JC Science cheat sheet

A hypothesis is a testable, falsifiable prediction; a theory is a well-supported explanation built from many tested hypotheses; a law describes a consistent relationship.

Variables: independent = what the investigator changes; dependent = what is measured; controlled variables are kept constant so the test is fair.

A control group receives no treatment (or a placebo) and provides the baseline against which the experimental group is compared.

Validity = the method measures what it claims; reliability = repeated trials give consistent results; accuracy = closeness to the true value; precision = closeness of repeated readings to each other.

Random errors scatter above and below the true value and are reduced by averaging repeats; systematic errors shift all readings the same way and are not fixed by averaging.

Calculate a mean by summing values and dividing by n; the range (max − min) shows spread, and an outlier is a value far outside the pattern and should be checked, not silently deleted.

A line graph suits continuous data (time, temperature); a bar chart suits categories; always label axes with quantity and unit and give the graph a title.

Conclusions must be limited to the evidence collected; correlation does not prove causation, and a single trial cannot establish a general rule.

Cell structures: nucleus (genetic control), cytoplasm (reactions), cell membrane (control of entry/exit), mitochondria (aerobic respiration), ribosomes (protein synthesis); plant cells add a cellulose wall, chloroplasts and a permanent vacuole.

Diffusion moves particles from high to low concentration without energy input; osmosis is water diffusion across a semi-permeable membrane from dilute to concentrated solution; active transport uses energy to move substances against a gradient.

Enzymes are protein catalysts with a specific active site (lock-and-key); amylase digests starch to maltose, protease digests protein to amino acids, lipase digests fat to fatty acids and glycerol.

Digestion: mechanical breakdown in the mouth, acid plus pepsin in the stomach, bile from the liver emulsifies fats and neutralises stomach acid, and villi in the small intestine absorb nutrients into the blood.

Aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy), occurring mainly in mitochondria; anaerobic respiration in muscle gives lactic acid, and in yeast gives ethanol and carbon dioxide.

Blood flow: right atrium → right ventricle → lungs → left atrium → left ventricle → body; arteries carry blood away from the heart at high pressure, veins return it with valves, capillaries allow exchange.

Excretion removes metabolic waste: kidneys filter blood to form urine (removing urea), lungs excrete carbon dioxide, and skin loses water and salts in sweat.

Balanced diet needs carbohydrates, proteins, fats, vitamins, minerals, fibre and water; deficiency examples include vitamin C and scurvy, vitamin D and rickets, iron and anaemia.

DNA is a double helix of nucleotides; a gene is a section coding for a protein; chromosomes are DNA plus protein, and humans have 46 (23 pairs) in body cells.

Alleles are alternative versions of a gene; dominant alleles are expressed when present, recessive only when both alleles match; genotype is the allele pair, phenotype is the visible trait.

Punnett squares predict offspring ratios: a cross of two heterozygotes (Aa × Aa) gives 3:1 dominant to recessive phenotype and 1:2:1 genotype ratio.

Sex determination: females are XX and males XY; the father's sperm determines the sex of the offspring.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically different haploid gametes, halving the chromosome number.

Adaptation types: structural (body shape, e.g. streamlined fish), behavioural (migration, hibernation), functional (physiological, e.g. reduced water loss).

Natural selection: variation exists in a population, selection pressures favour some variants, survivors reproduce and pass on advantageous alleles, so allele frequencies change over generations.

Evidence for evolution includes fossils, homologous structures, and DNA/protein sequence similarity; extinction occurs when a species cannot adapt to changed conditions.

An ecosystem is a community of organisms plus the non-living environment; a population is one species in an area; a community is all populations present.

Food chains transfer energy from producers (photosynthesis) to consumers; arrows show direction of energy flow; decomposers break down dead matter and recycle nutrients.

Only about 10% of energy passes to the next trophic level; the rest is lost as heat, in movement, and in undigested waste, so food chains rarely have more than four or five links.

Abiotic factors include light, temperature, moisture, pH and oxygen; biotic factors include predators, competition and disease.

Biodiversity is the variety of species and genetic variation within an ecosystem; high biodiversity improves ecosystem stability and resilience.

