GCSE Science (Single Award)

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Cells BIO ▶

Animal vs Plant Cells

Feature	Animal Cell	Plant Cell
Cell membrane	Yes	Yes
Cytoplasm	Yes	Yes
Nucleus	Yes	Yes
Mitochondria	Yes	Yes
Cell wall	No	Yes (cellulose)
Chloroplasts	No	Yes (for photosynthesis)
Large vacuole	No (small temporary)	Yes (permanent, sap-filled)

Key Organelles

Nucleus — contains DNA; controls cell activities
Cell membrane — controls what enters/leaves the cell; partially permeable
Cytoplasm — jelly-like substance where chemical reactions occur
Mitochondria — site of aerobic respiration; releases energy
Ribosomes — site of protein synthesis
Chloroplasts — contain chlorophyll; site of photosynthesis (plant cells only)

Specialised Cells

Red blood cells — no nucleus (more room for haemoglobin), biconcave disc (large surface area)
Nerve cells — long axon to carry electrical impulses, branched endings for connections
Root hair cells — long hair-like projection increases surface area for water absorption
Sperm cells — tail for swimming, many mitochondria for energy, acrosome with enzymes
Palisade cells — packed with chloroplasts near top of leaf for maximum photosynthesis

Know at least three specialised cells and be able to explain how their structure relates to their function.

Cell Structure — Annotated Diagram Guide

When drawing or labelling cell diagrams in the exam, include these features with label lines pointing to the correct location:

Feature	Animal Cell Diagram	Plant Cell Diagram
Outer boundary	Cell membrane only (drawn as a single line around the cell)	Cell wall (thick outer rectangle) with cell membrane just inside it
Centre	Large circular nucleus with a nucleolus dot inside; draw near the centre of the cell	Nucleus pushed to one side by the large vacuole
Cytoplasm	Fill the space between nucleus and membrane; label the area	Thin layer of cytoplasm around the edges (vacuole takes up most of the space)
Mitochondria	Draw 2-3 small oval/sausage shapes with inner folds in the cytoplasm	Same — small ovals in the cytoplasm layer
Ribosomes	Tiny dots scattered in the cytoplasm (too small to see with a light microscope)	Same — tiny dots in the cytoplasm
Vacuole	Small, temporary vacuoles (optional — draw as tiny circles)	Large permanent vacuole filling most of the cell, labelled "sap-filled vacuole"
Chloroplasts	Not present	Draw 3-4 small oval shapes with internal disc-like structures; place in the cytoplasm

In diagrams, always use a ruler for label lines, never let lines cross, and make sure each label line touches the structure it refers to. Plant cells should look rectangular; animal cells should look more rounded or irregular.

Microscopy & Magnification

magnification = image size / actual size

Rearranged: image size = magnification × actual size and actual size = image size / magnification

A cell has an actual diameter of 0.05 mm. Under a microscope, the image measures 25 mm across. What is the magnification?
Step 1 — Write the formula: magnification = image size / actual size
Step 2 — Substitute: magnification = 25 mm / 0.05 mm
Step 3 — Calculate: magnification = ×500
Step 4 — Units check: Both measurements are in mm, so they cancel out. Magnification has no units — just write ×500.

A photograph of a cell is 30 mm wide and was taken at ×600 magnification. What is the actual size of the cell?
Step 1 — Write the formula: actual size = image size / magnification
Step 2 — Substitute: actual size = 30 mm / 600
Step 3 — Calculate: actual size = 0.05 mm = 50 µm
Step 4 — Units check: Convert mm to µm by multiplying by 1000 (0.05 × 1000 = 50 µm). Cells are typically measured in micrometres (µm).

Quick Check: Name two organelles found in plant cells but NOT animal cells.

Cell wall (made of cellulose) and chloroplasts (contain chlorophyll for photosynthesis). Plant cells also have a large permanent vacuole.

Movement Across Membranes BIO ▶

Diffusion

The net movement of particles from an area of high concentration to an area of low concentration (down the concentration gradient). Passive process — no energy needed.

Example: oxygen diffusing from alveoli into blood; carbon dioxide diffusing out.

Osmosis

The movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane. It is a special type of diffusion.

Active Transport

The movement of substances against the concentration gradient (from low to high concentration). Requires energy from respiration.

Example: root hair cells absorbing mineral ions from soil (where concentration is lower in soil than in the root).

Feature	Diffusion	Osmosis	Active Transport
Direction	High → Low	Dilute → Concentrated	Low → High
Energy needed?	No	No	Yes
Membrane needed?	No	Yes (partially permeable)	Yes
What moves?	Any particles	Water only	Specific substances

Students often say osmosis is "water moving from high to low concentration". It is water moving from a DILUTE solution (high water concentration) to a CONCENTRATED solution (low water concentration).

Nutrition BIO ▶

Food Groups

Nutrient	Function	Source
Carbohydrates	Energy source	Bread, pasta, rice, potatoes
Proteins	Growth and repair	Meat, fish, eggs, beans
Lipids (fats)	Energy store, insulation	Butter, oil, nuts
Vitamins	Various (e.g. Vit C prevents scurvy)	Fruits, vegetables
Minerals	Various (e.g. iron for haemoglobin, calcium for bones)	Meat, dairy, vegetables
Fibre	Keeps food moving through gut	Wholegrain, fruit, veg
Water	Solvent for reactions, transport	Drinks, food

Balanced Diet

A balanced diet contains the right proportions of all seven nutrient groups. Requirements vary depending on age, gender, and activity level. Deficiency diseases result from lack of specific nutrients.

Digestive System Overview

Mouth — teeth break food (mechanical digestion); amylase breaks down starch
Oesophagus — moves food to stomach by peristalsis
Stomach — churns food; produces protease and hydrochloric acid (pH 2)
Small intestine — further digestion; absorption of nutrients through villi
Large intestine — absorbs water
Liver — produces bile (emulsifies fats)
Pancreas — produces enzymes (amylase, protease, lipase)

Enzymes are biological catalysts — they speed up reactions without being used up. Each enzyme has a specific shape (lock and key model) and works best at an optimum temperature and pH.

Respiration BIO ▶

Aerobic Respiration

Occurs in mitochondria with a constant supply of oxygen.

glucose + oxygen → carbon dioxide + water (+ energy)

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Anaerobic Respiration

Occurs without oxygen, e.g. during intense exercise.

In animals: glucose → lactic acid (+ some energy)

In yeast (fermentation): glucose → ethanol + carbon dioxide (+ some energy)

Feature	Aerobic	Anaerobic
Oxygen	Required	Not required
Energy released	Lots	Small amount
Products	CO₂ + H₂O	Lactic acid (animals) / ethanol + CO₂ (yeast)
Where	Mitochondria	Cytoplasm

Respiration is NOT breathing. Breathing (ventilation) is the physical movement of air in and out of the lungs. Respiration is the chemical reaction that releases energy from glucose in cells.

During exercise, muscles need more energy. Heart rate increases to deliver more oxygen and glucose to muscle cells. If oxygen supply cannot keep up, anaerobic respiration occurs, producing lactic acid which causes muscle fatigue and cramp.

Photosynthesis BIO ▶

The process by which plants convert light energy into chemical energy (glucose).

carbon dioxide + water → glucose + oxygen

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Occurs in chloroplasts using chlorophyll to absorb light energy.

Factors Affecting Rate

Light intensity — more light = faster rate (up to a point)
Carbon dioxide concentration — more CO₂ = faster rate (up to a point)
Temperature — increases rate up to optimum; enzymes denature at high temperatures

Each of these can be a limiting factor — the factor in shortest supply that limits the overall rate.

Investigate the effect of light intensity on the rate of photosynthesis using pondweed (Elodea). Count oxygen bubbles produced at different distances from a light source. Independent variable: distance from light. Dependent variable: number of bubbles per minute.

Quick Check: What is the word equation for photosynthesis?

carbon dioxide + water → glucose + oxygen (requires light energy and chlorophyll)

Ecology Basics BIO ▶

Key Terms

Ecosystem — a community of living organisms and their physical environment interacting together
Habitat — the place where an organism lives
Population — all organisms of one species in a habitat
Community — all the populations of different species in a habitat
Producer — organism that makes its own food (plants, by photosynthesis)
Consumer — organism that eats other organisms
Decomposer — organism that breaks down dead material (bacteria, fungi)

Food Chains & Food Webs

A food chain shows the flow of energy from one organism to another. Energy is lost at each level (as heat from respiration), so food chains rarely have more than 4-5 levels.

Example: grass → rabbit → fox → eagle

A food web shows interconnected food chains in an ecosystem.

Human Impact on the Environment

Pollution — air (burning fossil fuels), water (sewage, fertilisers), land (landfill, pesticides)
Deforestation — reduces biodiversity, increases CO₂, destroys habitats
Greenhouse effect — CO₂ and methane trap heat; leads to global warming and climate change
Overfishing — reduces fish populations below sustainable levels

When asked about "effects of removing a species from a food web", trace through ALL the connections — think about what would increase AND decrease in number.

Inheritance Basics BIO ▶

DNA, Genes & Chromosomes

DNA — a long molecule found in the nucleus; carries genetic information
Gene — a short section of DNA that codes for a specific protein (and hence a characteristic)
Chromosome — a long, coiled molecule of DNA; humans have 23 pairs (46 total)
Allele — different versions of the same gene

Dominant & Recessive

Dominant allele — always expressed, even with only one copy (shown as capital letter, e.g. B)
Recessive allele — only expressed when two copies present (shown as lowercase, e.g. b)
Homozygous — two identical alleles (BB or bb)
Heterozygous — two different alleles (Bb)
Genotype — the alleles an organism has (e.g. Bb)
Phenotype — the physical characteristic shown (e.g. brown eyes)

Punnett Square: Cross two heterozygous parents (Bb x Bb) for eye colour (B = brown, b = blue).

	B	b
B	BB	Bb
b	Bb	bb

Ratio: 3 brown (BB, Bb, Bb) : 1 blue (bb) — so 75% chance of brown eyes, 25% chance of blue eyes.

Quick Check: What is the difference between genotype and phenotype?

Genotype is the combination of alleles an organism has (e.g. Bb). Phenotype is the physical characteristic that is expressed (e.g. brown eyes).

