O-LevelBiologyTransport in Humans5090/22 · May/June 2015 · Q59 Marks

Table 5.1 shows the mean daily water intake and loss by a person. Table 5.1 water intake / dm³ water loss / dm³ drinks 1.50 faeces 0.10 food 0.75 sweat 0.52 urine 1.50 exhaled air Total 2.25 Total 2.50

(a)(i)Using the information in Table 5.1, calculate the daily loss of water in exhaled air.[1]
(a)(ii)Explain why exhaled air contains water.[2]
(b)Explain why, even though 2.25 dm³ of water are taken in through the mouth, the faeces contain only 0.10 dm³ of water.[3]
(c)Explain the importance of water in urine.[2]
(d)The difference between water intake and water loss by a person is accounted for by water produced by a metabolic process in the body. Name this metabolic process.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.

[1] (a)(i) 0.38 + dm³ ;
[2] (a)(ii) evaporation/water vapour ;
[2] (a)(ii) from (moist lining of) alveoli/lungs ; Ig other named parts of breathing system
[max 3] (b) 1. water is absorbed + blood ;
[max 3] (b) 2. (from) ileum/small intestine/colon/large intestine ;
[max 3] (b) 3. ref need to prevent water loss/importance of water in body (e.g. solvent/transport);
[max 3] (b) 4. water lost by other methods/ref. to any named other method of water loss;
[2] (c) water is a solvent/dissolves ;
[2] (c) any one named solute ; A salts
[1] (d) respiration; if qualified must be aerobic

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