Human impacts: deforestation, habitat fragmentation, pollution (eutrophication from fertiliser run-off), greenhouse gas emissions, overfishing and introduction of invasive species.

Conservation measures include protected areas, seed banks, breeding programmes, wildlife corridors, and sustainable resource use such as quotas and replanting.

Sampling with quadrats estimates population size: mean count per quadrat × total area ÷ quadrat area; random placement avoids bias.

Atoms contain protons (positive, in the nucleus), neutrons (neutral, nucleus) and electrons (negative, in shells); atomic number = protons, mass number = protons + neutrons.

An element contains one kind of atom; a compound contains elements chemically combined in fixed proportions; a mixture contains substances not chemically combined and can be separated by physical means.

Isotopes are atoms of the same element with different neutron numbers; relative atomic mass is the weighted mean of isotope masses.

Separation: filtration removes insoluble solids, evaporation/crystallisation recovers dissolved solids, simple distillation separates solvent from solution, fractional distillation separates liquids by boiling point, chromatography separates dissolved colours.

Chromatography: a substance is identified by its Rf value = distance travelled by spot ÷ distance travelled by solvent front.

The periodic table arranges elements by increasing atomic number; group number gives outer-shell electrons, period number gives the number of shells.

States of matter: solids have fixed shape and vibrate in place, liquids flow and take container shape, gases fill any container; changes of state are physical, not chemical.

Purity test: a pure substance melts and boils at a sharp, fixed temperature; impurities lower the melting point and raise the boiling point.

Acids release H⁺ ions in water (pH below 7), alkalis release OH⁻ (pH above 7); neutralisation: acid + base → salt + water; acid + metal → salt + hydrogen; acid + carbonate → salt + water + carbon dioxide.

Indicators: litmus (red in acid, blue in alkali), universal indicator gives a colour scale, phenolphthalein is colourless in acid and pink in alkali.

pH is a logarithmic scale of hydrogen ion concentration; a change of one pH unit is a tenfold change in H⁺ concentration.

Rate of reaction is increased by higher temperature, higher concentration, greater surface area, and catalysts; these all increase collision frequency or energy.

Collision theory: particles must collide with at least the activation energy for a reaction to occur; a catalyst lowers activation energy without being used up.

Exothermic reactions release energy to the surroundings (temperature rises, ΔH negative); endothermic reactions absorb energy (temperature falls, ΔH positive).

Conservation of mass: total mass of reactants equals total mass of products; equations must be balanced so atoms are conserved.

Reactivity series (e.g. K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au) predicts displacement: a more reactive metal displaces a less reactive one from its salt solution.

Speed = distance ÷ time; velocity includes direction; acceleration = change in velocity ÷ time (m/s²); on a distance–time graph slope = speed, on a velocity–time graph slope = acceleration and area under line = distance.

Newton's laws: an object stays at rest or in uniform motion unless a resultant force acts; F = ma; every action has an equal and opposite reaction.

Weight = mass × gravitational field strength (W = mg, g ≈ 9.8 N/kg on Earth); mass is in kg and does not change with location.

Friction and air resistance oppose motion and convert kinetic energy to heat; resultant force is the single force equivalent to all forces combined.

Work done = force × distance moved in the direction of the force (joules); power = work done ÷ time (watts).

Kinetic energy = ½mv²; gravitational potential energy = mgh; energy is conserved but degrades to less useful forms, mainly heat.

Pressure = force ÷ area (Pa); pressure in a liquid increases with depth; a smaller area gives greater pressure for the same force.

Moments: moment = force × perpendicular distance from pivot; a lever is balanced when clockwise moments equal anticlockwise moments.

Current is the rate of charge flow (amperes), voltage is energy transferred per unit charge (volts), resistance opposes current (ohms); V = IR (Ohm's law).

Series circuits: same current everywhere, voltages add, total resistance = sum of resistances; parallel circuits: same voltage across branches, currents add, total resistance is less than the smallest branch.

Electrical power P = VI = I²R = V²/R; energy transferred = power × time (kWh for domestic bills).

