Topic 6: Learn And Churns

Question 1

Explain the importance of reflex actions (3 marks)

Answer 1

1. Automatic/ involuntary adjustments to changes in the environment
2. Reducing damage to tissues/ prevents injury/ e.g burning
3. Role in homeostasis/ example;
   4.posture/balance
   5.finding food/ mate
4. Escape from predators

Question 2

Describe te sequence of events which allows information to pass from one neurone to the next neurone across the cholinergic synapses (6 marks)

Answer 2

1. Impulses cause calcium ions to enter axons
   2.vesicles fuse with presynaptic membrane
2. Acetylcholine released
   4.acetylcholine diffuses across synaptic cleft
   5.binds with receptors on postsynaptic membrane
3. Sodium ions enter post synaptic neurone
4. Depolarisation of postsynaptic membrane
5. If above threshold, action potential produced

Question 3

Explain how a resting potential is maintained in a neurone (4 marks)

Answer 3

1. Membrane is relatively impermeable to sodium ions/gated channels are closed/fewer channels
2. Sodium ions pumped/actively transported out
3. By sodium ion carriers
4. Inside is negative compared to outside/ 3 sodium ions out for 2 potassium ions in

Question 4

Describe how the release of acetylcholine into a neuromuscular junction causes the cell membrane of a muscle fibre to depolarise (3 marks)

Answer 4

1. Movement by diffusion
2. Binding to receptors on the postsynaptic membrane
3. Causing sodium channels to open/ sodium ions move into muscle cell

Question 5

Describe how a pacinian corpuscle produces a generator potential when stimulated (3 marks)

Answer 5

1. Increase pressure deforms/ changes stretch mediated sodium ion channels
   2 sodium channels open & sodium ions flow in
2. Depolarisation- eating to generator potential

Question 6

What does the data suggest about the control of heart rate by the sympathetic and parasympathetic nervous system in response to changes in arterial blood pressure (3 marks)

Answer 6

1. Parasympathetic greater effect than sympathetic
2. Parasympathetic keeps heart rate down/ decreases heart rate (as blood pressure increases)
3. Sympathetic keeps heart rate up/increase heart rate
4. Parasympathetic greatest/ greater effect at high blood pressure/ sympathetic greatest effect at low blood pressure

Question 7

Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane (4 marks)

Answer 7

1. Action potential arrives/ depolarisation occurs
2. Calcium ions enter synaptic knob
3. Vesicles fuse with the membrane
4. Acetylcholine diffuses across the synaptic cleft
5. Binds to receptors

Question 8

the binding of GABA to receptors on the postsynaptic membranes causes negatively charged chloride ions to enter the postsynaptic neurones.
explain how this will inhibit transmission of the nerve impulses by postsynaptic neurones (3 marks)

Answer 8

1. inside becomes more negatively charged/ hyperpolarised
2. stimulation doesn’t reach threshold level/ action potential not produced
3. depolarisation does not occur/ reduces effect of sodium ions entering

Question 9

Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular junctions. When a cannabinoid binds to its receptors, it closes calcium ion channels
suggest how cannabinoids could prevent muscle contraction
(4 marks)

Answer 9

1. prevents influx of calcium ions into the pre-synaptic membrane
   2.synaptic vesicles don’t fuse with membrane/release neurotransmitter
2. neurotransmitter doesn’t diffuse across synapse/doesnt bind to receptors on post synaptic membrane
3. no action potential/depolarisation of post-synaptic membrane/ sodium ion channels do not open

Question 10

Explain what causes the conduction of impulses along a non-myelinated axon to be slower than along a myelinated axon
(3 marks)

Answer 10

1. non-myelinated- whole membrane is depolarised
2. myelinated-depolarisation/ion movement only at the nodes
3. impulses jump from node to node/salatory conduction

Question 11

describe how calcium ions are involved in synaptic transmission
(2 marks)

Answer 11

1. nerve impulses causes calcium ions to enter presynaptic neurone
2. calcium ion entry causes fusion of vesicles with presynaptic membrane/ release of transmitter

Question 12

when a person looks directly at an object, it’s image is focused on the fovea. When the image is focused on the fovea, the person sees the object in colour. Explain why. (3 marks)

