RI Nov 17 H2 P2 ans

Raffles Institution Nov 2017 (H2 Biology) Paper 2 2023 Nov 2017 H2 Bio Paper 2 N17P2Q1 (a) (i) State the number of glycogen molecules shown in Fig. 1.1. [1] 2 (ii) Name the type of molecule forming the central core of the glycogen granule, in Fig. 1.1. [1] Protein / polypeptide (iii) Suggest the role of the molecule forming the central core of the glycogen granule. [1] 1. binds / holds 2 glycogen molecules together; 2. enzymes that catalyse the synthesis of glycogen (b) Explain how the structure of glycogen is related to its role in living organisms. [4] 1. Large molecule/long chain so insoluble in water ; 2. Hence does not affect water potential of cells / no osmotic effect ; 3. Helical molecule so more glucose* units per unit volume, thus compact structure for storage ; 4. Extensively branched so provides many ends for hydrolysis of glycosidic bonds ; 5. which releases more glucose* molecules per unit time ; (c) Describe how the structure of cellulose is different from the structure of glycogen. [3] Cellulose Glycogen monomer β-glucose* α-glucose* bonds β-1,4 glycosidic bonds* α-1,4 and α-1,6 glycosidic bonds* Orientation of monomer Alternate glucose units are rotated 180 0/inverted with respect to each other All glucose units in the chain have same orientation Structure of each molecule forming straight / linear unbranched chains ; Forms helical coil which is extensively branched ; Bonds between molecules Hydroxyl groups projecting outwards in both directions allow intermolecular/ interchain hydrogen bonding  leading to microfibril formation for cellulose No interchain hydrogen bonding in glycogen Note: must be written in full sentences

Raffles Institution Nov 2017 (H2 Biology) Paper 2 2023 N17P2Q2 (a) (i) Explain why proteins are required for the transport of glucose across the cell surface membrane. [3] 1. Glucose is polar* and thus, hydrophilic*; 2. Glucose is too large to pass through the transient pores of the phospholipid bilayer ; 3. The hydrophobic core* of the phospholipid bilayer would repel glucose ; 4. Transport proteins / protein channel provides a hydrophilic* channel/pore through the membrane for the passage of the solutes; (ii) Describe the structural features of a protein that enable it to transport glucose into a cell. [2] 1. The protein is a transmembrane protein that; 2. has amino acid* residues with R groups that is non-polar / uncharged, allowing it to form hydrophobic interactions* with the hydrophobic core* of the phospholipid bilayer*; 3. The protein has a hydrophilic* pore/channel that is lined with amino acids* with polar / charged R groups that allows hydrophilic gluc