Natural Sciences Elective (Biology, Chemistry, Physics)
Biology
Revise cell structure and division, DNA and protein synthesis, Mendelian genetics, evolution by natural selection, and human physiology - digestion, circulation, respiration, excretion, and the nervous and endocrine systems. Be able to interpret a pedigree, complete a Punnett square, and explain the difference between mitosis and meiosis. Ecology questions often ask about energy flow, trophic levels, and the carbon cycle.
Chemistry
Know atomic structure, periodic trends, ionic and covalent bonding, intermolecular forces, mole calculations, balancing equations, acid–base reactions, pH, redox, and organic functional groups. Practise stoichiometry with limiting reagents, and distinguish empirical from molecular formulae. Safety and apparatus questions reward precise terminology.
Physics
Cover kinematics, Newton's laws, work and energy, momentum, electricity and circuits, waves and optics, and thermal physics. Draw free-body diagrams and state sign conventions before calculating. Unit conversion is a major source of error: convert grams to kilograms, centimetres to metres, and minutes to seconds before substituting.
Worked example
For 2H₂ + O₂ → 2H₂O, 4 g of H₂ is 2 mol. The equation requires 1 mol O₂, which is 32 g, and produces 2 mol H₂O, which is 36 g. If only 16 g of O₂ is available, oxygen is limiting and the expected water mass is 18 g. Rule of thumb: convert to moles, identify the limiting reagent, then convert back to the requested unit.