Combined Science Paper 2 November 2021

1. Athe total amount of energy passed on to the next trophic level
2. Bthe total mass of dead remains and waste present in a given area
3. Cthe total mass of living material present in a given area
4. Dthe total number of individual organisms counted in a given area

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1. AConsumers near the top breed more slowly, so their young are counted at a separate level
2. BOrganisms higher up the chain are physically larger, so fewer of them fit into the same area of habitat
3. CEnergy is lost at each trophic level, so less is available to build the biomass of the level above
4. DThe producers at the base take in far more water than the consumers above them ever do

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1. ATheir numbers rise, because they begin feeding directly on the plants that remain
2. BTheir numbers rise, because there is less competition for the space that is left behind
3. CTheir numbers stay the same, because they feed on other animals rather than on plants
4. DTheir numbers fall, because less food is passed up the chain and reaches them

1. Aglucose gives lactic acid + a small amount of energy
2. Blactic acid + oxygen gives glucose + a large amount of energy
3. Cglucose + oxygen gives carbon dioxide + water + energy
4. Dglucose gives ethanol + carbon dioxide + energy

1. AMany stomata are spread over the upper surface, where the moving air is warmest
2. BA thick waxy cuticle covers the upper surface, and water cannot pass through it
3. CThe lamina is broad and very thin, so the whole leaf is exposed to the moving air
4. DThe outer cell walls are thin and uncovered, so water passes out of them easily

1. AIts wall is one cell thick and permeable, so substances diffuse quickly into and out of the blood
2. BIts lumen is wide and lined with rings of cartilage, so blood flows through without resistance
3. CIts wall is thick and muscular, so blood is carried away from the heart under high pressure
4. DIt has valves spaced along its length, so blood cannot be pushed backwards down the vessel

1. Athe joining of two elements into a compound by passing a current through them
2. Bthe movement of electrons along a metal wire when a cell is connected to it
3. Cthe breakdown of a compound by passing an electric current through it
4. Dthe breakdown of a compound by heating it strongly in the absence of air

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1. AIt melts at a low temperature, and it reacts with the electrolyte to release the products
2. BIt conducts electricity well, and it stays unchanged by the electrolyte and the products
3. CIt conducts electricity well, and it dissolves in the electrolyte as the current passes
4. DIt insulates against electricity, and it stays unchanged by the products of the reaction

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1. ADissolving the sugar is a physical change, because no new substance is made and the sugar can be recovered
2. BHeating the iron with sulphur is a physical change, because the two solids are just mixed together more finely
3. CDissolving the sugar is a chemical change, because the sugar disappears and can no longer be seen in the water
4. DBoth of the changes are physical, because the starting materials of each of them can be separated by filtering

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1. AThey are far apart with no fixed pattern, and they move quickly in all directions
2. BThey are packed closely with no fixed pattern, and they slide over one another
3. CThey are far apart in a fixed pattern, and they are held still by strong forces
4. DThey are packed closely in a fixed pattern, and they vibrate about fixed positions

1. AEnergy is used up whenever work is done, so the total energy of the universe falls slowly
2. BEnergy can be created by a machine, but no machine is able to change it into another form
3. CEnergy changes completely into useful energy whenever one form is turned into another form
4. DEnergy cannot be created or destroyed, but it can be changed from one form into another

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1. ACoal is burnt inside the generator itself, and the heat that is released is changed straight into an electric current by the coils
2. BWater falling down a pipe turns the turbines, and the coal is burnt to keep the coils of the generator warm enough to work well
3. CCoal is burnt in a boiler to turn water into high pressure steam, the steam turns turbines, and the turbines drive generators
4. DCoal is burnt in a boiler to turn water into high pressure steam, the steam turns generators, and the generators drive turbines

1. Apressure = height x density x gravitational field strength
2. Bpressure = density divided by height x gravitational field strength
3. Cpressure = force divided by area
4. Dpressure = mass x height x gravitational field strength

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1. AThe tube must be full of air, and the outlet end must be held above the liquid surface in the container
2. BThe tube must be full of liquid, and both of its ends must be held at exactly the same height
3. CThe tube must be full of liquid, and the outlet end must be held below the liquid surface in the container
4. DThe tube must be empty of liquid, and the container must be closed tightly at the top with a lid

