker contraction, contract slower, can sustain contraction for longer, fatigue slower, many capillaries, higher numbers of mitochondria, lower concentration of glycolysis enzymes in cytoplasm, higher myoglobin concentration, thick filaments contain less myosin molecules, lower phosphocreatine concentration, lower glycogen concentration, better for endurance, common in calf muscles. Fast fibres are the opposite of the above (e.g. better for intense bursts of exercise and are common in biceps).
What is the difference between myoglobin and haemoglobin?
Myoglobin has one polypeptide chain and one haem group. There is no cooperative oxygen binding and acts as an oxygen store in muscle fibres due to very high affinity for oxygen. Haemoglobin has four polypeptide chains and four haem groups. Carries oxygen in red blood cells and has cooperative binding (one oxygen binding makes it easier for the next to bind).
