BJC General Science cheat sheet

Hypothesis: a testable, falsifiable prediction stated before data collection; it must be able to fail.

Variables: independent = changed by investigator; dependent = measured response; controlled = held constant.

Control group receives no treatment or a placebo, giving a baseline for comparison with the experimental group.

Validity: the experiment tests what it claims; reliability: repeated trials give consistent results.

Hazard symbols: corrosive (skin damage), flammable (ignition risk), oxidising (feeds fire), toxic (poison).

Safety rules: tie back hair, wear goggles, never taste chemicals, waft vapours toward the nose, add acid to water.

Data types: quantitative = numerical measurements; qualitative = descriptive observations.

Graph choice: line graph for continuous change, bar chart for categories, scatter for correlation between two variables.

SI base units: metre (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), mole (amount).

Prefixes: kilo = 1000, centi = 0.01, milli = 0.001; convert by moving the decimal point three places per kilo–milli step.

Volume: 1 cm³ = 1 mL; 1000 cm³ = 1 L; 1 m³ = 1 000 000 cm³.

Density formula: density = mass ÷ volume, units g/cm³ or kg/m³; rearrange to mass = density × volume.

An object floats in a fluid when its density is less than the fluid's; it sinks when its density is greater.

Measuring cylinder: read the bottom of the meniscus at eye level to avoid parallax error.

Mass is the amount of matter (kg); weight is the force of gravity on that mass (N), so weight changes with location.

Precision = closeness of repeated readings; accuracy = closeness to the true value.

Element: one type of atom; compound: two or more elements chemically combined in fixed ratio; mixture: not chemically combined.

Particle model: solids vibrate in fixed positions, liquids slide past each other, gases move fast and far apart.

Changes of state: melting, freezing, evaporation, condensation, sublimation; mass is conserved throughout.

Filtration separates an insoluble solid from a liquid; the residue stays on the paper, the filtrate passes through.

Evaporation or crystallisation recovers a dissolved solid from its solution.

Simple distillation separates a solvent from a solution by boiling then condensing the vapour.

Chromatography separates dissolved substances by differing solubility and travel up the paper.

A pure substance melts and boils at a single sharp temperature; impurities lower the melting point and raise the boiling point.

Cell structures: nucleus (genetic control), cytoplasm (reactions), membrane (control of entry), mitochondria (respiration), ribosomes (protein synthesis).

Plant-only structures: cellulose cell wall, chloroplasts for photosynthesis, and a large permanent vacuole.

Photosynthesis: carbon dioxide + water → glucose + oxygen, requiring light and chlorophyll.

Respiration: glucose + oxygen → carbon dioxide + water + energy; occurs in all living cells.

Enzymes are protein catalysts; each has an optimum temperature and pH, and is denatured by high temperature.

Nutrients: carbohydrates and fats for energy, protein for growth and repair, vitamins and minerals for health, fibre and water.

Root hair cells absorb water by osmosis and mineral ions by active transport; xylem carries water up, phloem carries sugars.

Diffusion moves particles down a concentration gradient; osmosis is water movement across a partially permeable membrane.

Digestion: mechanical breakdown plus enzymes; absorption of nutrients occurs mainly in the small intestine via villi.

Circulation: double system; arteries carry blood away from the heart, veins return it, capillaries allow exchange.

Gas exchange occurs in alveoli, which have thin walls, a large surface area, and a rich blood supply.

Breathing mechanics: intercostal muscles and diaphragm contract to increase chest volume and lower pressure, drawing air in.

Excretion: kidneys filter blood, reabsorb useful substances, and remove urea and excess water as urine.

Nervous system: receptors detect stimuli; impulses travel via sensory neurone, relay neurone, motor neurone to effectors.

Hormones are slower, longer-lasting chemical messengers carried in the blood; insulin controls blood glucose.

Health risks: smoking damages alveoli and raises cancer risk; excess sugar and inactivity raise type 2 diabetes risk.

Sexual reproduction fuses gametes (sperm and egg) to form a zygote; offspring show genetic variation.

Asexual reproduction produces genetically identical clones from one parent, e.g. runners, bulbs, cuttings.

Genes are sections of DNA on chromosomes; humans have 46 chromosomes in 23 pairs in body cells.

Alleles: dominant alleles are expressed when present; recessive alleles only when both are recessive.

Genotype is the allele combination; phenotype is the observable characteristic.

Punnett square: cross parental gametes to predict offspring ratios, e.g. 3:1 phenotype for two heterozygous parents.

