ZHSS 2024 P2 MS ANS

ZHSS 2024 Prelim Paper 2 Answers Section A [70 marks] Q/no. Answer Mark 1ai • Cell wall [1] 1aii • Deoxyribonucleic acid / DNA [1] 1aiii • Attaching/sticking to surfaces of host cells/objects (for infection/colonisation). • Joining other bacteria to exchange genetic material (i.e., gene transfer). Any 1 [1] 1b • Kissing. • Sexual activity/intercourse. • Sharing of eating utensils. • Touching surfaces contaminated by infected person then puts hand in mouth. Any 2 [2] 1c • Bacteria will evolve to become resistant to antibiotics / May increase the number of antibiotic-resistant strains of the bacteria. • May cause antibiotics to become less effective/ineffective when it is used to treat severe cases. • Antibiotics do not shorten the illness / reduce the duration of symptoms (diarrhoea, fever, stomach cramps). [2]

• Antibiotics can prolong the time a person carries the bacteria, which increases the risk of infecting others. Any 3 1d • Nucleus controls cell activities/cell growth/repair of worn-out parts / essential for cell division / contains DNA/genetic material/chromosomes/chromatin. • Chloroplast contains chlorophyll for photosynthesis. • Vacuole contains cell sap which stores dissolved substances/sugars/minerals salts/amino acids. • Mitochondrion is the site of aerobic respiration to provide energy for the cell. • Golgi body/apparatus chemically modifies substances made by the ER / stores and packages substances in vesicles for secretion out of the cell. • Rough endoplasmic reticulum transports proteins made by ribosomes to Golgi body/apparatus for secretion out of the cell. • Smooth endoplasmic reticulum synthesises fats/steroids/hormones / detoxification/converts harmful substances into harmless substances. Any 3 [4] 2a Diffusion Active transport • Does not require energy. Requires energy. • Molecules/particles/substances move from a region of higher concentration to a region of lower Molecules/particles/substances move from a region of lower concentration to a region of higher concentration / against a concentration gradient. [3]

concentration / along a concentration gradient. • Occurs regardless of the presence of a partially permeable membrane. Occurs in the presence of a partially membrane. 2bi • All the glucose and amino acids, and some salts are selectively reabsorbed from the tubules/nephron into the blood/capillaries. • Glomerular filtrate (in tubules) has a higher water potential than the blood (in capillaries). • Water molecules leaves the glomerular filtrate through the partially permeable membrane of cells and into the blood by osmosis. • Most water is reabsorbed at the loop of Henle by osmosis and forms part of the urine [4] 2bii • ADH increases the permeability of the cells in the walls of the collecting duct (V). • More water is reabsorbed from the collecting duct into the blood capillaries. [2] 3a • When a stimulus disrupts a system/body,