14.12 Past Paper Practice
Question 1
Read through the following passage on homeostasis and then answer the questions. Homeostasis is the regulation of the internal environment within narrow limits. This gives the organism a degree of independence from the external environment. The regulation is carried out by negative and positive feedback mechanisms which when not required are damped. All living organisms possess some powers of homeostasis but homeostasis is best developed in birds and mammals.
A
(i) What do you understand by the term ‘internal environment’? [2]
- the internal conditions of the body;
- such as:
- body temperature
- blood pH
- blood salt concentration
- blood osmotic pressure
- such as:
(ii) Distinguish negative feedback control from positive feedback control. [2]
- negative feedback control is when a varying physiological value is returned to its mean value by the controlling
- mechanism (credit example. eg. sweating to reduce body temperature);
- positive feedback control is when a physiological value is pushed above its mean value by the controlling
- mechanism (credit example eg. increased uterine contractions in birth);
(iii) Give one example of negative feedback control and one example of positive feedback control in mammals. [2]
- -ve : normal body temperature/blood pressure/blood osmotic pressure/blood pH/ventilation rate/any correct eg;
- +ve : oxytocin release during birth/oxytocin release in suckling/body temperature during fever/any correct eg;
(iv) What do you understand by the term ‘damping’? [1]
- the reduction or suppression of a feedback control mechanism when the required physiological value is reached;
- (usually feedback control mechanisms are not completely turned off)
B
State one example of homeostatic control in each of the following organisms. [3]
Amoeba:
Marram grass:
Human:
- Amoeba: osmoregulation/water removal by the contractile vacuole;
- Marram grass: water loss from leaves by hinge cells closing stomata/rolling leaf up;
- Human: control of blood pressure/blood osmotic pressure/blood salt and water concentration by ADH mechanism
- any other valid examples;
Describe the roles of the following in homeostasis in humans.
(a) Thermoreceptors. [3]
(b) Baroreceptors. [3]
(c) Glucoreceptors. [3]
(d) Proprioceptors. [3]
- (a) thermoreceptors in skin sense surface/shell temperature;
- thermoreceptors in hypothalamus sense core/blood temperature;
- relay nerve impulses to heat gain/heat loss/thermoregulatory centres in hypothalamus;
- (b) baroreceptors sense blood pressure;
- situated in walls of arterial arches/bases of great veins/aortic and carotid bodies;
- relay nerve impulses to vasomotor centre in brain/medulla (to regulate cardiac output/blood pressure);
- (c) glucoreceptors sense blood glucose concentrations;
- situated on cell membranes of alpha and beta cells of the islets of Langerhans;
- if blood glucose concentration rises beta cells stimulated to release insulin to lower it
- if blood glucose concentration falls alpha cells stimulated to release glucagon to raise it;
- (d) proprioceptors are tension and pressure receptors;
- situated in muscles and tendons/ ligaments/joint capsules;
- send nerve impulses to cerebellum to regulate muscle tone/enable balance/coordinated movements
Question 2
The graph below shows the changes in blood glucose concentration of a human subject over several hours. Prior
to point A the subject had not eaten or drunk for a period of 8 hours. At point A the subject drank 200 cm3 of a
suspension containing 100 mg of glucose.
A
(i) Comment on the blood glucose concentration prior to point A. [2]
- low/decreasing value as it used up/fasting blood glucose concentration;
- value is not obscured by absorption of glucose from gut to blood;
By reference to the graph determine the increase in blood glucose concentration between 1 hour and 1 hour 30 minutes. [1]
- 4.2 millimoles dm-3; (allow range 4.1 to 4.3)
B
With reference to the hormones involved, and to the biochemical changes occurring, explain the changes that
occur in blood glucose concentration between A and B and B and C.
A and B. [3]
B and C. [3]
- A-B: glucose being absorbed from gut (into blood stream);
- faster than it is being converted to glycogen;
- and stored in liver/muscles;
- under the influence of insulin;
- B-C: glucose absorption from gut to blood is reducing/stopping;
- β-cells release more insulin;
- α-cells release less glucagon;
- conversion to glycogen for storage is faster than absorption;
Question 3
Read through the following passage which refers to ADH and then fill in the spaces with the most appropriate word or words.
The presence or absence of ADH in the blood is controlled by …………………………………………….. . Receptors in
the …………………………………… sense an increase in the ………………………………………… of the blood plasma and
transmit nerve impulses to the ………………………………………………………. which releases ADH into the blood by
……………………………… . ADH attaches onto target receptors on the ……………………………………………………. cell
membranes. It has the effect of making these membranes …………….……………………which thus allows water to
be……………………………………….. .
- negative feedback;
- hypothalamus;
- osmolality/osmotic pressure/sodium ion concentration;
- posterior pituitary body;
- neurosecretion;
- collecting duct;
- water permeable;
- reabsorbed;
Question 3
(a) What is meant by homeostasis? [2]
- the regulation of the internal environment within narrow limits;
- thus making it independent of the external environment;
(b)Explain how the following assist in homeostasis.
(i) The contractile vacuole in Amoeba: [3]
- Any three of:
- in freshwater, water enters the Amoeba by osmosis/
- this water is collected into the contractile vacuole and expelled/
- by an active/energy requiring process/thus maintains the osmotic concentration of Amoeba’s cytoplasm/prevents bursting
(ii) The elongated loop of Henle found in desert dwelling mammals: [3]
- desert animals must conserve water since little is available;
- long loop of Henle means more salt is pumped out of loop into medulla of kidney;
- thus allows more water to be reabsorbed from collecting ducts (if ADH is present);
- (reject more water would be reabsorbed through the loop of Henle – it is impermeable to water)
Question 4
The table below shows a typical daily water balance of a human body.
A
(i) Why must water gain be balanced by water loss? [2]
- so that water content of body is maintained at constant level/no dehydration/ no over dilution;
- so that blood concentration/osmotic pressure/volume/blood pressure can be kept constant;
Select two of the above quantities which would increase during a period of vigorous exercise. In both cases explain why the values increase. [4]
- sweat;
due to temperature rise and so more secretion of sweat to cool body (using latent heat); - respiration;
more energy required so faster respiration thus more metabolic water released;
(exhaled air; more respiration thus more gas exchange thus more water lost by evaporation;)
(iii) Suggest why only small volumes of concentrated urine are produced during very hot weather. [3]
- more water loss by increased sweating;
- thus rise in blood concentration sensed by osmoreceptors (in hypothalamus);
- thus ADH secretion stimulated and more water reabsorbed from urine in collecting ducts (to blood);
B
Explain how the human controls water loss. [5]
- osmoreceptors in hypothalamus;
- sense when blood is too concentrated or too dilute;
- if too concentrated ADH release from posterior pituitary is stimulated;
- ADH in blood causes collecting tubule walls to become water permeable;
- so that water is reabsorbed from urine;
- high salt concentration in renal medulla (which results from counter current mechanism) enhances water reabsorption;
- (allow converse points about ADH not released as alternative scheme)
Question 5
The diagram below illustrates the counter current principle as it operates in the loop of Henle and in the vasa recti (plural: vasa recta). Figures refer to the NaCl concentration in millimoles dm-3.
