Biology Paper 2 June 2023

Tap to enlarge

1. APhotosynthesis, since these bodies hold the chlorophyll that traps light energy and uses it to make sugar.
2. BProtein synthesis, since these bodies carry the ribosomes on which amino acids are joined into long chains.
3. CAerobic respiration, since these bodies carry a folded inner membrane holding the enzymes that release energy from glucose.
4. DOsmosis, since these bodies draw water in from the cell sap and so keep the whole cell firm and turgid.

Tap to enlarge

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

1. AThe ovum has chloroplasts through its cytoplasm, while the palisade cell has none of them.
2. BThe palisade cell has a large permanent vacuole, while the ovum has no such vacuole.
3. CThe palisade cell has a nucleus, while the ovum loses its own nucleus as it matures.
4. DThe ovum has a cellulose cell wall, while the palisade cell is bounded only by a cell membrane.

Tap to enlarge

1. AIt protects the cell and, once one sperm has entered, it changes so that further sperms are kept out.
2. BIt beats steadily to move the cell along the oviduct towards the sperms swimming up to meet it.
3. CIt carries the whole food store of the cell, the yolk, which feeds the growing embryo until it implants.
4. DIt holds the haploid nucleus of the cell, which fuses with the sperm nucleus at fertilisation.

1. AThe stored food makes the ovum heavy, so that it sinks down the oviduct and reaches the uterus far more quickly.
2. BThe stored food nourishes the zygote and the young embryo before it implants and draws food from the mother.
3. CThe stored food supplies the energy used to spin the jelly coat around the outside of the cell.
4. DThe stored food is respired by the sperms as they swim up the oviduct to reach the ovum.

Tap to enlarge

1. AThe rate stays the same from A to B and then rises sharply to a peak somewhere beyond C.
2. BThe rate climbs steadily all the way from A to C, so the curve is a straight line sloping up to the right.
3. CThe rate falls steadily all the way from A to C, so the curve is a straight line sloping down to the right.
4. DThe rate rises slowly at first and then steeply to a peak at B, and falls sharply after B to near zero at C.

Tap to enlarge

Answer this when you sit the paper.

1. AThe enzyme molecules multiply as they are heated, so that there are many more active sites for the substrate to fill.
2. BThe substrate molecules are broken down by the heat itself, so the enzyme is left with much less work to do.
3. CThe enzyme and substrate molecules gain kinetic energy, so they collide more often and more of the collisions succeed.
4. DThe enzyme molecules are denatured more slowly, so many more of them are left to work on the substrate.

Answer this when you sit the paper.

1. AThe heat dissolves the enzyme in the water of the mixture, so that its molecules become far too dilute to meet the substrate.
2. BThe heat drives the enzyme molecules apart so quickly that they can no longer collide with any of the substrate molecules.
3. CThe heat turns the enzyme into a different enzyme, one that acts on a substrate which is not present in the mixture.
4. DThe heat breaks the bonds holding the folded shape of the enzyme, so the active site changes and the substrate no longer fits.

Answer this when you sit the paper.

1. AEach enzyme acts on one substrate or one type of reaction, because the substrate must fit its active site.
2. BEach enzyme is needed in large amounts, because one molecule can deal with only one substrate molecule.
3. CEach enzyme is used up in the reaction it controls, so a fresh supply must be made for every substrate molecule.
4. DEach enzyme works fastest at a pH of 7, since the cytoplasm of every living cell is exactly neutral.

Answer this when you sit the paper.

Answer this when you sit the paper.

Answer this when you sit the paper.

1. AThe xylem, the star shaped core of dead lignified vessels at the very middle of the root.
2. BThe endodermis, the ring of cells that controls the water passing into the central tissues.
3. CThe cortex, the wide layer of loosely packed cells in which the root stores its food.
4. DThe epidermis, the single outer layer of cells whose cells grow out into root hairs.

1. AIts thick waterproof outer wall, which stops the water it has already absorbed from leaking back out.
2. BIts many chloroplasts, which trap the light reaching the soil and make food for the root.
3. CIts narrow, greatly elongated shape, which gives a large surface area in contact with soil water.
4. DIts ring of beating cilia, which sweeps soil water inwards towards the middle of the root.

