T6 Organisms response to changes in the environment

Question 1

Give one similarity and one difference between a taxis and a tropism 2 marks

Answer 1

1. Similarity − directional response (to a stimulus) / movement
   towards / away from a stimulus;
2. Difference − taxis (whole) organism moves and tropism a growth (response).
   Must be clear which one, taxis or tropism, they are referring to
   Taxis occurs in animals / motile organisms and tropism occurs in plants

Question 2

Explain how a resting potential is maintained across the axon membrane in a neurone.
3 marks

Answer 2

1. Higher concentration of potassium ions inside and higher concentration of
   sodium ions outside (the neurone)
   OR
   potassium ions diffuse out
   OR
   sodium ions diffuse in;
   Accept ‘more’ for ‘higher concentration’.
   Accept ‘sodium ions can’t diffuse in (due to alternative explanation).
2. (Membrane) more permeable to potassium ions (leaving than sodium ions
   entering)
   OR
   (Membrane) less permeable to sodium ions (entering than potassium ions
   leaving);
   Accept for ‘less permeable to sodium ions’ is ‘impermeable to
   sodium ions’ or ‘sodium
   gates/channels are closed’ (alternative explanation).
3. Sodium ions (actively) transported out and potassium ions in;
   reference to ions or Na+
   and K+
   is required. If mentioned once allow
   for all mark points.
   If an answer provides two or three of these mark points without any
   reference to ions – award one maximum mark.
   Accept 3 Na+
   out and 2 K+
   in but reject if numbers used are
   incorrect.

Question 3

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon. 3 marks

Answer 3

1. Myelination provides (electrical) insulation;
   Reject thermal insulation.
   Accept description of (electrical) insulation.
2. (In myelinated) saltatory (conduction)
   OR
   (In myelinated) depolarisation at nodes (of Ranvier);
3. In non-myelinated depolarisation occurs along whole/length (of axon);
   Accept action potentials for depolarisation.
   ‘Messages’ or ‘signals’ disqualifies first of these marks credited.

Question 4

A scientist investigated the effect of inhibitors on neurones. She added a respiratory
inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.
Explain why. 3 marks

Answer 4

1. No/less ATP produced;
2. No/less active transport
   OR
   Sodium/potassium pump inhibited;
   Accept Na+
   not/fewer moved out and K+
   not/fewer moved in.
3. Electrochemical gradient not maintained
   OR
   (Facilitated) diffusion of ions causes change to 0 mV
   OR
   (Results in) same concentration of (sodium and potassium) ions (either
   side of membrane)
   OR
   No net movement of (sodium and potassium) ions;
   Accept reaches electrical equilibrium/balance.
   Accept concentration gradient of sodium and potassium ions not maintained.

Question 5

Damage to the myelin sheath of neurones can cause muscular paralysis.
Explain how. 3 marks

Answer 5

  1.   (Refers to) saltatory conduction
OR
(Nerve) impulses/depolarisation/ions pass to other neurones
OR
Depolarisation occurs along whole length (of axon);
Accept suitable description that refers to (transmission) from node to
node (of Ranvier).
Accept action potential for depolarisation.
1 and 2. Accept action potentials for impulses.
1, 2 and 3. Reject first mark awarded if answer refers to
messages/signals for impulses. Reject even if impulse/s also referred to.
2.   (Nerve) impulses slowed/stopped;
3.   (Refers to) neuromuscular junction
OR
(Refers to) sarcolemma;

Question 6

Suggest two advantages of simple reflexes. 2 marks

Answer 6

1. Rapid;
2. Protect against damage to body tissues;
3. Do not have to be learnt;
4. Help escape from predators;
5. Enable homeostatic control.

Question 7

Axon P was found to conduct impulses much faster than other axons in the nerve pathway
shown in the diagram.
Describe and explain one feature of axon P that might cause this difference. 2 marks

Don’t need to know the diagram to answer

Answer 7

1. Axon P is myelinated;
2. So shows saltatory conduction / impulses jump between nodes of Ranvier
   OR
3. Axon P has a larger diameter;
4. So less resistance to flow of ions.
   Mark as 1 & 2 OR 3 & 4

Question 8

Multiple sclerosis (MS) is a disease that involves damage to the myelin sheaths of neurones.
Movement in MS sufferers may be jerky or slow.
(a) Damage to the myelin sheaths of neurones can lead to problems controlling the contraction
of muscles.
Suggest one reason why. 2 marks

Answer 8

One suitable suggestion; explained;
E.g.
1. Action potentials travel more slowly / don’t travel;
Accept: fewer / no saltatory movement of potentials
2. So delay in muscle contraction / muscles don’t contract / muscles contract
slow(er);
OR
3. Action potentials / depolarisation ‘leaks’ to adjacent neurones;
Accept: neurones not insulated
4. So wrong muscle (fibres) contract.

