GCSE-readyKS3 Science: common mistakes
The wrong answers students pick most often in our Science questions, and why they are wrong. Read these before a test, then open the lesson for anything that surprises you.
Working scientifically
- Planning a fair test
- Not “The length of the wire”. He changes the length, so that is the independent variable.
- Not “The type of wire”. The type of wire should be kept the same: it is a control variable.
- Measuring and recording results
- Not “Newton”. The newton is the unit of force, including weight.
- Sampling plants and animals
- Not “So the quadrat lands on the most plants”. Choosing spots with the most plants would give an estimate that is too high.
- Not “One quadrat in the middle of the field”. One quadrat cannot show a change across the area.
Biology: cells and organisation
- Animal and plant cells
- Not “Cell wall”. The cell wall supports a plant cell, but it lets most substances through.
- Not “Chloroplasts”. Chloroplasts are for photosynthesis.
- Diffusion, single cells and body organisation
- Not “From low concentration to high concentration”. Moving from low to high would need energy, so it is not diffusion.
- Not “Making food”. Chloroplasts make food.
- Not “Detecting light”. The eyespot helps with light.
- Specialised cells
- Not “To store food for the embryo”. The egg cell stores food in its cytoplasm.
Chemistry: particles and mixtures
- Pure substances and separating mixtures
- Not “Evaporation”. Evaporation gets a dissolved solid out of a solution.
- Not “Filtration”. Salt is dissolved, so it passes through filter paper.
- Solutions and solubility
- Not “The solvent”. The water in the tea is the solvent.
- Distillation, crystallisation and chromatography
- Not “The residue”. The residue is the solid left behind.
- Not “The distillate”. The distillate comes from distillation.
- Not “Filtration”. Salt is dissolved, so it passes through filter paper.
Physics: forces
- Forces and their effects
- Not “There are no forces”. There are forces, but they cancel out.
- Not “Kilogram”. The kilogram is the unit of mass.
- Not “Joule”. The joule is the unit of energy.
- Friction, drag and changing motion
- Not “Gravity stops acting”. Gravity still acts: her weight does not change.
Biology: reproduction
- Human reproduction
- Not “Sperm duct”. The sperm duct carries sperm; it does not make them.
- Not “The release of an egg from the ovary”. That is ovulation.
- Not “The breakdown of the uterus lining”. That is a period.
- Flowers, pollination and seeds
- Not “Stigma”. The stigma receives pollen.
- Not “The joining of male and female nuclei”. That is fertilisation.
- Not “The spreading of seeds”. That is seed dispersal.
Chemistry: acids and alkalis
- Acids, alkalis and neutralisation
- Not “A salt and hydrogen”. A salt and hydrogen come from an acid reacting with a metal.
- Not “A glowing splint relights”. A glowing splint relighting is the test for oxygen.
- Not “Limewater turns milky”. Limewater turning milky is the test for carbon dioxide.
Physics: waves and sound
- Waves and sound
- Not “It gets louder”. Loudness depends on amplitude, not frequency.
- Not “Transverse: particles vibrate at right angles to the direction the wave travels”. That describes water waves and light.
- Wave features and echoes
- Not “The height of a peak”. That is the amplitude.
- Not “The number of waves each second”. That is the frequency.
Physics: space
- Space, gravity and the seasons
- Not “It goes down”. Her weight goes down, but her mass does not.
- Not “The time light takes to reach Earth”. It measures distance, not time.
- Not “The Earth getting much closer to the Sun in summer”. When it is summer in the UK it is winter in Australia, so distance cannot be the reason.
- The Solar System and light-years
- Not “Less than 50 kg”. Her weight is less on Mars, but her mass is the same.
- Not “Time”. It contains the word year, but it measures how far light goes.
Working scientifically
- Accuracy, precision and errors
- Not “95.0, 95.1, 95.0 °C”. These are precise but not accurate: all about 5 °C too low.
- Not “92, 100, 108 °C”. The mean is 100 °C, but the readings are spread out, so they are not precise.
Biology: food and digestion
- A healthy diet
- Not “Carbohydrate”. Carbohydrates are mainly for energy.
- Digestion and enzymes
- Not “Large intestine”. The large intestine mainly absorbs water.
- Not “Bile”. Bile is not an enzyme.
- How plants get water and minerals
- Not “Soil eaten through the roots”. Plants do not eat soil.
- Not “Sunlight turning into matter”. Light provides energy, not mass.
- Not “Stomata”. Stomata are holes in the leaf where water evaporates.