1. Amakes the food of the plant, because its cells are packed with chlorophyll.
2. Bstores starch for the plant, because its cells are wide and have no living contents.
3. Cstrengthens the plant, because its walls are thickened and stiffened with lignin.
4. Dtraps nitrogen for the plant, because bacteria live inside its hollow vessels.

1. AThe cells lose water, their vacuoles shrink and they become flaccid, so leaves and soft stems droop.
2. BThe cells take in air through the stomata, so they swell and the leaves are held out more firmly.
3. CThe cells take in salts from the soil, so their sap becomes stronger and the leaves stand upright.
4. DThe cells lose water, so their cell walls collapse inwards and the leaves become stiff and brittle.

1. AThe leaf takes in less carbon dioxide, so the rate of photosynthesis falls and less food is made.
2. BWater vapour is forced into the leaf from the air, so the cells become turgid again in minutes.
3. CMineral salts can no longer enter the leaf from the air, so it grows pale and turns yellow.
4. DOxygen is trapped inside the leaf, so the rate of aerobic respiration in the leaf rises sharply.

1. AIt funnels sound waves from the air around the head into the auditory canal.
2. BIt converts the vibrations of sound into nerve impulses and sends them to the brain.
3. CIt detects the position of the head, and so keeps the body balanced as it moves about.
4. DIt equalises the air pressure on the two sides of the eardrum during swallowing.

1. AIt carries the vibrations across the middle ear to the oval window of the cochlea.
2. BIt dissolves the weaker sound waves so that only the loudest reach the eardrum.
3. CIt traps dust and microorganisms and keeps the lining and the eardrum moist.
4. DIt amplifies the sound waves as they pass along the canal towards the eardrum.

Answer this when you sit the paper.

1. AIt converts the vibrations into nerve impulses that pass along the auditory nerve to the brain.
2. BIt holds the three small bones that carry the vibrations across the middle ear.
3. CIt keeps the air pressure in the middle ear equal to the pressure outside the head.
4. DIt collects the sound waves from the air all around the head and funnels them into the auditory canal.

Answer this when you sit the paper.

1. AThe eustachian tube is blocked by fluid, so the person can no longer taste or smell properly.
2. BThe semicircular canals fill with wax from the outer ear, so the sense of hearing is lost.
3. CThe auditory canal is sealed by a plug of wax, so the sound waves cannot reach the eardrum.
4. DThe eardrum is burst by the sudden large change in air pressure, so hearing is lost or reduced.

1. AA gene taken from a hearing parent can be injected into the ear, which repairs it at once.
2. BA grommet can be put into the pinna, which lets the trapped sound waves out of the outer ear.
3. CA course of antibiotics can be given, which clears the infection that damaged the inner ear.
4. DA device called a cochlear implant can be fitted, which stimulates the auditory nerve directly.

Answer this when you sit the paper.

1. ARingworm, which is spread by contact and forms round scaly patches on the skin.
2. BCholera, which is spread in dirty water and treated with rehydration salts and antibiotics.
3. CMalaria, which is spread by a mosquito and caused by a protozoan carried in its saliva.
4. DMeasles, which is spread in droplets and gives a fever, a runny nose and a red rash.

Answer this when you sit the paper.

1. AIt multiplies only inside a living host cell, using that cell's machinery to make copies of itself.
2. BIt has a protein coat around its core, and a coat of protein is found in no living cell.
3. CIt is destroyed by antibiotics, and a structure killed by a drug cannot have been alive.
4. DIt is far smaller than any bacterium, and nothing that small can carry out all the processes of life.

1. AIt has a single circular chromosome lying free in its cytoplasm, with plasmids beside it.
2. BIt has many small mitochondria in its cytoplasm but no true nucleus around its DNA.
3. CIt contains no cytoplasm and no cell membrane, only nucleic acid inside a protein coat.
4. DIt has a cell wall of cellulose instead of a cell membrane around its cytoplasm.

Answer this when you sit the paper.

Answer this when you sit the paper.

1. AIt is a chain of amino acids stored in the ribosomes that lie against the cell wall.
2. BIt is a circular strand of DNA lying free in the cytoplasm, with no membrane around it.
3. CIt is a set of paired chromosomes held inside a true nucleus by a double nuclear membrane.
4. DIt is a strand of RNA held inside the capsule that surrounds the outside of the cell.