Answer 12

1. colour detected by cone cells
2. fovea contains only/mainly cone cells
3. 3 types of cone cells(described) each sensitive to different wavelengths/red green or blue

Question 13

explain why vision using other parts of the retina has high sensitivity to light (3 marks)

Answer 13

1. many rods in other parts of the retina
2. rhodopsin/ rod cells very sensitive to light/ work in low light
3. rods connect in groups to ganglion cell/neurone
4. summation
5. if enough light above threshold, nerve impulses are sent to the brain along the optic nerve

Question 14

describe the role of calcium ions and ATP In the contraction of a microfibril
(5 marks)

Answer 14

1. calcium Ions diffuse into myofibrils from sarcoplasmic reticulum
2. calcium ions cause movement of tropomyosin
   3.causes exposure of the binding sites on actin
3. myosin heads attach to binding sites on actin
   5.hydrolysis of ATP causes myosin heads to bend
4. bending pulls actin molecule
5. attachment of a new ATP molecule to each myosin head causes myosin head to detach from actin sites

Question 15

describe the role of each of the following in muscle contraction; tropomyosin and ATP (4 marks)

Answer 15

1. blocks myosin binding site on actin
2. moves from binding site on actin due to calcium ions, allowing cross bridge formation
3. releases myosin from actin
4. causes myosin head to tilt
5. used in the active transport of calcium ions

Question 16

explain how muscles maintain posture (3 marks)

Answer 16

1. antagonistic muscles
2. working across joints
3. both contract to keep joint/ body at a certain angle/upright
4. isometric contraction
5. only a few fibres contract to avoid fatigue/ slow muscle fibres used

Question 17

describe the role of calcium ions in the contraction of a sarcomere
(4 marks)

Answer 17

1. moves tropomyosin
2. to reveal binding sites on actin
   3.allowing myosin heads to bind to actin/actinomyosin cross bridges formed/ activates ATPasa

Question 18

Dopamine is a neurotransmitter, the transmission of which is similar to acetylcholine. Dopamine stimulates the production of nervous impulses in the postsynaptic neurone. Describe how.
(3 marks)

Answer 18

1. dopamine diffuses across the synapse
2. attaches to receptors on the postsynaptic membrane
3. stimulates entry of sodium ions/depolarisation/action potential

Question 19

describe how a heartbeat is initiated/ coordinated
(5 marks)

Answer 19

1.SAN sends a wave of electrical activity/ impulses causing atrial contraction
2. non- conducting tissue prevents immediate contraction of the ventricles
3. AVN delays the impulse whilst the blood leaves the atria/ventricles fill
4. AVN sends wave of electrical activity/ impulses down the bundle of His
5. causing ventricles to contract from the base up

Question 20

explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta (5 marks)

Answer 20

1. atria has higher pressure than ventricle causing AV valves to open
2. ventricle has higher pressure than atrium due to filling causing AV valve to close
3. ventricle has higher pressure than the aorta causing semi lunar valve to open
4. higher pressure in aorta than ventricle causes semilunar valve to close
5. muscle/atrial/ventricular contraction causes increase in pressure

Question 21

a woman takes moderate exercise. explain what causes her heart rate to increase while she exercises ( 6 marks)

Answer 21

1. rate of respiration increases in muscle cells
2. carbon dioxide concentration increases/ph falls/ acidity increases
3. chemo receptors in aortic/carotid arteries
4. impulses to medulla/cardioacceleratory centre
5. increases the frequency of impulses
6. along the sympathetic pathway to the SAN

Question 22

the heart controls and coordinates the regular contraction of the atria and ventricles. Describe How (5 marks)

Answer 22

1. SAN- AVN- bundle of his/purkyne fibres
   2.impulses/electrical activity over atria
2. atria contract
   4.non conducting tissue (between atria and ventricles)
3. delay at AVN ensures atria are empty/ventricles fill before contract
4. Ventricles contract from Apex upwards

Question 23

explain how a rise in blood pressure results in a decrease in the rate of heartbeat (6 marks)

Answer 23

1. pressure receptors/baroreceptors in carotid arteries
2. send impulses to cardio-inhibitory centre in medulla
   3.impulses via parasympathetic nerves
3. to SAN
4. release of ACh/decreases impulse from SAN
5. decreases impulses to AVN/decreases impulses from AVN

