Combined Science Paper 2 June 2020

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1. Athe smaller pieces have a larger total surface area, so digestive enzymes can act on the food faster.
2. Bthe smaller pieces are absorbed directly through the wall of the mouth into the blood stream.
3. Cthe smaller pieces are already soluble, so no digestive enzymes are needed after the food has been chewed.
4. Dthe smaller pieces move more slowly through the gut, giving the stomach acid time to kill any bacteria present.

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1. Acontains a mild acid that changes the pH of the vagina, so sperm are killed before they reach the cervix.
2. Bcontains artificial hormones that stop the testes of the male partner from producing any mature sperm cells.
3. Ccontains artificial hormones that suppress ovulation, so no egg is released and fertilisation cannot take place.
4. Dcontains artificial hormones that thicken the wall of the uterus, so a fertilised egg is pushed out during menstruation.

1. AA firm, painless sore on the genitals that heals on its own after a few weeks.
2. BA dry, itchy rash between the fingers and on the wrists that is worse at night.
3. CSwelling of the glands in front of the ears, with pain on opening the mouth.
4. DA painful ulcer on the genitals that bleeds easily when touched, with swollen glands in the groin.

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1. Alimestone decomposes into calcium oxide and carbon dioxide, and the calcium oxide then reduces the iron ore to iron.
2. Bsolid coke reacts directly with the molten slag to release iron and leave a residue of calcium carbonate behind.
3. Chot air blown in at the top oxidises the iron ore to iron (III) oxide, which then melts and runs down the furnace.
4. Dcarbon monoxide reduces iron (III) oxide to iron, and is itself oxidised to carbon dioxide.

1. Athe reaction changes from an exothermic one to an endothermic one as soon as the temperature is raised.
2. Bthe products are formed at a steady rate until every one of the reactants has been used up completely.
3. Cthe reactants are used up in exactly equal masses, so the products have the same total mass as them.
4. Dthe products can react to re-form the reactants, so the reaction can proceed in either direction depending on the conditions.

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1. A250 degrees Celsius and 50 atmospheres, with a nickel catalyst
2. B450 degrees Celsius and 200 atmospheres, with an iron catalyst
3. C900 degrees Celsius and 400 atmospheres, with a platinum catalyst
4. D150 degrees Celsius and 5 atmospheres, with a copper catalyst

1. Ait forces the gas particles closer together, so they collide more often and more ammonia is formed.
2. Bit lowers the temperature at which the nitrogen and hydrogen will begin to react with each other.
3. Cit keeps the ammonia produced as a gas, so that it cannot break down into nitrogen and hydrogen again.
4. Dit removes the need to use any catalyst in the reaction vessel at that stage of the process.

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1. Athe force that a body exerts on the ground because of the pull of gravity on its mass.
2. Bthe amount of energy a body carries with it because of the motion that it already has.
3. Cthe distance a body travels before it comes to rest once the pushing force is removed.
4. Dthe reluctance of a body to change its state of rest or of uniform motion.

1. AMass acts downwards towards the centre of the earth, while weight acts in whichever direction the body moves.
2. BMass increases when a body is heated, while weight stays the same at every temperature reached.
3. CMass is measured in newtons, while weight is measured in kilograms on a beam balance.
4. DMass stays the same wherever the body is, while weight changes with the strength of gravity at that position.

1. Athe surface it is travelling on stops exerting any friction on it.
2. Bthe energy stored in it by the original push has all been used up.
3. Ca resultant force acts on it.
4. Dits total mass is changed by adding or removing material from it.

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1. Athe pupils are all in class at that hour, so every classroom light and fan in the school is switched on.
2. Bthe sun is directly overhead at that hour, so the electricity supplied to the school is at its weakest.
3. Clunch is being cooked at that hour, and the stoves and heaters draw a large current to produce heat.
4. Dthe school stores electricity during the night and releases all of it back into the supply at midday.

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1. Aglucose + water, in sunlight and chlorophyll, gives carbon dioxide + oxygen
2. Bglucose + oxygen, in sunlight and chlorophyll, gives carbon dioxide + water
3. Ccarbon dioxide + water, in sunlight and chlorophyll, gives glucose + oxygen
4. Dcarbon dioxide + oxygen, in sunlight and chlorophyll, gives glucose + water

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1. AThe oxygen combines with nitrogen to form proteins, and the glucose is passed out through the stomata during the night.
2. BThe oxygen is used by living things in respiration, and the glucose is used as food, being respired or stored as starch.
3. CThe oxygen dissolves in the soil water taken up by the roots, and the glucose is broken down to release carbon dioxide.
4. DThe oxygen is used to make chlorophyll in the leaves, and the glucose is used to keep the leaf cells firm and upright.

