Turn over 15 6 The effect of gas composition on the breathing rate of locusts was investigated. The method used was: Step 1 A locust was placed in a 20 cm3 clear plastic syringe, as shown in the diagram. The piston was inserted so it gently held the locust in place so that the locust had no room to move. plastic tubing 20 cm3 plastic syringe piston Step 2 The number of pumping movements of the abdomen which occurred in 30 seconds was counted. This was repeated three more times. Step 3 Gases of different compositions were added to the syringe through the plastic tubing. Step 4 For each different composition of gases, the number of pumping movements of the abdomen which occurred in 30 seconds was counted. Step 5 Between each composition of gases used, the piston was moved in and out ten times to replace the exhaled air with laboratory air. Step 6 The locust was then left for 5 minutes before the next composition of gases was added. (a) (i) State the purpose of Step 5. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) State the purpose of Step 6. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 16 (b) The table shows the results of the investigation. Gas composition (%) Number of movements in 30 seconds Mean Range SD oxygen carbon dioxide 21 0.1 26 22 31 29 27 9 3.9 16 4.1 41 44 46 49 45 8 3.4 100 0.0 5 12 6 8 8 7 3.1 94 6.0 48 42 46 49 46 7 3.1 88 12.0 44 46 50 53 48 9 83 17.0 54 51 53 49 52 5 2.2 (i) Calculate the standard deviation for the number of movements in 30 seconds when the gas has a composition of 88% oxygen and 12% carbon dioxide. Use the formula s n = − − ∑( ) x x 2 1 (3) Answer .............................................................. Turn over 17 (ii) Explain the relationship between the range and the standard deviation. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (c) Analyse the data to comment on the effect gas composition has on the breathing rate of this locust. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 6 = 11 marks)