N19 H2 P3 ans for uploading_updated 2023

2019 H2 A level Paper 3 2019 H2 Biology A Level Paper 3 [Turn over Section A Answer all the questions in this section. 1 (a) (i) Name the term used to describe the organisation of species according to their evolutionary relationships, as shown in Fig. 1.1. [1] Phylogeny* (ii) State how the information needed to construct a diagram such as that shown in Fig. 1.1 can be obtained through molecular techniques. [4] 1. Amplify DNA sequences of a homologous* gene common to all the species of organisms being compared via polymerase chain reaction; 2. Sequence the DNA fragments obtained from the different organisms; 3. Align the DNA sequences and calculate/compare the differences between them; 4. Species that are closely related have more similar nucleotide sequences than do distantly related species and should be shown to diverge from a more recent common ancestor in the phylogenetic tree. (iii) The five species named in Fig. 1.1 all share the characteristic of making curcumin. These five species have never all been classified together in a single genus. Explain why the characteristic of making curcumin is not sufficient to place all five species in the same genus. [2] 1. Compared only 1 characteristic which is insufficient evidence to show that they belong to the same genus; 2. The 5 species could still be significantly different morphologically compared to those in the same genus. R: successful interbreeding to give fertile viable offspring. (iv) The five species named in Fig. 1.1 occur in just two of the 400 or more families of flowering plants that exist. Suggest why the ability to make curcumin is limited to these two families of plants. [2] 1. The two families must have diverged from a common ancestor which had the ability to make curcumin; 2. The trait for making curcumin first emerged in this common ancestor. (b) (i) With reference to Fig. 1.2, describe the effect of curcumin on the percentage of cancer cells in each phase of interphase nine hours after entering G1 phase. [3] 1. The higher the concentration of curcumin the cells were exposed to, the greater the percentage of cancer cells still in G1 phase* nine hours later; 2. cite data from graph comparing 2 curcumin concentrations and the percentage of cancer cells at G1 phase. E.g. 76% of cells at G1 phase in 40 μmol dm-3 curcumin higher than 20% of cells at G1 phase in 0 μmol dm-3 curcumin. 3. The higher the concentration of curcumin the cells were exposed to, the lower the percentage of cancer cells in S phase* nine hours later;

2 2019 H2 Biology A Level Paper 3 4. cite data from graph comparing 2 curcumin concentrations and the percentage of cancer cells at S phase. E.g. 17% of cells at S phase in 40 μmol dm-3 curcumin lower than 74% of cells at S phase in 0 μmol dm-3 curcumin. 5. No significant effect of curcumin on