OCR Biology A Module 5 Flashcards

any change in the internal or external enviroment
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specific; detects one type of stimulus
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detect the presence of chemicals
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detect change in temperature
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detect mechanical forces or stress
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detect light during vision
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sensitive to changes in blood pressure
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sensitive to humidity
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sensitive to water
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cells that bring about a response to a stimulus to produce an effect
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cell signalling
hormonal or neuronal. detected by receptors on cell surface membranes
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sensory neurones
transmit nerve impulses from receptors to the cns. short dendrites and one long dendron to carry nerve impulses from receptor cells to the cell body, and one short axon to carry impulses from cell body to cns
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motor neurones
transmit nerve impulses from the cns to effectors. may short dendrites that carry nerve impulses from the cns to the cell body, one long axon carries nerve impulses from cell body to effector cells
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relay neurones
transmit nerve impulses between sensory and motor neurones. many short dendrites that carry nerve impuloses from sensory neurones to the cell body, ad many short axons that carry nerve impulses from the cell body to motor neurones`
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converts one form of energy to another, e.g. sensory neurones
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resting potential
receptor isnt stimulated; inside of cell is negatively charged relative to the outside, therefore there is a potential difference across the cell, generated by ion pumps ad channels. -70mv.
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generator potential
when a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell, altering the potential difference. bigger stimulus = bigger generator potential.
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action potential
if the generator potential is big enough (surpasses the threshold level) it triggers an action potential across a neurone
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pacinian corpuscle
mechanoreceptor in the skin. sensory nerve ending wrapped in lamellae connective tissue. deformed lamellae cause deformation of stretch-mediated sodium channels in the sensory neurones cell membrane, so sodium ions diffuse in (generator potential).
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sodium-potassium pumps
maintain resting potential in neurone's membrane. use active transport to move three na+ out of the neurone for every two k+ moved in. membrane is impermeable to na+ so they cant diffuse back in.
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potassium ion channels
maintain resting potential in neurone's membrane. allow facilitated diffusion of k+ out of the neurone down their concentration gradient
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electrochemical gradient
more positive ions move out of the cell than enter, making the outside of the cell more positively charged than the inside
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movement of action potentials
stimulus > depolarisation > repolarisation > hyperpolarisation > restig potential
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stimulus in an action potential
excites neurone cell surface membrane causing na+ chanels to open, so the membrane becomes more permeable to a+, which diffuse down their electrochemical gradient, making the inside of the neurone less negative
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depolarisation in an action potential
if the potential difference reaches the threshold, -55mv, voltage gated na+ channels open and more na+ diffuses into the neurone. this is positive feedback.
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repolarisation in an action potential
at a potential difference of around +30mv the na+ channels close and voltage gated k+ channels open, so k+ diffuses out of the membrane down its concentration gradient, bringing the membrane back to its resting potential. this is negative feedback.
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hyperpolarisation in an action potential
k channels are slow to close so theres a slight overshoot where too may k+ diffuses out of the neurone. the potential difference becomes less negative than the resting potential.
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resting potential in an action potential
the ion channels are reset as the sodium-potassium ion pump returns the membrane to its resting potential until the cell is excited by another stimulus.
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refractory period
during hyperpolarisation. after an action potential, a cell cant be excited again immediately as the ion channels are recovering. acts as a time delay between action potentials, ensuring they dont overlap and that they are unidirectional.
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wave of depolarisation
action potentials diffuse sideways as they move away from the refractory period as they cant fire an action potential.
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all-or-nothing principle
if the threshold value isnt reached, no action potential will occur, and it will always fire with the same charge if it is reached. bigger stimulus results in a higher frequency of impulses.
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increases speed of conduction via saltatory conduction. insulator myelin sheath of schwann cells with nodes of ranvier inbetween, bare membrane where sodium ion channels are concentrated. depolarisation only happens here, so the impulse jumps.
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axon diameter
action potentials are conducted quicker along axons with bigger diameters as theres less resistance to flow of ions in the cytoplasm.
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speed of conduction increases with temperature, but past 40°C the proteins on the membrane begin to denature ad the speed decreases.
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junction between neurones or between a neurone and an effector
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synaptic cleft
gap between cells at a synapse
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presynaptic neurone
