Combined Science Paper 2 June 2025

1. AIt acts as a solvent, so that digested food, salts and wastes can be carried in the blood.
2. BIt is joined into long chains in the cells to build the body's structural proteins.
3. CIt supplies the body with energy, releasing about 17 kJ for every gram taken in.
4. DIt is broken down in the liver to make the antibodies that fight infection.

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1. AOffice work uses the brain rather than the muscles, and the brain stores energy instead of releasing it.
2. BThe builder does heavy physical work, so his muscles respire faster and release more energy.
3. CThe builder eats larger meals, and the size of the meals eaten sets how much energy a person needs.
4. DThe office worker sweats less at his desk, so much less of his food energy is lost from the body as heat.

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1. AIt adds a sugary fluid to the sperms to give them energy for swimming.
2. BIt makes the hormone testosterone, which controls the male secondary sexual characteristics.
3. CIt carries urine from the bladder to the outside through the penis.
4. DIt stores sperms and holds them while they mature before ejaculation.

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1. AThe duct widens so much that urine passes back into the testes and kills the sperms as they form.
2. BThe lining thickens and pushes the sperms along faster, so they leave before they have matured.
3. CScarring narrows or blocks the duct, so sperms cannot reach the urethra and the man becomes infertile.
4. DThe bacteria feed on the testosterone in the duct, so the man slowly loses his body hair and deep voice.

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1. AOn the outer surface of the nucleus, held there by the neutrons.
2. BIn shells (energy levels) that surround the nucleus.
3. CInside the nucleus, packed in between the protons and the neutrons.
4. DSpread evenly through the whole atom, the nucleus included.

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1. AThe separation of a dissolved solid from its solution by heating the solution until the liquid boils away.
2. BThe flow of electrons through a metal wire, which carries charge without changing the metal itself.
3. CThe joining of two elements into a compound by heating them strongly out of contact with air.
4. DThe breaking down of a molten or dissolved compound into simpler substances by passing electricity through it.

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1. AThe acid reacts with the water to set the hydrogen free, which the current on its own cannot do.
2. BPure water contains very few ions, and the acid supplies ions so that the water conducts the current.
3. CThe acid coats the two electrodes and keeps them from being worn away by the gases given off.
4. DThe acid raises the boiling point of the water so that it does not boil away while the current flows.

1. AH2 -> 2H+ + 2e-, hydrogen molecules losing electrons at the negative electrode.
2. B2H2O -> 2H2 + O2, water splitting into both gases at the negative electrode.
3. C2H+ + 2e- -> H2, hydrogen ions gaining electrons at the negative electrode.
4. D4OH- -> 2H2O + O2 + 4e-, hydroxide ions losing electrons at the negative electrode.

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1. AThe float chamber fills up with air, so the engine loses power slowly over several minutes.
2. BAir alone passes through the throat, so the mixture becomes too rich and the exhaust gives off black smoke.
3. CNo petrol enters the air stream, so no burnable mixture is formed and the engine will not run.
4. DPetrol floods into the cylinder instead, so the engine races and runs at a very high speed.

1. AIn the intake stroke the burnt gases are pushed out through the exhaust valve, while in the exhaust stroke fresh petrol and air mixture is drawn into the cylinder.
2. BIn the intake stroke both valves stand open together, while in the exhaust stroke both valves are held shut by the camshaft.
3. CIn the intake stroke the spark plug fires the mixture, while in the exhaust stroke the mixture is squeezed ready for the next spark.
4. DIn the intake stroke the inlet valve is open and the piston moves down, while in the exhaust stroke the exhaust valve is open and the piston moves up.

1. AIt runs on leaded petrol, which burns far more completely than the fuels used in older engines.
2. BIt has a much larger cylinder, so it takes in more fuel and gives off more smoke at the same speed.
3. CIt works without a cooling system, so the heat of the burnt gases is used to drive the piston.
4. DIt burns less petrol for the same distance travelled, so it costs less to run.

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1. Acarbon dioxide + oxygen -> glucose + water
2. Bcarbon dioxide + water -> glucose + oxygen
3. Cwater + oxygen -> glucose + carbon dioxide
4. Dglucose + oxygen -> carbon dioxide + water

1. AIt rises steadily all the way to 45 degrees C, because the reacting molecules move faster at every higher temperature.
2. BIt falls steadily from 20 degrees C, because the heat drives water out of the leaf and shuts the stomata at once.
3. CIt stays the same throughout, because the rate of a reaction driven by light energy does not depend on temperature.
4. DIt rises to a maximum near 35 degrees C and then falls, because the enzymes are denatured above that temperature.