1. Athe chloroplasts pass light straight through to the lower surface, where the sugars are actually made.
2. Bthe chloroplasts sit where the light is strongest, so the greatest possible amount of light is absorbed.
3. Cthe chloroplasts store the starch made in the leaf, keeping it near the upper surface where it stays warm.
4. Dthe tightly packed cells leave no air spaces, so water vapour cannot escape from the top of the leaf.

1. Athey allow rain water to enter the leaf directly, so less water has to be drawn up from the roots.
2. Bthey give the leaf a rough lower surface which holds warm air against it during the cooler night hours.
3. Cthey let carbon dioxide diffuse in and reach every photosynthesising cell, and let oxygen diffuse out.
4. Dthey let the leaf lose heat quickly, so the enzymes of photosynthesis keep working in hot weather.

1. Abreakdown of glucose in the absence of oxygen to release alcohol, carbon dioxide and energy.
2. Bbreakdown of proteins in the absence of oxygen to release lactic acid, water and a little energy.
3. Cbreakdown of glucose in the presence of oxygen to release carbon dioxide, water and energy.
4. Dbuilding up of glucose from carbon dioxide and water using energy absorbed from sunlight.

1. Ahis blood carries too much oxygen to the muscles, and the excess oxygen poisons the muscle cells.
2. Bhis breathing rate rises so much that carbon dioxide is removed faster than the muscles can make it.
3. Chis muscles need more energy than the oxygen reaching them allows, so they respire anaerobically and lactic acid builds up.
4. Dhis muscles run out of glucose entirely, so no respiration of any kind can take place in them.

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1. AAn area of open grassland grazed by wild antelope and zebra during the wet season.
2. BA plantation of pine trees planted in rows and managed by people for timber.
3. CA patch of miombo woodland growing on a hillside that has never been cleared.
4. DA stretch of river running between banks of reeds and rushes into a lake.

1. AUrine passed from the bladder of an infected person who has been drinking water.
2. BSweat released through the skin of an infected person during hard exercise.
3. CTears made by the tear glands in the eye of an infected person who is crying.
4. DBreast milk fed by an infected mother to her baby during breastfeeding.

1. Aburning the grass around the pool so that the smoke drives the larvae down to the bottom.
2. Bspreading a thin film of oil on the water, which blocks the breathing tubes so the larvae suffocate.
3. Cadding table salt to the water so that the larvae take in salt and grow into smaller adults.
4. Dstirring the water each evening so that the larvae are carried away from the edges of the pool.

1. ASpraying the walls of houses with an insecticide that kills the mosquitoes that settle on them.
2. BFilling in or draining the pools of stagnant water where the female mosquito lays her eggs.
3. CPouring a layer of paraffin over the surface of every pond and pool near the homestead.
4. DClearing the tall grass and bush so that rain water drains away instead of collecting.

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1. Athe solution replaces the water and salts lost in the diarrhoea, so the patient does not die of dehydration.
2. Bthe solution kills the cholera bacteria in the intestine, so the patient stops passing watery stools at once.
3. Cthe sugar in the solution feeds the patient, so no other food or drink is needed until the illness passes.
4. Dthe salt in the solution thickens the blood, so the bacteria can no longer be carried around the body.

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1. Aburning magnesium ribbon in oxygen, which leaves a white ash of magnesium oxide behind.
2. Bdissolving magnesium ribbon in cold water and evaporating the clear solution left behind to dryness.
3. Cadding magnesium ribbon to dilute hydrochloric acid and collecting the white solid that settles out.
4. Dpassing carbon dioxide over heated magnesium ribbon and cooling the black powder that is produced.

1. Acopper is a transition metal and transition metals take no part in displacement reactions at all.
2. Bmagnesium is higher than copper in the reactivity series, so copper cannot displace it from its oxide.
3. Cmagnesium oxide is an ionic solid and copper is a metal, so the two cannot come into contact.
4. Dcopper is more reactive than magnesium, so it would need a much higher temperature to react.

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1. A66,7 %, since there are two atoms in the formula and oxygen contributes twice as much as magnesium
2. B16 %, since the relative atomic mass of oxygen is 16 and this is read directly as a percentage
3. C40 %, since the mass of oxygen divided by the molecular mass, multiplied by 100, is 16/40 x 100
4. D60 %, since oxygen is the lighter of the two atoms and takes the larger share of the total mass

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1. Athe excess solid dissolves completely, so the calcium sulphate formed is more concentrated than before.
2. Bthe excess solid makes sure that all the acid is used up, so no acid is left to contaminate the salt.
3. Cthe excess solid changes the type of salt formed from an acid salt to a normal salt in the solution.
4. Dthe excess solid keeps the mixture warm, so the reaction finishes long before the acid can evaporate away.

