as collective topics for work sheets

8/10/2019 As Collective Topics for Work Sheets

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Q1.Cystic fibrosis is a genetic disease that can affect many body systems, including the digestivesystem. In a carrier of this disorder, preimplantation genetic diagnosis can be used to detectthe presence of an allele for cystic fibrosis.(a) Explain how cystic fibrosis affects the digestive system.

(4)

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(b) Explain how preimplantationgenetic diagnosis is performed to detect cystic fibrosis.

(3) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

(c) Discuss either oneethical issue or onesocial issue relating to the use of preimplantation

genetic diagnosis.(2)

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(Total for question = 9 marks)


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Q2.Cystic fibrosis is a lifethreatening condition that can affect many different parts of the body. Itis a recessive genetic trait. !enetic screening can be used to test for the presence ofrecessive alleles. " person found to possess a recessive allele is called a carrier.#he diagram below illustrates a ris$ analysis following the screening for recessive alleles of acouple, who are planning a pregnancy.

(a) %uggest why cells from mouth swabs or blood samples are used rather than gametes.(2)

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(b) Explain why it is necessary to test for several different recessive alleles in the screening forcystic fibrosis.

(2)

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(c) In the ris$ analysis shown, if neither partner is a carrier then it is considered that the chanceof having a child with cystic fibrosis is low. Explain why the probability of having a child with


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cystic fibrosis is low and not&ero.(2)

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(d) In the ris$ analysis shown, if one of the partners is found to be a carrier then screening forcystic fibrosis may be offered to other family members. Explain why this screening is offered toother family members.

(2)

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..............................................................................................................................................(e) 'sing your $nowledge of monohybrid crosses, calculate the probability of having a childwith cystic fibrosis if both partners are found to be carriers. Draw a genetic diagram to explainhow you calculated this probability.

(5)

"nswer ..................................................................



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Q3.Cystic fibrosis is a genetic disorder caused by one of a number of possible gene mutations.renatal testing can be used to determine whether or not a fetus has cystic fibrosis.(a) ame onemethod of prenatal testing and explain how it can be used to detect cysticfibrosis.

(3)

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(b) Describe onebenefit and oneris$, to a pregnant woman, of prenatal testing.(4)

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(c) Discuss either oneethical issue or onesocial issue relating to the use of prenatal testing.(2)

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Q4.*any different diets are available for people who want to lose weight. #here is a lot ofconfusion over the merits of each one." scientist carried out an investigation to compare the effects of diet and diet +, onvolunteers.#he changes in mass of two groups of volunteers on each of these diets were monitored overa -month period.

#he graph below shows the mean changes in mass for each group of volunteers.

(a) (i) Compare the mean change in mass, over the first months, for these two groups ofvolunteers.

(3)

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(ii) %uggest why there was an increase in the mean mass of the volunteers on both dietsbetween months and - months.

(1)

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(iii) %tate twovariables that the scientist needed to control in this investigation.(2)

.............................................................................................................................................. ..............................................................................................................................................(b) %uggest why exercise is usually included as part of a weight loss programme.

(3)


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Q5.In an investigation into dieting and obesity, mice were fed a restricted /uantity of food. It hasbeen found that the stress of having less food causes the release of the hormonenoradrenaline. #his causes the mice to hunt for food.#hese foodrestricted mice will tolerate electric shoc$s in order to eat.(a) %uggest why this investigation might be regarded as unacceptable.

(2)

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(b) %uggest why this investigation might be regarded as unacceptable.

(i) %uggest how this increase in blood flow is brought about.(2)

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(ii) %uggest why this increase in blood flow would be of advantage to the foodrestrictedmice.

(2)

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Q6.!alactosaemia is a genetic disorder that affects an individual0s ability to metabolise themonosaccharide galactose.Dairy products contain the disaccharide lactose, which is bro$en down into galactose andglucose during digestion. If the galactose is not bro$en down further this may result in damageto the brain, $idneys or liver.(a) " student wanted to sweeten some strawberries, so she sprin$led some sugar on top of

them, one hour before eating them. #he student noticed that the sugar that she had sprin$ledon them was no longer visible and that there was some 1uice at the bottom of the bowl.

(i) In the space below, draw a diagram to show the products formed when these twomolecules 1oin together to form lactose.