1. AIt decreases, because the extra carbon dioxide dissolves in the cell sap and makes the leaf too acidic.
2. BIt stays the same, because the rate is fixed by the amount of chlorophyll and by nothing else.
3. CIt increases, because carbon dioxide is a raw material of photosynthesis, until another factor limits the rate.
4. DIt decreases, because carbon dioxide is the waste gas of photosynthesis and it builds up inside the leaf.

1. AIt makes the food that starts every food chain and releases the oxygen that animals need for respiration.
2. BIt breaks glucose down to release the energy that animals use for their movement and growth.
3. CIt removes water vapour from the air and returns it to the soil, where animals can drink it.
4. DIt takes in oxygen from the air at night, which keeps the amount of oxygen in the atmosphere steady.

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1. ARainfall over the area increases, because the few plants left take much less water out of the soil.
2. BIf one species is lost to disease or drought, the animals that fed on it have no other food and die out too.
3. CThe few species that remain grow much larger than usual, because each takes in the food of the missing species.
4. DDecomposers work far faster, so the nutrients in the soil are used up sooner than in a rich ecosystem.

1. AThe plants are alike, so a pest or disease able to attack one plant can attack every other plant in the field.
2. BThe plants take up different nutrients, so the soil is left short of the minerals the crop needs to grow.
3. CThe plants shade one another closely, so each of them receives too little light to make the food it needs.
4. DThe plants flower at different times, so the pest finds fresh flowers to feed on right through the season.

1. AAn animal in a web has more than one kind of food, so it survives when one food species dies out.
2. BA web puts every organism at the same feeding level, so no organism in it is eaten by another.
3. CA web holds more producers than consumers, so more energy is available at the top of the web.
4. DA web has fewer organisms in it, so less energy is lost as heat from one feeding level to the next.

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1. AThe soil holds much more water, so the roots of the crop are starved of the air they need.
2. BThe soil loses nitrates, so it becomes less fertile and crops grown in it grow poorly.
3. CThe soil gains nitrates, so crops grown in it need much less fertiliser than before.
4. DThe soil turns more acidic, so lime has to be added before any crop will grow in it.

1. ABy taking in nitrogen gas from the air through the lungs while breathing.
2. BBy eating plants or other animals and digesting the proteins in the food.
3. CBy absorbing nitrates from the soil through the walls of the intestine.
4. DBy building proteins from the carbon dioxide that they breathe out.

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1. ABy handling the dry soil in which the eggs of the parasite have been buried.
2. BBy the bite of a female mosquito that has fed on the blood of an infected person.
3. CBy breathing in the droplets coughed out by a person who already has the disease.
4. DBy larvae in infected water boring through the skin of a person who bathes or wades in it.

1. AAdult worms leave a person in the sweat, enter a snail through its shell, and pass back to a person as eggs in drinking water.
2. BEggs are swallowed by a snail on land, hatch into worms inside the snail, and infect a person who eats that snail raw.
3. CEggs are laid on the skin of a person, hatch into larvae that swim away and enter a snail, and that snail is later eaten raw by another person.
4. DEggs pass out in urine or faeces into water, hatch into larvae that enter a snail, and new larvae leave the snail and bore through human skin.

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1. AIn passive immunity the antibodies come from outside the body, while in active immunity the body makes its own antibodies.
2. BPassive immunity lasts a lifetime, while active immunity wears off within a few days of the infection.
3. CPassive immunity follows a vaccination, while active immunity is passed to a baby in its mother's breast milk.
4. DPassive immunity leaves memory cells behind, while active immunity works without any memory cells at all.

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1. Acalcium carbonate + hydrochloric acid -> calcium chlorate + water + oxygen
2. Bcalcium carbonate + hydrochloric acid -> calcium chloride + water + carbon dioxide
3. Ccalcium carbonate + hydrochloric acid -> calcium chloride + hydrogen
4. Dcalcium carbonate + hydrochloric acid -> calcium hydroxide + water + carbon monoxide

1. AWork close to an open flame, because the fumes given off are burnt away as they reach the heat.
2. BWarm the acid before use, because it reacts far too slowly with a carbonate while it is cold.
3. CWear goggles and gloves, because the acid is corrosive and burns the skin and the eyes.
4. DAdd the carbonate as one large lump, because a powder reacts so fast that the acid boils over.

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1. ABy evaporating the water from the solution until the salt crystallises out.
2. BBy filtering the solution, so that the dissolved salt is held back in the filter paper.
3. CBy adding limewater to the solution, which makes the dissolved salt settle out as a solid.
4. DBy boiling the solution and collecting the vapour that comes off, which carries the salt.

