Combined Science,
one step at a time.

A scientific biological drawing uses clear, unbroken lines, no artistic shading and ruled label lines. It should represent the observed specimen and include scale or magnification where appropriate.

Watch for: Do not repeat the wording of Cell structures. Explain the underlying rule or relationship, apply it to the context and check the command word.

The spread suggests either natural variation or an anomalous result. Repeats under identical controlled conditions allow the anomaly to be investigated and a mean of concordant measurements to provide more reliable evidence.

Watch for: Do not repeat the wording of What happens in cells (and what do cells need)?. Explain the underlying rule or relationship, apply it to the context and check the command word.

Cells continuously require ATP for processes including active transport, synthesis and movement. Respiration transfers energy from substrates into ATP that can supply these processes.

Watch for: Do not repeat the wording of Respiration. Explain the underlying rule or relationship, apply it to the context and check the command word.

Photosynthetic rate is controlled by the factor in shortest supply. If enzyme-controlled reactions are limited by low temperature, extra carbon dioxide will have little effect.

Watch for: Do not repeat the wording of Photosynthesis. Explain the underlying rule or relationship, apply it to the context and check the command word.

Plant meristems retain cells that divide and differentiate throughout growth. Embryonic animal stem cells can form many cell types, whereas adult stem cells such as bone-marrow cells usually have a more limited range.

Watch for: Do not repeat the wording of Supplying the cell. Explain the underlying rule or relationship, apply it to the context and check the command word.

A potometer records water uptake by a shoot. Most replaces water lost through transpiration, but a small amount is used in photosynthesis, growth or maintaining cells, so uptake is only an estimate of transpiration.

Watch for: Do not repeat the wording of The challenges of size. Explain the underlying rule or relationship, apply it to the context and check the command word.

Electrical impulses travel from a receptor along a sensory neurone, across synapses through a relay neurone, then along a motor neurone to an effector. The response is rapid and automatic.

Watch for: Do not repeat the wording of Coordination and control - the nervous system. Explain the underlying rule or relationship, apply it to the context and check the command word.

Oestrogen and progesterone in the pill maintain hormonal feedback that inhibits FSH and LH, preventing normal follicle maturation and ovulation. IVF instead uses fertility hormones to stimulate egg maturation and release.

Watch for: Do not repeat the wording of Coordination and control - the endocrine system. Explain the underlying rule or relationship, apply it to the context and check the command word.

A receptor detects a stimulus, a coordination centre processes the information, and an effector produces a corrective response. Negative feedback reverses the deviation from the optimum.

Watch for: Do not repeat the wording of Maintaining internal environments. Explain the underlying rule or relationship, apply it to the context and check the command word.

Solar energy warms surface water and causes evaporation, while cooling produces condensation and precipitation. Living organisms also return water through respiration and transpiration.

Watch for: Do not repeat the wording of Ecosystems. Explain the underlying rule or relationship, apply it to the context and check the command word.

Height is polygenic, so alleles at many genes contribute, and environmental factors such as nutrition also affect growth. This produces a continuous range rather than a few discrete categories.

Watch for: Do not repeat the wording of Inheritance. Explain the underlying rule or relationship, apply it to the context and check the command word.

If populations are isolated, different selection pressures and mutations can change their allele frequencies. Over many generations the differences may become large enough to prevent successful interbreeding, producing separate species.

Watch for: Do not repeat the wording of Natural selection and evolution. Explain the underlying rule or relationship, apply it to the context and check the command word.

Replicated abundance data paired with pollution measurements can test the proposed association. Recording plausible confounders such as substrate, light and moisture helps assess whether distance from traffic rather than another factor explains the pattern.

Watch for: Do not repeat the wording of Monitoring and maintaining the environment. Explain the underlying rule or relationship, apply it to the context and check the command word.

Benefits may include higher yield and reduced insecticide use. Risks to investigate include effects on non-target organisms and transfer of the inserted allele to wild relatives. Evaluation must weigh evidence for both sides.

Watch for: Do not repeat the wording of Feeding the human race. Explain the underlying rule or relationship, apply it to the context and check the command word.

Some variants are associated with disease risk or drug response, so genome information may guide screening or treatment choice. Predictions are probabilistic and must be interpreted alongside environment and clinical evidence.