neurone before the synapse
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synaptic knob
swelling on the presynaptic neurone containing synaptic vesicles containing neurotransmitter chemicals.
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postsynaptic membrane
membrane after synapse
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chemicalssecreted from the synaptic knob which trigger an action potential / muscle contraction / hormone by binding to receptors on the postsynaptic membrane. removed from the synaptic cleft so response stops (taken back / broken down by enzymes).
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cholinergic synapses
uses the neurotransmitter acteylcholine which binds to cholinergic receptors.
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synaptic transmission across a cholinergic synapse step 1
action potential arrives at synaptic knob of presynaptic neurone, stimulating voltage-gated ca2+ ion channels to open, which diffuse into the synaptic knob
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synaptic transmission across a cholinergic synapse step 2
influx of ca2+ into synaptic kob causes vesicles to move into presynaptic membrane and fuse with it, releasing acetylcholine by exocytosis.
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synaptic transmission across a cholinergic synapse step 3
acetylcholine diffuses into the synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane, causing na+ channels to open, causing depolarisation, potentially generating an action potential.
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synaptic transmission across a cholinergic synapse step 4
acetylcholine is removed from the synaptic cleft by acetylcholinesterase and the products are reabsorbed by the presynaptic neurone and used to make more acetycholine.
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chemicals that mimic neurotransmitter action at receptors so more receptors are activated, e.g. nicotine which mimics acetylcholine
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effect of curare
blocks cholinergic receptors so they cant be activated by acetylcholine at neuromuscular junctions, resulting in paralysis
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effect of nerve gases
inhibit acetylcholinesterase, meaning that acetylcholine is left in the synaptic cleft to bind to receptors as theyre there for longer, leading to a loss in muscle control
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effect of opioids
block calcium ion channels in the presynaptic neurone meaning that acetylcholine release is inhibited
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synaptic divergence
one neurone connects to many neurones so that information can be dispersed to different parts of the body
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synaptic convergence
may neurones connect to one neurone so that neuronal information can be amplified.
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the effect of neurotransmitters released from many neurones is added together, meaning that synapses can accurately process information, finely tuning a response.
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spatial summation
two or more presynaptic neurones converge and release their neurotransmitters at the same time onto the same postsynaptic neurone.small amount transmitted from each added together is enough to exceed the threshold value.
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temporal summation
two or more nervous impulses arrive in quick succession from the same presynaptic neurone, making an action potential more likely as more neurotransmitter is released into the synaptic cleft.
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unidirectional transmission
nervous impulse only travels in one direction as neurotransmitters are only released from the presynaptic membrane and receptors are only on the postsynaptic membrane
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protein chemical messengers, produced by glands in multicellular organisms, that are transported by the circulatory system to target distant organs to regulate physiology and behavior
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secreted from adrenal glands when there is a low blood glucose concentration, when youre stressed, or when youre exercising. activates glycogenolysis and increases blood pressure.
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action of adrealine
first messender: adrenaline, binds to receptors activating adenyl cyclase, catalysing the production of second messenger cyclic amp from atp, activating a cascade reaction catalysing glycogenolysis
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adrenal cortex
secretes lipid soluble steroid hormones which bid to receptors on nucleus or in cytoplasm, acting as a transcription factor.
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e.g. cortisol which helps regulate metabolism as it controls conversion of biological molecules to energy, as well as cardiovascular function in response to stress. works with corticosterone to regulate immune response, suppress inflammation.
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e.g. aldosterone controls blood pressure by maintaining salt and water concentrations
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sex hormones
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adrenal medulla
produces hydrophilic non-steroid hormones that arent vital to life but help the body react to stress
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works with adrenaline in response to stress; increased heart rate, widening of pupils and air passages, narrowing of blood vessels
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islets of langerhans
areas of pancreas which contain endocrine tissue, found in clusters around blood capillaries. alpha cells ad beta cells
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alpha cells
secrete glucagon
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beta cells
secrete insulin
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pancreatic acini
areas of pancreas which contain exocrine tissue, produce and secrete digestive enzymes and pancreatic juice
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maintenance of a constant internal environment regardless of external surroundings
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optimum body temperature in humans
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negative feedback
mechanism that restores a level back to normal
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positive feedback
mechanism that amplifies change away from the normal level
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cant control their body temperature internally, therefore must alter its behaviour
