RI 2020 A level H2 P2

2020 H2 A level Paper 2 2020 H2 Biology A Level Paper 2 [Turn over Answer all questions. 1 Fig. 1.1 is an electronmicrograph showing parts of two liver cells. (a) Name the structures labelled A, B and C in Fig. 1.1. A Mitochondrion B Nucleus C Cell surface membrane or plasma membrane [3] (b) Membranes are used within cells to create separate compartments. Explain the advantages to cells of having separate compartments. [3] 1. Within a cell, compartmentalization allows the formation of unique environments optimal for specialized activities; 2. such as enzyme reactions where enzyme and substrate can accumulate at high concentration to increase the rate of enzyme-catalyzed reaction; 3. Enzymes and substrate involved in related metabolic reactions can be localized in the same compartment to increase the rate of enzyme-catalyzed reaction; 4. e.g Enzymes and substrates involved in Krebs cycle in mitochondria matrix or Calvins cycle in stroma of chloroplast; 5. Maintenance of optimal pH for enzyme action; 6. e.g. acidic pH for lysosomal enzymes in lysosomes; 7. For the establishment of proton gradients within specialized organelles such as mitochondria and chloroplasts for chemiosmosis and formation of ATP; 8. Allows storage of molecules within a separate environment to prevent degradation by other enzymes; 9. e.g. storage of starch in amyloplast; Any 3 of the above

2 2020 H2 Biology A Level Paper 2 Table 1.1 shows the percentage of the total area of all membranes of a liver cell contributed by each type of membrane. Table 1.1 Table 1.2 shows the percentage of the total volume of a liver cell contributed by each type of membrane-bound compartment. Table 1.2 (c) Explain the difference between the percentage of total cell membrane area contributed by the inner mitochondrial membrane and the percentage of total cell membrane area contributed by the outer mitochondrial membrane, as shown in Table 1.1. [3] 1. Inner mitochondria membrane take up 25% more total cell membrane area than the outer mitochondria membrane; 2. Inner mitochondria membrane/Cristae is highly folded to increase surface area; 3. Allowing more electron carriers* of electron transport chain and ATP synthase* to be embedded in it; 4. To increase the rate of oxidative phosphorylation/ATP* production; 5. Outer mitochondria membrane is not folded, hence smaller total cell membrane area;

3 2020 H2 Biology A level Paper 2 [Turn over (d) The ratio of the percentage of total cell membrane area to percentage of total cell volume for the nucleus is approximately 0.07 : 1. (Note to student: 0.4:6 = 4:60 = 0.07:1) (see on tables 1.1 and 1.2) (i) Use Table 1.1 and Table 1.2 to calculate the ratio of the percentage of total cell membrane area to percentage of total cell volume for th