Science
Five units, one style of question
Grade 9 science draws on biological diversity, matter and chemical change, environmental chemistry, electrical principles and technologies, and space exploration. Expect definitions, diagram interpretation, data tables, and “which explanation is best” reasoning.
Concepts to hold
Biological diversity: variation within a species, heritable versus acquired traits, natural selection, and threats such as habitat loss and invasive species. Chemistry: atomic number (protons) versus mass number (protons + neutrons); periodic table groups; physical change versus chemical change (a new substance with new properties); word equations; acids (pH below 7) neutralizing bases. Environmental chemistry: organic versus inorganic compounds, nutrients as pollutants, and bioaccumulation up a food chain. Electricity: voltage drives current through resistance, V = IR; in series, current is the same everywhere and voltage divides; in parallel, voltage is the same and current divides. Space: seasons come from the tilt of Earth's axis, not distance from the Sun; moon phases come from changing viewing angles, not Earth's shadow - that is a lunar eclipse.
Traps
Read coefficients and subscripts carefully: 2H₂O has four hydrogen atoms. Dissolving sugar is a physical change, not a chemical one. A “brighter bulb” answer usually needs a current argument, not voltage alone.
Worked example
A 12 V battery is connected across a 4 Ω resistor. I = V/R = 12/4 = 3 A. Double the resistance to 8 Ω and the current halves to 1.5 A.
Rule of thumb
Ask of every explanation: does it name the mechanism (tilt, viewing angle, current, new substance) or only describe what you see?