Magnets have north and south poles; like poles repel; a current-carrying wire in a magnetic field experiences a force (motor effect), and moving a magnet near a coil induces a current (generator effect).

Light travels in straight lines; reflection angle of incidence equals angle of reflection; refraction bends light towards the normal entering a denser medium; white light splits by a prism into a spectrum.

Sound is a longitudinal wave needing a medium; it travels fastest in solids and cannot travel through a vacuum; frequency determines pitch, amplitude determines loudness.

Wave equation: speed = frequency × wavelength (v = fλ); frequency in hertz, wavelength in metres.

Transverse waves oscillate perpendicular to travel (light), longitudinal waves oscillate parallel to travel (sound); the electromagnetic spectrum runs radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.

Rock types: igneous forms from cooling magma or lava (crystals if slow-cooled), sedimentary forms from compacted deposited layers and may contain fossils, metamorphic forms when existing rock is changed by heat and pressure.

The rock cycle links the three rock types through melting, cooling, weathering, erosion, deposition and metamorphism; weathering breaks rock in place, erosion transports the fragments.

The water cycle: evaporation, transpiration, condensation, precipitation and run-off; energy from the Sun drives the cycle.

Weather is short-term atmospheric conditions; climate is the long-term average pattern, typically assessed over 30 years.

Greenhouse gases (carbon dioxide, methane, water vapour) trap outgoing infrared radiation; increased concentrations raise average global temperature and sea level.

Solar system order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune; inner planets are rocky, outer planets are gas or ice giants.

Earth's tilt of about 23.5° causes seasons; day and night result from rotation on its axis, and a year is one orbit of the Sun.

The universe is expanding: distant galaxies show redshift, and the Big Bang model explains this from an initial hot dense state about 13.8 billion years ago.

Risk assessment weighs hazard severity against likelihood of exposure; risk = probability × consequence, and risk is reduced by engineering controls before personal protective equipment.

Informed consent requires that participants understand purpose, procedures, risks and their right to withdraw; ethics committees review research involving humans or animals.

Sustainability means meeting present needs without compromising future generations; the three pillars are environmental, social and economic.

Renewable energy sources (solar, wind, hydro, geothermal, biomass) are replenished naturally; fossil fuels are finite and release carbon dioxide when burned.

Reduce, reuse, recycle: recycling saves raw materials and energy but requires collection and processing, and not all materials recycle equally.

Scientific claims should be evaluated by checking the source, peer review, sample size, conflicts of interest and whether evidence supports the conclusion.

Vaccination and antibiotics are major public-health applications; antibiotic resistance is an example of evolution driven by overuse.

STEM careers include biomedical scientist, environmental scientist, chemical engineer, data analyst, science communicator and renewable-energy technician; many require specific qualifications and continuing professional development.

A hypothesis is a testable, falsifiable prediction; a theory is a well-supported explanation built from many tested hypotheses; a law describes a consistent relationship.

Variables: independent = what the investigator changes; dependent = what is measured; controlled variables are kept constant so the test is fair.

A control group receives no treatment (or a placebo) and provides the baseline against which the experimental group is compared.

Validity = the method measures what it claims; reliability = repeated trials give consistent results; accuracy = closeness to the true value; precision = closeness of repeated readings to each other.

Random errors scatter above and below the true value and are reduced by averaging repeats; systematic errors shift all readings the same way and are not fixed by averaging.

Calculate a mean by summing values and dividing by n; the range (max − min) shows spread, and an outlier is a value far outside the pattern and should be checked, not silently deleted.

A line graph suits continuous data (time, temperature); a bar chart suits categories; always label axes with quantity and unit and give the graph a title.

Conclusions must be limited to the evidence collected; correlation does not prove causation, and a single trial cannot establish a general rule.

Cell structures: nucleus (genetic control), cytoplasm (reactions), cell membrane (control of entry/exit), mitochondria (aerobic respiration), ribosomes (protein synthesis); plant cells add a cellulose wall, chloroplasts and a permanent vacuole.

Diffusion moves particles from high to low concentration without energy input; osmosis is water diffusion across a semi-permeable membrane from dilute to concentrated solution; active transport uses energy to move substances against a gradient.