A
(i) Explain the operation of the counter current principle in the loop of Henle. [4]
- ascending limb of loop of Henle is always impermeable to water;
- but has a very powerful active transport mechanism for pumping Na+/Cl– out of tubule (into interstitial fluid);
- this lowers the concentration as tubular fluid rises up ascending limb;
- Na+/Cl– diffuse into descending limb (from higher concentration in surrounding interstitial fluid);
- raising concentration of tubular fluid as it passes down the descending limb;
(ii) What are the functions of the counter current principle in the loop of Henle. [2]
- maintains a high salt concentration in the medulla/interstitial fluid;
- this enables water reabsorption from the collecting ducts (when ADH is present);
(iii) What is the function of the counter current principle in the vasa recti. [2]
- maintains blood salt concentration;
- and so helps to maintain blood osmotic pressure/blood pressure;
B
What effects do the hormones ADH (antidiuretic hormone) and aldosterone have on the functions of the nephron?
ADH. [2]
Aldosterone. [3]
- ADH: renders the collecting duct walls permeable to water;
- so that water may be reabsorbed or lost thus regulating blood volume/ pressure/concentration;
- Aldosterone: stimulates uptake of Na+ by active transport;
- from ascending limb of loop of Henle (thus retains body sodium ions);
- stimulates active secretion of K+ ;
- into distal convoluted tubule (thus lowering body potassium ion content);
Question 6
Read through the following account of control of kidney function and then answer the questions below.
The presence or absence of ADH in the blood is controlled by negative feedback. Receptors in the hypothalamus sense an increase in the sodium ion concentration and osmolality (osmotic pressure) of the blood plasma and cause the release of ADH by neurosecretion. ADH attaches to target receptors on the collecting duct cell membranes. This makes the ducts permeable to water so allowing the reabsorption of water back to the blood.
As a result the blood sodium ion concentration and osmolality fall as the blood volume and pressure rises. Thus the receptors are no longer stimulated and so ADH release is damped.
A
Explain what is meant by the following terms.
(i) Negative feedback. [2]
- when for instance, blood volume varies above or below its norm;
- a mechanism is operated to bring the varying value back to the norm;
(ii) Damped. [1]
- when a mechanism has operated to bring a value back to the norm, the mechanism activity is reduced (but not totally switched off);
(iii) Neurosecretion. [1]
- when a hormone is secreted as a result of nervous stimulation;
B
(i) Where is the hypothalamus? [1]
- in the midbrain/just behind the pituitary body;
(ii) State one function of the hypothalamus. [1]
- to regulate physiological functions in general – such as sleep/body temperature/blood osmolality/any other valid example;
C
Explain why a rise in blood pressure will increase urine production. [4]
- Any four of:
- increased blood pressure increases glomerular blood pressure/
- increases ultrafiltration/
- thus a larger volume of glomerular filtrate is formed (per unit time)/
- raised blood pressure inhibits ADH release/
- thus collecting ducts become impermeable to water/
- thus no water reabsorbed from urine so urine volume increases;
Question 6
The diagram below shows the female urinary system in ventral view.
A
(i) Label A,B, C, and D on the diagram. [4]
A = renal artery; B = ureters; C =urethra; D = dorsal aorta;
(ii) State one way in which the anatomy of the male urinary system differs from that of the female. [1]
- male urethra is much longer (since it extends through the penis);
B
The kidneys produce urine as a result of carrying out their functions. State the two main functions of the kidneys. [2]
- removal of toxic waste products from blood/excretion;
- regulation of blood pH/osmolality/pressure/ref homoeostasis of body fluids;
C
What is the function of the sphincter muscle at X? [1]
- to prevent urination/micturition until a convenient time
- prevents constant dribbling of urine from bladder
- keeps bladder closed to reduce infection risk;
Question 7
The total blood volume of a human averages 60cm3 per kilogramme of body weight, and the average glomerular filtration rate is 125cm3 minute-l.
(a) Calculate the total blood volume of a person who weighs 120kg. Show your working. [2]
- 60 x 120; = 7200 cm3 or 7.2 dm3; (units essential)
(b) Calculate the volume of glomerular filtrate produced per day by this person. Show your working. [2]
- 125 x 60 x 24; = 180,000 cm3 or 180 dm3; (units essential)
(c) How many times each day will the person’s blood be filtered by the kidneys? Show your working. [2]
180/7.2 = 25
(d) Though the glomerular filtration rate averages 125cm3min-l the rate of urine release from the kidneys is only about lcm3min-1. Suggest how this difference in volumes is accomplished. [3]
- Any three of:
- about 80% / much of the water is reabsorbed back to blood/
- in the proximal convoluted tubule/
- more water is reabsorbed via the collecting ducts/
- in the presence of ADH
Question 8
The diagram below is of a nephron from a mammalian kidney.
a) (i) Label structures A, B, C, D, E, F and G on the diagram. [7]
A = glomerulus;
B = renal/Bowman’s capsule;
C = proximal/first convoluted tubule;
D = descending limb (of loop of Henle);
E = ascending limb (of loop of Henle);
F = distal/second convoluted tubule;
G = collecting duct;
(ii) Comment on the permeability to water of structures C, E and G. [3]
C is very permeable to water;
E is never permeable to water;
G is only water permeable if ADH is present;
(b) (i) Name two substances actively reabsorbed from C. [2]
- Any two of:
- glucose
- amino acids
- (some) urea
(ii) Name two substances actively secreted into F. [2]
- Any two of:
- hydrogen ions
- potassium ions
- creatinine
- hydrogen carbonate ions
- ammonia
(c) (i) Structure E has powerful active transport mechanisms for reabsorbing Na+ and Cl- ions back into the surrounding tissue fluid. What is the purpose of this? [2]
- to achieve a high salt concentration in the medulla of the kidney/ around the collecting ducts;
- so that water may be reabsorbed osmotically from urine in collecting ducts (in presence of ADH);
(ii) Explain why the fluid concentration in G may remain the same as that in F? [2]
- Any two of:
- ADH release is suppressed when blood volume/pressure is too high/ blood concentration too dilute/
- ADH increases permeability of collecting ducts to water/
- thus in absence of ADH water is not reabsorbed
Question 9
The diagram below shows the histological appearance of kidney tissue.
Give explanations for each of the following facts.
(a) Proximal convoluted tubule cells have many mitochondria and bear microvilli on the luminar borders. [4]
- have many mitochondria to produce much ATP;
- required as energy supply for large amount of active transport carried out (by these cells);
- allowing reabsorption of glucose/some amino acids/ some salts/ some urea;
- microvilli increase surface area available for reabsorption;
(b)The glomerular capillaries and inner surfaces of the renal capsule are made of specialised cells, called podocytes. [3]
- podocytes are epithelium/pavement cells;
- which are raised off their basement membrane;
- thus the cavities of the glomerular capillaries and renal capsule are only separated by the basement membranes;
- this increases the efficiency of transport into the capsules of small molecules from the blood plasma/increases the efficiency of ultra filtration;
(c) Drinking coffee increases the volume of urine produced per unit time. [3]
- coffee contains caffeine;
- caffeine inhibits the release of ADH;
- thus no water can be reabsorbed by collecting ducts from urine;
Question 10
The table below refers to normal glomerular filtrate and to normal urine. If a feature is correct place a tick (3) in the box and if it is incorrect place a cross (7) in the box. [5]
(about 2 g of amino acids are ; excreted per day as amino acids)
Question 11
The pH of blood plasma must be maintained in the range 7.35 to 7.45. There are three main physiological ways of achieving this, one of which involves the kidney.
