res6 bio stretch challenge

8/12/2019 RES6 Bio Stretch Challenge

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2/22 Pearson Education Ltd 2009This document may have been altered from the original

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more than just rote learning ! the thinking skillsdemonstrated through Stretchand 'hallenge help to prepare you for these situations& Similarly) mostbusinesses will be looking for people who have good problem solving skills andthe ability to apply knowledge in different conte"ts ! so practising such skillsduring your A% course will stand you in good stead whatever you choose to do&

"ow should I prepare for Stretch and Challenge #uestions?

Stretch and 'hallenge #uestions are just part of your e"amination paper) so all theusual advice for revision applies& *ou need to know the content of the course) as laidout by the specification& owever) to do well in Stretch and 'hallenge) you also needto practise thinking in different ways) rather than just learning content by rote&

$on't limit yourself to revising topics in isolation%

+ry to spot links between modules and use strategies such as concept maps toconnect up different topics& *ou could use the te"tbook spreads which introduceeach chapter) for e"ample&

&ead around the subect%

,se different sources) for instance) newspapers) maga.ines (e&g& ew Scientist)websites (e&g& ewScientist&com) the link for which can be found on this '0&*our goal isn$t to learnlots of additional information) but to be aware of howmany of the topics or ways of scientific thinking are relevant to everyday life& 1twill also help you recognise that different views on the same topic e"ist&

sk your teacher for advice%

+his could be about the best practice #uestions to use for Stretch and 'hallenge! including past e"amination #uestions) specimen e"amination #uestions orother materials specific to your school& 2ook at the e"amples in this documentand try answering the #uestions&

(hink carefully about your e)am techni#ue%

Allow yourself enough time to answer all your #uestions and be prepared tohave a go ! you3re sure to get some marks4 5ear in mind you need to do as wellas you can on the wholepaper&

What will Stretch and Challenge #uestions look like?

Stretch and 'hallenge #uestions can crop up anywhere in an A% e"amination paper)although they will not be flagged as such& owever) the e"amples below should help

you to spot Stretch and 'hallenge opportunities&



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Stretch and 'hallenge #uestions can account for around 6!789 of the marks inyour e"amination paper) so they could make the difference between one grade

and another& Sometimes a Stretch and 'hallenge #uestion could be the final part of a long

#uestion consisting of several parts) while at other times it will be a single#uestion&

1t is #uite likely that Stretch and 'hallenge #uestions will re#uire some sort ofe"tended prose answer) but they could e#ually ask you to draw a diagram)calculate something or solve a problem&

Stretch and 'hallenge #uestions often use the command words: explaindiscuss evaluate or suggest& ;ther e"amples include: deduce calculatesketch or annotate&

Sample #uestions

5elow is a set of sample #uestions covering all of your A% modules& owever) thenature of Stretch and 'hallenge #uestions means they may include material fromother topics& Although they are adapted from past papers they are just designed togive you a flavourof the type of #uestion you may be asked&

As with most #uestions) even if you do not achieve full marks you can usually pick upseveral marks using a careful approach& +he answers have been laid out to show any

potential marking points) i&e& if the #uestion carries si" marks) the correspondinganswer will have si" points to it if the #uestion has been allocated eight marks thenthe corresponding answer will have eights points) etc& 2ook carefully through each#uestion& +here are many opportunities to gain marks and don3t be put off by theslightly more comple" wording of the #uestion&

nd finally+

+he three key pieces of advice to remember if you want to aim for Stretch and'hallenge marks:

Aim to answer all the #uestions in an e"amination paper as well as you can&

2ook for #uestions that invite you to make links across different but familiartopics&

0on$t be afraid of #uestions that seem to be about something you haven$t comeacross before& 2ook hard ! it3s probably a Stretch and 'hallenge #uestion thatre#uires you to use your existingknowledge but in a new conte"t&



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Unit -!1,. Communication/ homeostasis and energy

0odule 1 Communication and homeostasis

2uestion 1

An investigation was conducted into the filtration and reabsorption of glucose in the kidney ofa mammal& +he glucose concentration in the plasma of the renal artery was increased& +heglucose concentrations were measured in the following fluids:

glomerular filtrate

urine&



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(i Suggest how the kidney of this mammal adapted to reduce the volume of urineproduced =@>