Enzymes are protein catalysts with a specific active site (lock-and-key); amylase digests starch to maltose, protease digests protein to amino acids, lipase digests fat to fatty acids and glycerol.

Digestion: mechanical breakdown in the mouth, acid plus pepsin in the stomach, bile from the liver emulsifies fats and neutralises stomach acid, and villi in the small intestine absorb nutrients into the blood.

Aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy), occurring mainly in mitochondria; anaerobic respiration in muscle gives lactic acid, and in yeast gives ethanol and carbon dioxide.

Blood flow: right atrium → right ventricle → lungs → left atrium → left ventricle → body; arteries carry blood away from the heart at high pressure, veins return it with valves, capillaries allow exchange.

Excretion removes metabolic waste: kidneys filter blood to form urine (removing urea), lungs excrete carbon dioxide, and skin loses water and salts in sweat.

Balanced diet needs carbohydrates, proteins, fats, vitamins, minerals, fibre and water; deficiency examples include vitamin C and scurvy, vitamin D and rickets, iron and anaemia.

DNA is a double helix of nucleotides; a gene is a section coding for a protein; chromosomes are DNA plus protein, and humans have 46 (23 pairs) in body cells.

Alleles are alternative versions of a gene; dominant alleles are expressed when present, recessive only when both alleles match; genotype is the allele pair, phenotype is the visible trait.

Punnett squares predict offspring ratios: a cross of two heterozygotes (Aa × Aa) gives 3:1 dominant to recessive phenotype and 1:2:1 genotype ratio.

Sex determination: females are XX and males XY; the father's sperm determines the sex of the offspring.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically different haploid gametes, halving the chromosome number.

Adaptation types: structural (body shape, e.g. streamlined fish), behavioural (migration, hibernation), functional (physiological, e.g. reduced water loss).

Natural selection: variation exists in a population, selection pressures favour some variants, survivors reproduce and pass on advantageous alleles, so allele frequencies change over generations.

Evidence for evolution includes fossils, homologous structures, and DNA/protein sequence similarity; extinction occurs when a species cannot adapt to changed conditions.

An ecosystem is a community of organisms plus the non-living environment; a population is one species in an area; a community is all populations present.

Food chains transfer energy from producers (photosynthesis) to consumers; arrows show direction of energy flow; decomposers break down dead matter and recycle nutrients.

Only about 10% of energy passes to the next trophic level; the rest is lost as heat, in movement, and in undigested waste, so food chains rarely have more than four or five links.

Abiotic factors include light, temperature, moisture, pH and oxygen; biotic factors include predators, competition and disease.

Biodiversity is the variety of species and genetic variation within an ecosystem; high biodiversity improves ecosystem stability and resilience.

Human impacts: deforestation, habitat fragmentation, pollution (eutrophication from fertiliser run-off), greenhouse gas emissions, overfishing and introduction of invasive species.

Conservation measures include protected areas, seed banks, breeding programmes, wildlife corridors, and sustainable resource use such as quotas and replanting.

Sampling with quadrats estimates population size: mean count per quadrat × total area ÷ quadrat area; random placement avoids bias.

Atoms contain protons (positive, in the nucleus), neutrons (neutral, nucleus) and electrons (negative, in shells); atomic number = protons, mass number = protons + neutrons.

An element contains one kind of atom; a compound contains elements chemically combined in fixed proportions; a mixture contains substances not chemically combined and can be separated by physical means.

Isotopes are atoms of the same element with different neutron numbers; relative atomic mass is the weighted mean of isotope masses.

Separation: filtration removes insoluble solids, evaporation/crystallisation recovers dissolved solids, simple distillation separates solvent from solution, fractional distillation separates liquids by boiling point, chromatography separates dissolved colours.

Chromatography: a substance is identified by its Rf value = distance travelled by spot ÷ distance travelled by solvent front.

The periodic table arranges elements by increasing atomic number; group number gives outer-shell electrons, period number gives the number of shells.

States of matter: solids have fixed shape and vibrate in place, liquids flow and take container shape, gases fill any container; changes of state are physical, not chemical.