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1. AWelding steel plates, because it burns in air with a very hot flame.
2. BMaking the bubbles in fizzy drinks and filling fire extinguishers.
3. CFilling electric light bulbs, because it keeps the filament from burning away.
4. DFilling weather balloons, because it is the lightest of the common gases.

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1. APlenty of oxygen, a temperature above 100 degrees C and a dry mixture.
2. BNo oxygen, a temperature close to 0 degrees C and a strongly acidic slurry.
3. CPlenty of oxygen, bright sunlight and a slurry made of water alone.
4. DNo oxygen, a warm temperature of about 35 degrees C and a moist slurry.

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1. ADung is soaked in strong acid in an open drum, and the gas that bubbles off it is collected in a plastic bag.
2. BDung is mixed with water and fed into an airtight digester, where bacteria break it down without oxygen and the gas collects at the top.
3. CDung is dried in the sun and then burnt in an open pit, and the smoke given off from the fire is piped away and stored in a tank as biogas.
4. DDung is heated with steam in an open tank, where oxygen from the air oxidises it into a gas that will burn.

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1. AIt is a greenish yellow gas with a choking smell, and it bleaches damp litmus paper.
2. BIt is a red brown liquid at room temperature, and it gives off a sweet smelling vapour.
3. CIt is a shiny grey solid at room temperature, and it dissolves in water to give an alkali.
4. DIt is a colourless gas with no smell at all, and it turns damp litmus paper blue.

1. AChlorine is a greenish yellow gas, while bromine is a red brown liquid.
2. BChlorine has a higher boiling point than bromine and a larger relative atomic mass.
3. CChlorine is a colourless liquid, while bromine is a shiny black solid.
4. DChlorine is less reactive than bromine, so it cannot displace bromine from a bromide.

1. APreserving fruit by freezing it inside a cold store for months.
2. BCoating iron roofing sheets to keep them from rusting in the rain.
3. CKilling bacteria in drinking water and in swimming pools.
4. DFilling balloons, because it is much lighter than the air around them.

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1. AThey react gently with cold water, giving an acidic solution and oxygen gas.
2. BThey gain one electron in their reactions, forming ions with a charge of minus one.
3. CThey become less reactive down the group, so potassium reacts more slowly than lithium.
4. DThey react vigorously with cold water, giving an alkaline hydroxide solution and hydrogen gas.

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1. ABy using a heavier load, so that its weight helps to pull it up the slope.
2. BBy roughening the surface, so that the load grips the plane as it moves.
3. CBy oiling the sloping surface, so that less work is done against friction.
4. DBy making the slope shorter, so that the effort acts over a smaller distance.

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1. APetrol refined from crude oil and burnt in a car engine.
2. BNatural gas piped from under the sea and burnt for heat.
3. CCoal dug out of a mine and burnt in a power station.
4. DWater flowing down a river and turning a turbine.

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1. AChemical energy in the cells, to electrical energy in the circuit, to light energy at the bulb.
2. BChemical energy in the cells, to sound energy in the circuit, to light energy at the bulb.
3. CElectrical energy in the cells, to chemical energy in the circuit, to heat energy at the bulb.
4. DLight energy at the bulb, to electrical energy in the circuit, to chemical energy in the cells.

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1. AIn parallel, so that the voltages of the three panels add together.
2. BIn series, so that the voltage stays the same as that of one panel.
3. CIn series, so that the voltages of the three panels add together.
4. DIn parallel, so that the voltage falls to a third of that of one panel.

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1. AThe friction of a brake block pressing against a bicycle wheel.
2. BThe upward push of a table on a book that is resting on it.
3. CThe pull of a magnet on an iron nail lying a short distance away.
4. DThe push of a hand on a trolley being moved along a level floor.

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1. AThe tread of a car tyre gripping the road, so that the car can turn and stop.
2. BThe oil poured into an engine, which is added to raise the friction between the moving parts.
3. CThe smooth runners of a sledge, which raise the friction with the snow so that it slides faster.
4. DThe ball bearings inside a wheel, which raise the friction so that the wheel turns more easily.

1. AFor every action force there is an equal and opposite reaction force, acting on a different body.
2. BA body moving at a steady speed in a straight line must have a steady resultant force acting on it.
3. CA body stays at rest, or keeps moving at a steady speed in a straight line, unless a resultant force acts on it.
4. DThe acceleration of a body is proportional to the resultant force on it and is in the direction of that force.