Chemistry: atoms and the periodic table
- Atoms, elements and compounds
- Not “Two or more elements chemically joined”. That is a compound.
- Not “Oxygen, O2”. O2 is a molecule of an element.
- Not “Air”. Air is a mixture.
- The periodic table
- Not “A period”. A period is a row.
- Metals, non-metals and their oxides
- Not “Red (strongly acidic)”. Non-metal oxides make acids.
Physics: electricity and magnetism
- Current, potential difference and resistance
- Not “In series with the component”. That is how an ammeter is connected.
- Not “The push from the battery”. That is potential difference.
- Not “How hard it is for charge to flow”. That is resistance.
- Circuit symbols and building circuits
- Not “Ammeter”. An ammeter has an A inside.
- Magnets and electromagnets
- Not “Copper”. Copper is a metal, but it is not magnetic.
Biology: breathing and moving
- Breathing and gas exchange
- Not “The pressure inside the chest rises”. Rising pressure inside would push air out.
- Measuring breathing and lung volume
- Not “The most air you can breathe out”. That is the vital capacity.
- The skeleton and muscles
- Not “Ligament”. Ligaments join bone to bone.
Chemistry: chemical reactions
- Chemical reactions and energy
- Not “Exothermic”. Exothermic reactions make things warmer.
- Balanced equations and conservation of mass
- Not “Mg + O2 → MgO”. There are 2 O on the left but only 1 on the right.
- Not “Mg + O2 → MgO2”. Changing MgO to MgO2 makes a different substance.
Physics: light
- Light, reflection and seeing
- Not “Lens”. The lens focuses light; it does not detect it.
- Refraction, lenses and colour
- Not “It speeds up”. Light speeds up when it leaves the glass, not when it enters.
- Not “It absorbs green light”. If it absorbed green, it could not look green.
Biology: drugs and health
- Drugs and health
- Not “Caffeine”. Caffeine is a stimulant.
- Not “Nicotine”. Nicotine is a stimulant.
- Not “Tar”. Tar causes cancer, but it is not what makes smoking addictive.
Working scientifically
- Analysing data and drawing conclusions
- Not “Positive correlation”. In a positive correlation both increase together.
Biology: photosynthesis and respiration
- Photosynthesis
- Not “Glucose and oxygen”. Glucose and oxygen are the products.
- Not “Water”. Water comes up from the roots through the veins.
- Not “Orange-brown”. Orange-brown is its colour when there is no starch.
- Aerobic and anaerobic respiration
- Not “Glucose and oxygen”. Those are the products of photosynthesis.
- Not “Ethanol”. Ethanol is made by yeast.
Chemistry: reactivity and materials
- The reactivity series and displacement
- Not “Aluminium”. Aluminium is more reactive than carbon, so carbon cannot remove its oxygen.
- Making salts
- Not “Hydrochloric acid”. Hydrochloric acid makes chlorides.
- Not “Sulfuric acid”. Sulfuric acid makes sulfates.
- Not “Calcium chloride and hydrogen”. Hydrogen comes from acid + metal, not a carbonate.
Physics: energy transfers
- Energy stores, transfers and machines
- Not “We should switch lights off”. That is saving energy at home, not the scientific law.
- Energy in systems: before and after
- Not “Energy is destroyed when it hits the ground”. Energy is never destroyed.
Biology: ecosystems
- Adaptation and competition
- Not “It helps it hide in snow”. The white fur gives camouflage.
Chemistry: Earth and atmosphere
- The Earth and the rock cycle
- Not “Oxygen and silicon”. Oxygen and silicon are the most common elements in the crust.
- Not “Layers of sediment are cemented together”. That is sedimentary rock.
- Not “Rock is changed by heat and pressure without melting”. That is metamorphic rock.
- The atmosphere, climate and resources
- Not “Oxygen”. Oxygen is about 21%.
- Not “Recycling uses no energy at all”. Collecting, sorting and melting still use some energy.
Chemistry: energy changes
- Exothermic and endothermic changes
- Not “Thermal decomposition of copper carbonate”. Thermal decomposition needs continuous heating, so it is endothermic.
Physics: electromagnetism
- Electromagnets and motors in action
- Not “Reversing the current”. Reversing the current makes it spin the other way, not faster.
Biology: genetics and evolution
- Variation, natural selection and extinction
- Not “Height”. Height can be any value in a range.
- Not “Height”. Height depends on both genes and the environment.
Physics: matter
- Density and the particle model
- Not “They get bigger”. The particles themselves do not grow; the gaps between them increase.