Purity test: a pure substance melts and boils at a sharp, fixed temperature; impurities lower the melting point and raise the boiling point.

Acids release H⁺ ions in water (pH below 7), alkalis release OH⁻ (pH above 7); neutralisation: acid + base → salt + water; acid + metal → salt + hydrogen; acid + carbonate → salt + water + carbon dioxide.

Indicators: litmus (red in acid, blue in alkali), universal indicator gives a colour scale, phenolphthalein is colourless in acid and pink in alkali.

pH is a logarithmic scale of hydrogen ion concentration; a change of one pH unit is a tenfold change in H⁺ concentration.

Rate of reaction is increased by higher temperature, higher concentration, greater surface area, and catalysts; these all increase collision frequency or energy.

Collision theory: particles must collide with at least the activation energy for a reaction to occur; a catalyst lowers activation energy without being used up.

Exothermic reactions release energy to the surroundings (temperature rises, ΔH negative); endothermic reactions absorb energy (temperature falls, ΔH positive).

Conservation of mass: total mass of reactants equals total mass of products; equations must be balanced so atoms are conserved.

Reactivity series (e.g. K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au) predicts displacement: a more reactive metal displaces a less reactive one from its salt solution.

Speed = distance ÷ time; velocity includes direction; acceleration = change in velocity ÷ time (m/s²); on a distance–time graph slope = speed, on a velocity–time graph slope = acceleration and area under line = distance.

Newton's laws: an object stays at rest or in uniform motion unless a resultant force acts; F = ma; every action has an equal and opposite reaction.

Weight = mass × gravitational field strength (W = mg, g ≈ 9.8 N/kg on Earth); mass is in kg and does not change with location.

Friction and air resistance oppose motion and convert kinetic energy to heat; resultant force is the single force equivalent to all forces combined.

Work done = force × distance moved in the direction of the force (joules); power = work done ÷ time (watts).

Kinetic energy = ½mv²; gravitational potential energy = mgh; energy is conserved but degrades to less useful forms, mainly heat.

Pressure = force ÷ area (Pa); pressure in a liquid increases with depth; a smaller area gives greater pressure for the same force.

Moments: moment = force × perpendicular distance from pivot; a lever is balanced when clockwise moments equal anticlockwise moments.

Current is the rate of charge flow (amperes), voltage is energy transferred per unit charge (volts), resistance opposes current (ohms); V = IR (Ohm's law).

Series circuits: same current everywhere, voltages add, total resistance = sum of resistances; parallel circuits: same voltage across branches, currents add, total resistance is less than the smallest branch.

Electrical power P = VI = I²R = V²/R; energy transferred = power × time (kWh for domestic bills).

Magnets have north and south poles; like poles repel; a current-carrying wire in a magnetic field experiences a force (motor effect), and moving a magnet near a coil induces a current (generator effect).

Light travels in straight lines; reflection angle of incidence equals angle of reflection; refraction bends light towards the normal entering a denser medium; white light splits by a prism into a spectrum.

Sound is a longitudinal wave needing a medium; it travels fastest in solids and cannot travel through a vacuum; frequency determines pitch, amplitude determines loudness.

Wave equation: speed = frequency × wavelength (v = fλ); frequency in hertz, wavelength in metres.

Transverse waves oscillate perpendicular to travel (light), longitudinal waves oscillate parallel to travel (sound); the electromagnetic spectrum runs radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.

Rock types: igneous forms from cooling magma or lava (crystals if slow-cooled), sedimentary forms from compacted deposited layers and may contain fossils, metamorphic forms when existing rock is changed by heat and pressure.

The rock cycle links the three rock types through melting, cooling, weathering, erosion, deposition and metamorphism; weathering breaks rock in place, erosion transports the fragments.

The water cycle: evaporation, transpiration, condensation, precipitation and run-off; energy from the Sun drives the cycle.

Weather is short-term atmospheric conditions; climate is the long-term average pattern, typically assessed over 30 years.

Greenhouse gases (carbon dioxide, methane, water vapour) trap outgoing infrared radiation; increased concentrations raise average global temperature and sea level.

