RI N22 H2 P3 Answers

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 gr