PNG Grade 10 Science cheat sheet

Cell structures and jobs: nucleus holds DNA and controls activity, mitochondria carry out aerobic respiration, ribosomes build proteins, chloroplasts (plants only) carry out photosynthesis, and the plant cell wall is made of cellulose.

Photosynthesis: carbon dioxide + water → glucose + oxygen (6CO2 + 6H2O → C6H12O6 + 6O2), powered by light absorbed by chlorophyll in chloroplasts.

Aerobic respiration: glucose + oxygen → carbon dioxide + water + energy (C6H12O6 + 6O2 → 6CO2 + 6H2O); anaerobic respiration in muscles gives lactic acid and much less energy.

Diffusion is the net movement of particles from high to low concentration; osmosis is the movement of water through a partially permeable membrane from a dilute solution to a more concentrated one.

Mitosis gives two identical diploid cells for growth and repair; meiosis gives four haploid gametes and creates variation by crossing over and random chromosome assortment.

Blood vessels: arteries carry blood away from the heart (thick muscular walls, high pressure, no valves); veins carry blood back to the heart (thin walls, valves); capillaries are one cell thick for exchange.

Human chromosomes come in 23 pairs; two alleles control each gene, a dominant allele shows even in a heterozygote, and sex is determined by the XY pair (XX female, XY male).

Digestive enzymes are specific: amylase breaks starch to maltose, protease breaks protein to amino acids, lipase breaks fats to fatty acids and glycerol.

Energy in a food chain flows producer → primary consumer → secondary consumer; only about 10% passes to the next level, and decomposers return nutrients to the soil.

Atomic particles: proton has charge +1 and sits in the nucleus, neutron has charge 0 and sits in the nucleus, electron has charge –1 and orbits in shells; atomic number = number of protons; mass number = protons + neutrons.

Electron shell filling is 2, 8, 8; the group number in the periodic table equals outer-shell electrons and the period number equals the number of occupied shells.

Ionic bonding: a metal loses electrons to become a positive ion (Na⁺) and a non-metal gains electrons to become a negative ion (Cl⁻), giving a giant lattice such as NaCl.

Covalent bonding: non-metal atoms share electron pairs, as in H2O, CO2, O2 and CH4; simple molecular substances have low melting points.

Acids have pH below 7, alkalis have pH above 7 and pH 7 is neutral; neutralisation is acid + base → salt + water, e.g. HCl + NaOH → NaCl + H2O.

Reactivity series (most to least reactive): K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au; metals above carbon are extracted by electrolysis, metals below carbon by heating with carbon.

In every reaction the total mass of reactants equals the total mass of products (conservation of mass), so equations must be balanced by adding coefficients, never by changing formulas.

Reaction rate increases with higher temperature, higher concentration, larger surface area (smaller pieces) and with a catalyst, which speeds the reaction without being used up.

Relative formula mass is the sum of the relative atomic masses in a formula, e.g. H2O = 2(1) + 16 = 18, and the mole is the amount containing 6.02 × 10²³ particles.

Motion formulas: speed v = d/t, acceleration a = (v – u)/t, and v = u + at for uniform acceleration; distance is in metres, time in seconds, speed in m/s.

Newton's laws: objects stay at rest or in uniform motion unless a net force acts; F = ma where force is in newtons and mass in kilograms; every action has an equal and opposite reaction.

Weight is the force of gravity on a mass, W = mg with g ≈ 9.8 N/kg on Earth, so a 10 kg object weighs about 98 N; mass in kg does not change with location.

Work = force × distance (joules); power = work ÷ time (watts); kinetic energy KE = ½mv²; gravitational potential energy GPE = mgh.

Ohm's law V = I × R; in a series circuit the current is the same everywhere and R total = R1 + R2; in a parallel circuit the voltage is the same across branches and 1/R total = 1/R1 + 1/R2.

Electrical power P = V × I = I²R, and energy used = power × time; domestic energy is billed in kilowatt-hours (1 kWh = 3.6 MJ).

Wave equation v = fλ; frequency is in hertz, wavelength in metres; sound is a longitudinal wave that needs a medium, while light is a transverse electromagnetic wave that travels through a vacuum at 3 × 10⁸ m/s.

Light rules: angle of incidence = angle of reflection; light entering a denser medium bends towards the normal and leaving it bends away; total internal reflection happens above the critical angle.

Density = mass ÷ volume; pressure = force ÷ area (pascals); liquid pressure increases with depth and depends on density and depth, not on the shape of the container.

Heat moves by conduction (solids, particle collisions), convection (fluids, moving currents) and radiation (infrared, needs no medium); Q = mcΔT gives heat energy change.

Earth's layers: solid crust, semi-solid mantle, liquid outer core (source of the magnetic field) and solid inner core; the lithosphere is the crust plus the rigid top of the mantle.

Plate tectonics: the lithosphere is broken into plates that move on the mantle; at divergent boundaries plates separate (Mid-Atlantic Ridge), at convergent boundaries one plate subducts (trenches, volcanoes, fold mountains), and at transform boundaries plates slide past each other (earthquakes).

Rock cycle: igneous rock forms when magma or lava cools, sedimentary rock forms from compacted layers of sediment and may contain fossils, and metamorphic rock forms when existing rock is changed by heat and pressure.

Earthquake terms: the focus is where the earthquake starts underground, the epicentre is directly above it on the surface, P waves arrive before S waves, and magnitude is recorded on the Richter or moment magnitude scale.

Earth's rotation on its tilted axis once every 24 hours causes day and night; revolution around the Sun once every 365.25 days plus the 23.5° tilt causes the seasons.

Solar system order from the Sun: Mercury, Venus, Earth, Mars (rocky inner planets), then Jupiter, Saturn, Uranus, Neptune (gas and ice giants); the Moon orbits Earth about every 27–29 days, giving phases.

An eclipse: solar eclipse occurs at new moon when the Moon blocks the Sun; lunar eclipse occurs at full moon when Earth's shadow falls on the Moon.

Water cycle stages: evaporation and transpiration, condensation into clouds, precipitation, then runoff and infiltration; weathering and erosion break down rock and help form soil.

Greenhouse gases such as carbon dioxide, methane and water vapour trap outgoing infrared radiation; weather is short-term atmospheric conditions while climate is the long-term average.