Sciences: Physics, Chemistry and Biology Essentials
Physics
Know the states of matter and changes of state, mass versus weight, density, simple electric circuits (series and parallel, conductors and insulators), magnetism, light travelling in straight lines, reflection, and the water cycle as a physical system. Traps: confusing mass (kg, unchanged) with weight (newtons, varies with gravity); forgetting that in series the current is the same everywhere while voltage divides; assuming all metals are magnetic (only iron, nickel, cobalt and some alloys are).
Chemistry
Know the difference between a mixture and a pure body, separation methods (filtration, decantation, evaporation, distillation), the signs of a chemical reaction (gas, precipitate, colour change, heat), acids and bases with indicator colours, air composition (roughly four-fifths nitrogen, one-fifth oxygen, plus carbon dioxide and rare gases), combustion needing oxygen, and the water molecule H₂O. Traps: calling dissolution a chemical reaction (it is physical); confusing an atom with a molecule.
Biology
Revise the parts of a plant and their functions, photosynthesis (needs light, water, carbon dioxide; produces glucose and oxygen), respiration, food chains and the role of decomposers, the human digestive, respiratory and circulatory systems, hygiene, and disease prevention. Traps: reversing photosynthesis and respiration equations; forgetting that energy flows one way through a food chain while matter cycles.
Rule of thumb
Whenever a question asks "why", answer with the mechanism: what enters, what changes, what leaves.
Worked example
A sealed jar contains a burning candle. The flame goes out. Explanation: combustion consumes oxygen and produces carbon dioxide; oxygen is used up, so combustion stops. This is a chemical change, not a change of state.