1. AIt is the condition in which one allele of a gene masks the effect of the other in a heterozygote.
2. BIt is the condition in which two alleles of the same gene are both fully expressed in a heterozygote.
3. CIt is the condition in which two genes lying on one chromosome are inherited together as a unit.
4. DIt is the condition in which a gene has three or more different alleles in a population.

Answer this when you sit the paper.

1. ARickets, in which the bones of a child stay soft for want of vitamin D.
2. BCholera, which follows the swallowing of water containing a particular bacterium.
3. CHaemophilia, in which the blood of the sufferer fails to clot properly after a wound.
4. DKwashiorkor, which follows a long period spent on a diet that is very short of protein.

1. AVisible light of low intensity, which is absorbed by the dark pigment of the skin.
2. BA diet short of protein, which leaves the cells without the amino acids they need to grow.
3. CA rise in the humidity of the air, which slows the loss of water from the body surface.
4. DGamma radiation, which is ionising and damages the DNA of the cells it passes through.

Answer this when you sit the paper.

1. A1 in 2, since half of the father's gametes carry the O allele he is heterozygous for.
2. B3 in 4, since three of the four boxes hold at least one O allele between them.
3. C0, since the mother has no O allele that she could pass on to a child.
4. D1 in 4, since one of the four boxes of the Punnett square would hold two O alleles.

1. AGroup B, because the recessive O allele gives the red cells the B antigen.
2. BGroup O, because carrying one O allele is enough to give a person group O.
3. CGroup A, because the A allele is expressed and the O allele is masked by it.
4. DGroup AB, because the two different alleles present are always expressed together.

Answer this when you sit the paper.

1. ABecause 25 degrees Celsius is the optimum temperature at which every kind of bacterium in the dish grows fastest.
2. BBecause at 37 degrees Celsius the agar jelly melts and the liquid culture runs out of the dish.
3. CBecause bacteria harmful to people grow best at body temperature, so a lower temperature discourages them.
4. DBecause the plastic of the culture dish softens above 30 degrees Celsius and lets in airborne spores.

1. AThey are put into the ordinary classroom bin once the lids have been taken off the dishes.
2. BThey are autoclaved or burnt before disposal, so that the microorganisms in them are killed.
3. CThey are emptied into the laboratory sink and rinsed away with plenty of cold running water.
4. DThey are left open on the bench overnight so that the air can dry the culture out completely.

1. ATo kill any microorganisms on it, so the culture is not contaminated and nothing escapes.
2. BTo make the loop hot, so that the bacteria transferred by it grow faster on the agar jelly.
3. CTo soften the wire, so that it can be bent to fit the shape of the culture dish.
4. DTo dry the wire completely, so that the drop of culture it carries cannot slide off it.

Answer this when you sit the paper.

1. ASo that pupils get used to the smell of burning and are not frightened when a real fire starts.
2. BSo that the fire alarm is worn in and its bell becomes quieter for the people standing near it.
3. CSo that the school building is emptied of the smoke that has built up during the term.
4. DSo that the whole school learns the escape routes and the assembly point and can leave calmly.

1. ASo that the number of fire extinguishers needed in each block of the school can be worked out.
2. BSo that the pupils who reached the assembly point first can be praised in the assembly.
3. CSo that anyone still inside the building is known about at once and can be searched for.
4. DSo that the classes can be sent back into the building again in the right order.

1. AA fire that has started in a store room somewhere and has not yet been noticed by anyone.
2. BA pupil who has arrived late for school and has not yet signed the register.
3. CAn emergency exit that is locked or blocked, so it cannot be used to leave the building.
4. DA classroom window that has been left open at the end of the school day.

1. AThe molecule is neutral in charge, so it takes no part in the reactions going on in the cell.
2. BThe molecule is polar, so it attracts and separates ions and dissolves other polar molecules.
3. CThe molecule is very small, so it passes through the spaces between the particles of a solid.
4. DThe molecule has a high boiling point, so it stays liquid over the whole range of body temperatures.

1. AHydrolysis, in which a molecule of water is used to split a large molecule into smaller ones.
2. BOxidation, in which oxygen is added to a molecule and energy is released from it.
3. CPhotolysis, in which light energy splits a molecule of water into hydrogen and oxygen.
4. DCondensation, in which a molecule of water is released as two of the units are joined together.

