Combined Science Paper 2 Specimen 2020

1. Aless oxygen and more carbon dioxide, because oxygen is used in respiration and carbon dioxide is produced.
2. Bmore oxygen and more carbon dioxide, because both gases are produced by respiration in the tissues.
3. Cmore oxygen and less carbon dioxide, because oxygen is released when glucose is broken down.
4. Dless oxygen and less carbon dioxide, because both gases are absorbed by the moist lining of the lungs.

1. Ait removes the excess oxygen that would otherwise build up in the leaf and stop respiration.
2. Bit carries manufactured food from the leaves down to the roots for storage over the dry season.
3. Cit creates a pull that draws water and dissolved mineral salts up the xylem from the roots to the leaves.
4. Dit supplies the leaf with the carbon dioxide that the palisade cells need for photosynthesis, since the vapour leaves the leaf through the very same open stomata.

1. Abecome more turgid, because the loss of water raises the pressure inside its vacuoles.
2. Bclose its stomata and store the extra water in its roots until the soil dries out.
3. Cgrow faster, because the rapid water movement carries more mineral salts to the leaves.
4. Dwilt, because its cells lose turgor and can no longer hold the leaves and stem firm.

1. Acool, moving and humid, so that the moving air is already saturated with water vapour.
2. Bcool, still and humid, so that water vapour collects around the leaf surfaces.
3. Cwarm, moving and dry, so that water evaporates quickly and the vapour is swept away.
4. Dwarm, still and dry, so that the water vapour stays in a layer close to the leaf.

1. Aa community of different organisms interacting with one another and with their non-living surroundings, established without human interference.
2. Bthe total mass of green plants in an area, which fixes the sunlight that all the other organisms depend on.
3. Cthe physical surroundings of an area, that is its soil, water, air, light and temperature, considered on their own, set apart from the plants and animals that happen to live in them.
4. Da group of organisms of the same species living together in one place and breeding among themselves.

1. Aonly the energy foods, that is carbohydrates and fats, in amounts matched to the work the person does.
2. Ball the food nutrients, in the correct proportions and in the amounts the body needs.
3. Cthe largest possible amount of protein, since protein is the nutrient used for growth and repair.
4. Dequal masses of carbohydrate, protein and fat, together with as much water as the person can drink.

1. Ais needed to build the bones and teeth of the developing foetus, and without enough of it in the diet the mother's own bones are weakened.
2. Bis needed to make the antibodies that pass across the placenta and protect the newborn baby from disease.
3. Cis needed to make the haemoglobin that carries oxygen from the mother's lungs to the foetus across the placenta, so a shortage of it leaves both the mother and her baby anaemic.
4. Dis the main energy store the foetus draws on during the last three months, when it grows most quickly.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

1. Asodium with one outer electron still in place, and chlorine with seven, the two shells simply drawn touching, because the two atoms are held side by side without either of them changing.
2. Bsodium with an empty outer shell shown as a positive ion, and chlorine with eight outer electrons shown as a negative ion.
3. Ca pair of electrons shared between the sodium and the chlorine, drawn in the overlap of the two shells.
4. Dsodium with eight outer electrons and chlorine with eight outer electrons, joined by a shared pair.

1. Amelting and dissolving both break the ionic bonds into free electrons, which then carry the current through the liquid.
2. Bthe solid contains no ions at all, and the ions are only formed at the moment the substance melts or dissolves.
3. Cthe solid is a poor conductor of heat, so the current cannot pass through it until it has been warmed up first.
4. Dthe ions in the solid are held in fixed positions in the lattice, and only become free to move when it melts or dissolves.

1. Aan acid, so that it reacts with the food in the stomach and stops any more acid being produced.
2. Ba salt, so that it dissolves in the stomach juices and dilutes the acid until it is harmless.
3. Can indicator, so that it shows the patient when the acid in the stomach has returned to normal.
4. Da base, so that it neutralises the excess hydrochloric acid to form a salt and water.

Answer this when you sit the paper.