(a) State two ways (not involving the kidney) by which the body controls blood pH. [4]
- by blood buffering systems;
- such as haemoglobin/phosphate/ hydrogen carbonate/protein buffering systems;
- by control of ventilation/inspiration and expiration rate;
- which regulates the H+ and HCO3– concentrations in blood plasma;
(b)Describe how the kidneys adjust the pH of the blood back to normal when it has become too acidic. [5]
- many hydrogen ions pass from plasma to glomerular filtrate during ultrafiltration (thus raising blood pH);
- hydrogen ions are actively secreted from blood into the distal convoluted tubules (also raising blood pH);
- but this lowers pH of tubular fluid;
- around pH 4.8 the active transport pumps can no longer force more H+ into the tubule;
- therefore distal tubule cells also actively secrete ammonia/NH3 into tubule;
- this combines with H+ and Cl– to make ammonium chloride (credit equation);
- buffering the urine pH (to pH 6.0);
Question 12
The table below shows the results of an investigation into the flow and composition of the fluids in a nephron. The positions of A, B, C, D, E and F are shown on the nephron diagram.
(a) Explain the difference in flow rate between the points:
(i) A and B. [1]
- volume smaller
- has passed through a filter;
(ii) C and F. [1]
- more water is reabsorbed in collecting duct (in the presence of ADH);
(b)Suggest reasons for each of the following.
(i) The changes in urea concentration from A to F. [3]
- blood urea passes freely from A to B during glomerular filtration;
- higher concentration at C due to water reabsorption reducing the volume of tubular fluid in proximal convoluted tubule;
- even more water reabsorption in F causes further concentration of urea in urine;
(ii) The change in salt concentration between C and D, and D and E. [3]
- from C to D as tubular fluid passes down into higher salt concentrations of medulla, salt diffuses into the tubule raising the concentration;
- from D to E active transport pumps salt out of tubule into surrounding interstitial fluid;
- thus concentration of salt falls in tubular fluid from D to E:
(iii) The difference in protein concentration between A and B. [2]
- proteins are large molecules/high molecular weight;
- cannot cross membranes separating glomerular blood and capsule fluid/substances with a molecular weight
- greater than 65,000 cannot cross filter;
(iv) The difference in glucose concentration between B and C. [1]
- all glucose actively reabsorbed in proximal convoluted tubule;
Question 13
(a) Are the following statements true or false? Justify your answer.
(i) The main function of the kidneys is to make urine. [3]
- false;
- the kidneys are concerned with the regulation of blood and other body fluids, (this results in urine formation);
- the kidneys are concerned with excretion of toxic metabolic waste products, (this also results in urine formation);
(ii)A greater volume of urine is produced on a hot day than on a cold day. [3]
- false;
- on a hot day more water is lost from blood by sweating;
- thus blood volume falls/blood concentration rises and ADH release is stimulated causing water reabsorption from urine in collecting ducts;
(iii) The main excretory end product in reptiles and birds is uric acid. [3]
- true;
- uric acid is insoluble and so does not poison the embryo in the closed environment of the egg;
- also can be excreted as solid urine thus conserving water;
(b)(i) Briefly explain what is meant by the term “renal dialysis”. [3]
- Any three of:
- dialysis is the separation of large molecules from small molecules/
- across a differentially permeable membrane/
- principle used in kidney machine/haemodialysis/peritoneal dialysis/
- to remove toxic waste products from patient with kidney failure
(ii) Under what circumstances would a kidney transplant be performed? [3]
- in incurable/irreversible kidney damage/patients on long term dialysis;
- when a kidney becomes available, usually from a recently dead donor/car accident victim;
- tissue antigens/ref HLA antigens of donor kidney and recipient must be close matching to avoid rejection problems;
Question 14
Explain what is meant by the term homeostasis and describe the principles of homeostasis in mammals. [7]
any seven from:
1 maintain constant internal environment ;
2 despite changes in the, internal / external, environment ;
3 changes in, factor / stimulus, detected by receptor ;
4 named factor ; e.g. temperature / water potential / blood glucose concentration
5 impulses to CNS / input ;
6 ref. to central control / CNS, decision ;
7 impulses to effector / output ;
8 hormones to target cells
9 named effector ; e.g. muscle / gland
10 corrective action ;
11 factor returns to set point ;
12 negative feedback ;
13 AVP ; e.g. fluctuations around set point
Question 15
1. The figure below shows diagrams of nephrons from the kidneys of three different mammals, X, Y and Z.
| X | Y | Z | |
| name of mammal | beaver | house mouse | desert living gerbil |
| water potential of urine | high | low | very low |
Explain the relationship between the length of the section D in the nephrons and the water potential of the urine each mammal produces. [3]
the longer the loop of Henle the lower the water potential (of urine); ora
ions pass out from ascending limb into, medulla / tissue fluid;
creating lower water potential in the medulla / AW;
water reabsorbed from collecting duct in medulla ;
by osmosis ; (linked to previous marking point)
AVP; e.g. ref to countercurrent multiplier max 3
2. The hypothalamus produces anti-diuretic hormone (ADH) that is released by the posterior pituitary gland into the blood.
Brain damage can occur due to trauma to the head. Traumatic brain injury (TBI) can cause many and varied malfunctions of parts of the brain. One condition that can arise from TBI is a lack of ADH in the blood.
Suggest the symptoms you would expect in a person with a lack of ADH. [3]
1. frequent need to urinate/diuresis;
2. large volume of urine/very dilute urine;
3. persistent feeling of thirst/excessive drinking;
4. electrolyte/mineral, imbalance;
5. AVP; e.g. dehydration, 3 max
3. The first stage in the formation of urine is glomerular filtration. This results in the production of glomerular filtrate in the Bowman’s (renal) capsules. Below is a diagram that shows the structures and forces involved in the filtration process.
(a) The normal blood hydrostatic pressure in other capillaries is 3.3 kPa.
(i) Using the diagram, explain why the blood pressure in the glomerular capillaries is considerably higher than in other capillaries. [2]
wide / large, afferent arteriole ;
narrow / small, efferent arteriole ;
afferent arteriole, wider / larger, than efferent arteriole – 2 marks
ref to ‘bottleneck’ effect / AW ; R build up pressure on own to achieve filtration ;
must be greater than 6.7 kPa for filtration ; 2 max
(ii) Using the data given in the diagram, calculate the effective filtration pressure.
Answer = ………………………………….kPa. [2]
award two marks if correct answer (1.3) is given
incorrect answer (or no answer) but correct working = 1 mark 8 – (4 + 2.7) A 8 – 6.7
1.3 ; ;
(b) The presence of protein molecules in the urine of an individual is a sign of kidney disease or kidney damage.
(i) Explain why it is unusual for protein molecules to appear in the urine. [2]
(too) large / RMM greater than 69000 or 70000 ;
to pass through basement membrane ;
(ii) Explain why protein in the urine is often a symptom of chronic high blood pressure. [2]
glomerular blood pressure is greater ;
proteins forced through ;
damage to capillaries / AW ;
damage to basement membrane ; 2 max
(c) A complex barrier exists between the blood plasma in the glomerular capillaries and the fluid in the renal capsule.
Describe in detail the structure of the region labelled A on the diagram above. [4]
1 endothelium of capillaries ;
2 large / many, fenestrations / gaps / holes ;
3 modified epithelial cells of capsule / podocytes ;
4 slit pores / foot-like processes ; A finger like
5 basement membrane ;
6 made up of, collagen / glycoproteins / molecular mesh ;
accept annotated diagrams 4 max
(d) Coffee contains the drug caffeine, which inhibits the release of ADH.
