Previous IB Exam Questions: Excretion

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Use these model essay question responses to prepare for essay questions on your in class tests, as well as the IB Examination, Papers 2 & 3. These questions have appeared on recent IB examinations, exactly as shown below.

Following each question is the markscheme answer which was used to evaluate student answers on the examination paper.
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1. Outline ways in which the kidney helps in homeostasis. 5 marks

2. Outline the need for excretion in living organisms. 2 marks

3. Explain briefly the function of the loop of Henle in the human kidney. 2 marks

4. Compare the composition of the blood in the renal artery and renal vein. 2 marks

5. Define excretion and osmoregulation. 4 marks

6. explain how hypertonic urine is produced in the medulla of the human kidney. 4 marks

7. Discuss the relationship between the different nitrogenous waste products and the habitats of birds and amphibians. 5 marks

(Up to 4 from the following;)

(1 for the following)

8. H1. Doses of aspirin from 75 to 325 mg day–1 have been used in patients to help prevent cardio-vascular disease. However, there has been little research into the effect of aspirin on renal function in older patients. One test of renal function is known as a clearance test which involves estimating the rate of production of glomerular filtrate by measuring the concentration of creatinine in the urine. A five-week study was carried out on 83 older patients (56-98 years of age) treated with low-dose aspirin (100 mg day–1) and 40 control patients who received no aspirin. Other medications and diet were kept constant from one week prior to the start of the study. Aspirin was given to the patients for two weeks and then stopped. Blood and urine samples were monitored prior to treatment (baseline) and at the end of week 2 and week 5. The table below shows blood and urine levels of different metabolites starting with baseline levels, after two weeks on aspirin, and at the end of the five-week period.

(a) Calculate the percentage change in blood uric acid concentration from baseline to the end of week 2 for the aspirin treatment group.[1 mark]

(b) Suggest why the researchers collected the baseline data. [1 mark]

(b) for comparison with data collected (after two and five weeks) with and without aspirin treatment

(c) Describe the effect of two weeks of aspirin treatment. [2 marks]

(c) blood levels of creatine, urea and uric acid increased (over control group); urine creatine clearance decreased (while control group increased);

(d) Deduce whether the effect of aspirin on renal function is likely to be permanent. [3 marks]

(d) the effect is likely to be permanent; because uric acid concentration remains high after five weeks; and creatine clearance rate is still (very) low after five weeks; not enough data / long enough time to predict; or: the effect is unlikely to be permanent; as blood creatine concentration / most substances at the end of week five is lower than/close to baseline level; and blood urea concentration is reduced from the peak at two weeks / dropping; not enough data/ long enough time to predict;

 

9. Organisms in a community need a supply of energy. This energy is trapped by photosynthesis and then flows through a food web. The organisms in the food web lose energy in various ways, including excretion. All the energy is eventually lost as heat.

(i) State one excretory product of mammals. [1]

(i) CO2 ; nitrogenous compound / urea; water;

(ii) State the need for excretion in all living organisms. [1]

(ii) waste substances are toxic / can cause damage / harmful

10. The walls of blood capillaries in the kidney are fenestrated. How does the fenestration of these capillaries help in the production of urine?


A. A larger volume of fluid can be filtered out of the blood per minute.
B. Small molecules are allowed through but not large ones.
C. Higher blood pressures can be tolerated without damage to the capillaries.
D. Phagocytes are able to escape from the capillaries and prevent kidney infections.

Answer: "A"

11. How are excretory products removed from the blood during kidney dialysis, without removing glucose?


A. The dialysis membrane allows excretory products to pass through, but not glucose.
B. A potential difference across the dialysis membrane draws through excretory products only.
C. Excretory products dissolve in dialysis fluid but glucose does not.
D. The dialysis fluid contains glucose but not excretory products.

Answer "D"

12. Explain the control of ADH (antidiuretic hormone) secretion.

Award [4 max] for:
produced in hypothalamus;
via neurosecretory cells;
passes from hypothalamus to (posterior) pituitary;
attached to carrier protein / neurophysin;
(stored) in posterior pituitary / neurohypophysis;
released under stimulus by osmoreceptors in hypothalamus;
osmoreceptors stimulated by high blood plasma concentration/reduced blood pressure;
increases water reabsorption (in kidneys);


Award [2 max] for:
site of action is collecting duct;
promotes constriction of blood vessels;
increases blood pressure;
there is a negative feedback control of ADH/vasopressin secretion; [6 max]

13. Blood vessels carry blood to and from the kidney. Draw a labelled diagram to show the
internal structure of the kidney, including the vessels that are connected to it. [5 marks]

Award [1] for each of the following structures clearly drawn and correctly labelled.
cortex shown at the edge of kidney;
medulla shown inside the cortex (with pyramids);
pelvis shown on the concave side of the kidney;
ureter shown connecting with the pelvis / on concave side / hilum;
renal artery shown connected to the concave / pelvis side / away from cortex;
renal vein shown connected to the concave / pelvis side / away from cortex;

14. Compare the composition of blood arriving at the kidney with the composition of blood
carried away from it.

Accept answers referring to blood flow to the kidney instead of in the renal artery and
blood flow from the kidney instead of in the renal vein.
more oxygen in the renal artery / less in the renal vein / oxygenated versus deoxygenated;
less carbon dioxide in the renal artery / more in the renal vein;
more urea in the renal artery / less in the renal vein;
more ammonia / ethanol / toxins / hormones in the renal artery / less in the renal vein;
Reject answers for the points above if “none” instead of “less” is indicated.
more salt/NaCl /Na+/ Cl− ions (in total) in renal artery than in renal vein;
more water (in total) in renal artery than in renal vein;
lower salt concentration / higher water concentration in vein than in artery with ADH; [4 max]

15. H1. The plasma solute concentration, plasma antidiuretic hormone (ADH) concentration and feelings
of thirst were tested in a group of volunteers. These graphs show the relationship between
intensity of thirst, plasma ADH concentration and plasma solute concentration.

