RI 2020 A level H2 P3

2020 H2 A level Paper 3 2020 H2 Biology A Level Paper 2 [Turn over Section A Answer all questions. 1 Animals that possess hair are classified within the phylum Chordata and class Mammalia. (a) Define biological classification and explain how classification relates to phylogeny.[3] 1. Biological classification groups organisms based on overall morphological similarities and usually does not consider their evolutionary history; 2. It uses a naming system where each organism is given a binomial name* and grouped into a domain, kingdom, phylum, class, order, family, genus and species in a hierarchical manner; 3. Phylogeny also groups organisms but they are grouped based on their evolutionary history / ancestor-descendent relationships using molecular data and; 4. It does not rank organisms but instead assigns each organism a position on a phylogenetic tree* based on its evolutionary relationship with other organisms on the tree; (b) (i) Epithelial stem cells and melanocyte stem cells are examples of a particular type of stem cell. State two key features of this type of stem cell. [2] 1. They are multipotent* stem cells that can differentiate into a limited range of specialized cell types in the presence of the correct molecular signals; 2. They are able to undergo extensive proliferation and self-renewal by mitosis* in the presence of the correct molecular signals and hence give rise to a constant pool of cells; (ii) Discuss how the presence of stem cells within the skin and the presence of hairs covering the skin influence the harmful effects of high levels of ultraviolet light on the health of mammals. [4] 1. The presence of hairs covering the skin play a protective role as they reduce exposure of the skin by blocking the harmful ultraviolet radiation; 2. Since stem cells are near the skin surface , the high levels of ultra violet light can damage the DNA is stem cells as; 3. the ionizing radiation can cause the DNA is the stem cells in the skin to mutate and if these mutations are in genes that regulate cell cycle checkpoints/proto oncogenes/ tumour suppressor genes; 4. it could lead to uncontrolled cell division/ tumour formation and increase the chances of an individual getting cancer; 5. especially because stem cells already have telomerase activity;

2 2020 H2 Biology A Level Paper 3 (c) (i) The shape of MC1R is characteristic of a particular group of transmembrane receptor proteins. Name this group of proteins.[1] 7 pass transmembrane G-protein coupled receptor *

3 2020 H2 Biology A level Paper 3 [Turn over (ii) In cats with agouti hairs, ASIP is secreted at intervals during hair growth. With reference to Table 1.1 and the information provided, explain how this interrupted pattern of ASIP secretion leads to striped agout