4 2 A spirometer can be used to study the performance of an athlete. snabbiology.wordpress.com The trace produced by a spirometer can be used to determine the respiratory minute ventilation and the oxygen consumption of an individual. (a) Describe how a spirometer trace can be used to calculate the respiratory minute ventilation and the oxygen consumption per minute. (4) respiratory minute ventilation .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... oxygen consumption per minute .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 5 Turn over (b) A student compared the spirometer trace for a pair of healthy, genetically identical twins. State two variables that would have to be controlled to make this a valid comparison. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 2 = 6 marks)