Health and Disease BIO ▶

Pathogens

Microorganisms that cause disease. Four types:

Pathogen	Examples	Treated with
Bacteria	Salmonella, TB	Antibiotics
Viruses	Flu, COVID-19, HIV	No cure (antivirals can help)
Fungi	Athlete's foot	Antifungals
Protists	Malaria (spread by mosquitoes)	Antimalarials

Body Defences

Skin — physical barrier; produces antimicrobial substances
Mucus & cilia — trap and remove pathogens in airways
Stomach acid — HCl kills pathogens in food
White blood cells — phagocytosis (engulf pathogens), produce antibodies (specific), produce antitoxins

Vaccination

A vaccine contains a dead or weakened form of the pathogen. White blood cells produce antibodies. Memory cells remain so the body can respond quickly if infected again with the same pathogen.

Antibiotics kill BACTERIA, not viruses. Do not say antibiotics can treat the flu or a cold — these are caused by viruses.

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Atomic Structure CHEM ▶

Sub-Atomic Particles

Particle	Relative Charge	Relative Mass	Location
Proton	+1	1	Nucleus
Neutron	0	1	Nucleus
Electron	-1	~0 (1/1836)	Shells (orbits)

Key Numbers

Atomic number (bottom number) = number of protons = number of electrons (in a neutral atom)
Mass number (top number) = protons + neutrons
Number of neutrons = mass number − atomic number

Sodium has atomic number 11 and mass number 23. Therefore: protons = 11, electrons = 11, neutrons = 23 − 11 = 12.

Electron Configuration

Electrons fill shells: 1st shell = max 2, 2nd shell = max 8, 3rd shell = max 8.

Example: Sodium (11 electrons) = 2, 8, 1

The electron configuration tells you the group number (electrons in outer shell) and the period (number of shells). Sodium is 2,8,1 — Group 1, Period 3.

Quick Check: An atom has 17 protons and a mass number of 35. How many neutrons does it have, and what is its electron configuration?

Neutrons = 35 − 17 = 18. Electron configuration: 2, 8, 7. This is chlorine (Cl).

Periodic Table CHEM ▶

Organisation

Groups (columns) — elements in the same group have the same number of outer electrons, so similar chemical properties
Periods (rows) — each new period adds a new electron shell
Metals — found on the left and centre of the periodic table
Non-metals — found on the right side of the periodic table

Key Groups

Group	Name	Properties
1	Alkali metals	Soft, reactive, react with water; reactivity increases down the group
7	Halogens	Reactive non-metals; reactivity decreases down the group; diatomic molecules
0	Noble gases	Unreactive (full outer shell); used in lighting, balloons (He)

Group 1 metals get MORE reactive going down, but Group 7 halogens get LESS reactive going down. Do not mix these up in the exam.

Bonding Overview CHEM ▶

Property	Ionic	Covalent	Metallic
Between	Metal + non-metal	Non-metal + non-metal	Metal + metal
What happens	Electrons transferred	Electrons shared	Sea of delocalised electrons
Structure	Giant ionic lattice	Simple molecules (usually)	Giant metallic lattice
Melting point	High	Low (simple), High (giant)	High
Conducts electricity?	When molten/dissolved	No (usually)	Yes (always)
Example	NaCl	H₂O, CO₂	Iron, copper

In ionic bonding, metals LOSE electrons (become positive ions) and non-metals GAIN electrons (become negative ions). Both achieve a full outer shell.

Sodium chloride (NaCl): Sodium (2,8,1) loses 1 electron to become Na⁺ (2,8). Chlorine (2,8,7) gains 1 electron to become Cl⁻ (2,8,8). The opposite charges attract — this is ionic bonding.

Chemical Reactions CHEM ▶

Writing Equations

Word equations: reactants → products

Balanced symbol equations: same number of each atom on both sides.

Balancing: Mg + O₂ → MgO. Count: 1 Mg each side (ok), but 2 O on left, 1 O on right. Fix: 2Mg + O₂ → 2MgO. Now balanced: 2 Mg, 2 O each side.

Types of Reaction

Combustion — fuel + oxygen → carbon dioxide + water (burning)
Neutralisation — acid + base → salt + water
Decomposition — one substance breaks down into two or more simpler substances
Displacement — a more reactive element takes the place of a less reactive one
Oxidation — gaining oxygen (or losing electrons)
Reduction — losing oxygen (or gaining electrons)

Remember OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

Quick Check: Balance this equation: Fe + Cl₂ → FeCl₃

2Fe + 3Cl₂ → 2FeCl₃. Check: 2 Fe each side, 6 Cl each side.

Acids and Alkalis CHEM ▶

The pH Scale

pH runs from 0 to 14. pH 7 = neutral. Below 7 = acidic. Above 7 = alkaline.

Strong acids — hydrochloric (HCl), sulfuric (H₂SO₄), nitric (HNO₃)
Alkalis — sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂)
Indicators — litmus (red in acid, blue in alkali), universal indicator (colour range), phenolphthalein

Neutralisation

acid + alkali → salt + water

acid + metal → salt + hydrogen

acid + carbonate → salt + water + carbon dioxide

Naming Salts

Hydrochloric acid → chloride salts (e.g. sodium chloride)
Sulfuric acid → sulfate salts (e.g. copper sulfate)
Nitric acid → nitrate salts (e.g. potassium nitrate)

Neutralisation titration: Use a burette to add acid to alkali (with indicator) until the indicator changes colour. This finds the exact volume needed for neutralisation.

Rates of Reaction CHEM ▶

Collision Theory

For a reaction to occur, particles must collide with sufficient energy (activation energy) and the correct orientation.

Factors Affecting Rate

Factor	Effect	Why (collision theory)
Temperature increase	Faster rate	Particles move faster, more frequent and energetic collisions
Concentration increase	Faster rate	More particles in same volume, more frequent collisions
Surface area increase (smaller pieces)	Faster rate	More particles exposed to react
Catalyst added	Faster rate	Lowers activation energy; provides alternative reaction pathway

Marble chips (CaCO₃) react with hydrochloric acid. Using powder instead of large chips increases the surface area, so the reaction is faster. You can measure the rate by collecting the CO₂ gas produced over time using a gas syringe.

A catalyst is NOT "used up" in the reaction. It speeds up the reaction by providing an alternative pathway with lower activation energy, but it is chemically unchanged at the end.

Earth and Atmosphere CHEM ▶

Composition of Air

Nitrogen — approximately 78%
Oxygen — approximately 21%
Argon — approximately 0.9%
Carbon dioxide — approximately 0.04%
Water vapour — variable amounts

Greenhouse Effect

Greenhouse gases (CO₂, methane, water vapour) absorb heat radiation from the Earth's surface and re-radiate it back, keeping the Earth warm enough for life. Without the greenhouse effect, Earth would be too cold.

Climate Change

Human activities are increasing greenhouse gases:

Burning fossil fuels — increases CO₂
Deforestation — fewer trees to absorb CO₂
Agriculture — cattle produce methane; rice paddies release methane

Consequences: rising sea levels, more extreme weather, habitat loss, species extinction.

Remember: the greenhouse effect itself is natural and essential for life. The problem is the ENHANCED greenhouse effect caused by human activities increasing greenhouse gas levels.

Materials and Their Uses CHEM ▶

Material	Properties	Uses
Metals (e.g. iron, copper, aluminium)	Strong, conduct heat and electricity, malleable, ductile	Wires (copper), structures (steel), aircraft (aluminium)
Polymers (plastics)	Lightweight, flexible, electrical insulators, can be moulded	Packaging, clothing, pipes
Ceramics (e.g. glass, clay)	Hard, brittle, heat resistant, electrical insulators	Bricks, tiles, pottery, glass windows
Composites (e.g. fibreglass, concrete)	Combine properties of two or more materials	Boats (fibreglass), buildings (reinforced concrete)

Choosing Materials

The material chosen for a job depends on its properties: strength, hardness, flexibility, cost, density, conductivity, resistance to corrosion, and environmental impact.

In exam questions asking "why is material X used for purpose Y", always link specific PROPERTIES to the specific USE. E.g. "Copper is used for wires because it is a good conductor of electricity and is ductile (can be drawn into thin wires)."

Quantitative Chemistry CHEM ▶

Relative Atomic Mass (Ar) & Relative Formula Mass (Mr)

Relative atomic mass (Ar) — the average mass of atoms of an element compared to 1/12th the mass of a carbon-12 atom. Found on the periodic table (the larger number).

Relative formula mass (Mr) — the sum of all the relative atomic masses in a formula.

Calculate the Mr of calcium carbonate, CaCO₃.
Ca = 40, C = 12, O = 16
Mr = 40 + 12 + (16 × 3) = 40 + 12 + 48 = 100

Calculate the Mr of magnesium hydroxide, Mg(OH)₂.
Mg = 24, O = 16, H = 1
Mr = 24 + (16 + 1) × 2 = 24 + 34 = 58

The Mole Concept

A mole is a quantity of substance. One mole of any substance contains 6.02 × 10²³ particles (Avogadro's number).

The key formula linking moles, mass, and Mr:

amount (mol) = mass (g) / Mr

Rearranged: mass = amount × Mr and Mr = mass / amount

How many moles in 11 g of carbon dioxide (CO₂)?
Mr of CO₂ = 12 + (16 × 2) = 44
Amount = mass / Mr = 11 / 44 = 0.25 mol

What is the mass of 2 mol of sodium hydroxide (NaOH)?
Mr of NaOH = 23 + 16 + 1 = 40
Mass = amount × Mr = 2 × 40 = 80 g

Balancing Equations & Conservation of Mass

In a chemical reaction, atoms are not created or destroyed — they are rearranged. The total mass of reactants always equals the total mass of products. This is the law of conservation of mass.

A balanced equation has the same number of each type of atom on both sides.

Balance: N₂ + H₂ → NH₃
Left: 2 N, 2 H. Right: 1 N, 3 H. Not balanced.
Step 1: Put 2 in front of NH₃ → N₂ + H₂ → 2NH₃
Now: Left: 2 N, 2 H. Right: 2 N, 6 H. H not balanced.
Step 2: Put 3 in front of H₂ → N₂ + 3H₂ → 2NH₃
Now: Left: 2 N, 6 H. Right: 2 N, 6 H. Balanced!

Calculating Masses of Reactants and Products

Use the balanced equation to find the molar ratio, then convert between moles and mass.

What mass of magnesium oxide is produced when 6 g of magnesium burns?
2Mg + O₂ → 2MgO
Step 1: Moles of Mg = mass / Ar = 6 / 24 = 0.25 mol
Step 2: From the equation, 2 mol Mg → 2 mol MgO (ratio 1:1)
So 0.25 mol Mg → 0.25 mol MgO
Step 3: Mass of MgO = amount × Mr = 0.25 × (24 + 16) = 0.25 × 40 = 10 g

Concentration

concentration (g/dm³) = mass of solute (g) / volume of solution (dm³)

Remember: 1 dm³ = 1000 cm³. To convert cm³ to dm³, divide by 1000.