(3)

(ii) ame the chemical reaction that 1oins the galactose and glucose molecules together.(1)

..............................................................................................................................................(iii) ame the bond that 1oins the galactose and glucose molecules together.

(1)

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(b) #he pedigree diagram below shows the inheritance of galactosaemia in a family.


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#he normal allele is represented by ! and the defective recessive allele by g.

lace a cross in the box next to the correct letter that completes each of the followingstatements.(i) "n allele is a

(1) A form of a gene length of D" ! part of a gene " protein

(ii) If 2ohn is hetero&ygous for galactosaemia, 2ane0s genotype must be(1)

A !! !g ! gg " impossible to tell

(iii) %amir0s genotype must be

(1) A !! !g ! gg " impossible to tell

(c) (i) 'se a genetic diagram to calculate the probability that %ahan and "lina0s first child will behetero&ygous (a carrier) if %ahan is hetero&ygous.

(4)


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"nswer ................................................................................................................(ii) 3hat is the probability that their second child would also be a carrier4

(1)

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Q#.D" and lipids are important molecules found in living organisms.(a) " triglyceride is one type of lipid.5or each of the descriptions below, put a cross ( ) in the box that corresponds to the correctstatement about lipids or triglycerides.

(i) #riglycerides are composed of6(1)

7 glycerol molecules and 7 fatty acid molecules glycerol molecule and 7 fatty acid molecules glycerol molecule and fatty acid molecule 7 glycerol molecules and fatty acid molecule

(ii) #he bond between a glycerol molecule and a fatty acid molecule is6(1)

" glycosidic bond " peptide bond " phosphodiester bond

"n ester bond

(iii) #his bond is formed by6(1)

8ydrolysis Condensation " chain reaction "n automatic reaction

(iv) 'nsaturated lipids6(1)

Do not have any double bonds 8ave double bonds only between carbon atoms 8ave double bonds between carbon atoms and between carbon and oxygen atoms 8ave double bonds only between carbon and oxygen atoms

(v) %aturated lipids have6(1)

*ore hydrogen atoms than unsaturated lipids 5ewer hydrogen atoms than unsaturated lipids #he same number of hydrogen atoms as unsaturated lipids o hydrogen atoms

(b) D" is a doublestranded molecule composed of mononucleotides.(i) In the space below, draw a diagram to show twomononucleotides 1oined together in asin$lestrand of D" (polynucleotide). 'se the symbols shown below for each component inyour diagram.

(3)


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(ii) ame an en&yme involved in D" replication.(1)

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Q%.D" is found in chromosomes and consists of doublestranded polynucleotidemolecules. #he se/uence of bases in D" forms the basis of what is $nown as thegenetic code.

(a) Explain why a molecule of D" can be described as a &ou'lestran&e&polnu*leoti&e.

(3)

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9(b) Describe how the se/uence of bases in a D" molecule would be used to form

the primary structure of a protein.(5)

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Q9.In the late :;


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(Total for question = # marks)


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Q1+.rotein synthesis in cells involves molecules of D" and >".(a) #he table below describes some features of the molecular structure of D" and >".lace a tic$ ( ) in the box next to each statement to show whether it applies to D" only,>" only or to both D" and >".

(b) #he diagram below shows the se/uence of the lastsix amino acids in a protein molecule.#he t>" anticodon that corresponds to each amino acid is also shown.

'sing this information, explain how each of the following processes leads to the synthesis ofthis se/uence of amino acids.

(i) #he formation of m>" during transcription in the nucleus(3)

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(ii) #he translation of m>" into the se/uence of amino acids in a ribosome(3)

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(c) %uggest why the final triplet of nucleotides, on the strand of m>" involved in the synthesisof this se/uence of amino acids, did not correspond with any anticodon on t>".

(2)

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(Total for question = 1+ marks)


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Q11.En&ymes are biological catalysts that change the activation energy of chemical reactions.9(a) Explain the meaning of the terms 'iolo$i*al *atalstand a*ti,ation ener$.

(4)

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(b) #he graph below shows the results of an investigation into the effect of en&ymeconcentration on the initial rate of this reaction.

Explain why it is necessary to measure the initial rateof reaction when investigating the effect

of en&yme concentration on the rate of reaction.(2)

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(c) In this investigation, the substrate concentration was a factor that was $ept constant.%uggest twoother factors that should be $ept constant. 5or each factor, state how it can be

$ept constant. (4)

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Q12.En&ymes are biological catalysts. #hey are involved in many chemical reactions in the body,including the digestion of lipids.(a) #he graph below shows the effect of an en&yme on the initial rate of reaction at differentconcentrations of the substrate.