1. AAtmospheric pressure acts on the outlet end alone, and this pressure draws the liquid back up into the container
2. BAir is drawn out of the tube, and atmospheric pressure on the liquid surface then pushes liquid up and over the bend
3. CAir is blown into the tube, and the trapped air then lifts the liquid up and over the bend as that air expands
4. DHeat from the surroundings makes the liquid in the tube expand, and the expansion forces it up and over the bend

1. ALeaving it in an open pit beside the house, so that it is well out of the way of children
2. BCollecting it and sending it for recycling, so that the materials are used to make new goods
3. CBurning it in an open fire in the yard, so that the pieces are broken down by the flames
4. DThrowing it into the nearest stream, so that the water carries it away from the homestead

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1. ABad smells are themselves the germs, so once the smell has been covered up the pupils are no longer at any risk
2. BPathogens survive poorly outside the body, so a dirty toilet is mainly unpleasant rather than a real risk to health
3. CDirt in a toilet turns the water acidic, and it is that acid in the water which causes diseases such as cholera
4. DHouseflies breed and feed on the dirt and then carry pathogens onto food, so disease spreads through the school

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1. AIt treats and supplies the piped drinking water used in the towns and rural areas
2. BIt marks the national school examinations taken in the science subjects each year
3. CIt draws up and enforces the policies by which the environment is looked after
4. DIt sets the price that households pay for the electricity they use each month

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1. AThe sperm duct joins the two testes to each other, and the prostate gland adds a fluid that cools the stored sperm
2. BThe sperm duct stores urine before it leaves the body, and the prostate gland is where the sperm themselves are made
3. CThe sperm duct carries sperm from the testis to the urethra, and the prostate gland adds a fluid that activates them
4. DThe sperm duct carries sperm from the testis to the urethra, and the prostate gland makes the male hormone testosterone

1. AEggs leave the body in urine or faeces and hatch in water into larvae that enter snails, and larvae from the snails pierce human skin
2. BEggs are laid on the human skin and hatch there, and the larvae then burrow inwards to reach the water snails living in the blood
3. CAdult worms leave the body in the urine and are swallowed by water snails, and people become infected by eating those snails uncooked
4. DEggs leave the body in the urine and are picked up by mosquitoes, and the mosquitoes inject the young larvae when they next bite a person

1. ABoiling milk before it is drunk so that any eggs in it are destroyed by the heat
2. BSpraying the inside walls of the houses with a residual insecticide twice a year
3. CPassing urine and faeces into a toilet instead of into or beside a river or dam
4. DSleeping under a net treated with insecticide on every night of the rainy season

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1. Aa meal made up mainly of carbohydrate foods, so that plenty of energy is supplied for the day
2. Ba meal in which the mass of the food eaten is equal to the mass of the water drunk with it
3. Ca meal containing all of the food nutrients in the correct proportions for the body's needs
4. Da meal containing protein and vitamins but no fat or carbohydrate, so that weight is not gained

1. AIt is digested into glucose, which the body then stores in the liver as a supply of energy
2. BIt coats the wall of the stomach, so that the acid there cannot damage the lining of the gut
3. CIt supplies the mineral ions that the blood needs in order to clot after a person is injured
4. DIt adds bulk that the gut muscles can grip, so food is moved along and constipation is prevented

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1. AIt supplies the fibre that keeps the blood pressure of a hard working person from rising
2. BIt supplies the vitamins that the body is unable to make for itself during the working day
3. CIt supplies the energy that the body releases in respiration for the heavy work of the day
4. DIt replaces the mineral ions that are lost from the body in the sweat produced during work

1. AThrough contact with the body fluids of a person who is infected with it
2. BThrough breathing in spores that are released from the soil during ploughing
3. CThrough the bite of an infected female anopheles mosquito during the night
4. DThrough drinking water that contains the eggs of the parasite that causes it

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1. AThey have the same number of occupied electron shells around the nucleus
2. BThey have the same number of protons held inside the nucleus of the atom
3. CThey have the same total number of electrons arranged around the nucleus
4. DThey have the same number of electrons in the outermost shell of the atom

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1. Aatoms of the same element with the same proton number but different mass numbers
2. Batoms of the same element with the same mass number but different proton numbers
3. Catoms of different elements that happen to hold the same number of neutrons
4. Datoms of the same element that have gained or lost electrons to become ions

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1. AY and Z are both metals, so each of them has a high melting point and each conducts both heat and electricity well
2. BY is a metal with a high melting point that conducts electricity well, while Z is a non-metal with a low melting point that does not conduct
3. CY is a metal with a low melting point that conducts heat poorly, while Z is a non-metal with a high melting point that conducts heat well
4. DY is a non-metal with a low melting point that conducts electricity well, while Z is a metal with a high melting point that does not conduct

