OxfordAQA International GCSE Biology: Water and ion balance: liver, kidneys and ADH (9201) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions are aligned to the OxfordAQA International GCSE Biology (9201) specification, Version 5.2, for exams May/June 2018 onwards. They cover section 3.4.3, Control of water and ion content of the body, statements a to g. The qualification is untiered.

Links: the OxfordAQA Biology hub, the printable checklist, the study guide, the revision notes and the free 10-minute diagnostics.

Questions

1. State three routes by which water or ions leave the body of a healthy person. [3]

2. A volunteer records their water budget for one day. Water in: 1400 cm³ from drinks, 600 cm³ from food and 300 cm³ from respiration. Water out: 350 cm³ from the lungs, 450 cm³ from the skin and 100 cm³ in other ways. The rest leaves in urine.

(a) Calculate the volume of urine produced. [3] (b) Calculate the percentage of the total water output that left through the lungs. Give your answer to 3 significant figures. [2]

3. Describe what happens to excess amino acids in the liver. [3]

4. A patient with a damaged liver has a high concentration of ammonia in the blood.

(a) Explain why the ammonia concentration is high. [3] (b) Describe what happens to old red blood cells in a healthy liver. [2] (c) A drug is detoxified in the liver. Describe what happens to the products of the breakdown. [2]

5. (a) Describe what happens to glucose, to dissolved ions and to water in a healthy kidney after the blood has been filtered. [4] (b) The urine of a healthy person contains no glucose. Explain why. [1]

6. The concentration of urea in a person’s blood plasma is 0.3 g per dm³. The concentration in their urine is 20 g per dm³.

(a) Calculate how many times more concentrated the urea is in the urine than in the plasma. Give your answer to 3 significant figures. [2] (b) Suggest why urine can be much more concentrated in urea than blood plasma. [2]

7. A hiker normally produces 1.6 dm³ of urine per day. After a day of hard walking in hot weather, the volume is 0.8 dm³.

(a) Calculate the percentage decrease in urine volume. [2] (b) Give the normal volume in cm³. [1] (c) Explain, with reference to ADH, why the volume decreased. [4]

8. A student drank 1000 cm³ of water. Urine volume was measured every hour.

Hour after drinking	1	2	3	4
Urine volume (cm³)	30	150	210	90

(a) Calculate the total volume of urine produced in the four hours. [1] (b) The volume in hour 3 was how many times the volume in hour 1? [1] (c) Explain the change in urine volume between hour 1 and hour 3 with reference to ADH. [4] (d) Predict how the concentration of the urine in hour 3 compared with hour 1. Give a reason. [2]

9. Explain why the control of ADH release is an example of negative feedback. [4]

10. Two people, A and B, each excrete 12 g of urea in their urine in one day. Person A’s urine volume is 0.4 dm³ and person B’s is 1.5 dm³.

(a) Calculate the concentration of urea in each person’s urine in g per dm³. [2] (b) Which person had the greater release of ADH? Explain your answer. [2] (c) Suggest why both people can excrete the same mass of urea but different volumes of urine. [2]

11. A runner loses 1.2 dm³ of sweat in 2 hours of training.

(a) Calculate the mean rate of sweat loss in dm³ per hour. [1] (b) Name two substances, other than water, that are lost in sweat. [2] (c) After training she eats a meal that is very high in protein. Describe how excess protein from the meal leads to urea in her urine. [4] (d) She then drinks 1.0 dm³ of water in a few minutes. Describe how her body responds so that the water content of the blood returns to normal. [3]

Answers

1. Lungs: water is lost when we breathe out [1]; skin: water (with urea and ions) is lost in sweat [1]; kidneys: excess water and excess ions are lost in urine [1] [3] Examiner insight: Name the route and the substance together. “Breathing” alone can be too vague, so write “water in the breath from the lungs”.

2. (a) Total in = 1400 + 600 + 300 = 2300 cm³ [1]; other losses = 350 + 450 + 100 = 900 cm³ [1]; urine = 2300 − 900 = 1400 cm³ [1] (b) Total output = 2300 cm³ (balanced budget) [1]; 350 ÷ 2300 × 100 = 15.2% [1] Examiner insight: Show the working lines, and give the unit. In (b) the total output is the denominator, not the lung loss on its own or the urine volume.

3. Excess amino acids are deaminated [1]; this forms ammonia [1]; the ammonia is converted into urea (for excretion) [1] Examiner insight: The three words deaminated, ammonia and urea, in that order, make a complete answer. Saying the nitrogen part is “broken down” without naming ammonia leaves a gap.