4 g of sodium chloride is dissolved in 500 cm³ of water. What is the concentration?
Volume = 500 / 1000 = 0.5 dm³
Concentration = 4 / 0.5 = 8 g/dm³

A solution has a concentration of 20 g/dm³. What mass of solute is in 250 cm³ of this solution?
Step 1 — Write the formula: concentration = mass / volume
Step 2 — Rearrange for mass: mass = concentration × volume
Step 3 — Convert volume: 250 cm³ = 250 / 1000 = 0.25 dm³
Step 4 — Substitute: mass = 20 × 0.25
Step 5 — Calculate: mass = 5 g
Step 6 — Units check: g/dm³ × dm³ = g. Correct.

A student dissolves 12 g of sugar in water and makes a 250 cm³ solution. They then need to find what volume of this solution contains exactly 3 g of sugar.
Step 1 — Find concentration: C = mass / volume = 12 / 0.25 = 48 g/dm³
Step 2 — Rearrange for volume: volume = mass / concentration
Step 3 — Substitute: volume = 3 / 48 = 0.0625 dm³
Step 4 — Convert: 0.0625 × 1000 = 62.5 cm³
Step 5 — Units check: g / (g/dm³) = dm³. Correct.

Dilution Calculations

When you dilute a solution, the amount of solute stays the same but the volume increases. Use:

C₁ × V₁ = C₂ × V₂

where C₁ and V₁ are the initial concentration and volume, C₂ and V₂ are the final concentration and volume.

25 cm³ of acid with concentration 40 g/dm³ is diluted to 100 cm³. What is the new concentration?
C₁ × V₁ = C₂ × V₂
40 × 25 = C₂ × 100
1000 = C₂ × 100
C₂ = 1000 / 100 = 10 g/dm³

Always show your working in calculation questions — you can get method marks even if your final answer is wrong. Write the formula first, then substitute, then calculate.

Quick Check: Calculate the Mr of sulfuric acid, H₂SO₄ (H=1, S=32, O=16).

Mr = (1 × 2) + 32 + (16 × 4) = 2 + 32 + 64 = 98

Quick Check: How many moles in 20 g of NaOH (Mr = 40)?

Amount = mass / Mr = 20 / 40 = 0.5 mol

Earth Science & Environment CHEM ▶

The Carbon Cycle

Carbon is constantly recycled between the atmosphere, oceans, living organisms, and rocks:

Photosynthesis — plants absorb CO₂ from the atmosphere to make glucose
Respiration — all living organisms release CO₂ back into the atmosphere
Combustion — burning fossil fuels releases stored carbon as CO₂
Decomposition — decomposers break down dead organisms, releasing CO₂
Dissolving — CO₂ dissolves into oceans; marine organisms use it for shells
Fossil fuels form — dead organisms buried and compressed over millions of years

The carbon cycle is balanced when the amount of CO₂ removed from the atmosphere equals the amount added. Human activities have upset this balance.

The Greenhouse Effect & Climate Change

The greenhouse effect is a natural process where greenhouse gases (CO₂, methane, water vapour) in the atmosphere trap heat that would otherwise escape into space. Without it, Earth would be too cold for life.

The enhanced greenhouse effect is caused by human activities increasing greenhouse gas levels:

Burning fossil fuels (transport, power stations, industry) — increases CO₂
Deforestation — fewer trees to absorb CO₂ through photosynthesis
Agriculture — cattle and rice paddies produce methane
Landfill sites — decomposing waste produces methane

Evidence for Climate Change

Ice core data — trapped air bubbles show CO₂ levels over thousands of years
Rising global average temperatures (measured since 1850)
Retreating glaciers and melting ice caps
Rising sea levels
Coral bleaching and shifting wildlife habitats

Reducing Carbon Emissions

Use renewable energy sources instead of fossil fuels
Improve energy efficiency in buildings and transport
Carbon capture and storage (CCS) technology
Plant more trees (afforestation)
Reduce, reuse, recycle to cut manufacturing emissions
International agreements (e.g. Paris Agreement) to limit emissions

Renewable vs Non-Renewable Energy Sources

Feature	Renewable	Non-Renewable
Examples	Solar, wind, hydroelectric, tidal, geothermal, biomass, wave	Coal, oil, natural gas, nuclear
Will it run out?	No — replenished naturally	Yes — finite supply
CO₂ emissions	Very low / zero during use	High (fossil fuels); none (nuclear)
Reliability	Depends on weather/conditions (intermittent)	Reliable — available on demand
Cost	High setup cost; low running cost	Lower setup; ongoing fuel costs
Environmental impact	Visual impact; habitat disruption	Air pollution; oil spills; nuclear waste

Sustainability

Sustainability means meeting the needs of the present without compromising the ability of future generations to meet their own needs. This includes:

Using resources at a rate that allows them to be replenished
Reducing waste and pollution
Recycling metals, plastics, glass, and paper
Using renewable energy sources
Developing biodegradable materials as alternatives to plastics

Do not say "nuclear energy is renewable." It is NOT renewable because uranium is a finite resource. However, it does not produce CO₂ during generation (but does produce radioactive waste).

Quick Check: Name three greenhouse gases.

Carbon dioxide (CO₂), methane (CH₄), and water vapour. Nitrous oxide (N₂O) is also accepted.

Particle Model & States of Matter CHEM ▶

The Three States of Matter

All matter is made up of tiny particles (atoms, ions, or molecules). The arrangement, movement, and spacing of these particles determines whether a substance is a solid, liquid, or gas.

Particle Arrangement — Visual Guide

Property	Solid	Liquid	Gas
Arrangement	Particles packed in a regular, fixed pattern (like stacked oranges in a box). Touching neighbours on all sides.	Particles close together but in an irregular, jumbled arrangement. Still touching, but no fixed pattern.	Particles widely spaced and randomly scattered with large gaps between them.
Movement	Vibrate about fixed positions only. They do not move from place to place.	Slide and flow past each other. They can move around but stay close together.	Move rapidly in all directions, bouncing off each other and the walls of the container.
Forces between particles	Strong forces hold particles in place	Weaker forces than solid — particles can move past each other	Very weak forces — particles are essentially independent
Energy	Lowest energy of the three states	More energy than solid — enough to overcome some forces	Highest energy — particles have overcome almost all attractive forces
Shape & volume	Fixed shape and fixed volume	No fixed shape (takes shape of container) but fixed volume	No fixed shape and no fixed volume (fills entire container)
Density	High (particles closely packed)	High (slightly less than solid, usually)	Very low (particles far apart)
Can be compressed?	No (no space between particles)	No (very little space)	Yes (large spaces between particles)

Drawing particle diagrams: Draw circles to represent particles. For a solid, draw them in neat rows touching each other. For a liquid, draw them touching but jumbled with no pattern. For a gas, draw them far apart with lots of space and add arrows showing random movement directions.

Changes of State

Solid → (melting) → Liquid → (evaporating/boiling) → Gas

Gas → (condensing) → Liquid → (freezing) → Solid

Solid → (sublimation) → Gas (skipping the liquid state, e.g. dry ice)

During a change of state, energy is transferred but the temperature stays constant. The energy goes into breaking or forming bonds between particles, not into raising the temperature.

Changes of state are physical changes, not chemical changes — no new substances are formed and the process is reversible. The particles themselves do not change; only their arrangement and energy change.

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Forces PHYS ▶

Types of Force

Gravity (weight) — pulls objects towards Earth; W = mg
Friction — opposes motion between surfaces in contact
Air resistance (drag) — friction from air; increases with speed
Normal contact force — support force perpendicular to a surface
Tension — force in a stretched string or rope
Upthrust — upward force on an object in a fluid
Magnetic force — attraction or repulsion between magnets
Electrostatic force — between charged objects

Balanced & Unbalanced Forces

Balanced forces — resultant force is zero; object stays stationary or moves at constant speed.

Unbalanced forces — resultant force is not zero; object accelerates (speeds up, slows down, or changes direction).

Resultant Force

The overall force when all forces are combined. Forces in the same direction: add them. Forces in opposite directions: subtract the smaller from the larger.

A car has a driving force of 5000 N forwards and friction of 2000 N backwards. Resultant force = 5000 − 2000 = 3000 N forwards. Since the resultant is not zero, the car accelerates.

Quick Check: A skydiver falls at constant speed. What can you say about the forces?

The forces are balanced. Weight (gravity) downwards equals air resistance upwards. The resultant force is zero, so the skydiver falls at constant (terminal) velocity.

Speed and Motion PHYS ▶

Speed Equation

speed = distance / time

v = d / t

Units: speed in m/s, distance in m, time in s.

Distance-Time Graphs

Flat line — object is stationary (not moving)
Straight diagonal line — constant speed
Steeper line — faster speed
Curved line — changing speed (accelerating or decelerating)
Gradient of a distance-time graph = speed

A cyclist travels 600 m in 2 minutes. Speed = distance / time = 600 / 120 = 5 m/s. (Remember to convert 2 minutes to 120 seconds first!)

Always check your units. If distance is in km and time in hours, speed will be in km/h. If the question asks for m/s, convert first: 1 km = 1000 m, 1 hour = 3600 s.

Energy PHYS ▶

Energy Stores

Kinetic — energy of a moving object
Gravitational potential — energy stored due to height
Elastic potential — energy stored in a stretched/compressed object
Chemical — stored in food, fuel, batteries
Thermal (internal) — energy of particles; related to temperature
Nuclear — stored in the nucleus of an atom
Magnetic — energy stored in magnetic fields
Electrostatic — energy stored in electric fields

Energy Transfers

Energy can be transferred by: heating, radiation (light, sound), electrical current, and mechanical work (forces).

Conservation of Energy

Energy cannot be created or destroyed, only transferred from one store to another. The total energy in a closed system is always the same.

Efficiency

efficiency = (useful energy output / total energy input) x 100%

A light bulb uses 100 J of electrical energy. It produces 15 J of light energy and 85 J of thermal energy. Efficiency = (15 / 100) x 100% = 15%.