Solar system order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune; inner planets are rocky, outer planets are gas or ice giants.

Earth's tilt of about 23.5° causes seasons; day and night result from rotation on its axis, and a year is one orbit of the Sun.

The universe is expanding: distant galaxies show redshift, and the Big Bang model explains this from an initial hot dense state about 13.8 billion years ago.

Risk assessment weighs hazard severity against likelihood of exposure; risk = probability × consequence, and risk is reduced by engineering controls before personal protective equipment.

Informed consent requires that participants understand purpose, procedures, risks and their right to withdraw; ethics committees review research involving humans or animals.

Sustainability means meeting present needs without compromising future generations; the three pillars are environmental, social and economic.

Renewable energy sources (solar, wind, hydro, geothermal, biomass) are replenished naturally; fossil fuels are finite and release carbon dioxide when burned.

Reduce, reuse, recycle: recycling saves raw materials and energy but requires collection and processing, and not all materials recycle equally.

Scientific claims should be evaluated by checking the source, peer review, sample size, conflicts of interest and whether evidence supports the conclusion.

Vaccination and antibiotics are major public-health applications; antibiotic resistance is an example of evolution driven by overuse.

STEM careers include biomedical scientist, environmental scientist, chemical engineer, data analyst, science communicator and renewable-energy technician; many require specific qualifications and continuing professional development.

A hypothesis is a testable, falsifiable prediction; a theory is a well-supported explanation built from many tested hypotheses; a law describes a consistent relationship.

Variables: independent = what the investigator changes; dependent = what is measured; controlled variables are kept constant so the test is fair.

A control group receives no treatment (or a placebo) and provides the baseline against which the experimental group is compared.

Validity = the method measures what it claims; reliability = repeated trials give consistent results; accuracy = closeness to the true value; precision = closeness of repeated readings to each other.

Random errors scatter above and below the true value and are reduced by averaging repeats; systematic errors shift all readings the same way and are not fixed by averaging.

Calculate a mean by summing values and dividing by n; the range (max − min) shows spread, and an outlier is a value far outside the pattern and should be checked, not silently deleted.

A line graph suits continuous data (time, temperature); a bar chart suits categories; always label axes with quantity and unit and give the graph a title.

Conclusions must be limited to the evidence collected; correlation does not prove causation, and a single trial cannot establish a general rule.

Cell structures: nucleus (genetic control), cytoplasm (reactions), cell membrane (control of entry/exit), mitochondria (aerobic respiration), ribosomes (protein synthesis); plant cells add a cellulose wall, chloroplasts and a permanent vacuole.

Diffusion moves particles from high to low concentration without energy input; osmosis is water diffusion across a semi-permeable membrane from dilute to concentrated solution; active transport uses energy to move substances against a gradient.

Enzymes are protein catalysts with a specific active site (lock-and-key); amylase digests starch to maltose, protease digests protein to amino acids, lipase digests fat to fatty acids and glycerol.

Digestion: mechanical breakdown in the mouth, acid plus pepsin in the stomach, bile from the liver emulsifies fats and neutralises stomach acid, and villi in the small intestine absorb nutrients into the blood.

Aerobic respiration: glucose + oxygen → carbon dioxide + water (+ energy), occurring mainly in mitochondria; anaerobic respiration in muscle gives lactic acid, and in yeast gives ethanol and carbon dioxide.

Blood flow: right atrium → right ventricle → lungs → left atrium → left ventricle → body; arteries carry blood away from the heart at high pressure, veins return it with valves, capillaries allow exchange.

Excretion removes metabolic waste: kidneys filter blood to form urine (removing urea), lungs excrete carbon dioxide, and skin loses water and salts in sweat.

Balanced diet needs carbohydrates, proteins, fats, vitamins, minerals, fibre and water; deficiency examples include vitamin C and scurvy, vitamin D and rickets, iron and anaemia.

DNA is a double helix of nucleotides; a gene is a section coding for a protein; chromosomes are DNA plus protein, and humans have 46 (23 pairs) in body cells.

Alleles are alternative versions of a gene; dominant alleles are expressed when present, recessive only when both alleles match; genotype is the allele pair, phenotype is the visible trait.