Watch for: Do not repeat the wording of Monitoring and maintaining health. Explain the underlying rule or relationship, apply it to the context and check the command word.

Liquid particles are close together with an irregular arrangement and can move past one another. Wide separation is characteristic of a gas and would misrepresent density and compressibility.

Watch for: Do not repeat the wording of The particle model. Explain the underlying rule or relationship, apply it to the context and check the command word.

Most alpha particles passed through, showing atoms are mostly empty space, but rare large deflections required a tiny, dense, positively charged nucleus. Later work identified protons and neutrons in the nucleus.

Watch for: Do not repeat the wording of Atomic structure. Explain the underlying rule or relationship, apply it to the context and check the command word.

Two spots show the sample contains at least two soluble components. A matching Rf under the same conditions supports the presence of the reference dye, though additional evidence can strengthen identification.

Watch for: Do not repeat the wording of Purity and separating mixtures. Explain the underlying rule or relationship, apply it to the context and check the command word.

Metallic bonding is electrostatic attraction between positive metal ions and delocalised electrons. Simple molecules contain covalent bonds within discrete molecules, ionic solids contain giant ion lattices, and polymer chains contain covalent bonds.

Watch for: Do not repeat the wording of Bonding. Explain the underlying rule or relationship, apply it to the context and check the command word.

Carbon has four outer-shell electrons available for covalent bonding and can bond strongly to other carbon atoms, producing chains, branches and rings with many functional groups.

Watch for: Do not repeat the wording of Properties of materials. Explain the underlying rule or relationship, apply it to the context and check the command word.

Carbon dioxide forms a cloudy calcium carbonate suspension in limewater. Hydrogen gives a squeaky pop, oxygen relights a glowing splint, and chlorine bleaches damp litmus after first turning blue litmus red.

Watch for: Do not repeat the wording of Introducing chemical reactions. Explain the underlying rule or relationship, apply it to the context and check the command word.

An endothermic reaction absorbs energy overall, so the products lie at a higher energy level than the reactants. The profile must also show the activation-energy barrier.

Watch for: Do not repeat the wording of Energetics. Explain the underlying rule or relationship, apply it to the context and check the command word.

An excess of insoluble base ensures no acid remains. Unreacted copper(II) oxide is filtered off, then the filtrate is concentrated and cooled to crystallise hydrated copper(II) sulfate.

Watch for: Do not repeat the wording of Types of chemical reactions. Explain the underlying rule or relationship, apply it to the context and check the command word.

Drying and weighing the cathode before and after gives the mass of copper deposited. Current, time, electrode area and concentration should be controlled or measured for a valid comparison.

Watch for: Do not repeat the wording of Electrolysis. Explain the underlying rule or relationship, apply it to the context and check the command word.

Magnesium has a greater tendency to lose electrons and form Mg²⁺, so it displaces hydrogen ions from acid. Copper lies below hydrogen and does not react with dilute non-oxidising acids in this way.

Watch for: Do not repeat the wording of Predicting chemical reactions. Explain the underlying rule or relationship, apply it to the context and check the command word.

Enzymes are biological catalysts. Above their optimum temperature, bonds maintaining protein shape can break, changing the active site and reducing successful enzyme–substrate binding.

Watch for: Do not repeat the wording of Controlling reactions. Explain the underlying rule or relationship, apply it to the context and check the command word.

The reactant side has four moles of gas per equation amount and the product side has two. Higher pressure favours the side with fewer gas molecules, increasing ammonia yield.

Watch for: Do not repeat the wording of Equilibria. Explain the underlying rule or relationship, apply it to the context and check the command word.

Recycling avoids much ore extraction and energy-intensive electrolysis. A life-cycle assessment still considers raw materials, manufacture, use, transport and end-of-life, and conclusions depend on data and weighting.

Watch for: Do not repeat the wording of Improving processes and products. Explain the underlying rule or relationship, apply it to the context and check the command word.

Volcanic outgassing supplied water vapour, carbon dioxide and nitrogen. Cooling condensed water to oceans; carbon dioxide decreased through dissolution, carbonate formation and photosynthesis, while photosynthetic organisms raised oxygen.

Watch for: Do not repeat the wording of Interpreting and interacting with Earth systems. Explain the underlying rule or relationship, apply it to the context and check the command word.