4. (a) Excess amino acids are still deaminated, forming ammonia [1]; the damaged liver cannot convert ammonia into urea as fast [1]; so ammonia builds up in the blood [1] (b) Old red blood cells are broken down [1]; the iron is stored [1] (c) The breakdown products are carried in the blood to the kidneys [1]; they are excreted in the urine [1] Examiner insight: In (a), explain the cause (liver cannot make urea) and then the consequence (ammonia accumulates). A statement of the result only is usually not enough for full marks.

5. (a) All the glucose is reabsorbed [1]; dissolved ions needed by the body are reabsorbed [1]; as much water as the body needs is reabsorbed [1]; urea, excess ions and excess water are released in the urine [1] (b) All the glucose that was filtered is reabsorbed back into the blood, so none is left to leave in urine [1] Examiner insight: Use the words “all” for glucose and “as much as needed” for water. “Some glucose is reabsorbed” can contradict what a healthy kidney does.

6. (a) 20 ÷ 0.3 [1] = 66.7 times [1] (b) Water is reabsorbed from the filtered fluid [1]; urea is released in the urine and not reabsorbed with the water, so it becomes more concentrated [1] Examiner insight: Give “times” or a ratio, not a unit. In (b) mention both the water and the urea; one without the other is half an explanation.

7. (a) (0.8 − 1.6) ÷ 1.6 × 100 [1] = −50%, a 50% decrease [1] (b) 1.6 × 1000 = 1600 cm³ [1] (c) Sweating lowered the water content of the blood [1]; the pituitary gland released more ADH [1]; the kidneys reabsorbed more water [1]; so less urine was produced, and it was more concentrated [1] Examiner insight: A decrease can be written as a negative value or in words. Always divide by the original value, 1.6, not the new one.

8. (a) 30 + 150 + 210 + 90 = 480 cm³ [1] (b) 210 ÷ 30 = 7 times [1] (c) Drinking raised the water content of the blood [1]; the pituitary gland released less ADH [1]; the kidneys reabsorbed less water [1]; so a larger volume of urine was produced [1] (d) The urine in hour 3 was more dilute (less concentrated) [1]; more water was left in the urine because less was reabsorbed [1] Examiner insight: Start (c) with the cause (blood water content up). Skipping straight to ADH leaves out the first link in the chain, and answers that stop at “less urine” or “more urine” describe the data without explaining it.

9. The water content of the blood is detected by receptors (in the brain) [1]; if it is too low, more ADH is released from the pituitary gland, and if it is too high, less is released [1]; the kidneys reabsorb more or less water as a result [1]; this reverses the original change, so the water content returns towards normal [1] Examiner insight: Negative feedback answers gain credit when the response is shown to oppose the change. Whichever case you describe, finish by saying the condition returns towards normal.

10. (a) Person A: 12 ÷ 0.4 = 30 g per dm³ [1]; person B: 12 ÷ 1.5 = 8 g per dm³ [1] (b) Person A [1]; more ADH caused more water to be reabsorbed, giving a smaller volume of concentrated urine [1] (c) ADH changes how much water is reabsorbed [1]; it does not change the amount of urea the kidneys release, which depends on how much urea the liver makes [1] Examiner insight: Name the person and then give the reason; a name with no reason, or the reverse, gains only part of the credit. State the unit “g per dm³” in (a).

11. (a) 1.2 ÷ 2 = 0.6 dm³ per hour [1] (b) Urea [1]; ions (salts) [1] (c) Excess amino acids are deaminated in the liver [1]; this forms ammonia [1]; ammonia is converted into urea [1]; the urea is carried in the blood to the kidneys and released in urine [1] (d) The water content of the blood rises [1]; less ADH is released, so the kidneys reabsorb less water [1]; a larger volume of dilute urine is produced, so the water content falls back to normal [1] Examiner insight: In (c) say that the liver makes the urea and the kidneys remove it. In (d), mention the effect on the blood water content at both the start and the end of the loop.

Where marks are usually lost

• Saying the kidneys make urea instead of the liver.
• Missing the ammonia step between amino acids and urea.
• Writing “more water is made” or “less water is made” instead of reabsorbed.
• Stating the change in urine without the cause in the blood water content.
• Writing that the kidney releases ADH. It is the pituitary gland.
• Describing a healthy kidney as releasing glucose in urine.
• Using the new value as the divisor in a percentage change.
• Confusing “more concentrated” with “larger volume”.
• Leaving out units, or mixing cm³ and dm³.

Next steps

• Reread the study guide for any answer you lost marks on.
• Use the revision notes for recall.
• Tick off the topic on the printable checklist and return to the OxfordAQA Biology hub.
• Try all free 10-minute diagnostics at /diagnostics/.
• Book a free trial class at /trial/.

Official syllabus

OxfordAQA International GCSE Biology (9201), specification Version 5.2, for exams May/June 2018 onwards, published by OxfordAQA. Section 3.4.3, Control of water and ion content of the body.