Biology Paper 2 November 2006

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1. Athe two side chains react with one another and a molecule of carbon dioxide is released from the pair
2. Bthe two carboxyl groups react with one another and a molecule of hydrogen is released from the pair
3. Cthe amino group of one reacts with the carboxyl group of the other and a molecule of water is released
4. Dthe amino group of one reacts with the amino group of the other and a molecule of water is taken in

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1. Athe covalent bonds that hold each amino acid residue to the one that follows it
2. Bhydrogen bonds, ionic bonds and disulfide bridges between the side chains of the residues
3. Cpeptide bonds and glycosidic bonds between the residues at either end of the chain
4. Dester bonds between the side chains and the phosphate groups attached to the chain

1. Aits chains are short and identical, it forms crystals in the cell and it carries oxygen
2. Bits chains are coiled into a compact ball, it dissolves readily in water and it acts as an enzyme
3. Cits chains are twisted into long strands, it is insoluble in water and it has a structural role
4. Dits chains are branched like a polysaccharide, it dissolves in lipids and it stores energy

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1. ApH
2. Bsubstrate concentration
3. Ctemperature
4. Dinhibitor concentration

1. AThe enzyme splits into two subunits, each of which binds to one half of the sucrose molecule.
2. BThe active site is already an exact fit for sucrose and stays completely rigid as the substrate enters it.
3. CThe sucrose molecule changes shape to match the rigid active site of the enzyme it is approaching.
4. DThe active site changes shape slightly so that it moulds itself closely round the sucrose molecule.

1. Athe sucrose molecules move too fast to be caught by the active sites of the enzyme molecules
2. Bthe enzyme reacts with the water in the solution and is used up as the reaction proceeds
3. Cthe hydrogen bonds holding the tertiary structure break, so the active site loses its shape
4. Dthe peptide bonds of the chain are hydrolysed, so the enzyme is digested into its amino acids

1. Aa small circle of DNA in a bacterium that replicates separately from the main chromosome
2. Ba loop of messenger RNA that carries the gene from the bacterium out into the culture medium
3. Ca protein coat that surrounds the bacterial chromosome and protects it from enzyme attack
4. Da length of linear DNA held inside the nucleus of the bacterium and copied at cell division

1. Areading the amino acid sequence, working out the messenger RNA codons for it and assembling the complementary DNA
2. Breading the amino acid sequence and joining the amino acids end to end to make a strand of DNA of the same length
3. Ccutting the protein into short lengths with a restriction enzyme and joining those lengths into a circle with ligase
4. Dtreating the protein with DNA polymerase, which copies the order of the amino acids straight onto a sugar backbone

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1. Athe bacterial cell wall has to be removed completely first, after which the cell cannot divide any further
2. Bonly a small proportion of the treated bacteria take up a plasmid, so the successful cells must be identified
3. Cthe plasmid is digested by the restriction enzyme as soon as it enters, so no foreign gene survives the step
4. Dthe bacterium already carries the same gene, so the new plasmid is rejected before it reaches the cytoplasm

1. Athe bacteria can be released into a patient's blood, where they take over the work of the faulty organ
2. Bthe bacteria break the plasmid down and release the sugars stored inside it for use in the food industry
3. Cthe bacteria become resistant to antibiotics, which can then be used to treat a much wider range of illness
4. Dhuman insulin can be made in quantity, so a diabetic is not dependent on hormone extracted from animals

1. Athe mother is heterozygous, and one child is homozygous dominant while the other is heterozygous
2. Bthe mother is homozygous recessive, and both children are heterozygous for the earlobe gene
3. Cthe mother is heterozygous, and both of the children are homozygous dominant for that gene
4. Dthe mother is homozygous dominant, and both children are homozygous recessive for that gene

1. Amust be homozygous recessive, since attached earlobes appear somewhere in the family line
2. Bmust be homozygous dominant, since every one of his children has the dominant phenotype
3. Cmust be heterozygous, since his wife has attached earlobes and passes a recessive allele on
4. Dcannot be settled from this evidence, since a homozygous or a heterozygous father fits it

1. Asons who are carriers of the allele and daughters who show colour blindness in every case
2. Bsons with normal colour vision and daughters who are carriers of the recessive allele
3. Csons who are colour blind and daughters who have normal colour vision and are not carriers
4. Dsons and daughters who are all colour blind, since the father passes his allele to every child