Energy Resources

Renewable	Non-Renewable
Solar, wind, hydroelectric, tidal, geothermal, biomass	Coal, oil, natural gas, nuclear
Will not run out; generally less pollution	Will run out; produce CO₂ (fossil fuels) or nuclear waste

Electricity PHYS ▶

Key Terms

Current (I) — the rate of flow of charge, measured in amps (A)
Voltage (V) — the energy transferred per unit of charge (potential difference), measured in volts (V)
Resistance (R) — how much a component opposes current flow, measured in ohms (Ω)

Ohm's Law

V = I × R (voltage = current × resistance)

Rearranged: I = V / R and R = V / I

Series vs Parallel Circuits

Feature	Series	Parallel
Current	Same throughout	Splits at junctions; adds up to total
Voltage	Shared between components; adds up to supply	Same across each branch
Resistance	Total = R₁ + R₂ + ...	Total is less than smallest individual
If one component breaks	Whole circuit stops	Other branches still work

A 12 V battery is connected to a 4 Ω resistor. What is the current? I = V / R = 12 / 4 = 3 A.

Circuit Diagrams — Series vs Parallel (Drawing Guide)

You must be able to draw and interpret circuit diagrams using standard symbols. Here is how each type is structured:

Feature	Series Circuit	Parallel Circuit
Layout	All components connected in a single loop, one after another. Draw: battery → wire → ammeter → wire → lamp 1 → wire → lamp 2 → wire → back to battery. One continuous path.	The circuit splits into two or more branches (like a road fork). Draw: battery → wire → junction point where the wire splits into two paths → each path has its own component (e.g. lamp) → paths rejoin → wire → back to battery.
Ammeter placement	Placed anywhere in the single loop (current is the same everywhere). Draw it as a circle with a capital A inside.	Place in the main line (before the split) to measure total current, or in a branch to measure that branch's current.
Voltmeter placement	Connected in parallel across the component you want to measure. Draw it as a circle with a capital V, with wires connecting to each side of the component.	Same — always in parallel across the component being measured.
Standard symbols to know	Cell: long thin line (positive) and short thick line (negative). Battery: two or more cells. Lamp: circle with a cross inside. Resistor: rectangle. Variable resistor: rectangle with an arrow through it. Switch: gap with a movable arm. Ammeter: circle with A. Voltmeter: circle with V.

When drawing circuits: use a ruler for straight lines, draw wires as sharp right-angle turns (not curves), and always use standard circuit symbols. Never draw pictorial representations of components (e.g. do not draw a realistic battery — use the symbol).

Investigate the relationship between voltage and current for a resistor. Use a variable resistor to change current, measure V with a voltmeter (in parallel) and I with an ammeter (in series). Plot V against I — a straight line through the origin shows the resistor obeys Ohm's law.

Quick Check: Two 6 Ω resistors are connected in series to a 12 V battery. What is the current?

Total resistance = 6 + 6 = 12 Ω. Current = V / R = 12 / 12 = 1 A.

Waves PHYS ▶

Wave Properties

Wavelength (λ) — distance from one point on a wave to the same point on the next wave (metres)
Frequency (f) — number of waves passing a point per second (hertz, Hz)
Amplitude — maximum displacement from the rest position
Wave speed: v = f × λ

Transverse vs Longitudinal

Feature	Transverse	Longitudinal
Oscillation direction	Perpendicular to wave direction	Parallel to wave direction
Examples	Light, water waves, EM waves	Sound, ultrasound, seismic P-waves
Can be polarised?	Yes	No

Electromagnetic Spectrum (in order of increasing frequency)

Radio → Microwave → Infrared → Visible → Ultraviolet → X-rays → Gamma rays

All EM waves travel at the speed of light (3 × 10⁸ m/s) in a vacuum. Higher frequency = higher energy = more dangerous.

Wave	Use	Danger
Radio	TV, radio broadcasts	Low risk
Microwave	Cooking, mobile phones	Heating of body tissue
Infrared	Heaters, remote controls, thermal imaging	Burns
Visible light	Seeing, fibre optics	Eye damage (intense)
Ultraviolet	Sun tanning, sterilisation	Skin cancer, eye damage
X-rays	Medical imaging, airport security	Cell damage, cancer
Gamma rays	Cancer treatment, sterilisation	Cell damage, cancer

Remember the EM spectrum order with: "Raging Martians Invaded Venus Using X-ray Guns" (Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma).

Magnetism and Electromagnets PHYS ▶

Magnetic Fields

A magnetic field is the region around a magnet where a magnetic force acts
Field lines go from north to south (outside the magnet)
Closer field lines = stronger magnetic field
Like poles repel, unlike poles attract

Electromagnets

A coil of wire carrying an electric current creates a magnetic field. Placing an iron core inside the coil makes the field much stronger.

Advantages over permanent magnets: can be switched on and off; strength can be varied by changing the current.

Making Electromagnets Stronger

Increase the current
Increase the number of coils
Use an iron core

Uses of Electromagnets

Scrapyard cranes (pick up and release metal)
Electric bells and buzzers
Relays (switches)
MRI scanners

Radioactivity PHYS ▶

Radioactive Decay

Unstable nuclei emit radiation to become more stable. This is a random process.

Types of Radiation

Property	Alpha (α)	Beta (β)	Gamma (γ)
What is it?	2 protons + 2 neutrons (helium nucleus)	High-speed electron	Electromagnetic wave
Charge	+2	-1	0
Penetration	Stopped by paper/skin	Stopped by aluminium	Reduced by thick lead/concrete
Ionising power	Strongest	Moderate	Weakest
Range in air	A few cm	A few metres	Unlimited (inverse square law)

Half-Life

The time taken for the number of radioactive nuclei (or activity) to halve.

A sample has an activity of 800 Bq and a half-life of 3 hours. After 3 hours: 400 Bq. After 6 hours: 200 Bq. After 9 hours: 100 Bq. (Three half-lives have passed.)

Uses and Dangers

Medical — gamma rays to treat cancer (radiotherapy); tracers in the body
Smoke detectors — alpha source (americium-241)
Carbon dating — measuring carbon-14 to determine age of fossils/artefacts
Dangers — radiation can damage or kill cells; can cause cancer and mutations

Irradiation (being exposed to radiation) is different from contamination (radioactive material getting on or in the body). Irradiation stops when the source is removed; contamination is an ongoing risk.

Space PHYS ▶

The Solar System

The Sun is a star at the centre. Planets orbit the Sun. Moons orbit planets. Our solar system is part of the Milky Way galaxy.

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

Inner planets (rocky/terrestrial): Mercury, Venus, Earth, Mars. Outer planets (gas/ice giants): Jupiter, Saturn, Uranus, Neptune.

Lifecycle of Stars

Nebula — cloud of dust and gas
Protostar — gravity pulls gas together; temperature rises
Main sequence star — stable; fusion of hydrogen into helium (our Sun is here)
Red giant (or red supergiant for massive stars) — hydrogen runs out; star expands
For average stars: White dwarf → Black dwarf
For massive stars: Supernova → Neutron star or Black hole

The Sun is a main sequence star. It will eventually become a red giant, then a white dwarf. It is NOT massive enough to become a supernova or black hole.

Physics Calculations — Worked Examples PHYS ▶

Speed, Distance & Time

speed = distance / time distance = speed × time time = distance / speed

Use the formula triangle: D on top, S and T on the bottom. Cover what you want to find.

A car travels 150 km in 2.5 hours. What is its average speed?
speed = distance / time = 150 / 2.5 = 60 km/h

A runner moves at 8 m/s for 25 seconds. How far do they travel?
distance = speed × time = 8 × 25 = 200 m

How long does it take sound (340 m/s) to travel 1700 m?
time = distance / speed = 1700 / 340 = 5 s

Velocity-Time Graphs

Gradient (slope) of a velocity-time graph = acceleration
Area under the graph = distance travelled
Flat line = constant velocity (no acceleration)
Upward slope = acceleration
Downward slope = deceleration
Line at zero = stationary

A car accelerates from 0 to 20 m/s in 10 seconds, then travels at 20 m/s for 5 seconds.
Acceleration = change in velocity / time = (20 − 0) / 10 = 2 m/s²
Distance during acceleration = area of triangle = ½ × base × height = ½ × 10 × 20 = 100 m
Distance at constant speed = area of rectangle = 20 × 5 = 100 m
Total distance = 100 + 100 = 200 m

Weight, Mass & Gravity

weight (N) = mass (kg) × gravitational field strength (N/kg)

W = m × g

On Earth, g = 10 N/kg (or 9.8 N/kg for more accuracy). Weight is a force measured in newtons; mass is measured in kilograms.

What is the weight of a 65 kg person on Earth (g = 10 N/kg)?
W = m × g = 65 × 10 = 650 N

An object weighs 180 N on Earth. What is its mass?
m = W / g = 180 / 10 = 18 kg

Work Done

work done (J) = force (N) × distance (m)

W = F × d

Work done is the energy transferred when a force moves an object. 1 joule = 1 newton moved 1 metre.

A person pushes a box with a force of 50 N over a distance of 8 m. How much work is done?
W = F × d = 50 × 8 = 400 J

Power

power (W) = work done (J) / time (s)

P = W / t

Power is the rate of energy transfer. Measured in watts (W). 1 watt = 1 joule per second.

A crane does 12,000 J of work lifting a load in 30 seconds. What is its power?
P = W / t = 12000 / 30 = 400 W

A 2000 W motor runs for 5 minutes. How much energy does it transfer?
Time = 5 × 60 = 300 s
W = P × t = 2000 × 300 = 600,000 J (600 kJ)

Efficiency

efficiency = (useful energy output / total energy input) × 100%

Efficiency can never be more than 100%. Wasted energy is usually transferred as heat to the surroundings.

A motor uses 500 J of electrical energy. It converts 350 J into useful kinetic energy. What is its efficiency?
Efficiency = (350 / 500) × 100% = 70%

A light bulb is 20% efficient and uses 60 J. How much useful light energy does it produce?
Useful output = efficiency × total input / 100 = 20 × 60 / 100 = 12 J

Pressure

pressure (Pa) = force (N) / area (m²)

P = F / A

Pressure is measured in pascals (Pa). 1 Pa = 1 N/m².

A box weighing 200 N has a base area of 0.5 m². What pressure does it exert on the floor?
P = F / A = 200 / 0.5 = 400 Pa

A stiletto heel has an area of 0.0001 m² and the person weighs 600 N. What pressure does the heel exert?
P = F / A = 600 / 0.0001 = 6,000,000 Pa (6 MPa)
This is why stiletto heels can damage floors — the small area creates enormous pressure!

Density

density (kg/m³) = mass (kg) / volume (m³)

ρ = m / V

Density tells you how much mass is packed into a given volume. An object floats if its density is less than the liquid it is placed in.