(ii Suggest how desert mammals such as the kangaroo rat would be able to obtainwater from dry seeds =@>

=+otal: 78>

Sample answer

(a(i) %&Bmgcm!@

(ii igh levels of glucose in the blood would result in high levels in the glomerularfiltrate the kidney tubule will be unable to reabsorb all the glucose because cellmembrane glucose carriers would be saturated and could not transport anymore&

(b(i +he kangaroo rat will have e"tra long loops of enle and the collecting ducts

will be more permeable to water because of a large number of water permeablechannels (a#uaporins& +he cells of the kidney tubule and collecting duct willalso be more sensitive to A0&

(ii Seeds contain storage molecules that are broken down in aerobic respiration toproduce metabolic water&

4)aminer5s comments

(a Stretch and 'hallenge #uestions could involve using data or information) includinggraphs) so make sure you know how to take readings from graphs&

(i) 0on3t incorrectly read the graph and end up with the wrong answer ! someincorrect answers ranged from 7&@ to %&Cmgcm!@4 +he most common error is toread the scale on thexa"is incorrectly (i&e& taking a value of %&@ mgcm!@ratherthan the correct answer of %&Bmgcm!@&

(ii Students often fail to state that the glucose carriers in the pro"imal convolutedtubule would be saturated) so that glucose would appear in the urine& Stretchand 'hallenge #uestions will be partly synoptic) i&e& they will re#uire you to useknowledge from differentmodules&



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A0 being produced&

(ii +he Stretch and 'hallenge aspect in this part of the #uestion is combining yourknowledge of respiration reactions with adaptations for desert living& 5eprepared to use related (synoptic concepts in Stretch and 'hallenge#uestions& ere) e"aminers are looking for references to storage molecules inseeds ! such as starch being broken down to a respiratory substrate that isthen respired aerobically) releasing water& Diving an accurate e#uation foraerobic respiration could gain you the full three marks& Dood answers wouldrefer to water being formed in o"idative phosphorylation however) reference tocondensation reactions is not relevant here&

0odule ! 4)cretion

2uestion 1



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Symptoms would include: fre#uent need to urinate (diuresis large volume of urine or verydilute urine persistent feeling of thirst and/or e"cessive drinking&

4)aminer5s comments

+his is a Stretch and 'hallenge #uestion as it uses unfamiliarsituations to ask about coreideas&

A0 regulates the reabsorption of water in the distal convoluted tubule andcollecting duct) so a lack of this hormone would cause the production of lots ofurine and fre#uent urination& +his in turn will result in an increased thirst anddehydration) i&e& symptoms seen in diabetes insipidus&

'hanges that might occur in the cardiovascular system will not be credited as theywould not be symptoms e"hibited by a patient&

A lack of A0 would notresult in oedema (joints swelling with fluid) bloating)aggression) confusion or memory loss (as has been suggested in past answers4&

;ther points that could gain marks include electrolyte/mineral imbalance anddehydration&

2uestion !

+able 7 shows the concentrations of glucose and urea in the renal artery and renal vein&

(able 1

'oncentration/mg788cm!@plasmaEenal artery Eenal vein

Dlucose F8 C8

,rea @8 7B

5oth substances are present at a lower concentration in the renal vein than in the renalartery& owever) urea appears in the urine of a healthy individual but glucose does not&

?"plain why this is so& =6>

=+otal: 6>

Sample answer

5oth glucose and urea are filtered at the glomerulus because they are both small molecules&owever) all the glucose is reabsorbed by active uptake) and some glucose is used inrespiration in kidney cells& ;nly some of the urea is reabsorbed by diffusion&



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4)aminer5s comments

+he Stretch and 'hallenge aspect of this #uestion involves using the data in the table&

1t is unusual as you only have information regarding blood entering and leavingthe kidney& *ou have to apply your knowledge of filtrationand reabsorptiontoe"plain this information in terms of the concentrations of these substances foundin the urine&

