This set covers the skills in excretion and homeostasis: excretion versus egestion, kidney filtration and reabsorption, negative feedback, temperature control and glucose control. The questions go from easier recall to harder multi-step explanation.
Write your answer first, then open the answer. All data are invented for practice. You can log errors in the mistake log and retest queue as you go.
Questions
Q1 (recall). Define excretion and define egestion.
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Excretion is the removal of waste products of metabolism and of toxic materials from the body. Egestion is the removal of undigested food from the gut as faeces.
Q2 (sorting). Sort into excretion or egestion: (a) carbon dioxide breathed out, (b) undigested fibre in faeces, (c) urea in urine.
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(a) Excretion: made by respiration in cells. (b) Egestion: it was never absorbed into cells. (c) Excretion: urea is a waste product of metabolism.
Q3 (recall). Which organ makes urea, and which organ removes it from the blood?
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The liver makes urea from excess amino acids. The kidneys remove it from the blood and it leaves in urine.
Q4 (concept). In the kidney, what is the difference between filtration and selective reabsorption?
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Filtration forces water and small molecules out of the blood into the tubule, by size and under pressure. Selective reabsorption then takes useful substances such as all the glucose back into the blood, leaving urea and excess water and salts to leave as urine.
Q5 (calculation). A model kidney makes 120 dm³ of filtrate and 1.2 dm³ of urine in a day. The numbers are invented. What percentage of the filtrate is reabsorbed?
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Reabsorbed = 120 − 1.2 = 118.8 dm³. Percentage = 118.8 ÷ 120 × 100 = 99%. Check: 1.2 is 1% of 120, so the rest is 99%.
Q6 (application). In a model, the filtrate contains 5.0 units of glucose and the urine contains none. Explain this.
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Glucose is a small molecule, so it is filtered out of the blood into the filtrate. It is then selectively reabsorbed into the blood by active transport, so none reaches the urine.
Q7 (sequence). Put these in the order they occur in a negative-feedback loop: response, return towards set point, receptor detects change, condition moves away from set point.
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Condition moves away from set point, receptor detects change, response, return towards set point.
Q8 (explain). On a hot day a student’s skin flushes and she sweats. Explain how each response lowers body temperature.
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Skin arterioles widen (vasodilation), so more blood flows through skin capillaries and more heat is lost by radiation. Sweat evaporates, taking energy from the skin. Both increase heat loss, which opposes the rise in temperature.
Q9 (error spotting). A student writes: “When it is cold, the capillaries move away from the skin.” Correct the statement.
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Vessels do not move. Arterioles supplying the skin narrow (vasoconstriction), so less blood flows through skin capillaries and less heat is lost. Shivering may also release heat from muscle respiration.
Q10 (data). Invented glucose readings for a model patient: 0 min, 5.0 units; 30 min, 7.5; 60 min, 6.0; 120 min, 5.1. (a) Describe the pattern. (b) Name the hormone responsible for the fall. (c) Calculate the rate of fall from 60 to 120 minutes.
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(a) Glucose rises to a peak at 30 minutes, then falls back towards the starting value. (b) Insulin, released by the pancreas, makes the liver store glucose as glycogen. (c) 6.0 − 5.1 = 0.9 units in 60 minutes. 0.9 ÷ 60 = 0.015 units per minute.
If you got these wrong
- Q1 to Q3 (mixing excretion and egestion, or saying the kidney makes urea): go to distinguish excretion from egestion.
- Q4 to Q6 (kidney stages, percentages, glucose): go to filtration and selective reabsorption.
- Q7 (missing the return step): go to interpret a negative-feedback loop.
- Q8 and Q9 (vessels moving, one-sided answers): go to temperature regulation with competing effects.
- Q10 (wrong hormone, rate calculation): go to read a glucose-regulation diagram.
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