The table below shows observations from an outdoor education group. After walking for 90 minutes in dry weather, each student provided a urine sample. The g...
Question 1 Report
The table below shows observations from an outdoor education group. After walking for 90 minutes in dry weather, each student provided a urine sample. The group then rested in shade and drank water. A second sample was collected two hours later. The samples were compared using a colour scale, where 1 is very pale and 8 is very dark. A darker sample has a lower water content and a higher concentration of urea. The body detects changes in the water potential of the blood and alters the amount of water reabsorbed by the kidneys. This negative feedback response helps prevent cells gaining or losing too much water by osmosis.
| time of sample | mean urine volume in 2 h / cm3 | mean colour score |
|---|---|---|
| after walk | 110 | 7 |
| after drinking water | 390 | 2 |
(a) Describe two differences between the urine samples shown in Table 1. [2]
(b) Suggest why the students' blood had a lower water content after the walk. [2]
(c) Name the hormone that is released in greater amounts when the blood has a low water content. [1]
(d) Use the results to describe the effect of drinking water on water reabsorption by the kidneys. [2]
(e) What is the advantage of maintaining the water content of blood within limits? [1]
Answer Details
(a) After the walk, the mean urine volume is lower, 110 cm3 rather than 390 cm3. It is also darker, with a colour score of 7 rather than 2. [2 marks]
(b) The students lost water in sweat. Exercise also increases water loss by evaporation from the skin and by breathing. [2 marks]
(c) The hormone is ADH, antidiuretic hormone. [1 mark]
(d) After drinking water, the kidneys reabsorb less water. Consequently, a larger volume of dilute, pale urine is produced. [2 marks]
(e) Maintaining blood water content within limits prevents cells gaining or losing too much water by osmosis and maintains suitable conditions for cells. [1 mark]
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