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1. AIt feels soapy to the touch, has a pH below 7, and turns damp blue litmus paper red on contact.
2. BIt feels soapy to the touch, has a pH greater than 7, and reacts with acids to form a salt and water.
3. CIt has a sour taste, has a pH below 7, and gives off carbon dioxide when added to a carbonate.
4. DIt has a pH of exactly 7, has no effect on litmus paper, and reacts with neither acids nor bases.

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1. Adissolves the dyes in the ink, so that they are carried up the paper with it as it rises.
2. Bboils at a temperature below room temperature, so that it rises up the paper as a vapour.
3. Creacts with each of the dyes in turn, so that each one changes to a different colour on the paper.
4. Dis denser than the dyes in the ink, so that it pushes them ahead of it towards the top of the paper.

1. Aan ink mark would react with the filter paper and burn a hole in it once the solvent reached that level.
2. Bthe pencil line is thinner than an ink line, so the position of the spot can be measured more accurately.
3. Cthe pencil mark holds the ink spot in place, so the spot itself cannot be washed off the paper by the solvent.
4. Dan ink mark would dissolve in the solvent and rise up the paper, and its own dyes would confuse the results.

1. Athey have different colours, so the solvent carries the darker dyes further up the paper than the paler ones.
2. Bthey have different densities, so the heaviest dye sinks to the bottom of the solvent in the beaker.
3. Cthey have different boiling points, so each dye evaporates from the paper at its own height in turn.
4. Dthey have different solubilities in the solvent, so they are carried up the paper at different rates.

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1. Aelectrons move from the cloth to the rod, so the rod is left with an excess of electrons.
2. Belectrons move from the rod to the cloth, so the rod is left with an excess of electrons.
3. Cthe rubbing creates new electrons on the surface of the rod, adding negative charge to it.
4. Dprotons move from the rod to the cloth, so the cloth is left with an excess of positive charge.

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1. Athe sun is far hotter than the earth, and only radiation can carry heat between two bodies at very different temperatures.
2. Bthe air above the earth is a good conductor of heat, so the heat is passed along it particle by particle to the ground.
3. Cwarm air rises from the surface of the sun and travels outwards in a current until it reaches the earth's atmosphere.
4. Dradiation travels as electromagnetic waves, which need no material to carry them, and the space between is a vacuum.

1. AA flat, rough, black surface at the base of the cooker underneath the pot.
2. BA thick layer of glass wool packed all around the outside of the cooker.
3. CA curved, shiny surface that reflects the sun's rays towards a single point.
4. DA wide opening covered over with a sheet of dark plastic to trap the heat.

1. AThe radio, because its plastic casing cannot conduct electricity, so no earth wire is needed for safety.
2. BThe radio, because it draws a large current and the earth wire would melt at that current anyway.
3. CThe hot plate, because its metal casing carries the current away safely without any earth connection.
4. DThe hot plate, because it has the higher power rating and so needs fewer wires than a low power appliance.

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1. AJoin two damaged cables together with adhesive tape, so that the appliance can be used until a new cable is bought.
2. BRun several heaters from one socket using an adaptor, so that the current is shared between the appliances.
3. CConnect the metal casing of an appliance to the earth wire, so that a fault cannot leave the casing live.
4. DFit a thicker fuse wire in the plug, so that the fuse does not blow every time an appliance is switched on.

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1. ALeaving appliances on standby overnight, because an appliance uses less power starting from standby than from off.
2. BFitting energy saving bulbs in place of filament bulbs, and switching off appliances that are not being used.
3. CChoosing an appliance with a higher power rating, because it finishes the same job in a shorter time.
4. DConnecting several appliances to one socket, because they then share the current drawn from the supply.

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1. AChemical energy in the screen is converted to sound energy and then to light energy.
2. BLight energy from the room is converted to electrical energy stored in the battery.
3. CElectrical energy supplied to the screen is converted to light energy.
4. DSound energy from the keyboard is converted directly to electrical energy.

1. ALight, pressure and the taste of a food
2. BSound, text messages and video
3. CHeat, text messages and pressure
4. DSound, video and the mass of an object

1. AAn optical fibre cable, which carries the signal along a thin glass thread as pulses of light.
2. BA fuse wire fitted inside a plug, which melts and breaks a circuit that is overloaded.
3. CA resistance wire wound into a coil, which becomes hot when a current passes through it.
4. DAn insulated copper strip inside a plug, which connects the casing of an appliance to the ground.

1. AThe voice or text is converted to electrical impulses, which travel along the inner conductor while the outer conductor shields them from interference.
2. BThe voice or text is converted to pulses of light, which are reflected from side to side along the inside of the metal braid.
3. CThe signal is converted to heat in the inner conductor, and the outer conductor keeps that heat from escaping on the way.
4. DThe sound is carried along the cable as a pressure wave in the air trapped between the two conductors.