Question 9

Scientists investigated the use of substances called cannabinoids to control muscle problems
caused by MS.
(b) Cannabinoids are hydrophobic molecules. In the body, they easily pass into neurones.
Explain why.
1 mark

Answer 9

Lipid-soluble / pass through phospholipid bilayer.
Not just ‘pass through membranes’

Question 10

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

Answer 10

1. Prevents influx of calcium ions (into pre-synaptic membrane);
   Need idea of moving into pre-synaptic membrane / synaptic knob
   Accept Ca++ / Ca2+
2. (Synaptic) vesicles don’t fuse with membrane / vesicles don’t release
   neurotransmitter;
   Accept vesicles don’t release acetylcholine
3. Neurotransmitter does not diffuse across synapse / does not bind to receptors
   (on post-synaptic membrane);
   Accept: sarcolemma / muscle membrane for post-synaptic
   membrane
4. No action potential / depolarisation (of post-synaptic membrane) / sodium (ion)
   channels do not open / prevents influx of sodium ions.
   Accept Na+
   Accept prevents depolarisation of muscle cell
   Ignore: descriptions of events at post-sy

Question 11

Cannabinoids include substances found in cannabis that can enter brain tissue. Scientists
are developing artificial cannabinoids that can enter neuromuscular junctions but cannot
enter brain tissue.
Suggest why these artificial cannabinoids would be better to use than cannabis when
treating someone with MS. 2 marks

Answer 11

1. They won’t affect synapses in brain;
2. They won’t cause problems with the brain’s function / won’t damage brain;
   Accept: suitable named problem e.g. hallucination
   Ignore: unqualified references to ‘side effects’
   Accept: reference to addiction / harm of smoking (cannabis)
3. (So only the) muscle / neuromuscular junctions treated / affected

Question 12

During an action potental, the membrane potential rises to +40 mV and then falls. Explain why. 3 marks

Answer 12

Potassium channels open;
Potassium out;
Sodium channels close;
Do not penalise candidate who refers to sodium or potassium. Ions
are mentioned in question.
Reject pump

Question 13

After exercise, some ATP is used to re-establish the resting potential in axons. Explain how the resting potential is re-established. 2 marks

Answer 13

Pump / active transport / transport against concentration gradient;
Of sodium from axon / sodium out / of potassium in;
Do not penalise candidate who refers to sodium or potassium. Ions
are mentioned in question

Question 14

The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image
of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer. 3 marks

Answer 14

1. High (visual) acuity;
2. (Each) cone is connected to a single neurone;
   Accept no retinal convergence.
   Accept ‘bipolar/nerve cell’ for neurone.
3. (Cones send) separate (sets of) impulses to brain;
   Accept ‘optic nerve’ for brain.
   Reject ‘signals’, ‘messages’ for ‘impulses’.
   Accept ‘action potential’.

Question 15

The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night.
Do not refer to rhodopsin in your answer. 3 marks

Answer 15

1. High (visual) sensitivity;
   Accept retinal convergence.
2. Several rods connected to a single neurone;
   Accept ‘bipolar/nerve cell’ for neurone
   Accept 2, ‘many’ or
3. Enough (neuro)transmitter to reach/overcome threshold
   OR
   Spatial summation to reach/overcome threshold; more for ‘several’
   Reject ‘signals’, ‘messages’ for ‘impulses’.
   Accept named neurotransmitter.
   Accept depolarisation, ‘action potential’ or ‘generator potential’ for
   ‘to reach threshold’.
   Generator potentials combine to reach threshold/
   depolarisation/action potential/generator potential.

Question 16

Explain how the resting potential of –70 mV is maintained in the sensory neurone when no
pressure is applied. 2 marks

Answer 16

1. Membrane more permeable to potassium ions and less permeable to sodium ions;
2. Sodium ions actively transported / pumped out and potassium ions in.