1. Aa man has two X chromosomes, so he has twice the chance of inheriting the recessive allele
2. Bthe allele is carried on the Y chromosome, which is passed from a father to each of his sons
3. Ca man's Y chromosome carries a second copy of the allele, which reinforces the first copy
4. Da man has one X chromosome, so a single recessive allele on it is expressed in his phenotype

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1. Ajoin the two chromatids of one chromosome at the point where the DNA was copied
2. Bseparate the two chromosomes of the pair so that each can be drawn into its own cell
3. Chold the pair together while lengths of DNA are exchanged between the chromatids
4. Dattach the chromosome to the spindle so that it can be pulled towards a pole of the cell

1. Arepeated mitosis of the body cells, the growth of the embryo and the ageing of both parents
2. Bsemi conservative replication of DNA, the action of enzymes and the diet of the two parents
3. Ccrossing over in prophase I, independent assortment at metaphase I and random fertilisation
4. Dcrossing over in prophase I, independent assortment at metaphase I and DNA replication before it

1. Aone member of each pair came from the mother and one from the father at fertilisation
2. Beach chromosome is copied during interphase, which gives two chromatids joined together
3. Ceach pair carries a duplicate set of genes in case the first set is damaged by a mutation
4. Dthe chromosomes have to lie in pairs before the spindle fibres are able to attach to them

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1. Aevaporation from the mesophyll lowers the water potential there, so water moves from the xylem down a gradient
2. Bthe palisade cells actively pump water inwards from the xylem, using the ATP made in their own mitochondria
3. Cthe guard cells force water upwards through the leaf whenever the stomata are closed during the night
4. Dwater is pushed out of the xylem by the pressure of the sucrose being loaded into the phloem beside it

1. Ait dissolves in the xylem sap and is carried down the stem to the roots, where it enters the phloem for the return journey
2. Bit is converted to starch in the mesophyll, and the starch grains are then carried whole along the sieve tubes to the roots
3. Cit passes into the air spaces of the leaf as a vapour and condenses on the outside of the phloem sieve tubes below
4. Dit diffuses through the walls and the cytoplasm of the mesophyll and is then actively loaded into the companion cells and sieve tubes

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1. Aprovide a rigid layer of thickened cells that holds the leaf blade flat and out towards the sunlight
2. Bprovide a waterproof layer that stops water being lost from the underside of the leaf during the day
3. Cprovide the tissue in which most of the leaf's starch is stored between one growing season and the next
4. Dprovide large air spaces through which carbon dioxide diffuses to the cells and water vapour leaves the leaf

1. Athe group of organisms of one species that live in the same area and breed with one another
2. Bthe physical place in which the organism lives, described by the depth of water and the type of soil
3. Cthe role the organism plays in its community, including what it feeds on and what feeds on it
4. Dthe total number of organisms of that species that a particular habitat is able to support

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1. Athe flatworms among the pebbles break down dead material and release the energy stored in it
2. Bthe water plants trap sunlight and convert it into chemical energy in the compounds they make
3. Cthe fish take in dissolved oxygen through their gills and use it to release energy from food
4. Dthe mud at the bottom of the river absorbs heat during the day and releases it again at night

1. Amost of it is lost as heat in respiration, and more is left in the parts not eaten or not digested
2. Bmost of it is used up in building the bodies of the consumers, which store it as fat and protein
3. Cmost of it is recycled by the decomposers and returned to the producers at the start of the chain
4. Dmost of it is reflected from the surface of the water before the plants are able to absorb any of it

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1. Awater milfoil to dragonfly larva to fish
2. Bwater milfoil to fish to dragonfly larva
3. Cdragonfly larva to water milfoil to fish
4. Dfish to dragonfly larva to water milfoil

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1. Aovulation, growth of the follicle and degeneration of the corpus luteum
2. Bgrowth of the follicle, implantation of the embryo and the shedding of the uterus lining
3. Cfertilisation of the egg, ovulation and the repair of the lining of the uterus wall
4. Dgrowth of the follicle, ovulation and degeneration of the corpus luteum

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1. Afollicle stimulating hormone and luteinising hormone respectively
2. Bluteinising hormone and follicle stimulating hormone respectively
3. Coestrogen and progesterone respectively
4. Dprogesterone and oestrogen respectively