Describe the effects that the en&yme had on this reaction.

(2)

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(b) ?ipases are en&ymes that are involved in the brea$down of lipids, such as triglycerides.

(i) ame the bond bro$en by lipases.(1)

..............................................................................................................................................(ii) ame twoproducts formed from the brea$down of triglycerides by lipases.

(2)

.............................................................................................................................................. ..............................................................................................................................................(iii) %uggest what effect the brea$down of triglycerides could have on the p8 of a reactionmixture.


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(1)

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9(c) #he action of lipase can be investigated using a triglyceride as the substrate.

Describe an experiment, using lipase and a triglyceride, that could be carried out to collect datato plot a graph similar to the one shown in part (a).

(5)

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Q13.!enetic screening can be used to determine if an embryo has a genetic disorder, such ascystic fibrosis.(a) #he table below refers to the methods used in preimplantation genetic diagnosis andprenatal genetic screening.If the statement is correct, place a tic$ ( ) in the appropriate box and if the statement is

incorrect, place a cross ( ) in the appropriate box.

(2)

(b) (i) ame onemethod of prenatal genetic screening.

(1) ..............................................................................................................................................

(ii) Discuss either oneethical issue or onesocial issue relating to the use of this method ofprenatal genetic screening.

(2)

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(c) !ene therapy has the potential to treat some genetic disorders.

(i) Explain why gene therapy has the potential to treat some genetic disorders.(2)

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(ii) %uggest how patients with cystic fibrosis could be treated using gene therapy.(3)

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Q14."lbinism is a genetic trait resulting from the inheritance of recessive alleles.(a) (i) Distinguish between the terms alleleand $ene.

(2)

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(ii) Explain the meaning of the term re*essi,eallele.(1)

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(b) #he pedigree diagram below shows the inheritance of albinism in one family.

(i) aveeda is homo&ygous. Explain the meaning of the term -omo$ous.(1)

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(ii) %usan is also homo&ygous. ame the members of this family who are definitely carriersof albinism, giving reasons for your answer.

(4)

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(c) "lbinism occurs in a number of different animals, including s/uirrels as shown in the


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photograph below.

#he incidence of albinism in s/uirrels is in


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Q15.(a) #he 8uman !enome ro1ect is helping in the design of new drugs to treat a variety ofhuman diseases and in the

development of synthetic tissues.

(i) Explain the meaning of the term /uman 0enome.

(1)

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(ii) Describe oneethical implication associated with the use of information obtained from theanalysis of the

human genome.

(1)

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(b) *elanoma is an aggressive form of s$in cancer.

@ery few patients with this cancer survive for more than five years. %ome melanomasare associated with a

genetic mutation identified by the 8uman !enome ro1ect.

Drug > (> has

been shown to cause a ;.

(3)

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..............................................................................................................................................(ii) %uggest how drug > may have caused the melanoma to shrin$ in only a few mont-s.

(4)

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(iii) Drug > needs one more round of testing, in a phase III trial, before it can be approved foruse.


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Explain what is meant by a p-ase trial.

(2)

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(c) east cells were genetically modified, using human D", to produce collagen. #his collagen can be used to ma$e corneas.

#en patients who were blind were each given a synthetic cornea. #hey were allable to see with no reported complications due to tissue re1ection.

%uggest why these synthetic corneas were not re1ected.

(2)

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(Total for question = 13 mark)


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Q16.ne function of the cell membrane is to control which molecules can enter or leave the cell.#he diagram below represents the structure of the cell membrane.

(a) 5or each of the statements below, put a cross in the box that corresponds to the correctstatement.

(i) #he phospholipids form a bilayer because(1)

A the hydrophobic heads dissolve in the a/ueous (water) environment the hydrophobic heads move away from the a/ueous environment ! the hydrophobic tails dissolve in the a/ueous environment " the hydrophobic tails move away from the a/ueous environment

(ii) #he protein, labelled in the diagram, could be involved in

(1) A endocytosis exocytosis ! facilitated diffusion " phagocytosis

(iii) #he fluidity of the membrane is determined by the proportion of(1)

A cholesterol glycoprotein ! phospholipid

" protein

(b) " student carried out an experiment to investigate the effect of temperature on thepermeability of beetroot membranes. eetroots are root vegetables that appear red because the vacuoles in their cells containa watersoluble red pigment. #his pigment cannot pass through membranes.