A block has a mass of 500 g and a volume of 200 cm³. What is its density?
ρ = m / V = 500 / 200 = 2.5 g/cm³
(In kg/m³: 2.5 × 1000 = 2500 kg/m³)

A metal cube has a density of 7800 kg/m³ and a volume of 0.002 m³. What is its mass?
Step 1 — Write the formula: ρ = m / V
Step 2 — Rearrange for mass: m = ρ × V
Step 3 — Substitute: m = 7800 × 0.002
Step 4 — Calculate: m = 15.6 kg
Step 5 — Units check: kg/m³ × m³ = kg. Correct.

A stone has a mass of 250 g. It is lowered into a measuring cylinder containing 50 cm³ of water. The water level rises to 143 cm³. What is the density of the stone?
Step 1 — Find the volume: V = 143 − 50 = 93 cm³ (displacement method)
Step 2 — Write the formula: ρ = m / V
Step 3 — Substitute: ρ = 250 / 93
Step 4 — Calculate: ρ = 2.69 g/cm³ (to 3 s.f.)
Step 5 — Units check: g / cm³ = g/cm³. Correct.

For rearranging formulas, use the formula triangle method: write the equation with one quantity on top and two on the bottom. Cover the one you need to find — if the remaining two are side by side, multiply them; if one is above the other, divide.

Quick Check: A force of 120 N is applied to move a trolley 6 m. The work takes 15 seconds. Calculate: (a) work done (b) power.

(a) Work done = F × d = 120 × 6 = 720 J. (b) Power = W / t = 720 / 15 = 48 W.

Quick Check: A ball has mass 0.4 kg and volume 0.0005 m³. What is its density? Will it float in water (density 1000 kg/m³)?

Density = m / V = 0.4 / 0.0005 = 800 kg/m³. Yes, it will float because 800 kg/m³ is less than water's density of 1000 kg/m³.

Waves — In-Depth PHYS ▶

Wave Definitions

Wavelength (λ) — the distance from one point on a wave to the equivalent point on the next wave (e.g. crest to crest), measured in metres (m)
Frequency (f) — the number of complete waves passing a point per second, measured in hertz (Hz)
Amplitude — the maximum displacement from the rest (equilibrium) position; determines loudness (sound) or brightness (light)
Period (T) — the time for one complete wave to pass, measured in seconds. T = 1 / f
Wave speed (v) — how fast the wave travels, measured in m/s

The Wave Equation

wave speed = frequency × wavelength

v = f × λ

A sound wave has a frequency of 256 Hz and a wavelength of 1.3 m. What is the wave speed?
v = f × λ = 256 × 1.3 = 332.8 m/s

A radio wave travels at 3 × 10⁸ m/s and has a wavelength of 1500 m. What is its frequency?
f = v / λ = 3 × 10⁸ / 1500 = 200,000 Hz (200 kHz)

An FM radio station broadcasts at 100 MHz (100 × 10⁶ Hz). What is the wavelength?
λ = v / f = 3 × 10⁸ / (100 × 10⁶) = 3 m

A microwave oven produces waves with a frequency of 2450 MHz and a wavelength of 0.122 m. Verify the wave speed.
Step 1 — Write the formula: v = f × λ
Step 2 — Convert units: 2450 MHz = 2450 × 10⁶ Hz = 2.45 × 10⁹ Hz
Step 3 — Substitute: v = 2.45 × 10⁹ × 0.122
Step 4 — Calculate: v = 2.99 × 10⁸ m/s (approximately 3 × 10⁸ m/s — the speed of light, as expected for EM waves)
Step 5 — Units check: Hz × m = (1/s) × m = m/s. Correct.

Transverse vs Longitudinal Waves

Feature	Transverse	Longitudinal
Oscillation	Perpendicular (at right angles) to the direction of wave travel	Parallel to the direction of wave travel
What you see	Peaks (crests) and troughs	Compressions and rarefactions
Examples	Light, water waves, all EM waves, S-waves (seismic)	Sound, ultrasound, P-waves (seismic)
Can be polarised?	Yes	No
Travel through	Some need a medium (water waves); EM waves travel through a vacuum	Must have a medium (cannot travel through a vacuum)

Electromagnetic (EM) Spectrum

All EM waves are transverse, travel at the speed of light (3 × 10⁸ m/s) in a vacuum, and transfer energy. They differ in wavelength and frequency.

In order of increasing frequency (and increasing energy, decreasing wavelength):

Radio → Microwave → Infrared → Visible Light → Ultraviolet → X-rays → Gamma rays

EM Wave	Typical Use	Dangers
Radio waves	TV and radio broadcasting, Bluetooth, WiFi	Generally safe (low energy)
Microwaves	Cooking (microwave ovens), satellite communication, mobile phones	Heating of body tissue (internal)
Infrared (IR)	Heaters, remote controls, thermal imaging cameras, optical fibres	Skin burns
Visible light	Sight, photography, fibre optic communication	Eye damage at high intensity
Ultraviolet (UV)	Sunbeds, sterilising water, detecting forged banknotes, fluorescence	Skin cancer (melanoma), premature skin ageing, eye damage (cataracts)
X-rays	Medical imaging (bones), airport security scanners	Cell damage, cancer (ionising)
Gamma rays (γ)	Treating cancer (radiotherapy), sterilising medical equipment and food	Cell damage, cancer (most ionising)

Higher frequency EM waves carry more energy and are more dangerous. UV, X-rays, and gamma rays are ionising — they can knock electrons off atoms and damage DNA in cells.

Reflection

When a wave hits a boundary, it can bounce back. The angle of incidence (between incoming ray and the normal) equals the angle of reflection (between reflected ray and the normal).

The normal is an imaginary line perpendicular to the surface at the point of incidence.

Refraction

When a wave passes from one medium to another, it changes speed. If it enters at an angle (not along the normal), it also changes direction.

Light going from air into glass (less dense → more dense): slows down and bends towards the normal
Light going from glass into air (more dense → less dense): speeds up and bends away from the normal
If light hits the boundary along the normal (at 0°), it slows down but does NOT change direction

Refraction is a change in direction caused by a change in speed. Do NOT say "the wave bends because it slows down" without mentioning it must enter at an angle to the boundary.

Quick Check: A wave has a frequency of 500 Hz and a wavelength of 0.66 m. (a) What is its speed? (b) What is its period?

(a) v = f × λ = 500 × 0.66 = 330 m/s. (b) T = 1 / f = 1 / 500 = 0.002 s (2 milliseconds).

Want more detail? Visit the Double Award Physics page →

Scientific Method Overview PRAC ▶

The Scientific Method

Make an observation and ask a question
Form a hypothesis (a testable prediction)
Plan and carry out an experiment
Collect and analyse results
Draw a conclusion
Evaluate the method and suggest improvements

Types of Variable

Independent variable — the one you deliberately change
Dependent variable — the one you measure
Control variables — kept the same to make the test fair

Always identify all three types of variable when describing a practical. This is one of the easiest marks to pick up in practical questions.

Biology Practicals BIO ▶

Food Tests

Nutrient	Test	Positive Result
Starch	Iodine solution	Brown/yellow → blue-black
Glucose (reducing sugar)	Benedict's solution + heat	Blue → green → yellow → orange → brick red
Protein	Biuret reagent	Blue → purple/lilac
Fat/lipid	Ethanol emulsion test	Cloudy white emulsion

Osmosis in Potato Chips

Cut potato chips of equal size and mass. Place in different concentrations of sugar/salt solution. Leave for set time. Measure final mass. Calculate % change in mass.

IV: concentration of solution. DV: change in mass. CV: volume of solution, size of potato, temperature, time.

Effect of Light on Photosynthesis (Pondweed)

Place Elodea (pondweed) at different distances from a lamp. Count bubbles of oxygen per minute at each distance.

IV: distance from lamp (light intensity). DV: number of bubbles per minute. CV: temperature, CO₂ concentration, volume of water, same plant.

Chemistry Practicals CHEM ▶

Rate of Reaction: Marble Chips + Acid

Add marble chips (CaCO₃) to hydrochloric acid. Collect CO₂ gas using a gas syringe or measure mass loss on a balance. Record volume/mass at regular intervals.

IV: concentration of acid (or size of marble chips). DV: volume of gas produced (or mass lost). CV: mass of marble chips, volume of acid, temperature.

Neutralisation / Titration

Add acid from a burette to a known volume of alkali (with indicator) in a conical flask. Swirl until the indicator changes colour permanently. Record the volume of acid used.

Temperature Change in Neutralisation

Measure temperature of acid. Add alkali in small amounts. Record temperature after each addition. The temperature rises as neutralisation is exothermic.

Physics Practicals PHYS ▶

Investigating Resistance (Ohm's Law)

Set up a circuit with a battery, ammeter (in series), voltmeter (in parallel), variable resistor, and the resistor being tested. Vary the current using the variable resistor. Record voltage and current. Plot V-I graph.

IV: voltage (or current). DV: current (or voltage). CV: temperature, same resistor.

Investigating Speed

Use a ramp and trolley. Release trolley from different heights. Measure time to travel a set distance using light gates or a stopwatch. Calculate speed = distance / time.

IV: height of ramp. DV: speed of trolley. CV: same trolley, same distance, same surface.

Presenting & Evaluating Results PRAC ▶

Tables

Independent variable in the first column, dependent variable in subsequent columns
Include units in the column headers (not in the cells)
Record all readings to the same number of decimal places
Include repeats and calculate a mean (ignore anomalies when calculating)

Graphs

Independent variable on x-axis, dependent variable on y-axis
Label both axes with quantity and unit
Use a sensible scale — at least half the graph paper
Plot points accurately with a small cross
Draw a line of best fit (straight or curve) — it does not have to go through every point

Evaluating Experiments

Accuracy — how close to the true value
Precision — how close repeat measurements are to each other
Reliability — results are consistent when repeated (improved by repeating and averaging)
Validity — the experiment measures what it is supposed to measure; fair test
Anomalies — results that do not fit the pattern; should be identified and excluded from mean

Do not confuse accuracy with precision. A set of results can be precise (close together) but inaccurate (all far from the true value), like a dartboard where all darts hit the same wrong spot.

Practical: Light Intensity & Photosynthesis (Pondweed) PRAC ▶

Aim

To investigate the effect of light intensity on the rate of photosynthesis using aquatic pondweed (Elodea).

