Some populations of white clover, Trifolium repens, are described as cyanogenic because they produce hydrogen cyanide. Hydrogen cyanide is a poison which inhibits respiration and reduces grazing by herbivores. A group of scientists investigated the percentage of cyanogenic plants in populations of T. repens growing in different locations. The mean January temperature was also recorded. Table 2.1 shows the results of their investigation. Table 2.1 location,percentage of cyanogenic T. repens,mean January temperature /°C Almora, India,85,12.2 Fairbanks, Alaska, USA,5,-23.9 Karaj River, Iran,64,4.4 Konosu, Japan,50,4.2 Lennoxville, Quebec, Canada,71,-10.0 Mandan, North Dakota, USA,33,-12.8 Novosibirsk, Russia,0,-19.4 Pretoria, South Africa,68,10.0 Rabat, Morocco,100,12.5 The scientists calculated the Spearman's rank correlation coefficient to test the hypothesis: The proportion of cyanogenic plants in populations of T. repens increases as the mean January temperature increases.

1. (a)State a null hypothesis for this test.[1]
2. (b)(i)The formula for Spearman's rank correlation is rs = 1 - (6 × ΣD² / (n³ - n)) n = number of pairs of items in the sample D = difference between each pair of ranked measurements Complete Table 2.2 to show how the values for D² were calculated. Table 2.2 location,percentage of cyanogenic T. repens plants,rank of percentage of cyanogenic T. repens plants,mean January temperature /°C,rank of mean January temperature,difference in rank, D,D² Almora,85,,12.2,8,0,0 Fairbanks,5,,-23.9,1,1,1 Karaj River,64,,4.4,6,-1,1 Konosu,50,,4.2,5,-1,1 Lennoxville,71,,-10.0,4,3,9 Mandan,33,,-12.8,3,0,0 Novosibirsk,0,,-19.4,2,-1,1 Pretoria,68,,10.0,7,-1,1 Rabat,100,,12.5,9,0,0 ΣD² = 14[2]
3. (b)(ii)Complete the steps of the calculation to find the value of rs. Give your answer to two decimal places. rs = 1 - (6 × 14 / (___³ - ___)) rs = 1 - (84 / ___) rs = 1 - rs = ___________ (2 d.p.)[2]
4. (b)(iii)Explain why the scientists rejected the null hypothesis.[1]
5. (b)(iv)Suggest why there is a higher proportion of cyanogenic clover plants at locations with high mean January temperatures compared with the other locations studied.[1]