%ix cubes of beetroot were cut. ne piece of beetroot was placed into a tube containing< cm7of water and left for

-< minutes at ; FC. "fter the -< minutes, each piece of beetroot was removed from the

tubes and the colour of the fluid recorded.

#he procedure was repeated at five other temperatures.#he results are shown in the table below.


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'sing the information in the table, describe the effect that temperature has on thepermeability of the membranes of the beetroot cells.

(2)

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(c) " second student carried out a very similar experiment, using three samples of beetroot ateach temperature. %he used a colorimeter to determine the intensity of the colour of the fluid produced.

#he results of her experiment are shown in the table below.

(i) %tate twovariables that both of these students must $eep the same if their results are tobe compared.

(2)

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(ii) !ive tworeasons why the results obtained by the second student are more reliable than

those of the first student.(2)

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(iii) In the first student0s experiment at ; FC, the fluid was pale pin$ but the fluid in the secondstudent0s experiment was colourless.%uggest an explanation for this difference.

(2)

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(iv) Each of the students used their own results to describe the effect of temperature on thepermeability of the membranes of the beetroot cells.%uggest oneway in which these two descriptions might differ.

(1)

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+.(a)3e have not as$ed about the effect on the digestive system of Cystic 5ibrosis before andwere pleased to see some very good answers. #here were some students who did not read the/uestion properly and wrote about the effects on the respiratory system and there were otherswho had clearly seen the /uestion in last summer0s paper and described, in detail, how theabnormally thic$ mucus is produced.#he asteris$ against this /uestion indicates that +3C was assessed in the response to this

/uestion. articular care should be ta$en with spelling, puntuation and grammar, as well as theclarity of expression, on these /uestions.

esults lus aminer !omments


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#his response scored the maximum four mar$s. #he misspelling of pancreas on thesecond line prevented mar$ing point = from being awarded but did not affect theawarding of mar$ing points three, five, six, eight and nine. #he second mar$ point wasnot given as mucus is normally thic$ and we need to $now that it is abnormally thic$ inCystic 5ibrosis patients.

esults lus aminer Tip

?oo$ out for the two /uestions that have an asteris$ against them and pay particularattention to your spelling and the clarity of your answer. "lways try to write morestatements than there are mar$s, in case you cannot be awarded one of them.*a$e sure if you are writing about mutations, that they are occuring in the genes andnot in the protein.

(')#his /uestion was poorly done, despite previous similar /uestions being as$ed about this inthe past in the context of amniocentesis and chorionic villus sampling.In previous /uestions on genetic diagnosis we have expected the candidate to state that theD" is analysed and that the mutated C5#> gene is loo$ed for

esults lus aminer !omments#his is a typical example of the reponses that we fre/uently saw for this /uestion.#hecandidate was awarded the first mar$ing point only.

esults lus aminer Tip?oo$ carefully at previous mar$ schemes to learn what we award mar$s for. e carefulto use correct terminology a &ygote is different from an embryo.

(*)#his /uestion was probably the worst answered of all /uestions on the paper. Despite the factthat we have as$ed /uestions about ethics before there were still numerous answers refering todesigner babies and playing god." large proportion of candidates appeared to have forgotten the context of the /uestion andmade reference to abortion and miscarriages, voiding their answers.


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esults lus aminer !omments#his is an example of the answer being given in the wrong context to award the mar$s,

which is a shame as the candidate was trying to answer the /uestion appropriately.

esults lus aminer Tip"lways reread the /uestion to ma$e sure that your answer is in the correct context.

esults lus aminer !omments#his is a typical of a large number of response to this /uestion.

esults lus aminer Tip3hen discussing ethical issues, avoid terms such as 0playing god0 and 0designer babies0


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Q2.

esults lus aminer TipCandidates need to understand the difference between the term 0allele0 and 0gene0 andbe careful to use them in the correct context. "n appreciation of the terms 0haploid0 and0diploid0 is also needed, with some careful wording when describing them.

esults lus aminer !omments#his was a fairly typical response and illustrates the point about haploid and diploid. #he

fact that the gametes have half the D" is not the same as understanding that they onlyhave one set of each


#his candidate is a bit closer to appreciating the significance of the haploid cell but stillthe wording was not deemed to be good enough to award the third mar$ing point. "t theend of the response, the reference to 0gene0 prevented mar$ing point from beingawarded.