1t is also important to realise that the drop in glucose concentration as the bloodpasses through the kidney is due to the kidney cells using the glucose inrespiration ! this is a small synopticaspect of the #uestion&

Some of the urea diffuses back into the blood in the pro"imal convoluted tubuleand elsewhere so not all the urea is lost in the urine ! this is confirmed by the datain the table as the urea concentration in the renal vein is 7B mgcm!@&



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(i why the p of the thylakoid space (lumen is lower than that of the stroma

(ii what significance this has for A+G production& =H>

(b erbicides (weedkillers interfere with electron transport by accepting electrons&?"plain how this causes plants to die& =@>

=+otal: I>

Sample answer

(a

(i ydrogen ions are pumped into the thylakoid space as electrons are passedalong the electron carriers (D in



1;

otice that the answer to part (b builds upon your previous answerto part (a& +his isa common occurrence in Stretch and 'hallenge #uestions and can give you a clue asto where to begin your answer&

*ou can also gain marks in part (b for mentioning that autotrophic nutrition stops orthat no respiratory substrate will be produced ! however don3t mention foodas in Jtheplant does not produce food3&

ote: 1n the diagram can you identify the pigments GBC8) GI88and the typeof moleculerepresented by D +hese are not Stretch and 'hallenge elements but coreknowledge forrevision&

0odule , &espiration

2uestion 1



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Samples of homogenate

'omplete uclei only Eibosomes only Litochondira only 'ytosol

'arbondio"ide

?thanol 'arbondio"ide




?thanol

7& Dlucose %& Gyruvate @& Dlucoseand cyanide

H& Gyruvateand cyanide

(a Suggest why more carbon dio"ide is produced when the complete homogenate isincubated with just glucose or pyruvate present than when cyanide is also present&

=@>

(b Suggest why carbon dio"ide is produced when mitochondria are incubated withpyruvate but notwhen incubated with glucose&=@>

(c Suggest why ethanol production can still occur in the presence of cyanide& =@>

=+otal: F>

Sample answer

(a Without cyanide the complete homogenate can break down the glucose/pyruvate fullyto produce carbon dio"ide& owever) when cyanide is present pyruvate does not enterthe mitochondria& 'yanide inhibits an en.yme involved in o"idative phosphorylation& 1treduces A+G production& 1f o"idative phosphorylation stops) so does Mrebs cycle andlink reaction& Some carbon dio"ide is produced when pyruvate is converted to ethanal&

(b Gyruvate is the end product of glycolysis and it can enter mitochondria where carbondio"ide is produced (in the Mrebs cycle and the link reaction& Dlucose cannot enterthe mitochondria) and the en.ymes for breaking down glucose are only found in thecytoplasm not in mitochondria&

(c Gyruvate is converted to ethanal in cytoplasm and the ethanal is converted to ethanol&+he en.ymes for these conversions are not inhibited by cyanide&

4)aminer5s comments

+his #uestion re#uires some background knowledge of cellular respiration: ribosomes andnuclei are notinvolved glycolysis occurs only in the cytoplasm notin mitochondria) etc&owever) it is a Stretch and 'hallenge #uestion since the answers have to be deducedfromthe table and the information given&


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1*

Unit -!13. Control/ genomes and environment

0odule 1 Cellular control and variation

2uestion 1

epatitis (inflammation of the liver may be caused by viruses) alcohol or drugs&Symptoms include jaundice) fever) nausea and high levels of liver en.ymes in the blood&+he hepatitis A virus causes acute disease only whereas the hepatitis 5 and ' virusescan cause chronic disease resulting in the destruction of liver cells&

(a ?"plain the difference between a chronic and an acute disease& =%>

2iver cells damaged by hepatitis infection switch on the Fasgene which causes them to

self-destruct& Gioneering research has produced a strikingly successful treatment forhepatitis in mice&

+he Fasgene was silenced using the EA interference techni#ue in whichEA molecules ! %7 to %@ nucleotides long ! were injected into mice withhepatitis&

+he se#uence of this small interfering R!(siEA matched part of the Fasgene&

;nce in the liver cell) the two strands of the siEA were separated so that onestrand could bind to the mEA transcript of the Fasgene&