Describe and explain the effect of drinking coffee on the volume and concentration of urine produced. [4]
1 volume will increase ;
2 concentration decrease ;
3 (wall of), collecting duct / DCT, (relatively) impermeable to water ;
4 fewer water channels ; A aquaporins
5 in membrane of epithelial cells ;
6 less water reabsorbed (from the urine) ;
7 by osmosis (linked to marking point 6) ;
8 drinking increases liquid intake and therefore liquid loss ; 4 max
4. The presence of CG in the urine can be used in pregnancy testing. Information about a pregnancy testing kit is given below and in the figure.
• An absorbent membrane is dipped into urine.
• The membrane contains free antibodies that are specific to CG.
• The free antibodies are attached to coloured markers.
• There is a line of immobilised antibodies above position A.
• A positive result is shown by a coloured line at position A.
Using information from the figure, explain how the presence of CG in the urine results in a coloured line at position A. [4]
CG acts as antigen ;
move, attached to, free antibodies;
attach to, immobilised antibody ;
coloured particles, form line ;
ref to complementary shapes ;
ref to antigen, antibody complex ;
AVP ; e.g. further detail of antibody structure
monoclonal
CG-antibody complex 4 max
5. The following table shows the concentrations of glucose and urea in the renal artery and renal vein.
Both substances are present in lower concentration in the renal vein than in the renal artery. However, urea appears in the urine of a healthy individual but glucose does not. [5]
1 both filtered / AW ;
2 both small molecules / AW ; A RMM close to 69 000
3 (all filtered) glucose reabsorbed ;
4 active uptake, carrier / cotransporter, proteins ;
5 (some) glucose used in, respiration / active processes, in kidney ;
6 some urea reabsorbed ;
7 by diffusion ;
8 ref to reabsorption in PCT ; apply once to either glucose or urea 5 max
6. In both plants and animals, chemical messengers help to transfer information from one part of the organism to another to achieve coordination.
The table below lists some of these chemicals together with their functions.
Complete the table.
| name of chemical messenger | function |
| ………………………………………………………. | controls water permeability of collecting ducts in kidney |
| insulin | ………………………………………………………. ………………………………………………………. |
| glucagon | ………………………………………………………. ………………………………………………………. |
| ………………………………………………………. | stimulates stomatal closure during water stress |
| ………………………………………………………. | controls apical dominance |
[5]
ADH / anti diuretic hormone ;
reduces blood sugar levels / correct mechanism to achieve this ;
increases blood sugar levels / correct mechanism to achieve this ;
ABA / abscisic acid ;
auxin / IAA ;
7. An investigation was conducted into the filtration and reabsorption of glucose in the kidney of a mammal.
The glucose concentration in the plasma of the renal artery was increased. The glucose concentrations were measured in the following fluids:
• glomerular filtrate
• urine.
From the measurements obtained, the concentration of glucose in the fluid reabsorbed from the glomerular filtrate was calculated. The results of this investigation are shown below.
Use the data in the figure above to answer the following questions.
(i) Describe the relationship between plasma glucose concentration in the renal artery and the concentration of glucose in the glomerular filtrate. [1]
directly proportional / AW ;
(ii) State the plasma glucose concentration in the renal artery above which the kidney is unable to reabsorb all the glucose from the glomerular filtrate.
Answer = ……………….. mg cm-3. [1]
2.6 ;
(iii) Explain why plasma glucose concentrations in the renal artery greater than the figure you have given in (ii) would result in the presence of glucose in the urine. [3]
1 high levels of glucose in glomerular filtrate ;
2 unable to reabsorb all glucose (in, PCT / kidney tubule) ;
A no more glucose can be reabsorbed
3 ref to glucose carriers / AW ;
4 at threshold value carriers, all saturated / limiting factor ;
5 AVP ; e.g. ref to renal threshold 3 max
Question 16
The following questions relate to regulation of the internal environment.
(a)(i) Distinguish between regulators and non-regulators and give one example of each. [4]
regulators are organisms that regulate or control their physiological values within narrow limits;
any one of: mammals/birds/flowering plants/specific example of these;
non regulators do not control their physiological values within narrow limits;
any one of: cnidarians/algae/specific example of these;
(most other organisms are regulators for some values and non regulators for other values)
(ii) Distinguish between exogenous and endogenous rhythms and give one example of each. [4]
exogenous rhythms are those that are related to regular changes in environmental stimuli;
eg. heart rate /blood pressure;
endogenous rhythms are those that follow a spontaneous internal cycle;
eg. core temperature/sleep patterns;
(b)Long distance air travellers may feel extremely tired due to ‘jet lag’. Explain the physiological basis of ‘jet lag’. [4]
metabolism out of phase;
due to crossing time zones;
thus may need to be awake when body clock thinks it is time to sleep/body clock confused/ref body clock;
ref. to melatonin;
Question 17
The table below lists a number of homeostatic actions which are stimulated by certain hormones. Write the name
of one hormone for each action in the appropriate box. Some hormones may be named more than once.
| Action: | Hormone: |
| Breakdown of glycogen in the liver | |
| Non-shivering thermogenesis | |
| Lowering of blood glucose concentration | |
| Acceleration of heart beat | |
| Reduction of water loss in urine |
| Action: | Hormone: |
| Breakdown of glycogen in the liver | glucagon/adrenaline; |
| Non shivering thermogenesis | adrenaline; |
| Lowering of blood glucose concentration | insulin; |
| Acceleration of heart beat | adrenaline/thyroxine; |
| Reduction of water loss in urine | antidiuretic hormone; |
Question 18
Distinguish between each of the following pairs:
(a) Diabetes insipidus and diabetes mellitus. [4]
Any four of:
diabetes insipidus is a failure of ADH production/by the posterior pituitary/
thus excessive diuresis/water loss through urine occurs (resulting in dehydration/death)/
diabetes mellitus is a failure of the beta cells in the islets (of Langerhans) to produce insulin/
thus insufficient blood glucose is converted to glycogen and glucose is lost in urine;;;;
(b)Homeostasis and haemostasis. [4]
homeostasis is the regulation of the internal environment within narrow limits;
using negative and positive feedback mechanisms;
haemostasis is the stopping of bleeding after tissue damage;
enabled by the blood platelets/clotting cascade mechanism;
(c) Diuresis and deamination. [4]
diuresis is the loss of water in urine;
regulated by antidiuretic hormone;
deamination is the removal of (toxic) amine groups from unwanted amino acids;
occurs in the liver –> makes urea (for excretion);
Question 19
The diagram below illustrates the counter current principle as it operates in the loop of Henle and in the vasa recti. Figures refer to the NaCl concentration in millimoles dm-3.
(a) (i) Explain the operation of the counter current principle in the loop of Henle. [4]
ascending limb of loop of Henle is always impermeable to water;
but has a very powerful active transport mechanism for pumping Na+/Cl– out of tubule (into interstitial fluid);
this lowers the concentration as tubular fluid rises up ascending limb;
Na+/Cl– diffuse into descending limb (from higher concentration in surrounding interstitial fluid);
raising concentration of tubular fluid as it passes down the descending limb;
(ii) What are the functions of the counter current principle in the loop of Henle. [2]
maintains a high salt concentration in the medulla/interstitial fluid;
this enables water reabsorption from the collecting ducts (when ADH is present);
(iii) What is the function of the counter current principle in the vasa recti. [2]
maintains blood salt concentration;
and so helps to maintain blood osmotic pressure/blood pressure;
(b)What effects do the hormones ADH (antidiuretic hormone) and aldosterone have on the functions
of the nephron?