Question 17

Explain how applying pressure to the Pacinian corpuscle produces the changes in
membrane potential 3 marks

Answer 17

1. (Pressure causes) membrane / lamellae to become deformed / stretched;
2. Sodium ion channels in membrane open and sodium ions move in;
3. Greater pressure more channels open / sodium ions enter.

Question 18

Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones
are destroyed. Explain how this results in slower responses to stimuli.
2 marks

Answer 18

1. Less / no saltatory conduction / action potential / impulse unable to ‘jump’ from
   node to node;
2. More depolarisation over length / area of membranes.

Question 19

After the student had stared at a purple square, he saw a green afterimage.
Suggest why.
3 marks

Answer 19

1. (When staring at purple) red (sensitive) and blue (sensitive)
   cones are stimulated / green (sensitive) cones are not
   stimulated;
2. Red and blue cone cells become exhausted / stop working;
3. (Afterimage due to) green (sensitive) cone cells working;
   Allow 1 extra mark up to the maximum of 3 for additional detail to
   marking point 2 e.g. exhaustion of pigment, exhaustion of
   neurotransmitter, exhaustion of ATP

Question 20

Dopamine is a neurotransmitter released in some synapses in the brain. The transmission
of dopamine is similar to that of acetylcholine.
Dopamine stimulates the production of nerve impulses in postsynaptic neurones.
Describe how.
Do not include in your answer the events leading to the release of dopamine and the
events following production of nerve impulses at postsynaptic neurones 3 marks

Answer 20

1. (Dopamine) diffuses across (synapse);
2. Attaches to receptors on postsynaptic membrane;
   Ignore name/nature of receptor e.g. cholinergic
3. Stimulates entry of sodium ions and depolarisation/action potential;
   Accept Na+
   for sodium ions
   Accept generator potential for action potential

Question 21

Dopamine is a neurotransmitter released in some synapses in the brain. The transmission
of dopamine is similar to that of acetylcholine.
Dopamine stimulates the production of nerve impulses in postsynaptic neurones.
Dopamine has a role in numerous processes in the brain including pain relief. The release
of dopamine can be stimulated by chemicals called endorphins produced in the brain.

Endorphins attach to opioid receptors on presynaptic neurones that release dopamine.
Morphine is a drug that has a similar structure to endorphins and can provide pain relief.
Explain how. 2 marks

Answer 21

1. Morphine attaches to opioid receptors;
   Reject reference to active site
2. (More) dopamine released (to provide pain relief);
   Reject receptors release dopamine

Question 22

GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA
causes negatively charged chloride ions to enter postsynaptic neurones.
Explain how this inhibits postsynaptic neurones.
3 marks

Answer 22

1. (Inside of postsynaptic) neurone becomes more negative/hyperpolarisation/inhibitory
   postsynaptic potential;
   Ignore K+
   Accept -75mV or any value below this as equivalent to more
   negative
   Accept ‘decrease in charge’
2. More sodium ions required (to reach threshold)
   OR
   Not enough sodium ions enter (to reach threshold);
   Accept Na+
   for sodium ions
3. For depolarisation/action potential;
   Context must covey idea that depolarisation / action potential is less
   likely

Question 23

Describe the sequence of events involved in transmission across a cholinergic synapse.
Do not include details on the breakdown of acetylcholine in your answer. 5 marks

Answer 23

1. Depolarisation of presynaptic membrane;
   Accept action potential for depolarisation.
2. Calcium channels open and calcium ions enter (synaptic knob);
   Accept Ca2+
   .
3. (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic
   membrane and release acetylcholine/neurotransmitter;
   Accept abbreviations for acetylcholine as term is in the question.
4. Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
   Accept abbreviations for acetylcholine as term is in the question.
5. (Acetylcholine attaches) to receptors on the postsynaptic membrane;
6. Sodium ions enter (postsynaptic neurone) leading to depolarisation;
   Accept Na+
   .
   Accept ‘action potential’ or ‘generator potential’ for depolarisation.