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esults lus aminer !omments#his response also illustrates these two points about 0alleles and 0genes0 and thesignificance of a haploid cell. It is also worth pointing out here, that the use of the term

0C5 gene0 is actually referring to the unaffected gene and not the mutated one.

(e)

esults lus aminer Tip3hen a /uestion as$s for a genetic diagram to be drawn, there will be mar$s forshowing each stage. In this case for indicating the genotype of the parents, the allelespresent in the gametes, evidence of a cross being done, the genotype of the offspringand the corresponding phenotypes. #hat is in addition to actually answering the/uestion and stating the probability of a child having cystic fibrosis.


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esults lus aminer !omments#his was a very generous mar$ scheme and in this instance we did not insist on eachstep being clearly labelled. #his was a fairly typical layout that enabled the candidate, inthis case, to score mar$ing points -,7 and =. *any responses did score = mar$s as thegenotype of the parents was included. 5ewer candidates scored all ; mar$s as they didnot lin$ the phenotype to the corresponding genotype.

It is worth pointing out that conse/uential errors apply in a /uestion of this type, so candidatesshould be encouraged to at least attempt the /uestion and to not leave it blan$.


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Q3.Candidates who chose to describe amniocentesis in (a) generally scored well. 8owever,embryos were found in some odd places (such as the stomach), amniotic fluid was withdrawnfrom the embryo and D" was free floating in the fluidG Candidates describing chorionic villussampling did less well, even at the " grade boundary. " very common mista$e was to refer to themethod as chronic villus sampling and there was little understanding of the actual location of thefetal tissue. 3ea$er candidates described preimplantation techni/ues.

esults lus aminer !omments#his response was awarded mar$ing point

#here was good understanding of the benefits of prenatal testing. #he ma1ority of candidatesunderstood that there were ris$s and ethical issues surrounding the techni/ue, but failed to scorewell for one of two reasons. 5irstly, especially at the E boundary, there was confusion over whatconstituted a ris$ and what an ethical issue. %econdly, across the ability range, answers were


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poorly worded or too vague. 8opefully, with the publication of the mar$ scheme, candidates inthe future will be able to phrase their answers to similar /uestions more elo/uently.

esults lus aminer !omments#his candidate scored the first three mar$ing points but could not be awarded the fourthpoint as there was not a reference to healthy foetus.

esults lus aminer !omments#his was a very typical response that scored mar$ing point -6


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Q4.(a) (i)Compare /uestions can cause candidates problems for a number of reasons. %ome writeout two descriptions without stating any actual comparisons. %ome candidates find it difficult toidentify the main trends that need comparing. thers lose mar$s through poor exam techni/ueby not ma$ing enough statements, not refering to the values on the x axis and not reading offvalues from the graph with sufficient accuracy.

"ll of these were seen in the responses to this /uestion. n the whole, the ma1ority of candidatesattempted the /uestion and scored some of the mar$s.


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esults lus aminer !omments#his response would have scored well if the candidate had stated the periods of time inwhich the described changes were ta$ing place.

esults lus aminer Tip3hen answering /uestions of this nature, start each sentence with 0etween0 and then

/uote two values from the x axis. %o, in this /uestion6 etween < and - months thoseon diet .............. etween - and months those on diet ..............


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esults lus aminer !ommentsIn this response the candidate made time referencesbut were not specific enough aboutthe type of changes that were occuring. #he examiner will not assume that a change isa decrease 1ust before a negative sign is put in front of the number.

esults lus aminer Tip3hen describing changes always state whether something is increasing or decreasingand if there is no change then state that it is staying the same.


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(a) (iii)"ll candidates could give two variables but some answers could not be credited as theywere irrelevant to the context of the /uestion or were too vague.

esults lus aminer !ommentsIrrelevant references to the number of individuals in the study were seen a number oftimes. %ome candidates fail to appreciate that ta$ing the mean value of data allows forany differences in sample si&es.

esults lus aminer !ommentsIn this response, the number of calories is controlled by the diet plan and is thereforenot an appropriate suggestion. #he reference to lifestyle is too vague.

esults lus aminer Tip"lways read the /uestion through very carefully to ensure that your answer is going tobe relevant to the context of the /uestion.