Equipment

Elodea (pondweed) — freshly cut at an angle
Beaker of water (with a small amount of sodium hydrogen carbonate to provide CO₂)
Bench lamp (light source)
Metre ruler
Stopwatch
Thermometer

Method

Place the pondweed in the beaker of water, cut end facing upwards
Add a small amount of sodium hydrogen carbonate (NaHCO₃) to ensure CO₂ is not a limiting factor
Position the lamp at a set distance from the beaker (e.g. 10 cm)
Leave for 2 minutes to allow the plant to acclimatise
Count the number of oxygen bubbles produced in 1 minute
Repeat the count 3 times and calculate a mean
Move the lamp to the next distance (e.g. 20 cm, 30 cm, 40 cm, 50 cm) and repeat

Variables

Variable Type	Variable
Independent	Distance from lamp (light intensity)
Dependent	Number of oxygen bubbles per minute
Control	Temperature of water, CO₂ concentration, volume of water, same piece of pondweed, same lamp

Expected Results

As the lamp is moved closer (light intensity increases), the number of bubbles per minute increases. As the lamp is moved further away, fewer bubbles are produced. The relationship is not linear — light intensity is proportional to 1/distance².

Analysis & Conclusion

Plot a graph of bubbles per minute (y-axis) against distance from lamp (x-axis). The graph should show a decrease in bubble rate as distance increases. This shows that increasing light intensity increases the rate of photosynthesis — light is needed as an energy source for the reaction.

If asked to improve this experiment: use a gas syringe to collect and measure the volume of oxygen more accurately instead of counting bubbles (which can vary in size).

Practical: Food Tests PRAC ▶

Aim

To test food samples for the presence of starch, reducing sugars, protein, and fats/lipids.

Equipment

Food samples (dissolved/ground in water)
Test tubes, test tube rack, test tube holder
Iodine solution
Benedict's solution + water bath or Bunsen burner
Biuret reagent (or sodium hydroxide + copper sulfate solution)
Ethanol + water (for emulsion test)
Safety goggles

Test Methods & Results

Nutrient	Reagent	Method	Negative Result	Positive Result
Starch	Iodine solution	Add a few drops of iodine to the food sample	Stays brown/yellow	Turns blue-black
Reducing sugar (e.g. glucose)	Benedict's solution	Add Benedict's to the sample and heat in a water bath at 80°C for 5 minutes	Stays blue	Changes from blue → green → yellow → orange → brick red (more sugar = more colour change)
Protein	Biuret reagent	Add Biuret reagent to the sample and gently shake	Stays blue	Turns purple/lilac
Fat/Lipid	Ethanol	Dissolve food in ethanol, then pour into water	Solution stays clear	Cloudy white emulsion forms

Variables

Independent: type of food sample. Dependent: colour change observed. Control: volume of reagent, volume of food sample, time allowed for reaction, temperature (for Benedict's test).

Analysis

Record the colour change for each food sample with each reagent. A positive result indicates the nutrient is present. Benedict's test is semi-quantitative — the more sugar present, the further the colour changes from blue towards brick red.

Benedict's test requires HEAT. If you forget to heat the sample, you will get a false negative result. Also remember Benedict's only tests for REDUCING sugars (like glucose), not all sugars.

Practical: Investigating Enzyme Activity (Amylase) PRAC ▶

Aim

To investigate the effect of temperature (or pH) on the rate of enzyme activity, using amylase to break down starch.

Equipment

Amylase enzyme solution
Starch solution (1%)
Iodine solution
Spotting tile (dimple tile)
Water baths at different temperatures (e.g. 20°C, 30°C, 40°C, 50°C, 60°C)
Stopwatch
Thermometer
Test tubes, syringes/pipettes
For pH investigation: buffer solutions at different pH values

Method (Effect of Temperature)

Place drops of iodine into each well of a spotting tile
Put the starch solution and amylase solution in separate test tubes in the water bath at the first temperature
Wait 5 minutes for both solutions to reach the required temperature
Mix the amylase into the starch solution and start the stopwatch
Every 30 seconds, take a small sample with a pipette and add to a well of iodine on the spotting tile
Record the time when the iodine stops turning blue-black (starch has been fully broken down)
Repeat at each temperature. Repeat each temperature 3 times for reliability

Variables

Variable Type	Variable
Independent	Temperature of the water bath (or pH of buffer solution)
Dependent	Time taken for starch to be fully digested (iodine stays brown/yellow)
Control	Volume and concentration of starch, volume and concentration of amylase, pH (if testing temperature), temperature (if testing pH)

Expected Results

As temperature increases from room temperature, the enzyme works faster (less time to break down starch). The fastest rate occurs at the optimum temperature (around 37°C for amylase). Above the optimum, the enzyme becomes denatured — the active site changes shape, and the reaction slows dramatically or stops.

Analysis & Conclusion

Plot a graph of time taken (y-axis) against temperature (x-axis). The graph should show a decrease in time as temperature rises to the optimum, then a sharp increase as the enzyme denatures. Alternatively, plot rate of reaction (1/time) against temperature for an optimum curve.

When the enzyme is denatured, say the "active site has changed shape so the substrate can no longer fit" (lock and key model). Do NOT say the enzyme is "killed" — enzymes are not alive.

Practical: Osmosis in Potato Chips PRAC ▶

Aim

To investigate the effect of solution concentration on osmosis in potato tissue, by measuring the change in mass of potato chips placed in different concentrations of sucrose solution.

Equipment

Potato, cork borer, scalpel, ruler
Sucrose solutions at different concentrations (e.g. 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, 1.0 M)
Boiling tubes or beakers
Electronic balance (to 2 decimal places)
Paper towels
Stopwatch

Method

Use a cork borer to cut potato cylinders of equal length (e.g. 3 cm)
Blot each chip dry with paper towel and measure its initial mass
Place one chip into each solution (different concentrations)
Leave for 20–30 minutes
Remove each chip, blot dry gently, and measure the final mass
Calculate the percentage change in mass: % change = ((final − initial) / initial) × 100
Repeat the experiment 3 times and calculate mean % change for each concentration

Variables

Variable Type	Variable
Independent	Concentration of sucrose solution
Dependent	Percentage change in mass of potato chip
Control	Volume of solution, initial size/length of potato chips, time left in solution, temperature, type of potato, blotting method

Expected Results

In dilute solutions (e.g. distilled water, 0.0 M): the potato gains mass — water enters by osmosis (solution outside is more dilute than inside the cells)
In concentrated solutions (e.g. 0.8 M, 1.0 M): the potato loses mass — water leaves by osmosis (solution outside is more concentrated than inside the cells)
At one concentration, there will be no change in mass — this is where the solution concentration equals the concentration inside the potato cells

Analysis & Conclusion

Plot a graph of % change in mass (y-axis) against concentration (x-axis). The line should go from positive values (mass gain in dilute) through zero to negative values (mass loss in concentrated). Where the line crosses the x-axis is the concentration of the cell sap.

Always use % change in mass rather than actual mass change. This allows a fair comparison between potato chips that may have started at slightly different masses.

Practical: Investigating Resistance in a Wire PRAC ▶

Aim

To investigate how the length of a wire affects its resistance.

Equipment

Nichrome or constantan wire (at least 1 m)
Metre ruler
Ammeter
Voltmeter
Battery / power supply (low voltage, e.g. 1.5 V)
Crocodile clips
Variable resistor (optional, to keep current low)

Method

Set up the circuit: power supply → ammeter (in series) → wire → back to power supply, with a voltmeter connected in parallel across the wire
Attach crocodile clips to the wire at a length of 10 cm
Switch on the circuit and record the ammeter reading (I) and voltmeter reading (V)
Calculate resistance: R = V / I
Repeat for lengths of 20 cm, 30 cm, 40 cm, 50 cm, etc.
Repeat each length 3 times and calculate a mean resistance
Switch off between readings to prevent the wire heating up

Variables

Variable Type	Variable
Independent	Length of wire
Dependent	Resistance (calculated from V and I)
Control	Type of wire (material), thickness (diameter/cross-sectional area) of wire, temperature of wire

Expected Results

As the length of wire increases, the resistance increases proportionally. A wire twice as long has twice the resistance. This is because electrons have to travel through more of the wire, encountering more collisions with the metal ions.

Analysis & Conclusion

Plot a graph of resistance (y-axis) against length (x-axis). The graph should be a straight line through the origin, showing that resistance is directly proportional to length.

The wire heats up as current flows through it, which increases its resistance. Switch the circuit off between readings and keep the current low to minimise this effect — otherwise it is no longer a fair test.

Practical: Neutralisation Reactions & pH PRAC ▶

Aim

To investigate neutralisation by measuring the temperature change when acid reacts with alkali, and to monitor pH changes during neutralisation.

Equipment

Dilute hydrochloric acid (e.g. 1 mol/dm³)
Dilute sodium hydroxide solution (e.g. 1 mol/dm³)
Polystyrene cup (insulating container)
Thermometer (or temperature probe)
Measuring cylinder
Universal indicator paper or pH meter
Safety goggles

Method (Temperature Change)

Measure 25 cm³ of sodium hydroxide solution into a polystyrene cup
Record the starting temperature
Add 5 cm³ of hydrochloric acid, stir, and record the temperature
Continue adding 5 cm³ of acid at a time, recording the temperature each time
Continue until you have added excess acid (e.g. 50 cm³ total)

Variables

Variable Type	Variable
Independent	Volume of acid added
Dependent	Temperature change (and/or pH)
Control	Concentration of acid and alkali, starting temperature, starting volume of alkali, type of acid and alkali

Expected Results

The temperature rises as acid is added (neutralisation is exothermic). The maximum temperature is reached at the point of complete neutralisation. After this, adding more acid causes the temperature to decrease slightly (excess acid cools the mixture).

The pH starts high (alkaline), decreases as acid is added, passes through pH 7 at the neutralisation point, and continues to decrease into acidic values.

Analysis & Conclusion

Plot temperature against volume of acid added. The peak shows the neutralisation point. The reaction is: acid + alkali → salt + water (exothermic).

A polystyrene cup is used because it is an insulator — it reduces heat loss to the surroundings, making the temperature measurement more accurate.

Practical: Rates of Reaction (Marble Chips & Acid) PRAC ▶

Aim

To investigate how the concentration (or surface area) of reactants affects the rate of reaction between marble chips (calcium carbonate) and hydrochloric acid.

