AQA · GCSE · Combined Science · Higher

Evaluating a body-water percentage

Q02.8 3 marks

Use Figure 6 to compare the body water percentage at $600\ \mathrm{k\Omega}$ for categories A and B with the healthy range of 45% to 65%.

Graph titled Figure 6. The y-axis is body water percentage from 0 to 90. The x-axis is total resistance of legs in kΩ from 0 to 1200. Three downward-curving category lines are labelled A, B and C. At a total resistance of about 600 kΩ, category A is around 61% body water and category B is around 68%. — Figure 6

The total resistance of the student’s legs is $600\ \mathrm{k\Omega}$ . A healthy body water percentage is between 45% and 65%.

The different measurements of the mass of the student mean that the student could be in either category A or category B.

Evaluate if the student has a healthy body water percentage.

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Marking points

1 Use Figure 6 to read category A at about 61% body water for $600\ \mathrm{k\Omega}$ .
2 Use Figure 6 to read category B at about 68% body water for $600\ \mathrm{k\Omega}$ .
3 Compare both readings with the healthy range and conclude that A would be healthy but B would be unhealthy.

Full-mark answer

At $600\ \mathrm{k\Omega}$ , category A gives a body water percentage of about 61%, which is within the healthy range of 45% to 65%. Category B gives about 68%, which is above the healthy range, so it is unhealthy. Therefore the student might be healthy if they are in category A, but unhealthy if they are in category B.

Why this answer loses marks

The student is healthy because 61% is in the healthy range.

This ignores that the student could be category B, which gives an unhealthy value.

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