Natural Sciences (Physics, Chemistry, Biology)
Core concepts
Physics: mechanics (forces, Newton's laws, energy conservation), electricity and magnetism, waves and optics, and thermodynamics. Chemistry: atomic structure, periodic trends, bonding, reaction equations, stoichiometry, acids and bases, redox, and organic functional groups. Biology: cell biology, genetics and inheritance, evolution, homeostasis, ecology, and human physiology.
Traps examiners set
- Unit errors: mixing grams and kilograms or centimetres and metres before substituting into formulas.
- Unbalanced equations and forgetting to state phases or conditions.
- Moles versus mass: using molar mass in the wrong direction.
- Genetics: confusing genotype with phenotype, or misapplying the sum and product rules in dihybrid crosses.
- Homeostasis: naming the hormone but not the negative-feedback loop and its target organ.
Rule of thumb
Always write the given quantities with units, the formula, the substitution, and the answer with units. In chemistry, balance the equation before any stoichiometric calculation. In biology, answer mechanism questions as a chain: stimulus → receptor → control centre → effector → response.
Worked example
How many grams of water form when 4.0 g of hydrogen reacts completely with oxygen? The equation 2H₂ + O₂ → 2H₂O gives 4.0 g H₂ ≈ 2.0 mol, producing 2.0 mol H₂O ≈ 36 g. Skipping the mole step and comparing masses directly is the standard error.
Exam technique
Sketch diagrams, label axes with units, and state assumptions. In biology, use correct terminology rather than everyday words.