Sex determination: XX gives female, XY gives male; the father's sperm determines the sex of the child.

Variation arises from genetic differences, mutation, and environmental factors; natural selection acts on this variation.

Food chain order: producer → primary consumer → secondary consumer; arrows show the direction of energy flow.

Energy is lost at each trophic level through respiration, heat, and waste, so pyramids of energy narrow sharply.

Abiotic factors: light, temperature, water, oxygen, soil pH; biotic factors: predators, competition, disease.

Population size is affected by births, deaths, immigration, and emigration.

Carbon cycle: photosynthesis removes carbon dioxide; respiration, combustion, and decomposition release it.

Eutrophication: fertiliser runoff adds nitrates, algae bloom, decompose, and oxygen depletion kills fish.

Conservation strategies: protected areas, captive breeding, seed banks, habitat corridors, and reducing pollution.

Bioaccumulation: persistent toxins become more concentrated at higher trophic levels.

Force is measured in newtons; a resultant force of zero means balanced forces and no change in motion.

Weight = mass × gravitational field strength (W = mg); on Earth g ≈ 10 N/kg.

Speed = distance ÷ time; velocity includes direction; acceleration = change in velocity ÷ time.

Friction opposes motion and transfers kinetic energy to heat; air resistance increases with speed and surface area.

Newton's third law: every action has an equal and opposite reaction on a different object.

Energy forms: kinetic, gravitational potential, elastic, thermal, chemical, nuclear; total energy is conserved.

Kinetic energy = ½mv²; gravitational potential energy = mgh; work done = force × distance.

Pressure = force ÷ area; pressure increases when force rises or area falls.

Series circuit: same current everywhere, voltage shared, total resistance adds; one break stops all current.

Parallel circuit: same voltage across each branch, current splits, total resistance is lower than any branch.

Ohm's law: V = IR; power = VI = I²R; energy transferred = power × time.

Current is measured in amperes with an ammeter in series; voltage in volts with a voltmeter in parallel.

Magnetic field lines run from north to south outside a magnet; like poles repel, unlike poles attract.

Electromagnet strength increases with more turns, higher current, and an iron core.

Wave equation: speed = frequency × wavelength; frequency in hertz, wavelength in metres.

Transverse waves (light) oscillate perpendicular to travel; longitudinal waves (sound) oscillate parallel; sound needs a medium.

Earth's structure: crust, mantle, outer core (liquid), inner core (solid); tectonic plates move on the mantle.

Rock types: igneous forms from cooled magma, sedimentary from compacted layers, metamorphic from heat and pressure.

The rock cycle links melting, cooling, weathering, erosion, deposition, and metamorphism.

Solar system order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Day and night result from Earth's rotation; seasons result from axial tilt as Earth orbits the Sun.

Moon phases arise from the changing angle between Earth, Moon, and Sun; a lunar month is about 29.5 days.

Gravity keeps planets in orbit; orbital speed falls with distance from the Sun.

Fossil fuels are finite; renewable resources include solar, wind, hydroelectric, and geothermal energy.

Chemical reaction signs: new substance, colour change, gas produced, temperature change, precipitate formed.

Conservation of mass: total mass of reactants equals total mass of products in a closed system.

Word equation format: reactants → products; balance symbol equations so each element's atoms match.

Acids release hydrogen ions in water; they turn litmus red and react with metals to give hydrogen gas.

Neutralisation: acid + base → salt + water; acid + carbonate → salt + water + carbon dioxide.

pH scale 0–14: below 7 acidic, 7 neutral, above 7 alkaline; each step is a tenfold change in hydrogen ion concentration.

Indicators: litmus (red/blue), universal indicator (colour chart), phenolphthalein (colourless in acid, pink in alkali).

Rates of reaction increase with higher temperature, higher concentration, greater surface area, or a catalyst.

Peer review checks methods and conclusions before publication, improving scientific reliability.

A scientific theory is supported by repeated evidence and can be revised when new data appear.

Renewable vs non-renewable resources: renewables are replenished naturally; fossil fuels are finite and add carbon dioxide.

Risk assessment compares the likelihood of harm with the severity of harm and identifies control measures.

Ethical issues in science include informed consent, animal testing, genetic modification, and data privacy.

Technology applications: vaccines prevent disease, water treatment removes pathogens, fertilisers boost crop yield but pollute.

Life-cycle analysis evaluates a product's environmental impact from raw material to disposal.

Correlation does not prove causation; controlled trials are needed to establish cause and effect.