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1. Ait stops the corpus luteum breaking down, so progesterone is secreted all through the month
2. Bit stops the egg being fertilised, so an embryo cannot implant while the follicle is growing
3. Cit stops further follicles being stimulated, so usually one egg alone is released in a cycle
4. Dit stops the uterus lining thickening, so the endometrium stays thin throughout the cycle

1. Athe oestrogen level falls to zero at once, so the uterus lining is broken down and rebuilt around the implanted embryo
2. Bthe embryo secretes a hormone that keeps the corpus luteum alive, so progesterone stays high and the lining is not shed
3. Cthe corpus luteum breaks down on schedule, so progesterone falls and a lighter than usual menstruation still takes place
4. Dthe anterior pituitary secretes extra FSH, so a second follicle ripens and the ovarian cycle continues alongside the pregnancy

1. Aspecies, genus, family, order, class, phylum
2. Bclass, phylum, order, family, genus, species
3. Cphylum, class, order, family, genus, species
4. Dphylum, order, class, family, species, genus

1. Ashare common features and can interbreed to produce offspring that are themselves fertile
2. Bshare common features and live in the same habitat, feeding on the same kind of food
3. Cshare common features and can interbreed, though their offspring are sterile like the mule
4. Dshare common features and have the same number of chromosomes in each of their body cells

1. Ahave cells without a nucleus or membrane bound organelles, and take in food across the whole of the cell surface
2. Bhave a body of many cells with no cell walls at all, store fat as an energy reserve and take food into a gut
3. Chave a body of thread like hyphae with chitin in the walls, store glycogen and feed by absorbing digested food
4. Dhave a body of thread like hyphae with cellulose in the walls, store starch and make their own food by photosynthesis

1. Ait is taken in by endocytosis, the membrane folding inwards round each glucose molecule as it arrives
2. Bit passes through a channel or carrier protein, moving down its concentration gradient without ATP being used
3. Cit passes through a carrier protein that is driven by ATP, so it can be moved against its concentration gradient
4. Dit dissolves in the hydrophobic tails of the bilayer and diffuses straight across the membrane between them

1. Ais facilitated diffusion, because the ions pass through a protein that spans the whole of the membrane
2. Bis simple diffusion, because ions are small enough to pass between the phospholipid molecules freely
3. Cis osmosis, because the ions follow the water that moves out of the cell into the surrounding fluid
4. Dis active transport, because the ions move against the concentration gradient using ATP from respiration

1. Athe nitrate is taken in through the cell wall, which is why the inhibitor has an effect on the cell
2. Bthe nitrate is taken in by active transport, since the process depends on ATP from respiration
3. Cthe nitrate is taken in by osmosis, since water and the ions dissolved in it move in together
4. Dthe nitrate is taken in by simple diffusion through the gaps between the phospholipid molecules

1. Ait carries glycoprotein receptors with shapes complementary to particular hormone molecules
2. Bit carries pores large enough for whole hormone molecules to pass freely into the cytoplasm
3. Cit carries a layer of cellulose on which the hormones of the blood are able to settle and act
4. Dit carries the chromosomes on its inner surface, where a hormone can act on them directly

1. Athey store the cell's genetic information, which is copied each time the whole cell divides in two
2. Bthey supply the cell with glucose, which they manufacture from the carbon dioxide it produces
3. Cthey form the spindle on which the chromosomes are separated at each division of the nucleus
4. Dthey divide the cell into compartments and hold enzymes in place, as on the cristae of a mitochondrion

1. Athree separate strands of DNA have to be read together before a protein can be made
2. Ba sequence of three bases in the DNA specifies one amino acid in the polypeptide chain
3. Cthree different bases are found in DNA, and each of them specifies one amino acid
4. Deach amino acid is joined to three others when the polypeptide chain is being built

1. Amost amino acids are specified by more than one triplet of bases in the coding sequence
2. Bsome triplets of bases specify more than one amino acid, depending on where the reading starts
3. Cthe code has decayed over evolutionary time, so parts of it no longer specify anything at all
4. Deach triplet of bases overlaps the next one, so a single base is read as part of two triplets

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1. ADNA polymerase unwinds the whole molecule and builds a second complete copy of both strands
2. Bthe ribosome moves along the DNA and joins amino acids together in the order the bases give
3. Ctransfer RNA copies the base sequence of the DNA and carries that copy out of the nuclear pore
4. DRNA polymerase unwinds a length of the double helix and builds messenger RNA against one strand