Punnett squares predict offspring ratios: a cross of two heterozygotes (Aa × Aa) gives 3:1 dominant to recessive phenotype and 1:2:1 genotype ratio.

Sex determination: females are XX and males XY; the father's sperm determines the sex of the offspring.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically different haploid gametes, halving the chromosome number.

Adaptation types: structural (body shape, e.g. streamlined fish), behavioural (migration, hibernation), functional (physiological, e.g. reduced water loss).

Natural selection: variation exists in a population, selection pressures favour some variants, survivors reproduce and pass on advantageous alleles, so allele frequencies change over generations.

Evidence for evolution includes fossils, homologous structures, and DNA/protein sequence similarity; extinction occurs when a species cannot adapt to changed conditions.

An ecosystem is a community of organisms plus the non-living environment; a population is one species in an area; a community is all populations present.

Food chains transfer energy from producers (photosynthesis) to consumers; arrows show direction of energy flow; decomposers break down dead matter and recycle nutrients.

Only about 10% of energy passes to the next trophic level; the rest is lost as heat, in movement, and in undigested waste, so food chains rarely have more than four or five links.

Abiotic factors include light, temperature, moisture, pH and oxygen; biotic factors include predators, competition and disease.

Biodiversity is the variety of species and genetic variation within an ecosystem; high biodiversity improves ecosystem stability and resilience.

Human impacts: deforestation, habitat fragmentation, pollution (eutrophication from fertiliser run-off), greenhouse gas emissions, overfishing and introduction of invasive species.

Conservation measures include protected areas, seed banks, breeding programmes, wildlife corridors, and sustainable resource use such as quotas and replanting.

Sampling with quadrats estimates population size: mean count per quadrat × total area ÷ quadrat area; random placement avoids bias.

Atoms contain protons (positive, in the nucleus), neutrons (neutral, nucleus) and electrons (negative, in shells); atomic number = protons, mass number = protons + neutrons.

An element contains one kind of atom; a compound contains elements chemically combined in fixed proportions; a mixture contains substances not chemically combined and can be separated by physical means.

Isotopes are atoms of the same element with different neutron numbers; relative atomic mass is the weighted mean of isotope masses.

Separation: filtration removes insoluble solids, evaporation/crystallisation recovers dissolved solids, simple distillation separates solvent from solution, fractional distillation separates liquids by boiling point, chromatography separates dissolved colours.

Chromatography: a substance is identified by its Rf value = distance travelled by spot ÷ distance travelled by solvent front.

The periodic table arranges elements by increasing atomic number; group number gives outer-shell electrons, period number gives the number of shells.

States of matter: solids have fixed shape and vibrate in place, liquids flow and take container shape, gases fill any container; changes of state are physical, not chemical.

Purity test: a pure substance melts and boils at a sharp, fixed temperature; impurities lower the melting point and raise the boiling point.

Acids release H⁺ ions in water (pH below 7), alkalis release OH⁻ (pH above 7); neutralisation: acid + base → salt + water; acid + metal → salt + hydrogen; acid + carbonate → salt + water + carbon dioxide.

Indicators: litmus (red in acid, blue in alkali), universal indicator gives a colour scale, phenolphthalein is colourless in acid and pink in alkali.

pH is a logarithmic scale of hydrogen ion concentration; a change of one pH unit is a tenfold change in H⁺ concentration.

Rate of reaction is increased by higher temperature, higher concentration, greater surface area, and catalysts; these all increase collision frequency or energy.

Collision theory: particles must collide with at least the activation energy for a reaction to occur; a catalyst lowers activation energy without being used up.

Exothermic reactions release energy to the surroundings (temperature rises, ΔH negative); endothermic reactions absorb energy (temperature falls, ΔH positive).

Conservation of mass: total mass of reactants equals total mass of products; equations must be balanced so atoms are conserved.

Reactivity series (e.g. K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Ag, Au) predicts displacement: a more reactive metal displaces a less reactive one from its salt solution.

Speed = distance ÷ time; velocity includes direction; acceleration = change in velocity ÷ time (m/s²); on a distance–time graph slope = speed, on a velocity–time graph slope = acceleration and area under line = distance.