Question 24

Serotonin is a neurotransmitter released in some synapses in the brain. It is transported back out
of the synaptic gap by a transport protein in the pre-synaptic membrane.
(a) Serotonin diffuses across the synaptic gap and binds to a receptor on the post-synaptic
membrane.
Describe how this causes depolarisation of the post-synaptic membrane. 2 marks

It is important that a neurotransmitter such as serotonin is transported back out of
synapses. Explain why.
2 marks

Answer 24

1. Causes sodium ion channels to open;
2. Reject if wrong sequence of events
3. Sodium ions enter (cell and cause depolarisation);
   Reject sodium on its own only once
4. (If not removed) keeps binding (to receptors);
   Accept answers based on what happens if it is transported out − ie
   what should happen
5. Keeps causing action potentials / depolarisation (in post-synaptic membrane);
6. Accept keeps Na +
   channels open(ing)

Question 25

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

Answer 25

action potential arrives / depolarisation occurs;
calcium ions enter synaptic knob;
vesicles fuse with membrane;
acetylcholine diffuses (across synaptic cleft);
binds to receptors;

Question 26

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

Answer 26

inside becomes more negatively charged / hyperpolarised; stimulation does not reach
threshold level / action potential not produced;
depolarisation does not occur / reduces effect of sodium ions entering;

Question 27

During an epileptic seizure muscular contractions may occur. In which part of the brain
would neuronal activity produce muscular contractions of the right leg? 1 mark

Answer 27

motor area;
left cerebral hemisphere;

Question 28

Explian the role of glycogen granules in skeletal muscle 2 marks

Answer 28

1. As a store of glucose
   Ignore provide energy
   OR
   To be hydrolysed to glucose;
2. For respiration / to provide ATP;

Question 29

During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a
reduction in the ability of calcium ions to stimulate muscle contraction.
Suggest how.
3 marks

Answer 29

1. Low pH changes shape of calcium ion receptors
   Do not accept tropomyosin does not move
2. Fewer calcium ions bind to tropomyosin;
   Accept troponin
3. Fewer tropomyosin molecules move away;
4. Fewer binding sites on actin revealed;
5. Fewer cross-bridges can form
   OR
   Fewer myosin heads can bind
   Must include idea of fewer at least once

Question 30

Describe the roles of calcium ions and ATP in the contraction of a myofibril. 5 marks

Answer 30

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin heads
   to detach (from actin sites).

Question 31

ATP is an energy source used in many cell processes. Give two ways in which ATP is a
suitable energy source for cells to use. 2 marks

Answer 31

1. Releases relatively small amount of energy / little energy lost as heat;
   Key concept is that little danger of thermal death of cells
2. Releases energy instantaneously;
   Key concept is that energy is readily available
3. Phosphorylates other compounds, making them more reactive;
4. Can be rapidly re-synthesised;
5. Is not lost from / does not leave cells

Question 32

Describe how a Pacinian corpuscle produces a generator potential when stimulated.
3 marks

Answer 32

1. (Increased pressure) deforms / changes stretch-mediated sodium (ion) channel;
2. (Sodium channels open and) sodium ions flow in;
   Accept Na+
3. Depolarisation (leading to generator potential).
   Accept correct description of depolarisation

Question 33

Describe how a heartbeat is initiated and coordinated 5 marks

Answer 33

1. SAN sends wave of electrical activity / impulses (across atria) causing atrial
   contraction;
   Accept excitation
2. Non-conducting tissue prevents immediate contraction of ventricles / prevents
   impulses reaching the ventricles;
3. AVN delays (impulse) whilst blood leaves atria / ventricles fill;
4. (AVN) sends wave of electrical activity / impulses down Bundle of His;
5. Allow Purkyne fibres / tissue
6. Causing ventricles to contract from base up

Question 34

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 34

1. Atrium has higher pressure than ventricle (due to filling / contraction) causing
   atrioventricular valves to open;
   Start anywhere in sequence, but events must be in the correct
   order.
2. Accept bicuspid, reject tricuspid
3. Allow: blood passes through the valve = valve open / blood
   stopped from passing through the valve = valve closed
4. Ventricle has higher pressure than atrium (due to filling / contraction) causing
   atrioventricular valves to close;
5. Ventricle has higher pressure than aorta causing semilunar valve to open;
   Points 1, 2 and 3 must be comparative: eg higher 3. Allow aortic
   valve
6. Higher pressure in aorta than ventricle (as heart relaxes) causing semilunar
   valve to close;
7. Allow aortic valve
8. (Muscle / atrial / ventricular) contraction causes increase in pressure;

