Combined Science Paper 2 June 2019

1. AInsect pollinated flowers produce large amounts of light, smooth pollen, while wind pollinated flowers produce a little sticky pollen.
2. BInsect pollinated flowers have long, loosely attached anthers hanging outside, while wind pollinated flowers have small enclosed anthers.
3. CInsect pollinated flowers have large, brightly coloured petals, while wind pollinated flowers have small petals or none at all.
4. DInsect pollinated flowers have feathery stigmas hanging outside the flower, while wind pollinated flowers keep the stigma enclosed.

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1. AIt is changed into starch for storage in the leaf, and later moved as sucrose to other parts of the plant.
2. BIt is stored as glucose in the leaf cells, because glucose has no effect on the water balance of a cell.
3. CIt passes into the xylem and is carried upwards in the transpiration stream to the growing shoot tips.
4. DIt is broken down again into carbon dioxide and water inside the chloroplasts, and is lost through the stomata.

1. ASexual reproduction involves fertilisation and produces offspring that show genetic variation, while asexual reproduction does neither.
2. BSexual reproduction needs one parent plant and a seed, while asexual reproduction needs two parent plants of the same species.
3. CAsexual reproduction involves fertilisation of a gamete, while sexual reproduction produces offspring from a part of the parent plant.
4. DAsexual reproduction produces offspring showing genetic variation, while sexual reproduction produces offspring identical to the parent.

1. APassive immunity follows a vaccination, while active immunity develops after a person has had an attack of the disease itself.
2. BPassive immunity is produced by white blood cells in the bone marrow, while active immunity is produced by antibodies in the blood plasma.
3. CPassive immunity is short lived because the antibodies are received ready made, while active immunity is long lived because the body makes its own antibodies.
4. DPassive immunity is long lived because the body makes its own antibodies, while active immunity is short lived because the ready made antibodies are received from someone else.

1. AResistance to infection that comes from the body's own processes, without any help from medicine or vaccination.
2. BResistance to infection that follows an injection of a vaccine containing a weakened form of the pathogen.
3. CResistance to infection produced by a course of antibiotics taken until the last of the pathogens is killed.
4. DResistance to infection that comes from eating a balanced diet with enough vitamins and mineral salts each day.

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1. Aalkenes are made of carbon and hydrogen while alkanes contain oxygen as well, which makes the alkanes more stable.
2. Balkenes contain a carbon to carbon double bond and are unsaturated, while alkanes are saturated with single bonds.
3. Calkenes contain more hydrogen atoms for each carbon atom than alkanes, so their molecules are held together less tightly.
4. Dalkenes have larger molecules with higher boiling points than alkanes, so they take part in reactions more easily.

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1. AIt resists corrosion, so it does not rust when it is left in contact with water or with body fluids.
2. BIt has a low density, so a sink or an instrument made from it weighs much less than one made from pure iron.
3. CIt has a low melting point, so it can be shaped into sinks and instruments without the need for a hot furnace.
4. DIt conducts heat poorly, so a sink full of hot water stays warm much longer than one made of ordinary iron.

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1. AStraight lines running parallel to the wire in the same direction as the current, spreading out as the distance grows.
2. BCircles lying in planes that contain the wire, running from the top of the wire to the bottom as in a bar magnet.
3. CStraight lines pointing away from the wire in every direction, in much the same pattern as the field around a small positive charge.
4. DCircles centred on the wire, lying in planes at right angles to it, with their direction given by the right hand grip rule.

1. AThe wire becomes hot and glows, because the field of the magnets forces the current through a much smaller cross section.
2. BThe wire swings to and fro, because the magnetic field around the current carrying wire reverses many times each second.
3. CThe wire stays still, because the magnetic field of the current is far too weak to affect the field of the permanent magnets.
4. DThe wire moves, because the magnetic field around the current carrying wire interacts with the field of the permanent magnets.

1. AThe wire is pushed with a much larger force in the same direction, because the two magnetic fields now add together.
2. BThe wire is not pushed at all, because the reversed current cancels out the field of the permanent magnets.
3. CThe wire is pushed in the opposite direction, because reversing the current reverses the magnetic field around the wire.
4. DThe wire is pushed in exactly the same direction as before, because the field of the permanent magnets has not been changed at all.

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1. Athe amount of matter contained in the body, measured in kilograms on a balance.
2. Bthe gravitational force acting on the body because of the mass it contains.
3. Cthe force the body exerts on each square metre of the surface it rests on.
4. Dthe product of the mass of the body and the velocity at which it is moving.

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1. AThe pressure is greater on the 0.3 m by 0.5 m face, because standing the box on end increases the weight acting down.
2. BThe pressure is smaller on the 0.3 m by 0.5 m face, because the weight of the box is spread over a smaller area.
3. CThe pressure is the same on both faces, because the weight of the box itself has not been changed by turning it.
4. DThe pressure is greater on the 0.3 m by 0.5 m face, because the same weight now acts over a smaller area of contact.

