2024 VJC H2 Bio P2 MS

1 2024 H2 Biology Prelim Paper 2 Answer 1 Amoeba is a single-celled organism of the kingdom Protista. Am oeba gets its nutrients in a heterotrophic manner, taking in food from its surroundings. Fig. 1.1 shows the electron micrograph of an amoeba. Fig. 1.1 (a) With reference to Fig. 1.1 and the information provided, (i) identify structure X and Y and state a structural difference between them. [2] Identify  X: mitochondrion, Y: vesicle / phagocytic vesicle / food vacuole; Structural difference  X is double membrane bound / presence of cristae while Y is si ngle membrane bound / no infolding of membranes; (ii) explain the importance of structure X to the amoeba. [3]  Mitochondrion (X) allows for respiration to take place to produce ATP;  ATP is required for important metabolic processes within amoeba;  ATP is also important for phagocytosis / endocytosis process t o occur for amoeba to take in food from surrounding;

2 (b) Marseillevirus is a virus that infects amoeba. It is taken up by amoeba via phagocytosis. Upon membrane fusion, new progeny viruses are formed through DN A replication and protein synthesis. The progeny viruses are then released as the amoeba is lysed. Fig. 1.2 shows the structure of Marseillevirus. Fig. 1.2 With reference to Fig. 1.2 and the information provided, explai n how Marseillevirus challenges the cell theory. [3]  Identify why Marseillevirus is not considered as a cell making reference to figure 1.2;  Identify how Marseillevirus exhibits living characteristics with reference to the context;  Identify one tenet of the cell theory that it challenges (cell s are the basic unit of life / all living things are made from cells and all cells come from pre existing cells);

3 2 Some structural features of phospholipids are listed in Table 2.1. Table 2.1 features affect role in cell surface membrane synthesised by condensation hydrophobic fatty acid chains √ unsaturated fatty acid chains √ saturated fatty acid chains √ (a) (i) Indicate, with the use of a tick (√), which of the structural features in Table 2.1 affect the role of phospholipids in the cell surface membrane. [1] (ii) Outline how a property of phospholipids allows them to form an effective barrier as the cell surface membrane. [1]  Amphipathic nature of the phospholipid, having both hydrophilic and hydrophobic regions allow the formation of effective lipid bilayer as barrier; (b) Many multicellular organisms produce antimicrobial polypeptide s (APs) that protect them against prokaryotes. Fig. 2.1 shows one type of AP that acts on the cell surface membrane of prokaryotes. Fig. 2.1

4 Fig. 2.2 shows further information about a channel formed in th e cell surface membrane by the APs. Fig. 2.2 Using Fig. 2.2, calculate the cross-sectional area of the chann el through which ions can pass. Use π = 3.14 in your calculation. Give