BGCSE Science Single Award 0568 cheat sheet

Independent variable: the factor deliberately changed; dependent variable: the factor measured in response.

Control variables are kept constant so a fair comparison isolates the effect of the independent variable.

A hypothesis is a testable prediction; a conclusion must be judged against the evidence collected.

Repeat readings reduce the effect of random error; calculate a mean to improve reliability.

Anomalous results are identified as points far from the trend and are excluded with a stated reason.

Accuracy: closeness to the true value. Precision: closeness of repeated readings to each other.

A control group receives no treatment or a placebo, giving a baseline for comparison.

Correlation does not establish causation; a causal claim needs a mechanism and controlled evidence.

Read a measuring cylinder at the bottom of the meniscus, with the eye level with the mark.

Choose apparatus matching the required precision: burette 0.05 cm3, measuring cylinder 1 cm3, balance 0.01 g.

Hazard symbols identify risk; risk assessment states the hazard, the risk and the control measure.

A line graph suits continuous data; a bar chart suits discrete categories; a scatter graph tests correlation.

Draw a line of best fit through the trend, ignoring clear outliers, and describe gradient and intercept.

Scientific claims are peer reviewed and must be reproducible by other workers before acceptance.

A model is a simplification; state what it explains and where it fails to match reality.

Record raw data in a table with units in the headings and consistent decimal places.

Animal cell: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes. Plant cell adds cell wall, chloroplasts and a permanent vacuole.

Prokaryotic cells lack a nucleus and membrane-bound organelles; bacterial DNA lies free in the cytoplasm.

Magnification = image size / actual size; convert all lengths to the same unit first.

Diffusion moves particles down a concentration gradient; osmosis is diffusion of water through a partially permeable membrane.

Active transport moves substances against a gradient and requires energy from respiration.

Enzymes are proteins that catalyse reactions; a specific substrate fits the active site (lock and key).

Enzyme activity rises with temperature to an optimum, then falls as the enzyme denatures.

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

Aerobic respiration: glucose + oxygen -> carbon dioxide + water, releasing energy; anaerobic releases less.

Balanced diet needs carbohydrates, proteins, fats, vitamins, minerals, fibre and water.

Carbohydrases, proteases and lipases digest carbohydrates, proteins and fats; bile emulsifies fats and neutralises stomach acid.

Villi in the small intestine increase surface area; they have thin walls and a rich blood supply.

Arteries carry blood away from the heart under high pressure; veins return blood and contain valves.

Double circulation: blood passes through the heart twice per circuit, keeping lungs and body pressures separate.

Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in respiring tissues.

A reflex arc: receptor -> sensory neurone -> relay neurone in spinal cord -> motor neurone -> effector.

Homeostasis keeps internal conditions stable; insulin lowers blood glucose, glucagon raises it.

Vaccination exposes the body to antigens, stimulating lymphocytes to make antibodies and memory cells.

Mitosis produces genetically identical diploid cells for growth and repair; meiosis produces four haploid gametes.

Meiosis halves the chromosome number and creates genetic variation by independent assortment and crossing over.

Fertilisation restores the diploid number; in humans the zygote has 46 chromosomes, 23 from each parent.

Alleles: dominant alleles are expressed when present; recessive alleles need two copies.

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

A monohybrid cross of two heterozygotes gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

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

Continuous variation is controlled by many genes and environment; discontinuous variation falls into distinct categories.

Mutation changes the DNA base sequence and is the source of new alleles.

States of matter: solid particles vibrate in fixed positions; liquid particles slide; gas particles move freely and far apart.

Melting and boiling are physical changes; the particles themselves are unchanged.

Atomic number = protons; mass number = protons + neutrons; atoms are neutral so electrons equal protons.

Isotopes have the same proton number but different neutron numbers.

Electron shells fill 2, 8, 8; group number equals outer-shell electrons, period number equals shells used.

Group 1 metals become more reactive down the group; Group 7 halogens become less reactive down the group.