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Q5.(a)*ost candidates tac$led this /uestion item well and gained both mar$s. 8owever, only a fewgave mar$ing point 7.

#his example illustrates one of the alternative descriptions acceptable for mar$ing point one.

esults lus aminer !omments*ar$ing points and - awarded here.

" typical answer which gained both mar$s.

esults lus aminer !omments*ar$ing points and - successfully achieved.

(') (i)3hilst a good number of candidates dealt with this item well, it was not uncommon to seereferences to capillaries and veins vasodilating.

#his example offered a variety of correct elements.


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esults lus aminer !omments5ull mar$s awarded.

(') (ii)*any good answers were seen for this /uestion item but the emphasis is on increasedblood flow, so more glucose or more oxygen is being supplied.


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Q6.(a) (i)#his was generally a highscoring /uestion, with candidates being able to apply their$nowledge to the context of galactosaemia.

Candidates who $new how a glycosidic bond is formed were not phased by having to draw itbetween glucose and galactose, as opposed to two glucose molecules.

#here were some very clear drawings of the galactose molecule and the water molecule



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#his candidate drew the displayed structure for water, but we accepted both 8- orwater stated.

esults lus aminer TipIn /uestions of this type do not 1ust draw a circle around the 8 and an 8H always writethat 8- or water has been made. e very careful when copying out molecules in youranswer to /uestions of this type they must be drawn accurately so that no components

are missing.

(*)Candidates dealt very well with the genetic cross in the unfamiliar context of galactosaemia.

@ery few candidates scored the full four mar$s for part (i) as they omitted to write out thegenotype of %ahan and "lina.

#he ma1ority of candidates $new that the probability of the second child being a carrier wasidentical to that of the first.

Conse/uential error mar$ing was applied throughout this /uestion to ensure that a mista$e onlycost the candidate one mar$. 3e did expect the answer to part (ii) to be identical to the answer inpart (i).

esults lus aminer !omments#his was one of very few answers where the candidate stated the genotype of theparents. 'nfortunately it was often stated wrongly. #his candidate could not be awarded


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the first mar$ing point but the other three mar$s available to part (ii) were awarded, asthey followed through their cross correctly with the given genotypes.

esults lus aminer Tip>emember to follow through the whole of the genetic cross and not 1ust launch intodrawing the unnett s/uare, as this gives the information carried in the gametes withoutstating the genotypes of the parents.


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Q#.#he multiple choice section to this /uestion did not cause the candidates too many problems,with even the E grade candidates pic$ing up two or three mar$s.

Drawing the D" molecule was poorly done, with only the " grade candidates consistentlygaining all three mar$s. Common mista$es included drawing two mononucleotides hydrogenbonded together and not 1oined in a strandH and poorly drawn diagrams that did not showaccurately enough the position of the bonds (although we ignored this in awarding mar$ing point).

%ome examples are shown below.

esults lus aminer !omments#his response was awarded mar$ing point


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esults lus aminer !omments#his response could only be awarded mar$ing point

" surprisingly high number of candidates named >" polymerase as the en&yme in (b)(ii).


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Q%.(a) *ost candidates made a very good attempt at defining both parts of the term, describing0doublestranded0 separately from 0polynucleotide0.

esults lus aminer !omments#his is an example of some of the excellent responses that we saw.

esults lus aminer !omments#his candidate tried to define both parts, but unfortunately got confused between

nucleotides and basesH this was not an uncommon mista$e.

esults lus aminer Tip*a$e sure you understand the difference between a base and a nucleotide and thenread your answer through carefully to ma$e sure you have used the right term in theright place.

(b) %ome excellent responses were seen for this /uestion, with the better candidates scoring fullmar$s easily. #his was a +3C /uestion focussing on the clarity of response, so we were loo$ingfor the information to be presented in a logical se/uence. #his caused few candidates anyproblem.


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esults lus aminer !omments#his is an example of one of the excellent responses that we saw.


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esults lus aminer !omments#his response also scored the full five mar$s, but was a better response as it includedthe "- detail of posttranscriptional modification.


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esults lus aminer !ommentsot all responses were of such high /uality.

esults lus aminer TipDo not forget to thoroughly learn all your "% wor$, as you can be tested on any topicfrom either unit or unit -.