Question 35

Explain, in terms of pressure, why the semilunar valves open.
1 mark

Answer 35

Pressure is greater below valve / in ventricle than (artery);
Must be comparative
Reject: pressure is greater in ventricle than atrium
Neutral: pressure in ventricle increases
Accept: E / F / named artery
Accept: converse argument

Question 36

When a wave of electrical activity reaches the AVN, there is a short delay before a new
wave leaves the AVN. Explain the importance of this short delay. 2 marks

Answer 36

Allow atria to empty / contract / ventricles to fill;
Before ventricles contract;
OR
Delays contraction of ventricles;
Until after atria have contracted / ventricles have filled;
Neutral: ‘to pump blood’

Question 37

A woman takes moderate exercise. Explain what causes her heart rate to increase while
she exercises. 6 marks

Answer 37

1. rate of respiration increases (in muscle cells);
2. carbon dioxide concentration increases / pH falls / H+ increases / acidity
   increases;
3. chemoreceptors in aortic / carotid bodies / medulla (accept reference to aorta /
   carotid arteries not sinus);
4. (impulses to) medulla / cardioaccelerator centre;
5. increased frequency of impulses (award only once);
6. along sympathetic pathway to sinoatrial node / SAN (not pacemaker);

Question 38

Describe the route taken when electrical impulses are transmitted from the sinoatrial
node to the muscles of the ventricles in a healthy heart. 2 marks

Answer 38

(i) through cardiac muscle;
to atrioventricular node;
along bundle of His / Purkyne fibres;

Question 39

The maximum pressure in the left ventricle is higher than the maximum pressure in the
right ventricle. What causes this difference in pressure? 1 mark

Answer 39

thicker / more muscle in the left ventricle;

Question 40

Explain how the structures of the walls of arteries, veins and
capillaries are related to their functions. 6 marks

Answer 40

Artery
1. thickest wall, enabling it to carry blood at high pressure / withstand
pressure surges;
2. most elastic tissue, which smoothes out flow / maintains pressure;
3. most muscle which maintains pressure;
4. muscle in wall to control blood flow;
Vein
5. thin wall does not have to withstand high pressure;
Capillary
6. thin wall, allowing diffusion / exchange;
7. only endothelium present, allowing short diffusion pathway;
All vessels
8. have endothelium that reduces friction;

Question 41

Neonatal diabetes is a disease that affects newly born children. The disease is caused by a change in the amino acid sequence of insulin.
This change prevents insulin binding to its receptor. Explain why this change prevents
insulin binding to its receptor. 2 marks

Answer 41

1. Changes tertiary structure;
   Reject change in tertiary structure of receptor.
2. No longer complementary (to receptor);
   Reject ‘active site’ or reference to enzyme or substrate

Question 42

Using your knowledge of the kidney, explain why glucose is found in the urine of a person
with untreated diabetes. 3 marks

Answer 42

1. High concentration of glucose in blood/filtrate;
   Accept tubule for filtrate.
2. Not all the glucose is (re)absorbed at the proximal convoluted tubule;
   Reject no glucose is (re)absorbed.
3. Carrier/co-transport proteins are working at maximum rate
   OR
   Carrier/co-transport proteins/ are saturated;
   Accept all carrier/co-transport proteins are ‘in use’ but reject all
   carriers are ‘used up’.
   Accept symport for carrier protein.
   Accept not enough carrier proteins to absorb all the glucose.

Question 43

Describe the role of glucagon in gluconeogenesis.
Do not include in your answer details on the second messenger model of glucagon action.
2 marks

Answer 43

1.   (Attaches to receptors on target cells and) activates/stimulates enzymes;
Reject ‘produces enzymes’.
2. Glycerol/amino acids/fatty acids into glucose;
Reject ‘glucagon converts’ as context suggests enzyme action.
Ignore lipids/fats/proteins but reject glycogen.
Reject occurs in pancreas.