+his caused the mEA to be destroyed by en.ymes) thereby preventing thegene product from being made&

+his procedure prevented liver cell death and considerably increased thesurvival rate of mice with hepatitis&

(b(i 0escribe a way in which the functionof mEA differs from that of 0A& =%>

(ii 0escribe twoways in which the structureof siEA differs from mEA& =%>

(c 0escribe how one strand of the siEA can bind to the mEA of the Fasgene& =@>

=+otal: I>

Sample answer

(a 'hronic means slow to build up) long-lasting and treatable but incurable& Acute is#uick to build up and short-term) as it is curable&

(b(i 0A is transcribed to make mEA but mEA is translated to make proteins&

(ii siEA is double-stranded whereas mEA is single stranded& SiEA is a

shorter strand than mEA which is the same length as a whole gene&

(c 'omplementary base-pairing between siEA and bases in mEA by hydrogenbonding between purines and pyrimidines: A with , and ' with D



1,

4)aminer5s comments

*ou can tell this is a Stretch and 'hallenge #uestion as you need to read carefullyin orderto e"tract the unfamiliar information about siEA and use it to deduce your answers& 1t isalso synoptic) with information from your AS course on nucleic acid structure) and part (ais also from AS work&

+ry not to confuse:

transcription with translation

protein synthesis with 0A replication&

1n part (a you are asked to show understanding of general scientific terminology& +his is

part of Stretch and 'hallenge& Gart (b (i is using synoptic knowledge from AS units) so isagain an e"ample of the Stretch N 'hallenge style of #uestions& *ou can use theinformation in the #uestion to score both marks for the answer to part (b (ii) i&e& thesiEA molecule is double"strandedand is shorterthan mEA&+o gain full marks for the answer to part (c you need to carefully describe complementarybase-pairing (from your AS module on biological molecules&

ote: 5oth EA types have the pyrimidine base uracilinstead of thymine&

2uestion !

'ompare selective breeding with the evolutionary process& =C>

Ouality of written communication =7>

ote:

Sample answer

?volution occurs by natural selection and the environment is the selective agent) whereas

in selective breeding) humans are the selective agent& Selective breeding is for humanbenefit but might not be beneficial for the organism concerned& 1n evolution) the organismselected is well-adapted to its environment so it benefits the organism& 1n selectivebreeding) only a few characteristics are selected (e&g& milk yield or fat content in dairycows but in evolution) the whole phenotype could be involved&

5oth re#uire selection of parents to pass alleles to offspring but selective breeding is oftenfaster than evolution&

4)aminer5s comments

+his style of #uestion also comes under Stretch and 'hallenge as the answer re#uiressome e"tended writing and a mark has been allocated for the #ualityof your writing) i&e&spelling) punctuation and grammar&

When making comparisons) don3t just describe one term and then the other ! this puts the



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onus on the examinerto make the comparison4 +ry to use words such as whereasor butto link the two terms you are comparing&

2uestion *

0uchenne muscular dystrophy (0L0 is a genetic disease caused by the absence of theprotein dystrophin in muscle fibres&

1n the absence of dystrophin) muscle fibres gradually die&

A potential gene therapy for 0L0 involves injecting muscles with a vectorcarrying recombinant 0A (r0A for part of the normal allele for dystrophin&

Denetic screening is available for families with a history of 0L0&

0iscuss the advantages and disadvantages of genetic screening& =C>


=+otal: F>

Sample answer

Advantages:

Denetic screening can tell a family if a genetic disorder is not present to remove anydoubt) but if a disorder like 0L0 is found treatment to alleviate symptoms can be usedearlier& +his means less suffering for the individual and it could improve life e"pectancy or#uality of life& 1f a disorder is detected) it might be possible for a couple to choose to havean abortion or not to have children at all& Denetic screening also allows embryos to be

checked after 1P< (in vitro fertilisation&

0isadvantages:

Qust because an allele for a disorder is detected) it doesn3t mean that the individual willget the condition) there may also be inaccurate detections (false positives or falsenegatives&



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disadvantages of genetic screening&&&&3 as this is included in the #uestion andwill just waste time and two precious lines of your answer4

;ther points which could gain you marks include:o an e"ample of a problem with testing or risk of the test procedure

o the diagnosis and elimination of a disorder rather than just treating it) i&e&prevention is more appropriate than cure (as genetic disorders can onlybe eliminated by aborting a foetus

o genetic screening may result in less tolerance/discrimination for a disability

o tests are not available for all conditions

ote: +here is a ma"imum of five marks for the advantages and a ma"imum of five marksfor the disadvantages&

0odule !