1. AIt is a product only, being released from the leaf through the open stomata as water vapour.
2. BIt is a raw material, supplying hydrogen for building sugar and releasing oxygen when split.
3. CIt is a catalyst, speeding the reaction up without itself being used up or changed by it.
4. DIt is a pigment, absorbing the light energy that drives the reaction inside the chloroplast.

Answer this when you sit the paper.

1. AIt forms the fibres of the muscles, which shorten when the muscle contracts.
2. BIt is broken down in the liver to make the urea that leaves the body in the urine.
3. CIt is joined into long chains to build the enzymes that control the reactions of a cell.
4. DIt forms a layer under the skin that insulates the body and reduces the loss of heat.

1. AAs the store of energy the body keeps for the long term, since much is held in a small mass.
2. BAs the store of genetic information, since a dense molecule can hold more of a code.
3. CAs the substance that carries oxygen in the blood, since it takes up much oxygen per gram.
4. DAs the main solvent of the blood plasma, since a dense liquid dissolves more substances.

Answer this when you sit the paper.

1. AThe bacteria ferment the sugar and release an acid, which dissolves the calcium salts of the enamel.
2. BThe bacteria release an alkali, which softens the enamel and lets the dentine be worn away.
3. CThe sugar crystallises on the tooth and scratches the enamel away as the person chews.
4. DThe bacteria feed on the enamel itself, digesting it away as they multiply over the whole surface of the tooth.

1. ABecause the dentine below the enamel is harder than the enamel and cracks apart.
2. BBecause the pulp cavity holds the nerve endings and the blood vessels of the tooth.
3. CBecause the pulp cavity is filled with the acid the bacteria have made in the mouth.
4. DBecause the cement around the root dissolves and the tooth is pushed out of its socket.

Answer this when you sit the paper.

1. AIt kills the nerve in the pulp cavity, so a decaying tooth gives the person no pain at all.
2. BIt neutralises the sugar in the mouth, so the bacteria are left with nothing to feed on.
3. CIt coats the tooth in a layer of hard plastic, which the acid made in the mouth cannot pass through.
4. DIt is taken into the enamel, where it forms a harder salt that resists acid attack better.

1. AThey kill the bacteria of the mouth by drying them out as the person brushes the teeth.
2. BThey scrub away the plaque and lift the trapped food, so the bacteria lose the sugar they feed on.
3. CThey dissolve the enamel of the tooth, so that the decayed part of it is washed away by the rinse.
4. DThey harden into a smooth layer over the enamel, which the bacteria are unable to cling to.

1. AIt stops saliva from being made, so that the teeth are kept dry between meals.
2. BIt neutralises the acid made by the plaque bacteria, so the enamel is not dissolved.
3. CIt neutralises the alkali in the saliva, so that the mouth is left slightly acidic.
4. DIt reacts with the calcium of the enamel to make a fresh new layer of dentine.

Answer this when you sit the paper.

1. AIntroducing a fast breeding foreign species, which fills the same place in the food web.
2. BMoving the whole population into one small paddock, so that it is easier to guard.
3. CSetting aside national parks and game reserves, in which the habitat of the species is protected.
4. DClearing the woodland around a reserve, so that the animals can be seen and counted much more easily.

1. AThe money is used to fence the animals in so that they cannot breed outside the reserve.
2. BThe tourists take the place of the animal's natural predators in the food chain of the reserve.
3. CThe animal becomes worth more to the community alive than dead, so poaching is discouraged.
4. DThe community can then buy the meat of the animal from the reserve at a lower price.

1. ATo clear the paths through the reserve so that the tourist vehicles can pass along them.
2. BTo count the young animals that are born in the reserve during the rainy season.
3. CTo drive the natural predators of the endangered animal out of the reserve at night.
4. DTo stop the illegal killing of the animals for their horns, skins, tusks or meat.

Answer this when you sit the paper.

1. AThe phosphates settle and form a hard crust on the bed, which the water plants root into.
2. BThe salts raise the temperature of the water, so the oxygen dissolved in it bubbles away.
3. CAlgae bloom over the surface and block the light, then die and decay, using up the oxygen.
4. DThe nitrates poison the fish directly, so the plants of the lake are left with no predators.