Question 44

Metformin is a drug commonly used to treat type II diabetes. Metformin’s ability to lower the blood
glucose concentration involves a number of mechanisms including:
*   increasing a cell’s sensitivity to insulin
*   inhibiting adenylate cyclase.
(c)  Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose
concentration. 2 marks

Answer 44

1.   (More) insulin binds to receptors;
2.   (Stimulates) uptake of glucose by channel/transport proteins
OR
Activates enzymes which convert glucose to glycogen;
Accept activates enzymes for glycogenesis.
Reject active transport.
Accept carrier proteins or GLUT 4 for channel proteins.
Accept insulin stimulates addition of channel proteins in membranes

Question 45

Explain how inhibiting adenylate cyclase may help to lower the blood glucose
concentration. 3 marks

Answer 45

1.   Less/no ATP is converted to cyclic AMP/cAMP;
2.   Less/no kinase is activated;
3.   Less/no glycogen is converted to glucose
OR
Less/no glycogenolysis;
If no indication of less/no for any of the mark points award max 2 marks.
Accept all marks in context of adrenaline.
Ignore gluconeogenesis.

Question 46

Each year, a few people with type I diabetes are given a pancreas transplant. Pancreas
transplants are not used to treat people with type II diabetes.
Give two reasons why pancreas transplants are not used for the treatment of type II
diabetes. 2 marks

Answer 46

1. (Usually)Type II produce insulin;
2. Cells / receptors less sensitive / responsive (to insulin)
   OR
   Faulty (insulin) receptors;
3. (Treated / controlled by) diet / exercise;
4. Accept: cells / receptors do not respond.
5. Accept: ‘fewer receptors’
6. Accept: (Treated / controlled by) weight loss / medication /
   drugs.
7. Ignore: diabetes is caused by diet / exercise.

Question 47

When insulin binds to receptors on liver cells, it leads to the formation of glycogen from
glucose. This lowers the concentration of glucose in liver cells.
Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose
concentration. 2 marks

Answer 47

(Formation of glycogen)
1. Glucose concentration in cell / liver falls below that in blood (plasma) which
creates / maintains glucose concentration / diffusion gradient;
2. Glucose enters cell / leaves blood by facilitated diffusion / via carrier(protein) /
channel (protein);
Not just diffusion

Question 48

Describe how ultrafiltration occurs in a glomerulus.
3 marks

Answer 48

Ignore references to podocytes
1. High blood/hydrostatic pressure;
Ignore references to afferent and efferent arterioles
Ignore ‘increasing/high er blood pressure’ as does not necessarily mean
high
2. Two named small substances pass out eg water, glucose, ions, urea;
Accept correct named ions
Accept mineral ions/minerals
Accept amino acids/small proteins
Ignore references to molecules not filtered
3. (Through small) gaps/pores/fenestrations in (capillary) endothelium;
Accept epithelium for endothelium
4. (And) through (capillary) basement membrane;

Question 49

Osmoreceptors are specialised cells that respond to changes in the water potential of the blood.
(a) Give the location of osmoreceptors in the body of a mammal 1 mark

Answer 49

Hypothalamus

Question 50

When a person is dehydrated, the cell volume of an osmoreceptor decreases.
Explain why.
2 marks

Answer 50

1. Water potential of blood will decrease;
2. Water moves from osmoreceptor into blood by osmosis.

Question 51

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and
explain how the secretion of ADH affects urine produced by the kidneys. 4 marks

Answer 51

1. Permeability of membrane / cells (to water) is increased;
2. More water absorbed from / leaves distal tubule / collecting duct;
3. Smaller volume of urine;
4. Urine becomes more concentrated.

Question 52

Creatinine is a breakdown product of creatine found in muscle tissues. Apart from age and
gender, give two factors that could affect the concentration of creatinine in the blood. 1 mark

Answer 52

Any two of the following for 1 mark:
Muscle / body mass
Ethnicity
Exercise
Kidney disease – do not accept ‘health’

Question 53

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

Answer 53

Hydrostatic pressure / description of pressure / description of how pressure generated;
Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule /
glomeruli / renal capsule;
Through basement membrane;
Enabled by small size urea molecule;

Question 54

Explain how urea is concentrated in the filtrate. 3 marks

Answer 54

Reabsorption of water / by osmosis;
At the PCT / descending LoH;
At the DCT / CD;
Active transport of ions / glucose creates gradient (in context);
Ignore references to facilitated diffusion or to selective reabsorption.