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Q9.(')#his is the first time that we have used *eselson and %tahl0s experiment to test candidate0sunderstanding of D" synthesis. #he ma1ority of candidates did attempt to answer the /uestionand some of the more able candidates coped very well and scored full mar$s.

#he bands drawn in the test tubes in this response are typical of a number of answers that wesaw by the wea$er candidates. #he strands of D" drawn as two sets of parallel lines were nottypical.

esults lus aminer !omments"lthough the bands are in the wrong place in the tube in the bottom box, we applied aconse/uential error mar$ to mar$ing point . #his was only 1ust awardable as the bandshave been drawn rather carelessly and only 1ust show that they are of the same width.Candidates should be encouraged to draw diagrams carefully

esults lus aminer Tip

3hen completing tables, whether with words, numbers or diagrams always loo$ at theboxes that we have completed for clues as to what to do. 3e drew the D" as a helixand represented the heavy and light strand as solid and dotted lines respectively thisis what the candidate should have done.


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Q1+.(a)#his /uestion was answered reasonably well with most candidates gaining some credit. #hemost common error was to put a tic$ for >" only in the second row.

(') (i)#here was a very varied response to this /uestion. #here were some very clear,straightforward descriptions of transcription. 8owever, many candidates did not express thepoints clearly or gave confused answers which included details of translation. >eferences to theseparation of the D" strands were often vague. #he terms 0nucleotide0 and 0base0 werefre/uently used to describe the same structure.

esults lus aminer !omments#he candidate has used an ambiguous term 0unravel0 which could mean separate oruntwist. 8owever, full credit can be given for the rest of the answer.

#his is an example of being almost correct on several points but not really ma$ing it for a mar$.

esults lus aminer !omments#he first sentence confuses several processes. #here is no clear idea of the strandsseparating. #he answer also implies that >" is formed as the hydrogen bonds brea$.#he last sentence confuses >" and m>".

(') (ii)#he responses to this /uestion generally lac$ed the re/uired detail. #here were alsonumerous examples of confused terminology and poor expression. "lthough a large number ofcandidates $new that the anticodon is complementary to the codon, there was a great deal ofconfusion as to where these structures are found. #he anticodon was often attributed to theamino acid or the t>" molecule was described as the anticodon. *any candidates stated that

the amino acids were produced or formed rather than being bonded together. " common errorwas to name the bond as a phosphodiester bond.

#his answer shows a general lac$ of detail.


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esults lus aminer !omments#he reference to the t>" anticodon and the base pairing does not explain how them>" is involved. #here is no explanation of how the amino acids 1oin together.

#his answer shows more detail.

esults lus aminer !omments#he detail of the relationship between the anticodon and codon is clear. #here is also acorrect reference to the formation of peptide bonds.

(*)#his /uestion proved to be more discriminating than was expected. " variety of terms wasseen for the stop codon. "t this level, it is expected that terms used in the specification are$nown. *any candidates repeated information about t>" from the stem of the /uestion withoutexplaining its significance.

esults lus aminer !omments#he explanation implies that the stop codon has the information for the se/uence ratherthan the end of the se/uence. #he last sentence is really rewording part of the stem ofthe /uestion.


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Q11.o Examiner0s >eport available for this /uestion


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#" 8##E+'I@JContent#ypeJ C#E#JtextKhtmlH charsetusasciiJL Q12.(a)*ost candidates stated that the en&yme increases the rate of reaction. %ome candidates saidthat the rate of reaction with the en&yme present is nonlinear and correctly manipulated figures.It was pleasing to see that most candidates did phrase this correctly along the lines that therewas a decreasing rate of increase in the rate of reaction with increasing substrate concentration.

8owever, only a few candidates spotted that the increase in rate of reaction is the same with orwithout the en&yme present above substrate concentrations of


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#his candidate has recognised the effect of the en&yme and illustrated it with a correctmanipulation of the figures by stating how much higher the rate is at a particularconcentration.

#his response scored one of the two mar$s available.


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esults lus aminer !omments#his response is typical of the large number of responses which scored 1ust one mar$for recognising that the en&yme increases the rate of reaction.

esults lus aminer Tip3hen describing a graph worth more than one mar$ identify any changes in the trend

shown in the data andKor manipulate figures to illustrate the point made.

#his response scored both mar$s available.