Equipment

Marble chips (calcium carbonate, CaCO₃) — large, medium, and powdered
Hydrochloric acid at different concentrations (e.g. 0.5 M, 1.0 M, 1.5 M, 2.0 M)
Conical flask
Gas syringe (or inverted measuring cylinder and water trough)
Electronic balance (if measuring mass loss)
Cotton wool plug (if measuring mass loss — stops liquid splashing out but lets gas escape)
Stopwatch

Reaction

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Method

Measure a fixed mass of marble chips (e.g. 5 g) and place in a conical flask
Measure a fixed volume of acid (e.g. 50 cm³) at the first concentration
Add the acid to the marble chips and immediately start the stopwatch and connect the gas syringe
Record the volume of CO₂ gas collected every 30 seconds for 5 minutes
Repeat with different concentrations (or different sizes of marble chips)
Repeat each experiment 3 times for reliability

Variables

Variable Type	Variable
Independent	Concentration of acid (or size of marble chips for surface area investigation)
Dependent	Volume of CO₂ gas produced (or mass lost) over time
Control	Mass of marble chips, volume of acid, temperature, same type of marble chips

Expected Results

Higher concentration of acid → faster reaction (steeper curve on the graph, reaches maximum volume sooner). The total volume of gas is the same — the reaction just finishes sooner. Similarly, smaller chips (greater surface area) react faster than large chips.

Analysis & Conclusion

Plot volume of gas (y-axis) against time (x-axis) for each concentration on the same graph. Steeper initial gradient = faster rate. All lines level off at the same total volume (same amount of marble chips used).

The rate of reaction at any point = the gradient of the line at that point. The steepest part of the curve (at the start) is where the rate is fastest because the concentration of acid is highest.

Practical: Chromatography PRAC ▶

Aim

To separate and identify the different dyes/substances in a mixture using paper chromatography.

Equipment

Chromatography paper (or filter paper)
Beaker
Solvent (water for water-soluble dyes, or ethanol for other substances)
Pencil (NOT pen — pen ink would dissolve and run)
Ruler
Capillary tube (to apply spots)
Samples to test (e.g. food colourings, inks, plant pigments)
Watch glass or cling film (to cover beaker)

Method

Draw a pencil line (the origin line) near the bottom of the chromatography paper — above the level the solvent will reach
Place small spots of each sample on the pencil line, spacing them evenly
Pour a small amount of solvent into the beaker — the level must be BELOW the pencil line
Stand the paper in the solvent (spots must not touch the solvent)
Cover the beaker and leave until the solvent has risen close to the top
Remove the paper and immediately mark the solvent front with a pencil line
Allow the paper to dry

Variables

Variable Type	Variable
Independent	Type of sample / substance tested
Dependent	Distance travelled by each dye / Rf value
Control	Type of paper, type of solvent, volume of solvent, temperature, size of spots applied

Expected Results

Different dyes/substances travel different distances up the paper. A pure substance produces a single spot. A mixture separates into multiple spots. Substances separate because they have different solubilities in the solvent — more soluble substances are carried further.

Calculating Rf Values

Rf = distance travelled by substance / distance travelled by solvent front

Rf values are always between 0 and 1. Each substance has a unique Rf value in a given solvent, so Rf values can be used to identify unknown substances by comparison with known ones.

A dye spot travels 4.8 cm. The solvent front travels 8.0 cm.
Rf = 4.8 / 8.0 = 0.60

The origin line must be drawn in PENCIL, not pen. Pen ink would dissolve in the solvent and interfere with results. Also ensure the spots are above the solvent level — if the spots touch the solvent, the dyes dissolve directly into it instead of travelling up the paper.

Paper Structure & Timing EXAM ▶

CCEA GCSE Science (Single Award)

One written exam paper covering Biology, Chemistry, and Physics
The paper is divided into sections for each science
Mix of question types: multiple choice, short answer, structured questions, extended writing (6-mark QWC)
Grades: a single GCSE grade is awarded

Timing Tips

Roughly 1 minute per mark as a guide
Do not spend too long on one question — move on and come back
Leave 5-10 minutes at the end to check your answers
Attempt EVERY question — never leave a blank answer

Read each question at least twice before answering. Underline key words and command words to focus your response.

Command Words EXAM ▶

Command Word	What It Means	Example Response
State / Name / Give	Short, factual answer — no explanation needed	"Mitochondria"
Describe	Say what happens — give the key features	"The temperature increases then levels off"
Explain	Say what happens AND why	"Rate increases because particles have more energy, so more successful collisions"
Compare	Give similarities AND differences; use comparative language	"Both have a nucleus, however only plant cells have a cell wall"
Evaluate	Weigh up evidence, consider for and against, give a conclusion	"The data supports X because..., however Y could also..."
Suggest	Apply your knowledge to an unfamiliar context	Use scientific principles to reason an answer
Calculate	Use numbers and a formula; show your working	"V = IR = 3 x 4 = 12 V"

If a question says "explain", a simple description will not get full marks. You MUST give reasons (use "because", "this means that", "therefore").

Answering 6-Mark Questions (QWC) EXAM ▶

QWC = Quality of Written Communication. These questions test your ability to write a clear, logical, scientific argument.

Structure

Plan — spend 1 minute jotting key points before writing
Introduction — briefly state what you will discuss
Main body — write in a logical order; use paragraphs; include scientific keywords
Conclusion — summarise your main point

Top Tips

Use correct scientific terminology throughout
Write in full sentences (not bullet points unless told otherwise)
Check spelling of key scientific words
Link cause and effect clearly ("this leads to...", "because...", "resulting in...")
Aim for at least 6 distinct scientific points
Keep it focused — do not waffle or repeat yourself

Question: "Describe and explain how increasing temperature affects the rate of an enzyme-controlled reaction." Plan: (1) particles gain energy, (2) more collisions, (3) rate increases, (4) optimum temperature, (5) above optimum = denature, (6) rate drops to zero. Write each point in order with explanations and linking words.

Common Mistakes Across All Sciences EXAM ▶

Biology Mistakes

Saying respiration is breathing. Respiration is a chemical reaction in cells; breathing is the physical movement of air.
Confusing osmosis direction. Water moves from dilute to concentrated solution (high water potential to low).
Saying antibiotics cure viral infections. Antibiotics only work on bacteria.
Mixing up mitosis and meiosis. Mitosis = growth/repair (identical cells). Meiosis = gametes (genetically different).

Chemistry Mistakes

Not balancing equations. Always check the same number of each atom on both sides.
Confusing atoms and molecules. O is an oxygen atom; O₂ is an oxygen molecule.
Saying a catalyst is "used up". A catalyst is chemically unchanged at the end of a reaction.
Confusing ionic and covalent bonding. Ionic = metal + non-metal (transfer). Covalent = non-metal + non-metal (sharing).

Physics Mistakes

Forgetting units. Always include units in your answer (m/s, N, J, V, A, etc.).
Not converting units. Minutes to seconds, km to m, kW to W before calculating.
Confusing mass and weight. Mass (kg) is the amount of matter. Weight (N) is the force of gravity on the object. W = mg.
Mixing up current and voltage in circuits. Current is the same in series; voltage is shared. Voltage is the same in parallel; current is shared.

General Mistakes

Not reading the question carefully. Underline command words and key terms.
Not showing working in calculations. You can get marks for method even if the final answer is wrong.
Leaving questions blank. Always attempt an answer — an educated guess can earn marks.

Graph Skills EXAM ▶

Plotting Graphs

Independent variable on x-axis, dependent on y-axis
Label each axis with the quantity AND unit
Choose a sensible scale (use at least half the grid)
Plot points accurately with small crosses (x), not dots
Draw a line of best fit — straight line or smooth curve through the general trend

Reading Values

To find a value from a graph: go to the known value on one axis, draw a line to the curve/line, then across/down to the other axis. Use a ruler for accuracy.

Calculating Gradient

gradient = change in y / change in x = (y₂ − y₁) / (x₂ − x₁)

Choose two points on the line (NOT data points — use points ON the line of best fit) that are far apart for accuracy.

On a distance-time graph, two points on the line of best fit are (0, 0) and (10, 50). Gradient = (50 − 0) / (10 − 0) = 50/10 = 5 m/s. The gradient of a distance-time graph gives the speed.

Calculation Tips EXAM ▶

Step-by-Step Approach

Write the formula you are going to use
Substitute the values (with units)
Calculate the answer
Give the unit in your answer
Check — does the answer seem reasonable?

Rearranging Formulas

Use the triangle method: cover the quantity you want to find.

Example: V = I × R → to find I: I = V / R → to find R: R = V / I

Significant Figures

Give your answer to the same number of significant figures as the data in the question (usually 2 or 3 sf). If the question specifies, follow that.

Common Unit Conversions

From	To	Multiply by
km	m	× 1000
m	cm	× 100
cm	mm	× 10
hours	seconds	× 3600
minutes	seconds	× 60
kW	W	× 1000
kJ	J	× 1000

Forgetting to convert units before substituting into a formula is one of the most common errors. Always check: is distance in metres? Is time in seconds? Is energy in joules?

Key Term Glossary — All Three Sciences EXAM ▶

A comprehensive glossary of essential terms across Biology, Chemistry, and Physics. Use this as a quick-reference checklist — if you cannot define a term from memory, revise that topic.

Biology Terms

Term	Definition	Subject
Cell	The basic structural and functional unit of all living organisms	Biology
Mitosis	Cell division that produces two genetically identical daughter cells for growth and repair	Biology
Meiosis	Cell division that produces four genetically different gametes (sex cells) with half the chromosome number	Biology
Osmosis	Movement of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane	Biology
Diffusion	Net movement of particles from an area of high concentration to an area of low concentration	Biology
Active transport	Movement of substances against the concentration gradient, requiring energy from respiration	Biology
Photosynthesis	Process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen	Biology
Respiration	Chemical reaction in cells that releases energy by breaking down glucose (aerobic uses oxygen; anaerobic does not)	Biology
Enzyme	A biological catalyst (protein) that speeds up chemical reactions without being used up; has a specific active site	Biology
DNA	Deoxyribonucleic acid — the molecule that carries genetic instructions in all living organisms; found in the nucleus	Biology
Gene	A short section of DNA on a chromosome that codes for a specific protein (and therefore a characteristic)	Biology
Allele	A version of a gene; different alleles produce different variations of a characteristic	Biology
Ecosystem	A community of living organisms interacting with each other and their physical (abiotic) environment	Biology
Pathogen	A microorganism that causes infectious disease (bacteria, viruses, fungi, protists)	Biology
Antibody	A protein produced by white blood cells that binds to a specific antigen on a pathogen, marking it for destruction	Biology
Homeostasis	The maintenance of a constant internal environment in the body (e.g. temperature, blood glucose, water levels)	Biology
Receptor	A cell or structure that detects a stimulus (change in the environment), e.g. light receptors in the eye	Biology