Question 55

Describe how ultrafiltration produces glomerular filtrate. 5 marks

Answer 55

1. Blood pressure / hydrostatic pressure;
2. Small molecules / named example;
3. Pass through basement membrane / basement membrane acts as filter;
4. Protein too large to go through / large so stays behind;
5. Presence of pores in capillaries / presence of podocytes;

Question 56

Some people who have diabetes do not secrete insulin. Explain how a lack of insulin
affects reabsorption of glucose in the kidneys of a person who does not secrete insulin.
4 marks

Answer 56

1. High concentration of glucose in blood;
2. High concentration in tubule / in filtrate;
3. Reabsorbed by facilitated diffusion / active transport;
4. Requires proteins / carriers;
5. These are working at maximum rate / are saturated;
6. Not all glucose is reabsorbed / some is lost in urine;

Question 57

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic
hormone (ADH). Explain how these two features are adaptations to living in desert
conditions.
6 marks

Answer 57

For general principle, applied to either example:
1. More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
2. By osmosis;
3. From collecting duct / from end of second convoluted tubule;
4. Due to longer loop of Henle;
For loop of Henle, maximum 2 marks:
5. Sodium / chloride ions absorbed from filtrate in ascending limb;
6. Gradient established in medulla / concentration of ions increases down medulla;
For ADH, maximum 2 marks:
7. Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
8. Makes cells more permeable / inserts aquaporins in plasma membranes;
Note: to score full marks, candidates must make one specific statement about
Loop of Henle and one about ADH.

Question 57

A diabetic person and a non-diabetic person each ate the same amount of glucose. One
hour later, the glucose concentration in the blood of the diabetic person was higher than
that of the non-diabetic person. Explain why.
3 marks

Answer 57

In Diabetic person:
1. Lack of insulin / reduced sensitivity of cells to insulin;
2. Reduced uptake of glucose by cells / liver / muscles;
3. Reduced conversion of glucose to glycogen;
Penalise zero / no
once only

Question 57

A high blood glucose concentration could cause glucose to be present in the urine of
a diabetic person. Suggest how. 2 marks

Answer 57

Large amount / high concentration of glucose in filtrate;
Cannot all be reabsorbed / 1st convoluted tube too short to reabsorb
all of glucose / saturation of carriers;

Question 58

The urine of a non-diabetic person does not contain glucose. Explain why. 2 marks

Answer 58

Leaves the blood at kidney;
Taken back into blood / reabsorbed (from kidney tubule);
Reject some reabsorption
(Reabsorbed) in 1st convoluted tubule;
Kidney / named part needs to be mentioned once

Question 59

A test for glucose in urine uses immobilised enzymes on a plastic test strip. One of these
enzymes is glucose oxidase. Explain why the test strip detects glucose and no other
substance. 2 marks

Answer 59

Enzyme has specific shape to active site / active site has specific tertiary structure;
Only glucose fits / has complementary structure / can form ES complex;

Question 59

If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he
produces a larger volume of urine. Explain why. 3 marks

Answer 59

Glucose in filtrate lowers water potential;
Ignore ‘urine’. Accept increase solute potential
Lower Ψ gradient / less difference in Ψ filtrate − Ψ plasma;
Ignore ‘concentration’
Less water reabsorbed by osmosis;
Accept diffusion of water. Reject no water reabsorbed if implied

Question 60

In some forms of kidney disease, proteins from the blood plasma are found in the urine.
Which part of the nephron would have been damaged by the disease to cause proteins
from blood plasma to be present in the urine? Explain your answer.
3 marks

Answer 60

1. Glomerulus / Bowman’s capsule / renal capsule;
2. Basement membrane;
3. Proteins are large (molecules) / proteins cannot normally pass through filter /
   proteins
   can only pass through if filter damaged;

Question 61

Using your understanding of muscle fibres and respiration, explain why slow twitch muscle fibres have more capillaries and less glycogen than fast twitch fibres. 4 marks

Answer 61

1
Slow twitch fibres are adapted to respire aerobically while fast twitch fibres are adapted to respire anaerobically.
2
This means that slow twitch fibres require a good blood supply in order to keep the tissue supplied with sufficient oxygen.
3
Fast twitch fibres are adapted to high intensity, short activity and therefore require an immediate energy source. Glycogen can be rapidly broken down in the muscle to supply glucose for anaerobic respiration.
4
Slow twitch muscles are adapted to lower intensity, long duration activity. This means they have time for glucose to be supplied to them via the blood and do not require their own glycogen store.