Close contact improves transfer from heater to block and helps the thermometer represent the block temperature. Insulation is still needed because losses cannot be eliminated completely.

Watch for: Do not repeat the wording of Practical skills. Explain the underlying rule or relationship, apply it to the context and check the command word.

Most alpha particles passed through, but rare large deflections required a tiny dense positive nucleus. Subsequent evidence established protons, neutrons and electron energy levels.

Watch for: Do not repeat the wording of The particle model. Explain the underlying rule or relationship, apply it to the context and check the command word.

At the melting point, supplied energy changes the particles' potential energy and arrangement rather than raising temperature. The temperature remains constant until the change of state is complete.

Watch for: Do not repeat the wording of Changes of state. Explain the underlying rule or relationship, apply it to the context and check the command word.

Repeating under the same conditions and calculating a mean reduces the influence of random timing variation.

Watch for: Do not repeat the wording of Motion. Explain the underlying rule or relationship, apply it to the context and check the command word.

Velocity is a vector, so changing direction means acceleration even at constant speed. A centripetal resultant force acts toward the centre while instantaneous velocity is tangential.

Watch for: Do not repeat the wording of Newton's laws. Explain the underlying rule or relationship, apply it to the context and check the command word.

A permanent extension after unloading is plastic deformation and indicates that the spring was taken beyond its elastic behaviour. Loading and unloading data reveal this hysteresis or permanent change.

Watch for: Do not repeat the wording of Forces in action. Explain the underlying rule or relationship, apply it to the context and check the command word.

Matter contains positive and negative charges. When their totals are equal, they cancel to give zero net charge even though charged particles remain.

Watch for: Do not repeat the wording of Static and charge. Explain the underlying rule or relationship, apply it to the context and check the command word.

Adding a parallel branch increases total conductance. Both branches have the same potential difference and junction currents add, so total current is greater and R = V/I is below either branch resistance.

Watch for: Do not repeat the wording of Simple circuits. Explain the underlying rule or relationship, apply it to the context and check the command word.

Reversing either the current or the magnetic field reverses the forces on the coil sides, so the turning direction reverses. Reversing both would leave the rotation direction unchanged.

Watch for: Do not repeat the wording of Magnets and magnetic fields. Explain the underlying rule or relationship, apply it to the context and check the command word.

The disturbance and energy travel across the surface, while the cork oscillates about a fixed position. This is evidence that waves do not carry the medium along overall.

Watch for: Do not repeat the wording of Wave behaviour. Explain the underlying rule or relationship, apply it to the context and check the command word.

Non-ionising does not mean risk-free: sufficiently intense microwaves are absorbed by water-rich tissue and cause heating. Risk depends on frequency, intensity and exposure duration.

Watch for: Do not repeat the wording of The electromagnetic spectrum. Explain the underlying rule or relationship, apply it to the context and check the command word.

Irradiation is exposure to radiation from an external source and stops when the source is removed. Contamination means radioactive atoms are present on or inside the object and continue emitting until removed or decayed.

Watch for: Do not repeat the wording of Radioactivity. Explain the underlying rule or relationship, apply it to the context and check the command word.

Braking transfers energy from the car's kinetic store to thermal stores in the brakes, tyres and surroundings. Energy is conserved even though the car's kinetic energy decreases.

Watch for: Do not repeat the wording of Work done. Explain the underlying rule or relationship, apply it to the context and check the command word.

Total energy is conserved, but friction transfers organised mechanical energy into dispersed thermal energy, making it harder to use for the intended purpose.

Watch for: Do not repeat the wording of Power and efficiency. Explain the underlying rule or relationship, apply it to the context and check the command word.

Reaction time varies naturally, but an outlier may reflect anticipation, distraction or measurement error. Repeats improve reliability; a justified treatment of anomalies produces a more representative mean.

Watch for: Do not repeat the wording of Physics on the move. Explain the underlying rule or relationship, apply it to the context and check the command word.

Coal combustion releases carbon dioxide and other pollutants. Wind generation has no fuel emissions during operation, but turbines and infrastructure can affect habitats, views and land use.

Watch for: Do not repeat the wording of Powering Earth. Explain the underlying rule or relationship, apply it to the context and check the command word.