1. Amelt at a low temperature and dissolve the iron so that it can be run out of the bottom of the furnace.
2. Breact with the sandy impurities in the ore to form the molten slag that floats on top of the iron.
3. Cburn in the hot air blast to supply heat, and to form carbon monoxide which reduces the iron ore to iron.
4. Dcoat the inside of the furnace and protect the brick lining from the very high working temperature.

1. Aprovide the carbon that reduces the iron ore to molten iron in the hottest part of the furnace.
2. Bkeep the temperature of the furnace down so that the iron does not boil away as a vapour.
3. Cdecompose to calcium oxide, which reacts with the sandy impurities to form the molten slag.
4. Dreact with the waste gases at the top of the furnace so that no carbon dioxide escapes to the air.

Tap to enlarge

1. Apower stroke, in which the burning gases expand and force the piston down the cylinder.
2. Bexhaust stroke, in which the rising piston pushes the burnt gases out through the open exhaust valve.
3. Cinduction stroke, in which the falling piston draws the fuel and air mixture into the cylinder.
4. Dcompression stroke, in which the rising piston squeezes the fuel and air mixture into a small space.

Tap to enlarge

1. Athe closed valves hold the piston steady so that the crankshaft can turn it through half a revolution.
2. Bthe closed valves seal the cylinder so that none of the expanding hot gases escapes and all their push acts on the piston.
3. Cthe closed valves keep the spark plug dry so that the spark can jump across at the right moment.
4. Dthe closed valves let the cylinder cool between strokes so that the next charge of fuel is not ignited early by the heat left over from the stroke before it.

1. Aproduce the spark that sets the compressed fuel and air mixture alight at the top of the stroke.
2. Bpump the burnt exhaust gases out of the cylinder and along the exhaust pipe to the silencer.
3. Cspray a measured amount of fuel as a fine mist directly into the cylinder at the right moment.
4. Ddraw air through a narrow tube so that the pressure drop lifts fuel out of the float chamber.

1. Amix petrol with air in the correct proportion to form a combustible mixture for the cylinder.
2. Bignite the fuel and air mixture once the piston has compressed it into the top of the cylinder.
3. Cstore the petrol under pressure so that it is ready to be released into the cylinder.
4. Dcool the cylinder head by circulating water round it while the engine is running.

1. Ait meters the fuel accurately and atomises it finely, so combustion is more complete and less fuel and pollutant are wasted.
2. Bit works at a lower temperature, so the cylinder walls last longer than they do in a carburettor engine, and the engine therefore needs less cooling water to keep it safe.
3. Cit needs no electrical supply, so the engine can still be run when the battery is flat.
4. Dit removes the need for an air filter, since the fuel is sprayed straight into the cylinder.

Tap to enlarge

1. Aat ground level beside the storage tank, so that the pipes joining the two are as short as possible.
2. Binside the roof space, where the trapped warm air of the ceiling keeps the plate hot after sunset.
3. Cagainst a shaded wall of the house, where the plate is protected from rain and from the wind.
4. Don the roof, tilted and facing the sun, in the open and clear of trees and buildings.

1. Ais the best reflector of radiant heat, so the plate loses the least energy back to the sky.
2. Bconducts heat better than a shiny surface does, so the heat passes into the water more quickly.
3. Creflects the sunlight back on to the copper tubing, which then heats the water flowing through it.
4. Dis the best absorber of radiant heat, so the plate takes in the most solar radiation.

1. Acopper is a poor conductor of heat, so the water inside the tube cannot lose its heat back to the plate.
2. Ba thin tube holds the water at a high pressure, and water at high pressure boils at a lower temperature.
3. Ccopper reflects sunlight on to the plate behind it, so the plate absorbs more radiation than it otherwise would, which raises the temperature of the water flowing through the tube.
4. Dcopper is a good conductor of heat, and the thin tube gives a large surface area for the small volume of water inside it.