1. AIt is not broken down, so it builds up along the food chain and is most concentrated in the top predator.
2. BIt floats on the surface of the water, so the eagle takes it in through its feathers whenever it dives.
3. CIt is a mineral salt the eagle needs, so the bird seeks it out and takes in far too much of it.
4. DIt is broken down quickly in water, so only the animals near the outfall pipe take any of it in.

1. AThe effluent coats the river bed and stops the fish from laying their eggs in the gravel.
2. BThe effluent is a rich food, so the fish eat it and swim away downstream to look for more.
3. CThe effluent makes the water cloudy, so the fish cannot find their way back upstream.
4. DBacteria multiply as they break the effluent down and use up the dissolved oxygen.

1. AThey fix nitrogen from the air, changing it into compounds the plant can take up.
2. BThey oxidise the nitrites of the soil into the nitrates that plant roots absorb.
3. CThey reduce the nitrates of the soil to nitrogen gas, which returns to the air.
4. DThey break the proteins of dead plants down and release ammonia into the soil.

1. AThey fix nitrogen gas as ammonia, and then build that ammonia into plant protein.
2. BThey oxidise ammonia to nitrites, and then oxidise those nitrites to nitrates.
3. CThey reduce nitrates to nitrites, and then reduce those nitrites to nitrogen gas.
4. DThey break proteins down to amino acids, and then break those down to ammonia.

1. APutrefying bacteria, which break the proteins of dead tissue down into ammonia.
2. BDenitrifying bacteria, which reduce the nitrates of a waterlogged soil to nitrogen gas.
3. CNitrifying bacteria, which oxidise ammonia to nitrites and those nitrites to nitrates.
4. DNitrogen fixing bacteria, which change nitrogen gas into compounds in the root nodules.

Answer this when you sit the paper.

1. AThe maize gives out a gas that stops the seeds of other species from germinating at all.
2. BThe rainfall over a field is lower than the rainfall over woodland, so fewer species survive.
3. CThe soil of a cleared field holds no seeds, so nothing can grow in it without being planted.
4. DThe whole field is planted with a single crop and sprayed with herbicide to kill other plants.

1. ABecause the ploughing and replanting clear the ground before new species can establish.
2. BBecause the soil of a ploughed field holds too much oxygen for wild seeds to germinate.
3. CBecause the crop plants are always taller than any wild plant that could colonise the field.
4. DBecause the fertiliser added each season kills the seeds of the crop's own species.

Answer this when you sit the paper.

1. AA faulty gene is passed on in the gametes of one or of both of the parents.
2. BA nutrient is missing from the diet, so a process going on inside the body is left unsupported.
3. CA pathogen enters the body, multiplies in it and damages the tissues or releases toxins.
4. DAn organ of the body fails, so a substance that the body needs is no longer made.

1. AA pathogen is swallowed with food and then multiplies in the wall of the small intestine.
2. BAn insect vector injects a parasite into the blood while it is feeding on a person.
3. CA faulty gene inherited from both parents stops an enzyme from being made.
4. DA nutrient is missing from the diet over a long period, so a body process is unsupported.

1. ACholera, in which a bacterium in drinking water causes severe watery diarrhoea.
2. BHaemophilia, in which the blood of the person fails to clot properly after a wound.
3. CRickets, in which the bones of a child stay soft for want of vitamin D in the diet.
4. DRingworm, in which a fungus grows in round scaly patches on the skin of the body.

Answer this when you sit the paper.

1. AAn infectious disease can be cured by drugs, while a non infectious disease clears up on its own.
2. BAn infectious disease is caused by a pathogen and passes from one person to another, while a non infectious disease does not.
3. CAn infectious disease is inherited from the parents, while a non infectious disease is caught from water or from a vector.
4. DAn infectious disease affects only children, while a non infectious disease affects every age group.

Answer this when you sit the paper.

1. AMalaria, which is caused by a protozoan carried from person to person by a mosquito.
2. BScurvy, which is caused by a long shortage of vitamin C in the diet.
3. CTuberculosis, which is caused by a bacterium breathed in from the air in droplets.
4. DCholera, which is caused by a bacterium swallowed in dirty drinking water.