 

(a) Identify the plasma ADH concentration at a plasma solute concentration of 300 mOsmol kg-1 using the line of best fit. [1]

5.3 (+ or - 0.3) pmol dm-3 (unit needed)

(b) Compare intensity of thirst and plasma ADH concentration. [1]

a positive correlation;
no data below 280 mOsmol kg−1;

(c) Outline what would happen to plasma solute concentration and ADH concentration if a person were to drink water to satisfy his/her thirst. [2]

after drinking water, blood plasma / solute concentration decreases;
plasma ADH concentration decreases;
osmoreceptors in the hypothalamus monitor blood solute / blood plasma / plasma
concentration;
impulses passed to ADH neurosecretory cells to reduce / limit release of ADH;
drop in ADH decreases the effect of this hormone on the kidneys;
blood solute concentration returns to normal;

(d) State two reasons why a person's plasma solute concentration may increase.[2]

vomiting / diarrhoea / blood loss;
increase salt intake;
drink alcohol / coffee;
certain drugs / morphine / nicotine / barbiturates;
excess sweating / lack of water intake;
diabetes as it increases glucose in blood;

16. (a) Draw a labelled diagram of a nephron. [3]

For a diagram of a nephron, award [1] for every two of the following structures clearly drawn and correctly labelled. glomerulus; Bowman’s capsule; proximal convoluted tubule; loop of Henle; ascending and descending both labeled; distal convoluted tubule; collecting duct; afferent arteriole / efferent arteriole;

(b) Explain the process of ultrafiltration in the kidney. [3]

difference in diameter of efferent and afferent arteriole; leads to blood in glomerulus at high pressure; capillary wall is fenestrated / has pores / holes; basement membrane has pores; pores in basement membrane prevent large (protein) molecules from leaving blood plasma / only allows passage of small molecules; passive process;

(c) Compare the composition of blood plasma in the renal artery with the composition of the glomerular filtrate. [2]

(large) proteins in blood plasma but not in glomerular filtrate; all other substances equal in concentration;

 

17. What are the excretory products of birds, mammals and freshwater fish?

(Check with your instructor if you need help with any of these Paper I questions. Hint: there's a pattern)

18. What can be changed in the kidney over a period of time in order to carry out the process of
osmoregulation?


A. The amount of blood flowing to the kidney
B. The amount of fluid filtered from the blood in the glomeruli
C. The amount of solutes selectively reabsorbed in the proximal convoluted tubule
D. The amount of water reabsorbed in the collecting ducts

19. Which best describes the role of the kidney in homeostasis?


A. Storage of urine
B. Producing urine at a constant rate
C. Removing urea from the blood
D. Maintaining the water content of the blood between narrow limits

 

20. The proximal convoluted tubule is a part of the nephron (kidney tubule). Its function is selective reabsorption of substances useful to the body.

(a) Outline how the liquid that flows through the proximal convoluted tubule is produced. [2]

high pressure in afferent arterioles; leads to ultrafiltration in the glomerulus/through fenestrated capillaries in the glomerulus; drains through the Bowman’s capsule to the proximal convoluted tubule;

(b) (i) Water and salts are selectively reabsorbed by the proximal convoluted tubule. State
the name of one other substance that is selectively reabsorbed. [1]

(i) glucose / amino acids

(ii) State the names of the processes used to reabsorb water and salts.[2]

water by osmosis;

salts by active transport/facilitated diffusion;

The drawing below shows the structure of a cell from the wall of the proximal convoluted tubule.

 

(c) The actual size of the cell is shown on the diagram. Calculate the linear magnification of the
drawing. Show your working.

(d) Explain how the structure of the proximal convoluted tubule cell, as shown in the diagram, is adapted to carry out selective re-absorption.

microvilli increase the surface area for absorption / active transport; mitochondria produce ATP for active transport;

21. Discuss the relationship between the excretion of nitrogenous waste products and the habitat of an organism.

waste product used is related to water availability in the habitat;
birds and mammals adapted to conserve water but not freshwater fish;
freshwater fish excrete ammonia;
highly toxic / very soluble in water;
must be diluted in large volume of water;
mammals excrete urea;
less toxic;
can be more concentrated / less water needed to get rid of it;
birds excrete uric acid;
loss of very little water;
smaller mass of water is an advantage in flight;

 

22. Explain the control of ADH secretion.

produced in hypothalamus;
via neurosecretory cells;
passes from hypothalamus to pituitary;
attached to carrier protein / neurophysin;
(stored) in posterior pituitary / neurohypophysis;
released under stimulus by osmoreceptors in hypothalamus;
osmoreceptors stimulated by high blood plasma concentration / reduced blood
pressure;
increases water reabsorption (in kidneys);
site of action is collecting duct;
promotes constriction of blood vessels;
increases blood pressure;
there is a negative feedback control of ADH secretion;
Only [2 max] can be awarded in relation to the last four points.
Accept reference to vasopressin instead of ADH.