Natural Sciences: Biology, Chemistry, and Physics Essentials
Biology
Know the cell as the basic unit of life: the membrane, cytoplasm, nucleus, mitochondria, chloroplasts, and cell wall. Distinguish plant from animal cells (cell wall, chloroplasts, large vacuole). Understand photosynthesis (carbon dioxide plus water plus light gives glucose plus oxygen, in chloroplasts) against respiration (glucose plus oxygen gives carbon dioxide, water, and energy, in mitochondria). Revise heredity - dominant and recessive alleles, genotype versus phenotype, and simple monohybrid crosses - plus the main organ systems and basic ecology: food chains, producers, consumers, decomposers.
Chemistry
Separate elements, compounds, and mixtures; read the periodic table for atomic number, group, and period; balance simple equations; and distinguish physical from chemical change. Learn the pH scale (below 7 acidic, 7 neutral, above 7 basic), the difference between an atom, an ion, and a molecule, and the common reaction types: synthesis, decomposition, single and double replacement, combustion. A frequent trap is confusing a coefficient with a subscript - changing a subscript alters the substance, which is never allowed when balancing.
Physics
Expect speed, acceleration, force, pressure, work, energy, power, and simple electric circuits. Use v = s/t, F = ma, p = F/A, W = F·s, P = W/t, and Ohm's law U = I·R. Convert units carefully: km/h to m/s means dividing by 3.6.
Worked example
A car travels 150 m in 10 s. Speed is 150 / 10 = 15 m/s. In km/h that is 15 × 3.6 = 54 km/h. The trap is multiplying by 3.6 in the wrong direction; the number of km/h is always larger than the number of m/s.
Rule of thumb
Write the quantity, its symbol, and its unit before calculating. Most lost marks in this section come from unit mismatches, not from unfamiliar science.