1. Aa substance that is burned so that the energy stored in it is released as heat or power
2. Ba substance that stores an electric current until an appliance needs to draw on it
3. Ca substance that changes energy from one form into another without being used up
4. Da substance added to a fire in order to lower the temperature reached by the flame

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1. Asunlight, wind and falling water, none of which needs anything to be set alight
2. Bcoal, petrol and paraffin, each of which is taken out of the ground and set alight
3. Cdiesel, firewood and charcoal, each of which is widely used for cooking a meal
4. Dnatural gas, ethanol and candle wax, each of which burns with a steady flame

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1. Ahigher temperatures, fewer floods along the rivers and a steady fall in sea level
2. Bcooler summers, less evaporation from the lakes and fewer storms on the coast
3. Chigher temperatures, more frequent droughts and a greater risk of veld fires
4. Dlower temperatures, heavier winter snowfalls and a much thicker ozone layer

1. Athe reaction of an acid with a base in which a salt and water are formed
2. Bthe reaction of a base with water in which a salt and hydrogen are formed
3. Cthe breakdown of a salt on heating in which an acid and a base are formed
4. Dthe reaction of an acid with a metal in which a salt and hydrogen are formed

1. Aconcentration = mass divided by moles and concentration = moles divided by mass
2. Bconcentration = mass divided by volume and concentration = moles divided by volume
3. Cconcentration = volume divided by mass and concentration = volume divided by moles
4. Dconcentration = mass multiplied by volume and concentration = moles multiplied by volume

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1. AThe oil is cooled with common salt, and sodium hydroxide is then stirred in to dissolve the soap that has formed
2. BThe oil is heated with sodium hydroxide, and brine is then added to separate the soap out of the mixture
3. CThe oil is distilled on its own, and the vapour that is given off condenses as soap on the cold surface of the flask
4. DThe oil is heated with dilute hydrochloric acid, and sugar is then stirred in to bring the soap to the surface

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1. AIts top must rise above the highest point of the roof, and its lower end must be fixed to the roof timbers
2. BIts top must stand below the level of the roof, and its lower end must be left hanging clear of the wall
3. CIts top must be level with the gutters, and its lower end must be joined to the water pipes indoors
4. DIts top must rise above the highest point of the roof, and its lower end must be buried in the ground

1. AA car with a metal body gives good shelter to the people inside it during a storm
2. BAn earthed metal conductor rising above a roof can protect the building from a strike
3. CLightning is a very large electric discharge between a charged cloud and the ground
4. DWearing red clothing during a thunderstorm draws the lightning towards the person

1. AThe commutator spins the coil round mechanically, and the movement of the coil through the field is what produces the current
2. BThe current in the coil sets up a magnetic field which interacts with the field of the magnets, giving a force that turns the coil
3. CThe magnets attract the iron in the coil directly, and the current warms the coil so that it expands and shifts round a little
4. DThe current in the coil repels the current in the supply wires, and the coil is pushed round by that repulsion between them

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1. Aweaker magnets, fewer turns on the coil and a smaller current in the coil
2. Bstronger magnets, fewer turns on the coil and a smaller current in the coil
3. Cweaker magnets, more turns on the coil and a smaller current in the coil
4. Dstronger magnets, more turns on the coil and a larger current in the coil

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1. Aa force that pulls every object towards the centre of the earth as it travels
2. Ba force that opposes the movement of one surface over another surface
3. Ca force that keeps an object moving once it has been given a first push
4. Da turning effect produced by a force acting at a distance from a pivot

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1. AFor a body in equilibrium, the sum of the clockwise moments about a pivot is greater than the sum of the anticlockwise moments
2. BFor a body in equilibrium, the moment of a force is the force divided by the perpendicular distance from that force to the pivot
3. CFor a body in equilibrium, the total upward force acting on the body equals the total distance of the forces from the pivot
4. DFor a body in equilibrium, the sum of the clockwise moments about a pivot equals the sum of the anticlockwise moments

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1. AIt falls to zero, because the load is then balanced by the weight of the pivot itself
2. BIt becomes larger, because the effort now acts at a shorter distance from the pivot
3. CIt becomes smaller, because a short arm carries a turning effect more easily than a long one
4. DIt stays the same, because the load and its distance from the pivot have not been changed

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