ADH: [2]
ADH: renders the collecting duct walls permeable to water;
so that water may be reabsorbed or lost thus regulating blood volume/ pressure/concentration;
Aldosterone: [3]
Aldosterone: stimulates uptake of Na+ by active transport;
from ascending limb of loop of Henle (thus retains body sodium ions);
stimulates active secretion of K+ ;
into distal convoluted tubule (thus lowering body potassium ion content);
Question 20
Read through the following account of control of kidney function and then answer the questions below.
The presence or absence of ADH in the blood is controlled by negative feedback. Receptors in the hypothalamus
sense an increase in the sodium ion concentration and osmolality (osmotic pressure) of the blood plasma and
cause the release of ADH by neurosecretion. ADH attaches to target receptors on the collecting duct cell
membranes. This makes the ducts permeable to water so allowing the reabsorption of water back to the blood.
As a result the blood sodium ion concentration and osmolality fall as the blood volume and pressure rises. Thus
the receptors are no longer stimulated and so ADH release is damped.
(a) Explain what is meant by the following terms.
(i) Negative feedback: [2]
when for instance, blood volume varies above or below its norm;
a mechanism is operated to bring the varying value back to the norm;
(ii) Damped: [1]
when a mechanism has operated to bring a value back to the norm, the mechanism activity is reduced
(but not totally switched off);
(iii) Neurosecretion: [1]
when a hormone is secreted as a result of nervous stimulation;
(b) (i) Where is the hypothalamus? [1]
in the midbrain/just behind the pituitary body;
(ii) State one function of the hypothalamus. [1]
to regulate physiological functions in general – such as sleep/body temperature/blood osmolality/any other
valid example;
(c) Explain why a rise in blood pressure will increase urine production. [4]
Any four of:
increased blood pressure increases glomerular blood pressure/
increases ultrafiltration/
thus a larger volume of glomerular filtrate is formed (per unit time)/
raised blood pressure inhibits ADH release/
thus collecting ducts become impermeable to water/
thus no water reabsorbed from urine so urine volume increases;;;;
Question 21
The diagram below shows the female urinary system in ventral view.
(a) (i) Label A,B, C, and D on the diagram. [4]
A = renal artery; B = ureters; C =urethra; D = dorsal aorta;
(ii) State one way in which the anatomy of the male urinary system differs from that of the female. [1]
male urethra is much longer (since it extends through the penis);
(b) The kidneys produce urine as a result of carrying out their functions. State the two main functions of the
kidneys. [2]
1. removal of toxic waste products from blood/excretion;
2. regulation of blood pH/osmolality/pressure/ref homoeostasis of body fluids;
(c) What is the function of the sphincter muscle at X? [1]
to prevent urination/micturition until a convenient time/prevents constant dribbling of urine from bladder/keeps
bladder closed to reduce infection risk;
Question 22
In each of the following questions only one of the four responses is correct. In each case indicate the correct response by ringing around A, B, C or D.
(a) In the formation of urine the largest volume of water is reabsorbed from… [1]
A. The ascending limbs of the loops of Henle.
B. The collecting ducts.
C. The proximal convoluted tubules.
D. The distal convoluted tubules.
C;
(b) The main nitrogenous excretory end product is… [1]
A. Urea in mammals and insects.
B. Uric acid in birds and insects.
C. Uric acid in mammals and insects.
D. Ammonia in fish and mammals.
B;
(c) In which of the following mammalian organs does the blood gain most urea? [1]
A. Liver.
B. Kidney.
C. Spleen.
D. Pancreas.
A;
(d) Which of the following structures is lined by a transitional epithelium? [1]
A. The urethra.
B. The bladder.
C. The renal capsules.
D. The collecting ducts.
B;
Question 23
The total blood volume of a human averages 60cm3 per kilogramme of body weight, and the average glomerular
filtration rate is 125cm3 minute-l.
(a) Calculate the total blood volume of a person who weighs 120kg. Show your working. [2]
60 x 120; = 7200 cm3 or 7.2 dm3; (units essential)
(b) Calculate the volume of glomerular filtrate produced per day by this person. Show your working. [2]
125 x 60 x 24; = 180000 cm3 or 180 dm3; (units essential)
(c) How many times each day will the person’s blood be filtered by the kidneys? Show your working. [2]
180/7.2 ; = 25;
(d) Though the glomerular filtration rate averages 125cm3min-l the rate of urine release from the kidneys is only about lcm3min-1. Suggest how this difference in volumes is accomplished. [3]
Any three of:
about 80% / much of the water is reabsorbed back to blood/
in the proximal convoluted tubule/
more water is reabsorbed via the collecting ducts/
in the presence of ADH;;;
Question 24
The diagram below is of a nephron from a mammalian kidney.
(a) (i) Label structures A, B, C, D, E, F and G on the diagram. [7]
A = glomerulus;
B = renal/Bowman’s capsule;
C = proximal/first convoluted tubule;
D = descending limb (of loop of Henle);
E = ascending limb (of loop of Henle);
F = distal/second convoluted tubule;
G = collecting duct;
(ii) Comment on the permeability to water of structures C, E and G. [3]
C is very permeable to water;
E is never permeable to water;
G is only water permeable if ADH is present;
(b)(i) Name two substances actively reabsorbed from C. [2]
Any two of:
glucose/amino acids/(some) urea;;
(ii) Name two substances actively secreted into F. [2]
Any two of:
hydrogen ions/potassium ions/creatinine/hydrogen carbonate ions/ammonia;;
(c) (i) Structure E has powerful active transport mechanisms for reabsorbing Na+ and Cl– ions back into the surrounding tissue fluid. What is the purpose of this? [2]
to achieve a high salt concentration in the medulla of the kidney/ around the collecting ducts;
so that water may be reabsorbed osmotically from urine in collecting ducts (in presence of ADH);
(ii) Explain why the fluid concentration in G may remain the same as that in F? [2]
Any two of:
ADH release is suppressed when blood volume/pressure is too high/ blood concentration too dilute/
ADH increases permeability of collecting ducts to water/
thus in absence of ADH water is not reabsorbed;;
Question 25
Distinguish between each of the following pairs of structures.
(a) Ureter and urethra. [4]
ureter carries urine from kidney to bladder;
urethra carries urine from bladder to exterior;
ureter lined by a transitional epithelium;
urethra lined by compound/stratified squamous epithelium;
b) Urinary bladder and gall bladder. [4]
urinary bladder stores urine until a suitable time for release;
gall bladder stores bile (from liver) until food enters duodenum;
urinary bladder situated in pelvis/just ventral to rectum/lined by transitional epithelium;
gall bladder lies near liver/lined by columnar epithelium;
(c) Glomerulus and vasa recti. [4]
glomerulus is a knot of capillaries situated in the renal capsule;
vasa recti form a network of capillaries over the nephron tubules;
glomerulus is concerned with ultrafiltration/forming glomerular filtrate;
vasa recti are concerned with exchange of materials between tubular fluid and blood;
(d) Afferent arteriole and efferent arteriole. [4]
afferent arteriole carries blood from renal/arcuate artery branch to glomerulus;
efferent arteriole carries blood from glomerulus to vasa recti;
efferent arteriole narrower than afferent arteriole (so that blood pressure in the glomerulus is raised);
blood in efferent arteriole has reduced urea/glucose/salt/amino acid (or any other valid substance)
concentrations compared to afferent arteriole blood;
Question 26
Read through the following account of kidney function and then fill in the spaces with the most appropriate
word or words.