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control their body temperature internally through homeostasis, therefore they have a constantly high metabolic rate
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mechanisms to reduce body temperature
sweating, hairs lie flat, vasodilation
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mechanisms to increase body temperature
shivering, hormones, hairs stand up, vasoconstriction
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contains thermoregulatory centre
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forming glycogen from glucose
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forming glucose from non-carbohydrates
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forming glucose from glycogen
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control of insulin secretion by beta cells (1)
at a resting state the membrane is polarised as k+channels are open and ca2+ channels are closed. when glucose is diffused into the cells at high glucose concentration, more atp is made, triggering k+ channels to close, depolarising the membrane
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control of insulin secretion by beta cells (2)
depolarisation causes ca2+ ion channels to open, causing vesicles of insulin to leave by exocytosis.
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type 1 diabetes
autoimmune disease where the body attacks and destroys beta cells. treated with insulin therapy or islet cell transplants
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type 2 diabetes
beta cells dont produce enough insulin, or body cells dont respond well enough to it as insulin receptors on the membranes are inefficient. managed through lifestyle changes and medication.
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new developments in treating diabetes
gm bacteria and stem cells
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all the chemical reactions within a cell
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removal of the waste products of metabolism
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hepatic artery
supplies liver with oxygenated blood from the heart
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hepatic vein
takes deoxygenated blood away from the liver
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hepatic portal vein
brings blood from the duodenum and ileum, so its rich in the products from digestion.
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bile duct
takes bile to the gall bladder to be stored
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liver lobules
cylindrical structures made of hepatocytes arranged in rows radiating out from the centre. central vein in the middle connects to hepatic vein, and branches of the rest are found throughout
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blood from hepatic portal vein and hepatic artery is mixed in spaces between hepatocytes, lined with kupffer cells which act as macrophages
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bile caniliculi
connects the bile duct to the central vein, going into the bile ductules to take it to the gall bladder
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-nh2 removed from any excess amino acids forming ammonia nh3 and organic acids (which can be respired to give atp or converted to carbohydrate to be stored as glycogen
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ornothine cycle
conversion of ammonia and carbon dioxide to create urea and water
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breakdown of alcohol, drugs, and unwanted hormones
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blood from afferent arteriole takes blood at high pressure to the glomerulus, forcing blood out of the capillary wall, through the basement membrane, and through the bowman's capsule epithelium
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selective reabsorption (1)
takes place at the pct, the loop of henle and the dct.useful substances leave the nephron tubules and enter the capillary network. useful solutes are reabsorbed by active transport and facillitated diffusion in the pct
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selective reabsorption (2)
water enters by osmosis as the water potential of the blood is lower than the water potential of the filtrate in loop, dct and collecting duct. urine remains
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countercurrent multiplier system
ascending and descending limb of the loop of henle; assists with reabsorption.
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mechanism of countercurrent multiplier (1)
near the top of the ascending limb na+ and cl- are actively pumped out. as it is impermeable to water, it stays inside, creating a low water potential in the medulla, so water moves out of the descending limb into the medulla by osmosis
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mechanism of countercurrent multiplier (2)
the filtrate becomes more concentrated in the descending limb as the ions are impermeable to the walls, ad the water from the descending limb is reabsorbed into the capillary network. near the bottom of the ascending, na+ and cl- diffuse out.
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mechanism of countercurrent multiplier (3)
the medulla becomes more concentrated as the water cannot diffuse out of the tubule by active transport.the ion concentration in the medulla is high at a low water potential, so water moves out of the collecting duct to be reabsorbed into the blood.
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loop of henle length
the longer it is the more water they can absorb from the filtrate. longer ascending = more ions actively pumped out increasing medulla water potential.
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secreted from the posterior pituitary gland; binds to receptors in dct and collecting duct, creating aquaporins, making walls more permeable to aid reabsorption.
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glomerular filtration rate
rate at which blood is filtered from the glomerulus into the bowmans capsule. detects kidney failure.
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involves a dialysis machine, takes eight hours
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peritoneal dialysis
inside the body
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best solution to kidney failure
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Card 2


specific; detects one type of stimulus



Card 3


detect the presence of chemicals


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Card 4


detect change in temperature


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Card 5


detect mechanical forces or stress


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