Question 24

describe the role of the hormone glucagon in the control of blood sugar concentration (4 marks)

Answer 24

1. binds to specific receptor
2. on muscle/liver cell
3. activation of enzymes in liver
   4.hydrolysis of glycogen
4. facilitated diffusion of glucose out of liver cells
5. increases blood glucose levels

Question 25

explain the role of negative feedback in the control of the plasma glucose concentration (5 marks)

Answer 25

1. deviation of a value from the norm intitiates corrective mechanisms 2. fluctuations in plasma glucose concentration detected by hypothalamus/islets cells in pancreas 3. initial decrease, no food stimulates secretion of glucagon 4.increase in plasma glucose stimulates secretion of insulin from b cells 5.change in membrane permeability to glucose

Question 26

how does maintaining a constant body temp allow metabolic reactions in cells to proceed with maximum efficiency? (5 marks)

Answer 26

1. body temp/37 is optimum for enzymes 2. excess heat denatures enzymes/alters shape of active site/substracte cant bind 3.reactions slowed 4. reduces kinetic energy of molecules 5. fewer collisions/ es complexes formed

Question 27

describe how insulin reduces the concentration of glucose in the blood (3 marks)

Answer 27

1. insulin binds to specific receptors 2. insulin activates carrier proteins/more channels to form 3. insulin increases permeability of liver/muscle cells to glucose 4. insulin action results in glucose conversion to glycogen/glycogenesis

Question 28

stimulation of osmoreceptors can lead to the secretion of ADH. describe and explain how this affects urine produced by kidneys. (4 marks)

Answer 28

1.permeability of membrane to water increased 2. more water absorbed from distal tube/collecting duct 3. smaller volume of urine 4. urine becomes more concentrated

Question 29

explain how the loop of hence maintains the gradient of ions which allows water to be reabsorbed from the filtrate in the collecting duct. (5 marks)

Answer 29

1. active transport of chloride/sodium ions out of filtrate 2. from the ascending limb 3.into surrounding tissue fluid 4. ascending limb impermeable to water 5. lower WP in interstitial fluid compared to filtrate 6. water leaves the descending limb via osmosis 7. lower WP down the medulla 8. water is absorbed from the collecting duct via osmosis

Question 30

explain how ADH is involved in the control of the volume of urine produced (4 marks)

Answer 30

1. if WP of blood falls, detected by receptors in hypothalamus 2. leads to ADH released from pituitary gland 3. ADH makes cells of collecting duct/DCT more permeable to water 4. water leaves filtrate by osmosis 5. smaller volume of urine produced

Question 31

describe how ultrafiltration produces glomerular filtrate (5 marks)

Answer 31

1. blood pressure/hydrostatic pressure 2.small molecules/named example 3. pass through basement membrane (it acts as a filter) 4. proteins too large so stay behind 5. presence of pores in capillaries/podocytes

Question 32

explain how a lack of insulin affects the reabsorption of glucose in the kidneys of a person who doesn't secrete insulin (4 marks)

Answer 32

1. high concentration of glucose in the blood 2. high concentration in filtrate 3. reabsorbed by facilitated diffusion/active transport 4. requires proteins/carriers 5. these are working at maximum rate/saturated 6. not all glucose reabsorbed/some lost in urine

Question 33

some desert mammals have long loops of Henle and secrete large amounts of ADH explain how these 2 features are adaptations to living in desert conditions (6 marks)

Answer 33

1. more water reabsorbed/less lost in urine 2.by osmosis 3. from collecting duct 4.due to longer loop of hence 5. sodium/chloride ions absorbed from filtrate in ascending limb 6.gradient established in medulla/concentrations of ions increases down the medulla 7. (adh) acts on collecting duct/DCT 8. makes cells more permeable/ inserts aquaporins in plasma membrane

Question 34

in a mammal, urea is removed from the blood by the kidneys and concentrated in the filtrate. Describe how urea is removed from the blood. Explain how urea is concentrated in the filtrate (5 marks)

Answer 34

1. hydrostatic pressure is generated 2. causes ultrafiltration at glomeruli/renal capsule 3. through basement membrane 4. enabled by small size urea molecule 5. reabsorption of water by osmosis 6. at PCT/descending loop of hence 7.at DCT/collecting duct 8.active transport of ions/glucose creates a gradient