Blood enters the kidney under …………………………….. pressure through the ………………………………… which branches, eventually into afferent arterioles. These give rise to capillaries which form …………………………….. which lie inside ………………………………… capsules. Many of the small components of plasma are forced into the capsules by ………………………………………. . Large molecules, such as ………………………………………. cannot leave the blood and so exert an ……………………………………………….. which will draw water from the filtrate
back into the blood. The filtrate contains salts, excretory products such as ………………………………….., sugars such as ……………………………………….. and amino acids. [9]
high; renal artery; glomeruli; renal/Bowman’s; ultrafiltration/high pressure; proteins; osmotic pressure;
urea/uric acid/ammonia or any other; glucose;
Question 27
The diagram below shows the histological appearance of kidney tissue.
Give explanations for each of the following facts.
(a) Proximal convoluted tubule cells have many mitochondria and bear microvilli on the luminar borders. [4]
have many mitochondria to produce much ATP;
required as energy supply for large amount of active transport carried out (by these cells);
allowing reabsorption of glucose/some amino acids/ some salts/ some urea;
microvilli increase surface area available for reabsorption;
(b) The glomerular capillaries and inner surfaces of the renal capsule are made of specialised cells, called podocytes. [3]
podocytes are epithelium/pavement cells;
which are raised off their basement membrane;
thus the cavities of the glomerular capillaries and renal capsule are only separated by the basement membranes;
this increases the efficiency of transport into the capsules of small molecules from the blood plasma/increases the efficiency of ultra filtration;
(c) Drinking coffee increases the volume of urine produced per unit time. [3]
coffee contains caffeine;
caffeine inhibits the release of ADH;
thus no water can be reabsorbed by collecting ducts from urine;
….sooo, don’t drink coffee before your exam yani. 🙂
Question 28
(a) What is meant by homeostasis? [2]
the regulation of the internal environment within narrow limits;
thus making it independent of the external environment;
(b)Explain how the following assist in homeostasis.
(i) The contractile vacuole in Amoeba: [3]
Any three of:
in freshwater, water enters the Amoeba by osmosis/
this water is collected into the contractile vacuole and expelled/
by an active/energy requiring process/thus maintains the osmotic concentration of Amoeba’s cytoplasm/prevents bursting;;;
(ii) The elongated loop of Henle found in desert dwelling mammals: [3]
desert animals must conserve water since little is available;
long loop of Henle means more salt is pumped out of loop into medulla of kidney;
thus allows more water to be reabsorbed from collecting ducts (if ADH is present);
(reject more water would be reabsorbed through the loop of Henle – it is impermeable to water)
(c) (i) Name the disease in humans in which large volumes of very dilute urine is produced. [1]
diabetes insipidus;
(ii) What is the cause of this symptom? [1]
failure to synthesise ADH in the posterior pituitary gland;
Question 29
The table below refers to normal glomerular filtrate and to normal urine. If a feature is correct place a tick (✓) in the box and if it is incorrect place a cross (x) in the box. [5]
| Feature: | Glomerular filtrate: | Urine: |
| Contains glucose | ||
| Does not contain amino acids | ||
| Has a pH of 3.5 | ||
| Has the same composition as blood | ||
| Never contains protein |
| Feature: | GF | Urine |
| Contains glucose | ✓ | ✗ |
| Does not contain amino acids | ✗ | ✗ |
| Has a pH of 3.5 | ✗ | ✗ |
| Same composition of blood | ✗ | ✗ |
| Never contains protein | ✓ | ✓ |
(about 2 g of amino acids are ; excreted per day as amino acids)
Question 30
The pH of blood plasma must be maintained in the range 7.35 to 7.45. There are three main physiological ways
of achieving this, one of which involves the kidney.
(a) State two ways (not involving the kidney) by which the body controls blood pH. [4]
by blood buffering systems;
such as haemoglobin/phosphate/ hydrogen carbonate/protein buffering systems;
by control of ventilation/inspiration and expiration rate;
which regulates the H+ and HCO3– concentrations in blood plasma;
(b) Describe how the kidneys adjust the pH of the blood back to normal when it has become too acidic. [5]
many hydrogen ions pass from plasma to glomerular filtrate during ultrafiltration (thus raising blood pH);
hydrogen ions are actively secreted from blood into the distal convoluted tubules (also raising blood pH);
but this lowers pH of tubular fluid;
around pH 4.8 the active transport pumps can no longer force more H+ into the tubule;
therefore distal tubule cells also actively secrete ammonia/NH3 into tubule;
this combines with H+ and Cl– to make ammonium chloride (credit equation);
buffering the urine pH (to pH 6.0);
Question 31
The table below shows the results of an investigation into the flow and composition of the fluids in a nephron.
The positions of A, B, C, D, E and F are shown on the nephron diagram.
(a) Explain the difference in flow rate between the points:
(i) A and B. [1]
volume smaller/has passed through a filter;
(ii) C and F. [1]
more water is reabsorbed in collecting duct (in the presence of ADH);
(b)Suggest reasons for each of the following.
(i) The changes in urea concentration from A to F. [3]
blood urea passes freely from A to B during glomerular filtration;
higher concentration at C due to water reabsorption reducing the volume of tubular fluid in proximal convoluted tubule;
even more water reabsorption in F causes further concentration of urea in urine;
(ii) The change in salt concentration between C and D, and D and E. [3]
from C to D as tubular fluid passes down into higher salt concentrations of medulla, salt diffuses into the
tubule raising the concentration;
from D to E active transport pumps salt out of tubule into surrounding interstitial fluid;
thus concentration of salt falls in tubular fluid from D to E:
(iii) The difference in protein concentration between A and B. [2]
proteins are large molecules/high molecular weight;
cannot cross membranes separating glomerular blood and capsule fluid/substances with a molecular weight
greater than 65,000 cannot cross filter;
(iv) The difference in glucose concentration between B and C. [1]
all glucose actively reabsorbed in proximal convoluted tubule;
Question 32
(a) Are the following statements true or false? Justify your answer.
(i) The main function of the kidneys is to make urine. [3]
false;
the kidneys are concerned with the regulation of blood and other body fluids, (this results in urine formation);
the kidneys are concerned with excretion of toxic metabolic waste products, (this also results in urine formation);
(ii) A greater volume of urine is produced on a hot day than on a cold day. [3]
false;
on a hot day more water is lost from blood by sweating;
thus blood volume falls/blood concentration rises and ADH release is stimulated causing water reabsorption
from urine in collecting ducts;
(iii) The main excretory end product in reptiles and birds is uric acid. [3]
true;
uric acid is insoluble and so does not poison the embryo in the closed environment of the egg;
also can be excreted as solid urine thus conserving water;
(b)(i) Briefly explain what is meant by the term “renal dialysis”. [3]
Any three of:
dialysis is the separation of large molecules from small molecules/
across a differentially permeable membrane/
principle used in kidney machine/haemodialysis/peritoneal dialysis/
to remove toxic waste products from patient with kidney failure;;;
(ii) Under what circumstances would a kidney transplant be performed? [3]
in incurable/irreversible kidney damage/patients on long term dialysis;
when a kidney becomes available, usually from a recently dead donor/car accident victim;
tissue antigens/ref HLA antigens of donor kidney and recipient must be close matching to avoid rejection problems;
Question 33
MDMA is a compound that is often used as a recreational drug. It is commonly known as ecstasy. Unfortunately, a number of people have died soon after taking ecstasy.
A research team investigated the effects of MDMA. They chose to work with groups of mice. The mice in one group were injected with MDMA whilst a second group acted as a control.
