6 3 Water fleas are small animals that live in pond water. A student observed a water flea using a light microscope. The diagram shows the student’s drawing of the water flea. compound eye gut heart The diagram shows an eyepiece graticule and a stage micrometer used by the student to measure the diameter of the heart in this water flea. 50 60 70 0 1 2 3 4 5 6 7 8 9 10 eyepiece graticule stage micrometer (Source: http://biology4alevel.blogspot.com/2014/07/2-cell-structure-microscopy.html) Each small division on the stage micrometer is 0.01 mm. The diameter of the heart was found to be 0.2 mm. (a) Determine the number of eyepiece units that equal the diameter of the water flea heart. (1) Answer .............................................................. 7 Turn over (b) The water flea has a spherical heart with a diameter of 0.2 mm. Cardiac output is the volume of blood pumped out of a heart in one minute. The resting heart rate of a water flea is 200 beats min−1. The volume of a sphere is calculated using the formula 4 3 πr 3 where π = 3.142 (i) Calculate the cardiac output of a water flea at rest using the formula cardiac output = stroke volume × heart rate (3) Answer .............................................................. dm3 min−1 (ii) The cardiac output of a human heart at rest is 5.0 dm3 min−1. Give one reason why the cardiac output of a human heart at rest needs to be greater than the cardiac output of a water flea at rest. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 8 (c) A student investigated the effect of adrenaline and acetylcholine on the heart rate of water fleas using the following method: ● place a water flea in pond water on a microscope slide ● count the number of heart beats in one minute ● repeat with two other water fleas ● repeat this procedure using three water fleas placed in adrenaline solution and three water fleas placed in acetylcholine solution. The table shows the results of this investigation. Treatment Heart rate / beats min−1 Standard deviation (SD) Water flea 1 Water flea 2 Water flea 3 Mean Pond water 195 185 190 190 Adrenaline solution 240 236 238 238 ± 2.0 Acetylcholine solution 116 120 118 118 ± 2.0 (i) Calculate the standard deviation for the mean heart rate in the pond water. Use the formula SD = − − ∑( ) X X n 2 1 (2) Answer .............................................................. 9 Turn over (ii) Plot a graph to show the data for the mean heart rate and SD in each treatment. (2) (iii) Explain why abiotic variables should be controlled in this investigation. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 3 = 11 marks)