1. Ait keeps the pressure inside the tank steady so that the hot water flows out at a constant rate.
2. Bit absorbs sunlight falling on the tank and so adds to the heat collected by the copper plate.
3. Cit is a poor conductor of heat, so it cuts down heat loss from the hot water to the cooler surroundings.
4. Dit stops the water in the tank from freezing on cold nights and splitting the pipes, which would otherwise burst the copper tubing running across the roof.

Tap to enlarge

1. Athe hepatic portal circulation, because it carries absorbed food from the gut to the liver.
2. Bthe coronary circulation, because it supplies the muscle of the heart wall itself.
3. Cthe pulmonary circulation, because it carries blood between the heart and the lungs.
4. Dthe systemic circulation, because it serves the whole system of body organs.

1. Acontracts more often than the right ventricle does, so its muscle is worked harder and grows thicker.
2. Bholds a much larger volume of blood, so a thicker wall is needed to contain it.
3. Cpumps blood right round the body, so it must develop a much higher pressure than the right ventricle needs.
4. Dreceives blood directly from the vena cava, which arrives at a higher pressure than blood from the lungs.

1. Aa barking cough, swollen glands in the neck, and a thick grey membrane across the throat.
2. Ba high fever, chills and shivering, and headache with muscle and joint pains.
3. Can itching skin rash on the hands and wrists, with small blisters and no fever at all.
4. Dwatery diarrhoea, sunken eyes and severe dehydration, with no rise in temperature.

Answer this when you sit the paper.

Answer this when you sit the paper.

1. Aa rise in the number of red blood cells, and a permanent thickening of the heart muscle.
2. Bloss of hearing in both ears, and a gradual hardening of the bones of the arms and legs.
3. Cimproved concentration at first, followed by a lasting increase in the person's lung capacity.
4. Ddamage to the brain and nervous system, and damage to the liver and kidneys.

Tap to enlarge

Answer this when you sit the paper.

1. Aweaning the child on to protein rich foods such as beans, groundnuts, eggs, milk and fish.
2. Badding vitamin C rich fruits such as oranges and guavas to every meal the child is given.
3. Cgiving the child extra maize meal and sugar so that its daily energy intake is raised.
4. Dboiling all the child's drinking water and keeping the feeding utensils covered and clean.

1. Afrom the testis into the epididymis, then along the sperm duct to the urethra.
2. Bfrom the testis into the ureter, then along the bladder wall into the urethra.
3. Cfrom the testis into the oviduct, then along the sperm duct to the urethra.
4. Dfrom the testis directly into the urethra, without passing through any other tube.

1. Afrom the vagina straight into the ovary, where the egg is still held in its follicle.
2. Bfrom the vagina through the cervix, up through the uterus and into the oviduct.
3. Cfrom the vagina into the ureter, and then along the ureter into the oviduct.
4. Dfrom the vagina into the urethra, and then through the bladder wall into the uterus.

1. Amakes the woman's cycle regular, so that the days on which she can conceive are easy to predict.
2. Bkills any sperm that enter the vagina, so that none of them can reach the cervix.
3. Craises the chance of conception for a couple who are trying to start a family.
4. Dacts as a barrier to semen, so it prevents pregnancy and the spread of sexually transmitted infections.

1. Athe division of a fertilised egg into the many cells that will become the embryo.
2. Bthe release of a mature egg from the ovary into the funnel of the oviduct.
3. Cthe attachment of the developing ball of cells to the lining of the uterus.
4. Dthe fusion of a male gamete nucleus with a female gamete nucleus to form a zygote.

Tap to enlarge

Answer this when you sit the paper.

Tap to enlarge

Answer this when you sit the paper.

1. Aits wall is one cell thick and the capillary wall beside it is one cell thick, so gases diffuse a very short distance.
2. Bits wall is thick and muscular, so it can squeeze the air out of the lung at the end of each breath.
3. Cit is lined with a waterproof layer, so the gases stay in the air space until the blood is ready for them, instead of being lost into the tissue fluid that surrounds the air sac.
4. Dit is supplied by a single large blood vessel, so all the blood in the lung passes through it in turn.