(a) Suggest two reasons why the research team chose to use mice in this investigation. (2)
Easy to manage / can be kept safely in small space;
Genome / strains well known;
Physiology similar to humans / can be used to predict human behaviour
(b) How should the control group be treated?(1)
Same as control but inject with equal volume of solvent only;
(c) For each mouse, the scientists monitored the temperature of the skin on its tail and the temperature in its rectum (lower part of the gut).
The graphs show the mean temperatures, and standard deviations of these means, after the injections were administered.
(i) Explain why the tail temperatures were always lower than the temperature in the rectum. (2)
Heat lost from tail;
By conduction / convection / radiation;
Q Award credit to answers that refer to the evaporation of sweat from the tail.
Q Award credit to answers that are the converse of the above, relating to the rectal temperature
(ii) The scientists concluded that MDMA causes death by stimulating heat generation.
Use the data to evaluate their conclusion. (3)
Standard deviations show mean rectal temperatures are significantly different (in the two groups);
Rectal temperature indicates core temperature / heat generation;
Tail temperatures not significantly different (in the two groups);
Tail temperatures indicate no difference in heat loss;
None of the mice died (in this experiment);
Q If candidates fail to gain credit above, they can be awarded one mark for a clear statement that MDMA increases heat production but does affect not heat loss.
Question 34
a) Describe how insulin reduces the concentration of glucose in the blood. (3)
insulin binds to specific receptors (on membranes);
insulin activates carrier proteins / opens channels / causes more channels to form;
insulin increases the permeability of liver/muscle cells/tissues to glucose;
insulin action results in glucose conversion to glycogen / glycogenesis;
Some people produce no insulin. As a result they have a condition called diabetes. In an investigation, a man with diabetes drank a glucose solution. The concentration of glucose in his blood was measured at regular intervals. The results are shown in the graph.
(b) Suggest two reasons why the concentration of glucose decreased after 1 hour even though this man’s blood contained no insulin. (2)
glucose is used in cell respiration / as energy source / in metabolism;
(must qualify how glucose is used)
glucose enters cells / converted to glycogen in cells;
glucose is excreted / in urine;
(do not credit no reabsorption of glucose in kidneys)
(c) The investigation was repeated on a man who did not have diabetes. The concentration of glucose in his blood before drinking the glucose solution was 80 mg per 100 cm3. Sketch a curve on the graph to show the results you would expect. (1)
line from 80 mg, increasing but keeping below line for diabetic,
dropping to 80 mg;
(line must stablise at, or fluctuate around 80 mg)
(d) The diabetic man adopted a daily routine to stabilise his blood glucose concentration within narrow limits. He ate three meals a day: breakfast, a midday meal and an evening meal.
He injected insulin once before breakfast and once before the evening meal.
The injection he used before breakfast was a mixture of two types of insulin. The mixture contained slow-acting insulin and fast-acting insulin.
(i) Explain the advantage of injecting both types of insulin before breakfast. (2)
fast acting insulin reduces blood glucose from breakfast;
slow acting insulin reduces blood glucose from other meals
before the evening meal / eliminates the need to inject at lunch;
(must be a reference to the meals)
(one mark if neither of the above but a clear reference is
made to glucose conversion to glycogen);
(ii) One day, the man did not eat a midday meal. Suggest one reason why his blood glucose concentration did not fall dangerously low even though he had injected himself with the mixture of insulin before breakfast. (1)
glucagon is still active;
glycogen converted to glucose / glycogenolysis;
insulin injected at breakfast causes cells to take up glucose too slowly for levels to become dangerously low;
person is not active so little glucose used in respiration;
(do not credit statements about consuming large breakfasts) 1 max
Question 35
Emperor penguins are birds which live in the Antarctic. They cannot fly, but they are very good swimmers and feed on fish from the oceans around the Antarctic continent. To breed they have to leave the sea and move on to the ice. The drawing shows a male emperor penguin.
(a) Like mammals, birds maintain a constant body temperature. The emperor penguin maintains a core body temperature of about 38 °C. On the Antarctic ice the air temperature is often as low as –40 °C.
(i) Use the drawing to suggest how its shape helps the penguin to maintain its core body temperature in such low air temperatures. (2)
rounded shape / small head / short legs / small extremities;
low surface area:volume ratio limits heat loss;
(ii) At rest a penguin maintains a constant metabolic rate as the air temperature falls to – 10 °C. Below this temperature its metabolic rate increases. Explain why the metabolic rate can stay constant down to –10 °C, but rises when the temperature
falls below this. (2)
insulation / physical responses prevent heat loss/maintain temperature above –10 °C ;
below –10 °C heat loss greater than heat gain from respiration;
rate of respiration/metabolism increased to generate heat;
(b) At the start of winter emperor penguins walk about 100 km from the sea to the permanent ice shelf. Here each female lays a single egg which the male incubates in a pouch above his feet. The females return to the sea, but the males stay at the breeding site and do not feed. Large groups, often more than a thousand birds, huddle close together. They regularly change position within the huddle. When the chicks have developed, after 100 days, their fathers walk the 100 km back to the sea so that they can feed again.
When they leave the sea at the start of winter, the males weigh 35 kg and may have up to 20 kg of stored fat. Walking uses 7.5 g of fat per km. Research has shown that at the average temperatures on the ice a penguin standing on its own loses 200 g of its stored fat per day. However, when in a huddle only 100 g per day is lost.
(i) Explain how huddling close together helps to reduce the loss in mass from 200 g to 100 g per day. (2)
reduction in exposed surface area so less heat loss;
(not just: use or gain heat from each other)
less fat / food store used in maintaining temperature;
(ii) Use the information above to explain why the huddling behaviour is essential to the survival of the male penguins. You should include relevant calculations in your answer. (3)
figures used to calculate mass of fat used:
for birds that do not huddle (e.g. walking uses
100 × 7.5 = 750 g (0.75 kg) and 100 days
on ice uses 20 kg = 20.75 kg);
for birds that huddle only 10.75 kg used;
all stored fat used in 100 days if not in huddle /
insufficient fat reserve for single birds to return to sea;
Question 36
Figure 1 shows a seal which lives in the Arctic ocean. It is a mammal with a core body temperature of 37 °C. It has a layer of fat (blubber) under the skin which is 50 mm thick and which insulates it from the cold.
Figure 2 shows the temperature gradient in the surface tissues of the seal when it is in water at 0 °C.
(a) Describe the evidence from Figure 2 that blubber is an effective insulator. (2)
as distance from skin surface increases the temperature increases/steep temperature gradient;
temperature at depth of 50mm/inside of blubber similar to body core temperature;
(b) Figure 3 shows the arrangement of the blood vessels in the surface tissues of the seal.
Explain how this arrangement of the blood vessels helps the seal to maintain a constant body temperature. (4)
EITHER
1. increased (blood) temperature results in increased blood flow through
capillaries in blubber / vasodilation in blubber;
2. increased skin temperature;
3. increased loss of heat from skin;
4. decreased temperature results in reduced blood flow through
blubber capillaries/ vasoconstriction in blubber;
5. correct reference to (sphincter/circular) muscles of arterioles;
6. correct reference to role of shunt vessels;
OR
1. decreased (blood) temperature results in decreased blood flow
through capillaries in blubber / vasoconstriction in blubber;
2. decreased skin temperature;
3. decreased loss of heat from skin;
4. increased temperature results in increased blood flow through
blubber capillaries/ vasodilation in blubber;
5. correct reference to (sphincter/circular) muscles of arterioles;
6. correct reference to role of shunt vessels;
(c) The seal has no blubber in the flippers. Each artery carrying blood to the flipper is surrounded by veins from the flipper, as shown in Figure 4.