1. AC A U
2. BG T A
3. CG U A
4. DU A C

1. Athe introns are cut out and the exons joined together, and the molecule leaves through a nuclear pore
2. Bthe exons are cut out and the introns joined together, and the molecule leaves through a nuclear pore
3. Cthe molecule is converted back into DNA by reverse transcriptase before it can leave the nucleus
4. Dthe molecule is wound round histone proteins so that it is compact enough to pass out of the nucleus

1. Athe ascending limb takes water in from the medulla while the descending limb, running the other way, pumps sodium and chloride ions inwards
2. Bthe two limbs carry filtrate in the same direction, so the ions pumped out of one limb are taken straight back into the other
3. Cthe blood in the vasa recta flows in the same direction as the filtrate, which keeps the ions moving along the loop
4. Dthe ascending limb pumps sodium and chloride ions into the medulla while the descending limb, running the other way, loses water to it

1. Athe collecting duct passes through it, so water leaves the filtrate by osmosis and the urine is concentrated
2. Bthe collecting duct passes through it, so salts are forced back into the filtrate and the urine is made dilute
3. Cthe glomerulus lies within it, so the pressure there is high enough to force the filtrate out of the blood
4. Dthe loop of Henle ends there, so the urea in the filtrate is broken down before the urine reaches the bladder

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1. Athe liver removes the amino group as ammonia and converts it to the less toxic urea
2. Bthe kidney removes the amino group as urea and converts it into ammonia for excretion
3. Cthe liver converts the whole amino acid into urea, which is then stored in the gall bladder
4. Dthe muscles convert the surplus amino acids into lactate, which is breathed out as a vapour

1. Asubstances such as carbon dioxide are used up by the tissues faster than the body can make them
2. Bsubstances such as ammonia are toxic, and a build up would alter blood pH and damage enzymes
3. Csubstances such as ammonia are insoluble, and a build up would block the capillaries of the tissues
4. Dsubstances such as urea are needed by the gut bacteria, which cannot make them for themselves

1. Awater moves into or out of cells by osmosis, so cells would swell and burst or shrink otherwise
2. Bwater is the substrate of respiration, so a cell short of water cannot release energy from glucose
3. Cwater carries the oxygen dissolved in it, so a change in its potential stops oxygen reaching the cells
4. Dwater holds the chromosomes apart in the nucleus, so a change in its potential prevents cell division

1. Athe oxygen used by the liver in making glucose from the fats stored in the body during a fast
2. Bthe extra oxygen taken in after exercise to deal with the lactate that built up in the muscles
3. Cthe extra oxygen taken in during exercise to allow the muscles to respire aerobically throughout
4. Dthe oxygen carried by haemoglobin that is not released to the tissues while a person is at rest

1. Athe muscle converts it into protein, which is used to repair the fibres damaged during the sprint
2. Bthe kidney filters it from the blood, so that it leaves the body dissolved in the urine as it forms
3. Cthe blood carries it to the liver, where some is oxidised and the rest is converted back to glucose
4. Dthe blood carries it to the lungs, where it is broken down and breathed out as carbon dioxide gas

1. Athe cilia lining the bronchi grow through the alveolar walls and break them into a few large spaces
2. Bphagocytes drawn into the lungs release elastase, which destroys the elastic tissue of the alveolar walls
3. Cthe alveoli fill with tissue fluid, which sets hard and prevents the walls from stretching during a breath
4. Dthe smoke reacts with the mucus in the airways to form a solid layer over the surface of the alveoli

1. Athe smoke thins the walls of the bronchi, so they collapse whenever the person breathes out hard
2. Bthe smoke raises the temperature of the airways, so the bacteria living in them multiply much faster
3. Cthe smoke destroys the cilia and irritates the lining, so extra mucus is made and is not swept away
4. Dthe smoke destroys the goblet cells, so no mucus is made and the airways dry out and become inflamed

1. Athe nicotine in the smoke narrows the arteries of the lung, so the cells behind the blockage grow out of control
2. Bcarcinogens in the tar cause mutations in the genes that control cell division, so a tumour grows in the airway lining
3. Cthe tar coats the alveoli so thickly that oxygen can no longer reach the blood, and the starved cells begin to divide
4. Dcarbon monoxide in the smoke binds to the haemoglobin, and the cells it passes are turned into cancer cells

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