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1. ASyphilis, which is caused by a protozoan carried in the blood from one person to another.
2. BGenital herpes, which is caused by a bacterium and is cured by a course of antibiotics.
3. CGonorrhoea, which is caused by a fungus growing on the lining of the reproductive tract.
4. DGenital warts, which are caused by a virus passed on during sexual contact.

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1. AIt replaces the water and salts lost through severe diarrhoea and vomiting, which would otherwise cause dehydration.
2. BIt kills the bacteria living in the small intestine, so that the patient stops producing the watery diarrhoea.
3. CIt neutralises the toxin released by the bacteria, so that the walls of the intestine can absorb food again.
4. DIt coats the whole lining of the intestine with a layer of salt, so that no further bacteria can be taken in with food or water.

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1. AAn artery is lined with valves along its whole length, while a vein has a single valve where it enters the heart.
2. BAn artery is made of one layer of flattened cells, while a vein has several layers of muscle and elastic tissue.
3. CAn artery has a narrow lumen and a thick muscular wall, while a vein has a wide lumen and a much thinner wall.
4. DAn artery has a wide lumen and a thin wall, while a vein has a narrow lumen and a thick muscular wall.

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1. AIt keeps the upper surface flat and smooth, so that rain water runs off the leaf instead of soaking into it.
2. BIt reduces water loss, because the upper surface is hotter in the sun and water evaporates fastest from there.
3. CIt lets the upper surface absorb more light, because open stomata block the light reaching the chloroplasts.
4. DIt stops carbon dioxide escaping from the leaf, so that more of it is left in the air spaces for photosynthesis.

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1. AIt is removed by respiration in green plants and returned by photosynthesis in animals and in decaying matter.
2. BIt is removed by evaporation from the leaves of green plants and returned when rain washes it back out of the atmosphere.
3. CIt is removed when fuels are burned in air and returned by the photosynthesis of green plants during daylight.
4. DIt is removed by photosynthesis in green plants and returned by respiration, by decay and by the burning of fuels.

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1. APhotosynthesis in green plants, and the decay of dead material by soil bacteria.
2. BDenitrification by soil bacteria, and the burning of fuels in air.
3. CRespiration by animals, and the evaporation of water from the leaves of plants.
4. DLightning in a thunderstorm, and nitrogen fixation by bacteria in root nodules.

1. ASoil fertility rises while pests become fewer, because the same crop returns the same nutrients to the soil each season.
2. BSoil fertility falls and pests and diseases of that crop build up, because the same species is grown there each season.
3. CSoil fertility falls but pests and diseases become rarer, because the pests of other crops then have nothing to feed on.
4. DSoil fertility stays the same, but the crop plants grow more slowly because they compete with each other for light.

1. AIt keeps the number of predators low, because a predator feeds on a single species of prey at a time.
2. BIt uses less water than a community of a single species, because the plants shade one another from the sun.
3. CIt grows to the same height everywhere, because the different species all reach maturity at the same time.
4. DIt offers a wide variety of food sources and sustains itself, and disease spreads less easily through it.

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1. Asolubilities in water, so that one of the liquids dissolves while the other is left behind.
2. Bdensities, so that the denser of the two liquids sinks to the bottom and is run off first.
3. Cfreezing points, so that one of the liquids becomes a solid and can then be filtered off.
4. Dboiling points, so that the liquid with the lower boiling point evaporates off first.

1. AThe mixture is heated so strongly that both liquids boil together and pass on to the condenser as one.
2. BWater vapour condenses on the beads and runs back down, while ethanol vapour passes on to the condenser.
3. CEthanol vapour condenses on the beads and runs back down, while water vapour passes on to the condenser.
4. DBoth vapours condense on the beads and run back down, so that nothing but air reaches the condenser.

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1. AIt dissolves readily in water and has a high melting point, because strong forces hold its ions together.
2. BIt does not dissolve in water and has a low melting point, because its particles are held by weak forces.
3. CIt conducts electricity while it is solid, because its ions are free to move through the crystal lattice.
4. DIt burns readily in air with a bright lilac flame, because potassium metal is still present in the lattice.

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1. Athe concentration in mol/dm3 multiplied by the volume of the solution in dm3
2. Bthe concentration in mol/dm3 multiplied by the volume of the solution in cm3
3. Cthe concentration in mol/dm3 divided by the volume of the solution in dm3
4. Dthe volume of the solution in dm3 divided by the concentration in mol/dm3

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1. AIt is the one that produces the greatest number of bubbles in the three minutes, because it reacts fastest with the acid.
2. BIt is the one that changes colour in the acid, because a colour change shows the metal has taken in the most acid of the four.
3. CIt is the one that produces no bubbles at all in the three minutes, because the acid has already used it up.
4. DIt is the one that sinks to the bottom of the acid, because the heaviest metal holds the most energy to react.