1. Aa large total surface area, from millions of alveoli, and a dense network of blood capillaries around each one.
2. Ba small total surface area and a dry lining, so that the gases are not lost to the moisture.
3. Ca small number of very large air sacs, and a slow blood flow so each gas has time to diffuse across.
4. Da thick layer of muscle around each alveolus, and a rich supply of nerves to control the rate of diffusion.

1. Atranspiration, because water has been lost from the cell to its surroundings.
2. Bturgidity, because the cell contents have been pressed outwards against the wall.
3. Cplasmolysis, because the cytoplasm has shrunk away from the cell wall.
4. Ddiffusion, because the water molecules have spread from a high to a low concentration.

1. Aturgid, because the cell contents press outwards against the wall and the cell is firm.
2. Bhaemolysed, because water has entered the cell faster than it can leave again.
3. Cflaccid, because the cell wall has been stretched as far as it will go.
4. Dplasmolysed, because the vacuole has been pushed against the inside of the wall.

1. Aa charged particle formed when a particle of an element gains or loses electrons.
2. Bthe smallest particle of matter that cannot be broken down by any means at all.
3. Cthe smallest particle of an element that can take part in a chemical reaction.
4. Dthe smallest particle of a compound that can exist on its own in the free state.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

1. Athey would dissolve in the liquid oxygen and make it unsafe to store in the steel cylinders.
2. Bthey would react with the nitrogen at low temperature and turn it into ammonia and nitrates.
3. Cthey would solidify at the low temperatures used and block the pipes and the fractionating column.
4. Dthey would raise the boiling point of the nitrogen above that of the oxygen and spoil the separation.

1. Anitrogen is lighter than oxygen, so it floats to the top of the liquid and is drawn off there.
2. Bnitrogen has a lower boiling point, -196 degrees Celsius, than oxygen, -183 degrees Celsius.
3. Cnitrogen is unreactive, so it evaporates while the oxygen is held back by reaction with the column.
4. Dnitrogen makes up about four fifths of the air, and the most plentiful gas in a mixture boils off before the others do.

Answer this when you sit the paper.

1. Athe acid reacts with the electrodes and coats them so that they are not eaten away by the current.
2. Bpure water is very poorly ionised, so it hardly conducts, and the acid supplies ions to carry the current.
3. Cthe acid supplies the oxygen atoms that are given off at the anode during the electrolysis.
4. Dthe acid lowers the freezing point of the water so that the electrolysis can be run at any temperature.

1. Athe oxygen is given off at the anode, where the current is only half as large as it is at the cathode.
2. Bwater splits to give two molecules of hydrogen for every one molecule of oxygen, and equal volumes of gases contain equal numbers of molecules.
3. Can oxygen molecule is sixteen times as heavy as a hydrogen molecule, so it takes up half the space in the measuring tube at the same temperature and pressure.
4. Dhalf the oxygen produced dissolves in the acidified water instead of collecting in the tube.

1. Afilling electric light bulbs, because it stops the hot filament from burning away.
2. Bputting out fires in workshops, because it smothers the burning material.
3. Cfilling weather balloons, because it is the least dense of all the common gases.
4. Dsupplying patients with breathing difficulties in hospital through a mask or tent.

Tap to enlarge

Answer this when you sit the paper.

Answer this when you sit the paper.

1. Aproduces a gas that would escape from the top of the tower and be lost from the plant.
2. Bgives a weak acid rather than a strong one, so the product would be of no use in industry.
3. Cis far too slow at ordinary temperatures, so the plant would have to be run for several days to make even the small quantity of acid a laboratory would need.
4. Dis violent and very exothermic, and throws the acid up as a dense mist that is hard to collect and dangerous to breathe.

1. Atakes in heat from the surroundings, and can only go in the forward direction once it has started.
2. Btakes in heat from the surroundings, and can go in both the forward and the backward direction.
3. Cgives out heat to the surroundings, and can only go in the forward direction once it has started.
4. Dgives out heat to the surroundings, and can go in both the forward and the backward direction.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

Tap to enlarge

Answer this when you sit the paper.

Tap to enlarge

Answer this when you sit the paper.