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esults lus aminer !omments#his candidate has recognised that the en&yme increases the initial rate of reaction, butthey have also spotted that the rate of increase changes and actually matches theincrease of rate without the en&yme at the higher concentrations.

#his response scores no mar$s.


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esults lus aminer !omments#his response is typical of those that failed to score any mar$s as they have notanswered the /uestion as$ed. #hey are as$ed to describe the effects of the en&ymeand instead describe the effects of the substrate concentration. #hey explain what theen&yme does, but again that has not been as$ed in the /uestion.

esults lus aminer Tip>ead the /uestion carefully and answer the /uestion as$ed.

(') (i)ver three /uarters of candidates correctly recognised that it would be an ester bondbro$en. #he most common mista$es involved naming glycosidic, peptide and hydrogen bonds.

esults lus aminer !omments#his is a typical response that scored the mar$.

esults lus aminer !omments#his is an example of one of the most common errors resulting in the mar$ not beingawarded.

(') (ii)*ost candidates correctly recognised that glycerol and fatty acids were the products ofthe brea$down of triglycerides. #he most common error was to include water as a product of thishydrolysis reaction.

*ar$s were also lost for triglycerides, oxygen, energy, or glycogen. %everal candidates referredto fatty acid tails.

3e were pleased to see propan,-,7triol occasionally.


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#his response scores both available mar$s.

esults lus aminer !omments#his is an example of the most common correct response.

#his response scored no mar$s.

esults lus aminer !omments#his response illustrates two of the most common errors6 confusing glucose andglycerolH and thin$ing that water is a product of a hydrolysis reaction.

esults lus aminer Tip>emember that condensation reactions remove water and hydrolysis reactions addwater to the molecules.

(') (iii)#here were an alarmingly high number of candidates who thought that the p8 wouldincrease some even /ualifying this with the recognition that there would be more acid present.%ome responses ignored the /uestion as$ed and wrote about en&ymes and rates of reactioninstead. "s a result only 1ust over half of the candidates actually managed to obtain this mar$.

#his response gained the available mar$.

esults lus aminer !omments#his candidate has correctly recognised that the mixture would become more acidic andtherefore the p8 will decrease.

#his response scores no mar$s.



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#his response illustrates the most common error i.e. forgetting which way round thep8 scale goes.

esults lus aminer TipChec$ answers carefully to ma$e sure they ma$e sense is producing a lot of fattya*i&sli$ely to ma$e the mixture more al$alineKless acidic4

(*)" number of candidates described the catalase experiment from the 2anuary paper, othersincluded potatoes, beetroots and a variety of other variations of core practicals. *any candidatescorrectly referred to a range (or a number) of different substrate concentrations, but a si&eablenumber of candidates described a range of en&yme concentrations while $eeping the substrateconcentration constant. #his was disappointing, considering the amount of information thecandidates had to help them using the graph at the beginning of the /uestion. Candidates whodescribed a different experiment from the one as$ed for managed to gain access to a reasonablenumber of mar$s for recognising $ey design features of a plan.

*any candidates referred to repeats for reliability and also for controlling variables such as

temperature or volume of solutions. leasingly, some candidates also clearly referred to thevalue of repeats without the en&yme and to controlling the lipase concentration. It was alsopleasing to see a number of references to e/uilibrating the solutions and then mixing the en&ymeand substrate.

It was disappointing to note the number of candidates who still insist on using the word 0amount0,or describing room temperature as a reliable control variable.

>esponses ranged widely from poorly expressed answers lac$ing in detail to very fine answers,clearly expressed, some of which gathered around A or : mar$ing points for a maximum of ;.

#here were many responses with descriptions of how to plot and draw a graph as if this werepart of the experimental procedure.

%ome candidates spent some time on safety goggles, lab coats and the effect on any animalsin wor$ area.

#his response scored both mar$s available.


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esults lus aminer !omments#his is example of a candidate who clearly understands both the context of the

investigation and the $ey elements of what to include in a plan. #his candidate hasactually met ten separate mar$ points through their clear description of the differentvariables and how to measure them (including the rate of reaction),the need to mix thesolutions, what to repeat and suitable controls etc.

esults lus aminer Tip'se excellent examples li$e this to explore the features of a good exam description of apractical, but do not learn it under the assumption that we will as$ the same /uestionabout the same practical in next year0s examG

#his response scored two mar$s.


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#his response is typical of many candidates who ignored the conte

as collective topics for work sheets

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