Explain how this arrangement of blood vessels prevents excessive heat loss. (3)
counter-current principle;
temperature of blood flowing to flipper greater than that leaving it /
temperature of blood greater in artery than vein;
therefore heat (energy) transfer artery to vein;
less heat lost as not transferred to environment/transferred to body core;
(d) Like other mammals, seals produce urine which is more concentrated than their blood plasma. Explain the role of the loop of Henle in producing concentrated urine. (6)
1. salt/(sodium) ions diffuse into descending limb;
2. water moves out of descending limb;
3. salt/(sodium) ions actively removed from ascending limb;
4. ascending limb impermeable to water;
5. low water potential/ high concentration of ions in medulla/tissue fluid;
6. water leaves collecting duct / distal tubule;
7. due to difference in water potential / by osmosis;
Question 37
The kangaroo rat is a small desert mammal. It takes in very little water in its food and it rarely drinks. Its core body temperature is 38 °C.
(a) The kangaroo rat takes in some water by feeding and drinking. Describe another method by which the kangaroo rat could obtain water. (2)
metabolic water / from respiration;
allow condensation reactions. Ignore ‘oxidation’.
aerobic / use of oxygen;
(‘From aerobic respiration’ = 2 marks)
(b) At an environmental temperature of 28 °C and 100% saturation of the external air with water vapour, the temperature inside a kangaroo rat’s nasal passages was 31 °C. At the same environmental temperature but 0% saturation with water vapour, the temperature in the nasal passages was 26 °C. Explain the difference in temperature of the nasal passages and suggest how the lower nasal temperature helps the kangaroo rat to survive in hot, dry conditions. (4)
1 dry air (inhaled) causes evaporation from nasal passages / or converse;
2 cooling due to evaporation;
3 blood is cooled;
4 (cool blood) flows from nose to brain / cools brain / keeps brain at const. temp.;
5 allows activity (e.g. foraging for food / escaping predators / not restricted to staying in humid burrow (in hot conditions);
6 air with high water vapour content leaves lungs / is exhaled;
7 water condenses in nasal passages;
8 due to lower temperature;
9 water can be reabsorbed (into blood) / swallowed / water conservation / less water loss;
Question 38
Diabetes is a disorder affecting the ability to control blood glucose concentration. One type of diabetes can be due to an abnormality of the insulin receptors in the cell surface membranes of cells in the liver and muscles. A high blood glucose concentration and the presence of glucose in the urine are signs of this type of diabetes.
(a) (i) Suggest one way in which the insulin receptors might be abnormal. (1)
different shape/different tertiary structure/different sequence of amino acids;
(ii) Explain how the presence of abnormal insulin receptors results in a high blood glucose concentration. (2)
insulin unable to attach to receptors;
reduced/no uptake of glucose into cells / no carrier proteins/ channels for glucose transport;
(iii) Explain how the kidneys normally prevent glucose appearing in the urine of a nondiabetic person. (3)
glucose reabsorbed/absorbed into blood;
from proximal tubule;
by active transport/involving membrane carriers;
(b) Twin studies have been used to determine the relative effects of genetic and environmental factors on the development of this type of diabetes. The table shows the concordance (where both twins have the condition) in genetically identical and genetically
non-identical twins.
| Concordance in genetically identical twins / % | Concordance in genetically non-identical twins /% |
| 85 | 35 |
(i) What do the data show about the relative effects of environmental and genetic factors on the development of diabetes? (1)
larger genetic component;
(must be comparative)
(ii) Suggest two factors which should be taken into account when collecting the data in order to draw valid conclusions. (2)
number of cases studied;
matched samples;
age of twins;
named environmental factor;;
(allow 2 marks for 2 different factors if no overlap in effect)
family history of diabetes;
method of diagnosis;
same sex in non-identical twins; 2 max
Question 39
(a) One effect of getting into a cold shower is a reduction in the amount of blood flowing through the capillaries near the surface of the skin. Explain how the cold water causes this response. (4)
(thermo)receptors in skin;
(accept receptors in hypothalamus if after reference to cooled blood)
impulses via nerves / neurones to or from;
(once only)
hypothalamus;
heat gain/temperature centre (in hypothalamus);
contraction /constriction of arterioles;
(not capillaries, or just vasoconstriction)
diversion through shunt vessels;
(b) (i) When exercising at 30 °C, the body is more likely to overheat in humid conditions than in dry conditions. Explain why. (2)
reduced / no evaporation of sweat;
due to reduced gradient / saturation/high water content of air;
less heat loss by (latent) heat of evaporation;
(ii) Strenuous exercise leads to exhaustion more quickly in hot conditions than in cool conditions. One reason for this is a reduced blood supply to the muscles, which means that they receive less oxygen.
Suggest an explanation for the reduced blood supply to the muscles. (2)
skin vessels open/vasodilatation;
(movement dq)
blood diverted from muscles / limited total volume of blood;
Question 40
The graph shows the effect of increasing the environmental temperature on the metabolic rate of a small mammal.
(a) Suggest one way of measuring the metabolic rate. (1)
uptake of oxygen / production of carbon dioxide;
(b) The small mammal has ears which are usually pink, but they appear pale when the environmental temperature is low. Explain the pale appearance of the mammal’s ears when the environmental temperature is low. (3)
constriction / narrowing / shunt effect;
of arterioles;
less blood flow to capillaries;
reduces heat loss via radiation / conduction / convection;
(c) Use your knowledge of thermoregulation to explain
(i) the change in metabolic rate of the mammal when the environmental temperature increases from 5°C to 40°C; (3)
metabolism releases heat;
increase in environmental temperature provides heat / warms mammal;
less heat required from metabolism which falls / levels off;
(ii) the increase in metabolic rate after 40°C. (2)
lack of thermoregulatory control at high temp. / positive feedback;
increase in temperature increases metabolism / respiration;
Question 41
In an investigation, the blood flow in the hepatic artery of a small mammal was prevented by clamping the artery, as shown in the diagram.
The rate of blood flow and the concentration of glucose in the blood of the hepatic portal vein and hepatic vein were then measured at 15-minute intervals. Insulin was injected into the blood at 35 minutes and adrenaline was injected into the blood at 65 minutes. The results are shown in the table.
(a) Between 0 and 30 minutes, the concentration of glucose in the hepatic vein was slightly higher than that in the hepatic portal vein. Explain why. (2)
breakdown of glycogen (to glucose);
glucose released into blood / from liver;
hepatic portal vein low because little from gut / between meals
(b) Explain the effect of insulin on the concentration of glucose in the blood in the hepatic vein. (1)
insulin causes uptake of glucose (by liver) / glucose converted to glycogen (in liver);
(c) The effect of insulin on the glucose concentration in the hepatic vein was greater than its effect on the glucose concentration in the hepatic portal vein. Suggest one explanation for this. (1)
insulin affects liver and hepatic vein carries blood out of liver / hepatic portal vein carries blood into liver;
(d) Adrenaline has a similar effect to that of exercise on the redistribution of blood flow in the body. Explain how adrenaline caused a fall in blood flow in the hepatic portal vein between 60 and 75 minutes. (2)
constriction of arterioles/arteries in gut / vasoconstriction in gut /
dilation of arterioles/arteries in muscles / named muscle;
more blood flow to muscles / named muscle / less blood flow to gut;