HCI H2 Bio 2024 Prelim P2 Ans

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Examination Paper 2 / MS 1 HWA CHONG INSTITUTION (COLLEGE SECTION) 2024 JC2 9744 H2 BIOLOGY PRELIMINARY EXAMINATIONS PAPER 2 MARK SCHEME QUESTION 1 (a) Describe one feature visible in Fig. 1.1 that identifies the amoeba as a eukaryotic organism.[1] 1 it contains a true nucleus / a membrane bound nucleus / membrane bound organelle like the food containing vacuole (b)(i) Explain how the structure of the contractile membrane enables it to perform its function. [ 4] 1 presence of protein pumps / carriers for ions embedded on the contractile vacuole membrane 2 allow for active transport / pumping of ions into the lumen of contractile vacuole 3 resulting in the solute potential of the lumen being high / the lumen of the vacuole being of more negative water potential than the cytoplasm 4 so that excess water can enter the contractile vacuole by osmosis and expelled from the cell by exocytosis 5 presence of hydrophobic core of phospholipid bilayer / membrane 6 results in the membrane of contractile vacuole being impermeable to ions 7 allows accumulation of ions in the / prevents ions from leaving the lumen of the contractile vacuole so that solute potential of the lumen is high 8 so that excess water can enter the contractile vacuole by osmosis and expelled from the cell by exocytosis 9 contractile vacuole is made by phospholipids that form a bilayer / phospholipid bilayer 10 presence of weak hydrophobic interactions between fatty acid tails of the phospholipids / within the hydrophobic core 11 allow for membrane fluidity 12 that helps in fusion of the contractile vacuole with the cell surface membrane for exocytosis of water 13 presence of water channels / aquaporin embedded on the contractile vacuole membrane 14 allow for facilitated diffusion of water into the lumen of the contractile vacuole 15 so that excess water can enter the contractile vacuole by osmosis and expelled from the cell by exocytosis ref. to water moving from region of less negative water potential to region of more negative water potential 16 ref. to fluidity of the membrane allows for fusion of many small vesicles to the contractile vacuole to allow the vacuole to expand / increase in size (b)(ii) Explain how organelles of the endomembrane system are involved in the synthesis of proteins embedded within the membranes of contractile vacuoles. [4] 1 mRNA coding for proteins are translated by rough endoplasmic reticulum (RER) bound ribosomes forming polypeptides 2 movement of polypeptide into lumen of RER is halted when the polypeptide is midway through and the polypeptide continues to fold, resulting in a protein that is embedded in RER membrane 3 Transport vesicles with such proteins bud off the RER

HWA CHONG INSTITUTION / 2023-2024 H2 BIOLOGY / Preliminary Exam