20   8 Tuberculosis (TB) is a disease that affects the lungs. It is caused by the bacterium Mycobacterium tuberculosis. When these bacteria enter the body an immune response is triggered. (a) The initial response when bacteria enter the body is a (1) A non-specific response and bacteria are destroyed by antibodies B non-specific response and bacteria are destroyed by phagocytes C specific response and bacteria are destroyed by antibodies D specific response and bacteria are destroyed by phagocytes. (b) M. tuberculosis bacteria can remain dormant in the body after infection. Explain why these dormant bacteria are not destroyed by the immune system. 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Turn over 21   (c) The Human Immunodeficiency Virus (HIV) affects the immune system. People infected with HIV are more likely to develop TB. A study investigated the relationship between TB infections and HIV status. In 2008, the number of people in the world estimated to have TB was 9.4 million. The table shows the percentage of these people who were either HIV positive or HIV negative. The estimated number of deaths due to TB is also shown in the table. HIV status Percentage of people with TB in 2008 (%) Estimated number of patients with TB who died in 2008 Percentage of deaths due to TB (%) HIV positive 15 521 700 HIV negative 85 1 278 400 16 (i) Calculate the percentage of TB patients infected with HIV who died of TB. (2) ................................................................ % (ii) Describe the effect of HIV on the number of deaths from TB. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22   *(iii) There are increased numbers of deaths from TB as a result of HIV infection. The table shows data for deaths worldwide from HIV and TB in 2016. Type of infection Number of deaths TB only 1 300 000 HIV only 826 000 TB and HIV 374 000 Treatment of HIV with anti-viral drugs has reduced the incidence of TB associated with HIV infection. The replication of HIV reduces the T-helper cell count. These anti-viral drugs reduce the replication of the virus in the body. The graph shows the effect of this on the incidence of TB. 500 400 300 200 100 0 Number of T-helper cells mm−3 25 20 15 10 5 0 TB incidence / a.u. Turn over 23   Explain the effect of using anti-viral drugs to treat HIV on the number of deaths from TB. 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(Total for Question 8 = 14 marks) 24   BLANK PAGE Turn over 25   9 A biodiversity hotspot is a region that is both highly diverse and threatened with destruction. (a) Biodiversity can be measured by the number of (1) A different genes in a population. B different species in a habitat. C homozygotes in a habitat. D individuals in a population. (b) Biodiversity hotspots have at least 1500 endemic plant species. These hotspots have lost at least 70% of their natural vegetation. Explain how protection of these hotspots can affect global biodiversity. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 26   (c) A population of white-tailed deer Odocoileus virginianus was introduced from North America into Finland in 1934. There were four females and one male. The population has since increased rapidly. A study in 2012 compared the genetic diversity of the population in Finland with the population in North America. Ten genes were compared from 72 deer in each population. The allele richness (number of alleles in the population) of each gene was measured. A χ 2 test was carried out to compare the two populations. (i) The null hypothesis for this investigation is (1) A the allele richness in the population from Finland is higher than the USA. B the allele richness in the population from the USA is higher than Finland. C the population in the USA is more genetically diverse than the population in Finland. D there is no difference in allele richness between the two populations. Turn over 27   (ii) The values from the population in the USA can be taken as the expected values and a χ 2 test can be carried out. Gene Allele richness (Finland population) X (observed) Allele richness (USA population) Y (expected) X − Y (X − Y)2 (X − Y)2 / Y 1 6 14 8 64 4.57 2 4 5 1 1 0.2 3 7 13 6 36 2.77 4 7 15 8 64 4.27 5 6 6 0 0 0 6 8 12 4 16 1.33 7 2 3 1 1 0.33 8 4 4 0 0 0 9 4 9 10 3 4 Complete the table to calculate the χ 2 value, using the formula ( ) 2 2 O E E χ − = ∑ (3) Answer ................................................................ 28   (iii) The table shows the critical values of chi-squared at different levels of probability. Degrees of freedom Probability p=0.10 p=0.05 1 2.706 3.841 2 4.605 5.991 3 6.251 7.815 4 7.779 9.488 5 9.236 11.070 6 10.645 12.592 7 12.017 14.067 8 13.362 15.507 9 14.684 16.919 10 15.987 18.307 Deduce the effect of a small founder population on the allele richness in the population of white-tailed deer in Finland. 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Turn over 29   (d) The table shows the heterozygosity index for each population of white‑tailed deer. Heterozygosity index for Finland population Heterozygosity index for North American population 0.692 0.742 Climate change may affect the habitat of both populations of deer. Explain which population is more likely to adapt to changing conditions. 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(Total for Question 9 = 14 marks)