Chemistry Terms

Term	Definition	Subject
Atom	The smallest particle of an element that can take part in a chemical reaction; made of protons, neutrons, and electrons	Chemistry
Element	A substance made of only one type of atom; cannot be broken down by chemical means	Chemistry
Compound	A substance made of two or more different elements chemically bonded together in fixed proportions	Chemistry
Mixture	Two or more substances not chemically bonded; can be separated by physical methods (filtration, distillation, etc.)	Chemistry
Ion	An atom (or group of atoms) that has gained or lost electrons, giving it a positive or negative charge	Chemistry
Ionic bond	A strong electrostatic attraction between oppositely charged ions, formed by the transfer of electrons from a metal to a non-metal	Chemistry
Covalent bond	A shared pair of electrons between two non-metal atoms	Chemistry
Metallic bond	Positive metal ions held together by a sea of delocalised (free-moving) electrons	Chemistry
Catalyst	A substance that increases the rate of a chemical reaction without being chemically changed or used up itself	Chemistry
Exothermic	A reaction that transfers energy to the surroundings, causing the temperature to rise (e.g. combustion, neutralisation)	Chemistry
Endothermic	A reaction that takes in energy from the surroundings, causing the temperature to fall (e.g. thermal decomposition, citric acid + baking soda)	Chemistry
Oxidation	Gain of oxygen or loss of electrons (OIL RIG: Oxidation Is Loss)	Chemistry
Reduction	Loss of oxygen or gain of electrons (OIL RIG: Reduction Is Gain)	Chemistry
Acid	A substance with a pH less than 7 that produces H⁺ ions in aqueous solution	Chemistry
Alkali	A soluble base with a pH greater than 7 that produces OH⁻ ions in aqueous solution	Chemistry
Neutralisation	The reaction of an acid with a base to produce a salt and water; H⁺ + OH⁻ → H₂O	Chemistry
Relative formula mass (Mr)	The sum of the relative atomic masses of all the atoms in a chemical formula	Chemistry
Mole	A unit of amount of substance; one mole contains 6.02 × 10²³ particles (Avogadro's number)	Chemistry

Physics Terms

Term	Definition	Subject
Velocity	Speed in a given direction (a vector quantity); measured in m/s	Physics
Acceleration	The rate of change of velocity; measured in m/s²	Physics
Momentum	The product of an object's mass and velocity (p = mv); measured in kg m/s; conserved in collisions	Physics
Force	A push or pull that can change an object's speed, direction, or shape; measured in newtons (N)	Physics
Resultant force	The single force that has the same effect as all the individual forces acting on an object combined	Physics
Frequency	The number of complete waves passing a point per second; measured in hertz (Hz)	Physics
Wavelength	The distance from one point on a wave to the same point on the next wave (e.g. crest to crest); measured in metres	Physics
Amplitude	The maximum displacement of a point on a wave from its rest (equilibrium) position	Physics
Resistance	A measure of how much a component opposes the flow of electric current; measured in ohms (Ω)	Physics
Current	The rate of flow of electric charge around a circuit; measured in amps (A)	Physics
Voltage (potential difference)	The energy transferred per unit of charge passing between two points; measured in volts (V)	Physics
Density	The mass per unit volume of a substance; ρ = m/V; measured in kg/m³ or g/cm³	Physics
Work done	Energy transferred when a force moves an object through a distance; W = F × d; measured in joules (J)	Physics
Power	The rate at which energy is transferred or work is done; P = W/t; measured in watts (W)	Physics
Efficiency	The proportion of input energy that is usefully transferred; efficiency = useful output / total input × 100%	Physics
Half-life	The time taken for the number of radioactive nuclei (or activity) of a sample to halve	Physics
Specific heat capacity	The energy required to raise the temperature of 1 kg of a substance by 1°C; measured in J/kg°C	Physics

In the exam, always use the precise scientific definition. For example, do not say "speed" when you mean "velocity" (velocity includes direction). Do not say "heat" when you mean "temperature" (heat is energy transferred; temperature is how hot something is).

Biology Key Terms BIO ▶

CellBasic unit of life; smallest structure that can carry out life processes

NucleusOrganelle containing DNA; controls cell activities

MitochondriaOrganelles where aerobic respiration occurs

ChloroplastOrganelle containing chlorophyll; site of photosynthesis

DiffusionNet movement of particles from high to low concentration

OsmosisMovement of water through a partially permeable membrane from dilute to concentrated solution

Active transportMovement of substances against the concentration gradient using energy

EnzymeBiological catalyst that speeds up chemical reactions

RespirationChemical reaction in cells that releases energy from glucose

PhotosynthesisProcess by which plants use light energy to make glucose from CO₂ and water

GeneA section of DNA that codes for a specific protein

AlleleA version of a gene

DominantAllele expressed even when only one copy is present

RecessiveAllele only expressed when two copies are present

GenotypeThe combination of alleles an organism has

PhenotypeThe physical characteristic expressed

PathogenMicroorganism that causes disease

AntibodyProtein produced by white blood cells to destroy specific pathogens

VaccinationIntroducing dead/weakened pathogen to stimulate immunity

EcosystemCommunity of organisms interacting with their physical environment

ProducerOrganism that makes its own food (e.g. plants via photosynthesis)

DecomposerOrganism that breaks down dead material

Chemistry Key Terms CHEM ▶

AtomSmallest particle of an element that can take part in a chemical reaction

ElementSubstance made of only one type of atom

CompoundSubstance made of two or more elements chemically bonded

MoleculeTwo or more atoms chemically bonded together

MixtureTwo or more substances not chemically bonded

ProtonPositively charged particle in the nucleus

NeutronNeutral particle in the nucleus

ElectronNegatively charged particle orbiting the nucleus

IonCharged atom (lost or gained electrons)

Ionic bondTransfer of electrons between a metal and non-metal

Covalent bondSharing of electrons between non-metals

Metallic bondPositive metal ions in a sea of delocalised electrons

AcidSubstance with pH less than 7; produces H⁺ ions in solution

AlkaliSubstance with pH greater than 7; produces OH⁻ ions in solution

NeutralisationReaction between an acid and a base to form salt + water

CatalystSubstance that speeds up a reaction without being used up

OxidationGaining oxygen or losing electrons

ReductionLosing oxygen or gaining electrons

ExothermicReaction that releases heat energy to surroundings

EndothermicReaction that absorbs heat energy from surroundings

Greenhouse gasGas that absorbs and re-emits infrared radiation (CO₂, CH₄)

Physics Key Terms PHYS ▶

ForceA push or pull acting on an object; measured in newtons (N)

MassAmount of matter in an object; measured in kilograms (kg)

WeightForce of gravity on an object; W = mg; measured in newtons (N)

SpeedDistance travelled per unit time; v = d/t; measured in m/s

AccelerationRate of change of velocity; measured in m/s²

Resultant forceSingle force that has the same effect as all forces combined

EnergyThe capacity to do work; measured in joules (J)

Kinetic energyEnergy stored in a moving object

Potential energyEnergy stored due to position (gravitational) or shape (elastic)

EfficiencyRatio of useful energy output to total energy input (as %)

CurrentRate of flow of electric charge; measured in amps (A)

VoltageEnergy transferred per unit charge; measured in volts (V)

ResistanceOpposition to current flow; measured in ohms (Ω)

WavelengthDistance between identical points on consecutive waves

FrequencyNumber of waves passing a point per second; measured in Hz

AmplitudeMaximum displacement from the rest position

Transverse waveOscillation is perpendicular to wave direction

Longitudinal waveOscillation is parallel to wave direction

Half-lifeTime for the activity of a radioactive sample to halve

IsotopeAtoms of the same element with different numbers of neutrons

Electromagnetic spectrumFamily of transverse waves including radio, visible light, gamma

All Required Formulas EXAM ▶

Physics Formulas

Formula	Meaning	Units
v = d / t	Speed = distance / time	m/s, m, s
W = m × g	Weight = mass × gravitational field strength	N, kg, N/kg
V = I × R	Voltage = current × resistance	V, A, Ω
P = I × V	Power = current × voltage	W, A, V
E = P × t	Energy = power × time	J, W, s
v = f × λ	Wave speed = frequency × wavelength	m/s, Hz, m
efficiency = (useful output / total input) × 100%	Efficiency as a percentage	%

Biology Equations

Equation	Type
glucose + oxygen → carbon dioxide + water	Aerobic respiration
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O	Aerobic respiration (symbol)
carbon dioxide + water → glucose + oxygen	Photosynthesis
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂	Photosynthesis (symbol)
glucose → lactic acid	Anaerobic respiration (animals)
glucose → ethanol + carbon dioxide	Anaerobic respiration (yeast)

Chemistry Equations to Know

Equation	Type
acid + alkali → salt + water	Neutralisation
acid + metal → salt + hydrogen	Metal + acid
acid + carbonate → salt + water + CO₂	Carbonate + acid
2Mg + O₂ → 2MgO	Combustion of magnesium

Unit Conversions EXAM ▶

Quantity	Conversion
Length	1 km = 1000 m; 1 m = 100 cm; 1 cm = 10 mm
Mass	1 kg = 1000 g; 1 g = 1000 mg; 1 tonne = 1000 kg
Time	1 hour = 3600 s; 1 min = 60 s
Volume	1 litre = 1000 ml = 1000 cm³; 1 m³ = 1,000,000 cm³
Energy	1 kJ = 1000 J; 1 MJ = 1,000,000 J
Power	1 kW = 1000 W
Temperature	°C to K: add 273 (e.g. 25°C = 298 K)

First 20 Elements CHEM ▶

No.	Symbol	Name	Electron Config
1	H	Hydrogen	1
2	He	Helium	2
3	Li	Lithium	2, 1
4	Be	Beryllium	2, 2
5	B	Boron	2, 3
6	C	Carbon	2, 4
7	N	Nitrogen	2, 5
8	O	Oxygen	2, 6
9	F	Fluorine	2, 7
10	Ne	Neon	2, 8
11	Na	Sodium	2, 8, 1
12	Mg	Magnesium	2, 8, 2
13	Al	Aluminium	2, 8, 3
14	Si	Silicon	2, 8, 4
15	P	Phosphorus	2, 8, 5
16	S	Sulfur	2, 8, 6
17	Cl	Chlorine	2, 8, 7
18	Ar	Argon	2, 8, 8
19	K	Potassium	2, 8, 8, 1
20	Ca	Calcium	2, 8, 8, 2

A useful mnemonic for the first 20 elements: "Happy Henry Lives Beside Boron Cottage, Near Our Friend Nelly Na(ncy) Mg(gie) Always Sings Pop Songs Clearly Around K(itchen) Ca(nteen)".