Ionic bonding transfers electrons between metal and non-metal; covalent bonding shares electrons between non-metals.

Relative formula mass is the sum of relative atomic masses in the formula.

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

Word equation identifies reactants and products; balanced symbol equation conserves atoms of each element.

Exothermic reactions release energy to the surroundings; endothermic reactions absorb energy.

Rate increases with higher concentration, higher temperature, greater surface area and a catalyst.

Collision theory: reaction needs collisions with sufficient energy; a catalyst lowers the activation energy.

Oxidation is loss of electrons or gain of oxygen; reduction is gain of electrons or loss of oxygen.

Combustion of hydrocarbons produces carbon dioxide and water when oxygen is plentiful.

Thermal decomposition breaks a compound down using heat, for example metal carbonates giving an oxide and carbon dioxide.

Acid pH is below 7; neutral is 7; alkali pH is above 7.

Acid + metal -> salt + hydrogen; acid + carbonate -> salt + water + carbon dioxide.

Acid + base -> salt + water; this neutralisation reaction is used to treat indigestion and soil acidity.

The salt name comes from the acid: hydrochloric gives chloride, sulfuric gives sulfate, nitric gives nitrate.

Strong acids ionise completely in water; weak acids ionise only partially.

Universal indicator gives approximate pH; a pH meter gives a numerical value.

Measuring rate by gas collection: volume of gas per unit time; by mass loss: decrease in mass per unit time.

Reaction stops when a reactant is used up, shown by a plateau on a rate graph.

Speed = distance / time; acceleration = change in velocity / time.

Weight = mass x gravitational field strength (about 10 N/kg on Earth).

Resultant force = mass x acceleration; zero resultant force means constant velocity or rest.

Friction and air resistance oppose motion and transfer energy to the surroundings by heating.

Work done = force x distance moved in the direction of the force.

Kinetic energy = 1/2 m v^2; gravitational potential energy = m g h.

Energy is conserved but dissipates; efficiency = useful output / total input x 100%.

Pressure = force / area; pressure in a liquid increases with depth.

Moments: a force turns about a pivot; balanced when clockwise moment equals anticlockwise moment.

Wave speed = frequency x wavelength.

Transverse waves vibrate perpendicular to travel (light, water); longitudinal waves vibrate parallel (sound).

Frequency in hertz equals the number of waves passing a point per second.

Reflection: angle of incidence equals angle of reflection, measured from the normal.

Refraction occurs because speed changes between media; light bending towards the normal means it slowed down.

Sound needs a medium; it travels fastest in solids and cannot travel through a vacuum.

Light travels in straight lines; shadows show this, and a pinhole camera forms an inverted image.

The electromagnetic spectrum, in order of increasing wavelength: gamma, X-ray, ultraviolet, visible, infrared, microwave, radio.

Current is the rate of flow of charge; measured in amperes with an ammeter in series.

Potential difference is energy per unit charge; measured in volts with a voltmeter in parallel.

Resistance = potential difference / current.

Series circuit: same current everywhere, voltages add, resistances add.

Parallel circuit: same voltage across branches, currents add, total resistance is less than the smallest branch.

Electrical energy transferred = power x time; power = voltage x current.

Ohm's law: current is directly proportional to voltage for a fixed resistance at constant temperature.

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

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

Food chain: producer -> primary consumer -> secondary consumer; arrows show the direction of energy transfer.

Only about 10% of energy passes to the next trophic level; the rest is lost in respiration, movement and heat.

Photosynthesis by producers is the source of energy for nearly all food chains.

Pyramid of numbers or biomass represents trophic levels; a pyramid of biomass is always widest at the base.

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

Population size is affected by food supply, predation, disease and competition.

Renewable resources (wind, solar, hydroelectric) are replenished; fossil fuels are finite.

Recycling and reducing waste conserve raw materials and reduce pollution.

Biodiversity is the variety of species in an ecosystem; habitat destruction reduces it.