1. Athe magnet pushes the free electrons in the wire along it in the direction the coil is turning.
2. Bthe coil cuts through the magnetic field lines as it turns, and cutting field lines induces an e.m.f. in it.
3. Cthe friction between the brushes and the slip rings separates charge and builds up a voltage.
4. Dthe coil becomes hot as it turns, and a hot wire in a magnetic field produces a voltage of its own, in the way that a heated thermocouple junction does.

1. Athe brushes lift off the slip rings twice in each turn, which breaks and remakes the circuit.
2. Beach side of the coil moves up through the field and then down through it, so the direction of the induced current reverses every half turn.
3. Cthe speed of the coil rises and falls as it turns, so the current grows and then dies away again twice during every complete revolution that the coil makes.
4. Dthe strength of the magnet changes from north to south twice during every turn of the coil.

1. Aa horizontal straight line at a steady positive voltage above the time axis.
2. Ba curve that rises to a peak and then stays at that peak until the coil is stopped.
3. Ca sine curve, rising to a peak, falling through zero to an equal negative peak, and repeating.
4. Da straight line sloping steadily upwards from the origin as the coil continues to turn.

1. Adecrease, because the stronger field opposes the turning of the coil and slows the cutting down.
2. Bstay the same, because the output voltage of a generator is fixed by the number of turns on the coil.
3. Cincrease, and the frequency will rise with it, because the coil is dragged round faster by the field.
4. Dincrease, because the field lines are closer together, so the coil cuts more of them each second.

Answer this when you sit the paper.

Answer this when you sit the paper.

1. Afriction between the moving parts turns some of the work put in into heat, and some effort goes into moving the parts of the machine itself.
2. Bthe load is heavier than the effort in every machine, so part of the work put in is lost on the way.
3. Cenergy is destroyed as the machine works, so the work output must be smaller than the work input, and no machine can give back to the load what has been destroyed.
4. Dthe velocity ratio of a machine works out smaller than its mechanical advantage.

1. Arunning it faster, so that less time is available for the heat of friction to escape.
2. Blubricating the moving parts and using lighter moving parts, so less work is wasted.
3. Cincreasing the load it lifts, so that a larger share of the work done is useful work.
4. Dusing a longer rope and a taller frame, so that the effort moves through a greater distance.

1. AAn inclined plane and a barometer.
2. BA pulley and an inclined plane.
3. CA voltmeter and a wheel and axle.
4. DA thermometer and a pulley.

1. Aboil water in a boiler to produce steam at high pressure and temperature.
2. Braise water to the top of a tower, so that it can fall through the turbine afterwards.
3. Cturn the coil of the generator directly, by blowing the hot gases across it.
4. Dcharge a bank of batteries, from which the electricity is later drawn as it is needed.

1. Aseparates the burnt gases from the ash before they are released through the chimney.
2. Bturns the coil of a generator, so that kinetic energy is converted into electrical energy.
3. Ccondenses the steam back into water so that it can be pumped round the boiler again.
4. Draises the voltage of the electricity so that it can be sent along the transmission lines.

1. Ait burns without any residue, so the station cannot sell any by-product to recover its costs.
2. Bit releases carbon dioxide and sulphur dioxide, which cause global warming and acid rain, and it is non-renewable, so supplies will eventually run out.
3. Cit produces steam at too low a pressure to drive a turbine, and it has to be imported from other countries at a price that rises with every shipment brought across the border.
4. Dit is renewable and so encourages waste, and it releases oxygen that feeds fires nearby.

1. Athe thermal station uses a generator to produce the electricity, while the hydroelectric station uses a transformer to produce it.
2. Bthe thermal station needs no turbine at all, while the hydroelectric station needs a turbine to spin the generator, so only the hydroelectric station has moving parts under the water.
3. Cthe thermal station burns a fuel to raise steam that drives the turbine, while the hydroelectric station uses falling water to drive the turbine directly.
4. Dthe thermal station produces alternating current, while the hydroelectric station produces direct current that must be converted first.

Answer this when you sit the paper.

Answer this when you sit the paper.