1. AIt reacts faster than any of the other three metals, because copper lies above hydrogen in the reactivity series.
2. BIt gives off gas slowly at first and then much faster, because the heat released warms the acid as the reaction goes on.
3. CIt gives off no gas at all, because copper lies below hydrogen in the reactivity series and does not react with dilute acids.
4. DIt dissolves away quietly with no gas at all given off, because the copper reacts to form a blue solution of copper sulphate.

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1. Aa substance made up of atoms that all contain the same number of protons in their nuclei.
2. Ba substance that can be separated into its parts by filtering it or by using a magnet on it.
3. Ca substance made up of two or more elements chemically combined together in fixed proportions.
4. Da substance made up of two or more different elements simply mixed together in any proportion that is wanted.

1. AZinc oxide melts at a far higher temperature than copper does, so the two substances cannot mix while solid.
2. BCopper is less reactive than zinc, so it cannot take the oxygen from zinc oxide and displace the zinc.
3. CCopper has already combined with the oxygen of the air, so none of it is left to react with the zinc oxide.
4. DZinc oxide is an acidic oxide while copper is a metal, so the two of them are not able to react together.

1. Aa device that gives out more energy at its output than is supplied to it at its input.
2. Ba device that increases the amount of work done, so that less energy is needed for a job.
3. Ca device that makes work easier, for example by letting a small effort raise a large load.
4. Da device that changes electrical energy into movement, such as a motor turning a wheel.

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1. AIt raises the resistance of the metal casing, so that a very small current passes through anyone who touches it.
2. BIt carries current from the casing to the ground along a path of very low resistance, instead of through the person touching it.
3. CIt cuts off the supply to the whole appliance as soon as the metal casing becomes live, by melting through at its own thinnest point.
4. DIt stores the extra charge that builds up on the metal casing and releases it slowly, so the user feels no shock.

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1. Athe momentum of a body is found by multiplying its mass by the velocity at which it travels.
2. Bfor every action force there is an equal and opposite reaction force, acting on the other body.
3. Ca body stays at rest, or keeps moving at a steady speed, unless a resultant force acts upon it.
4. Dthe acceleration of a body is proportional to the resultant force that acts upon it.

1. AThe person presses down on the chair, and the chair presses up on the person with an equal and opposite force.
2. BThe person presses down on the chair with a force larger than the upward push of the chair, so the person stays seated.
3. CThe chair presses up on the person with a force larger than the person's weight, which is why the person does not fall.
4. DThe person's weight acts on the chair while the chair's weight acts on the floor, and these two forces are equal in size.

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1. AIt is the same as the practical value, because the mass of the object does not change while it is pulled.
2. BIt is higher than the practical value, because the calculation takes no account of friction with the surface.
3. CIt is lower than the practical value, because the calculation takes no account of the weight pressing down.
4. DIt is lower than the practical value, because part of the 300 N is used in lifting the object off the surface.

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1. AThe resistance rises, because the electrons meet more opposition along the greater length of wire.
2. BThe resistance falls, because the current is spread out over a greater length of the same thickness.
3. CThe resistance falls, because the electrons have more room to move along the greater length of wire.
4. DThe resistance stays the same, because it depends on the material of the wire and not on its length.

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1. AThe signal is carried by the glass fibre itself as a vibration, which is turned back into sound by a thin metal sheet at the receiver.
2. BThe signal is changed into pulses of light, which travel along the fibre and are changed back to the original signal at the receiver.
3. CThe signal is changed into electrical pulses, which travel along a copper core inside the fibre and are amplified at the receiver.
4. DThe signal is changed into radio waves, which travel through the air beside the fibre and are picked up by an aerial at the receiver.

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1. Aincrease the strength of a weak signal after it has travelled a long way along a cable.
2. Bchange a signal from one language into another before it is passed on to the receiver.
3. Cseparate the actual signal from the carrier wave that brought it, so the message can be used.
4. Dcombine the actual signal with a carrier wave, so that it can then be sent out over a long distance.

1. AA message can carry a handwritten signature, which an ordinary posted letter is not able to do.
2. BA message is stored on paper at the post office, so a copy can be collected if it is lost.
3. CA message reaches the person it is sent to within seconds, rather than in days or in weeks.
4. DA message can be sent to a person who has no electricity and no telephone network at home.

1. AIt falls as the distance grows, because a longer route passes through more exchanges that share the cost.
2. BIt rises sharply once the message crosses a national border, because a second network has to be paid.
3. CIt rises steadily with distance, in the same way as the postage charged on an ordinary letter.
4. DIt stays the same whatever the distance, so a message across the world costs no more than one next door.