N22 H2 P3 Answers for Uploading updated 2023

2022 H2 Paper 3 Section A Answer all the questions in this section. 1(a) Describe the role of insulin in a healthy person. [4] 1. Insulin is a protein hormone secreted by the beta cells of the Islets of Langherhans in the pancreas when glucose levels in blood rises above the norm; 2. It travels through the blood stream to the liver and muscle cell and binds to receptors on the cell surface membrane; Cellular responses include: 3. Translocation of glucose transporters from the membrane of cytoplasmic vesicles to the cell surface membrane. This increases glucose intake into cells as it increases permeability of the cell to glucose; 4. Activation of glycogen synthase which catalyses glycogen synthesis from glucose; 5. Increased rate of glycolysis and increased lipid & protein synthesis; 6. Hence bringing blood glucose levels back to norm; (b) Identify a human disease, not including any type of diabetes, that: (i) is caused mainly by genes [1] Sickle cell anemia; Haemophilia; R: colourblindness as it is not considered a disease (ii) is caused mainly by environmental factors. [1] Malaria; Dengue; Influenza; Acquired Immunodeficiency Syndrome; (c) (i) Explain how monozygotic twins develop from a single zygote to become individuals that have DNA that is 100% the same. [4] 1. Undifferentiated* zygotic stem cells formed from fertilization of gametes 2. Are capable of undergoing extensive proliferation* via mitosis and self- renewal* 3. During interphase, Semi-conservative DNA replication* occurs to produce daughter DNA molecules that are genetically identical. 4. During anaphase* of mitosis, genetically identical sister chromatids are separate equally into opposite poles forming genetically identical daughter cells. 5. Zygote and cells up to the 8-cell embryo remains totipotent* and can differentiate* into all cell types that make up an organism including extra- embryonic tissue* such as placenta*, and hence are able to form entire organism; 6. This is a result of differential switching on of genes which occurs when appropriate molecular signals are received;

(ii) Outline what Table 1.1 shows about the relative influence of genotype and environment on the two types of diabetes. [2] 1. The % of monozygotic twins where both develop a particular form of diabetes is relatively low. 2. this shows that environmentat factors have a significant influence in the development of diabetes, since monozygotic twins are genetically identical, 3. Comparing monozygotic and dizygotic twins, % of sets of twins with both individuals having diabetes are significantly lower in dizygotic twins. 4. This show that genotype have an influcence on developing diabetes. 5. Comparing 2 types of diabetes, higher % of sets of twins with both individuals having diabetes are significantly higher for type 2 diabetes compared to type 1 both mono and dizygotic twins. 6. This implied that genotype might have a greater influence on type 2 than type 1 diabetes. (d) (i) Explain what is meant by a substitution mutation. Support your explanation by showing an example of a substitution mutation. [2] 1. Substitution mutation where a nucleotide/base is replaced by a different nucleotide; 2. An example is when thymine* is replaced by adenine* in the DNA template strand of the β globin* gene resulting in sickle cell anaemia*; (ii) The haploid human genome consists of three billion (3 x 109) base pairs. According to one estimate, one SNP occurs every 300 base pairs. Calculate the expected number of SNPs in a human gamete. [1] 3 ×10ଽ 300 =10 000 000 (iii) With reference to Fig. 1.1, evaluate whether the SNPs associated with type 1 diabetes are the same as the SNPs associated with type 2 diabetes. [3] 1. The SNPs associated with type 1 and type 2 diabetes were mostly different as most of them/all but 2 occurred on different chromosomes / at different parts of the chromosome if they were on the same chromosome; 2. With the exception of the SNPs located on chromosome 6 and 16; 3. The SNPs on chromosome 6 were in the same approximate location and were associated with both type 1 and type 2 diabetes, however there were fewer SNPs and also lower degree of association with type 2 diabetes (2 crosses and degree of association between 5 and 10) than type 1 diabetes (more crosses and degree of association ranging from 5 to15) A: quoting chromosome 16

(e) Suggest, with reasons, whether Fig. 1.2 indicates a genetic or an environmental cause for the increase in the percentage of people in the USA with diabetes from 1958 to 2015. [2] Genetic cause 1. The data in Fig. 1.2 shows a steady increase in the percentage of people with diabetes from 0.9% in 1958 to 7.5% in 2015; 2. suggesting that the frequency of alleles associated with diabetes increased; 3. due to improving healthcare over the years allowing with individuals with the SNPs/alleles associated with diabetes surviving and passing them on to their offspring; OR Environmental cause 4. The data showed a gradual increase from 0.9% in 1958 to 3.4% in 1995 and a steep increase from 1995 to 7.5% in 2015; 5. Suggesting that the changes in lifestyle related to the increase in technology and fast food culture might have contributed to the steep rise in percentage of people with diabetes after 1995. (f) (i) Compare the effects of sodium nitrite on the three species of gut bacteria shown in Fig. 1.3. [4] 1. For all three species of bacteria, lower concentration of sodium nitrate has a lower percentage inhibition but as concentration increases, there is a steep increase in the percentage inhibition; 2. 100% inhibition was achieved for B. coprocola and B. longum at 0.8 mg cm-3 and 3 mg cm-3 respectively while the highest percentage inhibition of E. faecalis was only 95% at 100 mg cm-3; 3. 100% inhibition was achieved at lower sodium nitrate concentration for B. coprocola at 0.8 mg cm-3 than B. longum at 3 mg cm-3; 4. Very low concentration of sodium nitrate at 0.001 mg cm-3 could cause some inhibition of B. coprocola, but at least 0.02 mg cm-3 cause was required to cause any inhibition of B. longum and E. faecalis; (ii) The three species of bacteria in Fig. 1.3 were identified using a molecular method. DNA sequences were obtained and compared to DNA sequences in an online database. Explain why it is difficult to identify bacterial species without using a molecular method. [2] 1. Bacteria tend to have few morphological features that they can be identified by, while molecular methods compares differences in DNA sequence which is more quantitative; 2. The proportion of these 3 bacteria could be very small relative to other bacteria in the gut, but molecular methods like PCR are able to amplify the target sequence of these 3 bacteria so even a small presence can be detected; 3. AVP

(iii) With reference to the three species of bacteria in Fig. 1.3 and Table 1.2, predict and explain the possible effects of a gut concentration of 1 mg cm-3 of sodium nitrite on human health. [4] 1. At 1 mg cm-3 of sodium nitrate, 100% of beneficial bacteria B. coprocola and B. longum growth will be inhibited; 2. only 6.25% of E. faecalis will be inhibited, with majority surviving in the gut; 3. individuals will experience an increase in harmful bacteria, E. faecalis and will therefore experience gut inflammation and a reduction in protective mucus lining the gut, leaving the individual most susceptible to other pathogens; 4. due to lack of B. coprocola to reduce inflammatory disease of the gut and B. longum to reduce inflammation and prevent autoimmune response the inflammation will be made worse; [Total: 30] 2(a) Identify one molecule from Fig. 2.1 or Table 2.1 that: (i) is a fatty acid [1] arachidonic acid (ii) breaks an ester bond [1] phospholipase A2 (iii) has a structural role [1]