Newton's laws: an object stays at rest or in uniform motion unless a resultant force acts; F = ma; every action has an equal and opposite reaction.

Weight = mass × gravitational field strength (W = mg, g ≈ 9.8 N/kg on Earth); mass is in kg and does not change with location.

Friction and air resistance oppose motion and convert kinetic energy to heat; resultant force is the single force equivalent to all forces combined.

Work done = force × distance moved in the direction of the force (joules); power = work done ÷ time (watts).

Kinetic energy = ½mv²; gravitational potential energy = mgh; energy is conserved but degrades to less useful forms, mainly heat.

Pressure = force ÷ area (Pa); pressure in a liquid increases with depth; a smaller area gives greater pressure for the same force.

Moments: moment = force × perpendicular distance from pivot; a lever is balanced when clockwise moments equal anticlockwise moments.

Current is the rate of charge flow (amperes), voltage is energy transferred per unit charge (volts), resistance opposes current (ohms); V = IR (Ohm's law).

Series circuits: same current everywhere, voltages add, total resistance = sum of resistances; parallel circuits: same voltage across branches, currents add, total resistance is less than the smallest branch.

Electrical power P = VI = I²R = V²/R; energy transferred = power × time (kWh for domestic bills).

Magnets have north and south poles; like poles repel; a current-carrying wire in a magnetic field experiences a force (motor effect), and moving a magnet near a coil induces a current (generator effect).

Light travels in straight lines; reflection angle of incidence equals angle of reflection; refraction bends light towards the normal entering a denser medium; white light splits by a prism into a spectrum.

Sound is a longitudinal wave needing a medium; it travels fastest in solids and cannot travel through a vacuum; frequency determines pitch, amplitude determines loudness.

Wave equation: speed = frequency × wavelength (v = fλ); frequency in hertz, wavelength in metres.

Transverse waves oscillate perpendicular to travel (light), longitudinal waves oscillate parallel to travel (sound); the electromagnetic spectrum runs radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.

Rock types: igneous forms from cooling magma or lava (crystals if slow-cooled), sedimentary forms from compacted deposited layers and may contain fossils, metamorphic forms when existing rock is changed by heat and pressure.

The rock cycle links the three rock types through melting, cooling, weathering, erosion, deposition and metamorphism; weathering breaks rock in place, erosion transports the fragments.

The water cycle: evaporation, transpiration, condensation, precipitation and run-off; energy from the Sun drives the cycle.

Weather is short-term atmospheric conditions; climate is the long-term average pattern, typically assessed over 30 years.

Greenhouse gases (carbon dioxide, methane, water vapour) trap outgoing infrared radiation; increased concentrations raise average global temperature and sea level.

Solar system order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune; inner planets are rocky, outer planets are gas or ice giants.

Earth's tilt of about 23.5° causes seasons; day and night result from rotation on its axis, and a year is one orbit of the Sun.

The universe is expanding: distant galaxies show redshift, and the Big Bang model explains this from an initial hot dense state about 13.8 billion years ago.

Risk assessment weighs hazard severity against likelihood of exposure; risk = probability × consequence, and risk is reduced by engineering controls before personal protective equipment.

Informed consent requires that participants understand purpose, procedures, risks and their right to withdraw; ethics committees review research involving humans or animals.

Sustainability means meeting present needs without compromising future generations; the three pillars are environmental, social and economic.

Renewable energy sources (solar, wind, hydro, geothermal, biomass) are replenished naturally; fossil fuels are finite and release carbon dioxide when burned.

Reduce, reuse, recycle: recycling saves raw materials and energy but requires collection and processing, and not all materials recycle equally.

Scientific claims should be evaluated by checking the source, peer review, sample size, conflicts of interest and whether evidence supports the conclusion.

Vaccination and antibiotics are major public-health applications; antibiotic resistance is an example of evolution driven by overuse.

STEM careers include biomedical scientist, environmental scientist, chemical engineer, data analyst, science communicator and renewable-energy technician; many require specific qualifications and continuing professional development.