(b 'hinese scientists realise that it will only be a matter of time before insects developresistance to $t to"in& ?"plain how resistance to $t to"in could arise and spread inan insect population& =6>

(c Wild sunflowers are considered to be weeds by many farmers in the ,SA as theyhybridise readily with sunflowers grown as crops&

+wo e"periments involving wild sunflowers gave the following results: ,p to H%9 of the seeds produced by wild sunflowers growing at the margins of

a commercial sunflower field were hybrids&

+he hybrid offspring of wild sunflowers and e"perimental sunflowers produced



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689 more seeds than ordinary wild sunflowers& +he e"perimental sunflowershad been genetically engineered to produce insecticide&

0iscuss the potential ecological ha%ardsof growing a genetically-engineered cropsuch as sunflowers& =B>

=+otal: 76>

Sample answer

(a) +here has been an increase in the use of $tcotton between 7FFI and %887& ,sing the$tcotton means less or no insecticide is needed& +his can be deduced from thereduced number of cases of pesticide poisoning (%%9 compared with 69) a drop ofH&H +he cost of producing the cotton is also 8&B% ,SR/Mg less with $tcotton& +hisis probably because the farmers don3t have to buy so much insecticide&

(b A mutation (e&g& a deletion of a base in 0A could happen (by chance which givesthe insect resistance to the insecticide (e&g& by producing an en.yme which breaksdown the insecticide& +he resistant insects will survive and non-resistant will diewithout or with fewer offspring) so by natural selection the insecticide will select theresistant variety& +he resistant ones will therefore breed more and pass thefavourable allele on to their offspring&

(c Wild sunflowers become resistant because they cross with other varieties (e&g& H%9 ofseeds& +his means they become more invasive and spread #uickly because more

seeds are produced (689& +hey could also pass resistance to other weeds andincrease $tto"in resistance in insects& +here could be a to"in in seeds which couldbe passed up the food chain or kill beneficial insects& +he seed could also containan allergen if consumed by humans&

4)aminer5s comments

+here is a small synoptic aspect to this Stretch and 'hallenge #uestion as you need touse your knowledge from modules 7) % and @ of the ,nit



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should also try to include e"amples (as in the answer given above&

0on3t confuse insects with bacteria ! e&g& bacteria can pass 0A by

conjugation or plasmids but insectsdon3t& Also) it is better to talk about passing on the allelefor resistance not the gene&

(c



1:

Eeefs are under threat from a variety of sources& ;ne of these is the water that drainsfrom agricultural land that is rich in fertilisers& Another is the discharge of untreatedsewage into the sea&

(a ?"plain how these types of pollution could alter the ecological balance of a coralreef& =H>

(b +he immense biodiversity of the oceans includes:

corals that host symbiotic algae which die if the sea temperature rises by 7 T' animals such as polar bears that use floating ice as a base for sea fishing

e"peditions

sessile animals such as mussels that feed by filtering food particles from thewater and reproduce by releasing gametes into the water

reef-building animals such as corals that form hard calcium carbonateskeletons by e"tracting mineral ions such as calcium ('a%U from the water

seaweeds of different colours that occur in shallow water

animals such as fish that hunt prey using well-developed visual skills

large animals such as the blue whale

physically delicate organisms such as jellyfish that lose their shape in air&

,sing e"amples from the list above describe ande"plain how thepropertiesofwater make it a suitable environment for these organisms& =I>


ote:

Sample answer

(a +his pollution would cause eutrophication it would increase the growth of algae)which would then block out sunlight and compete with other species& Glants woulddie& +he dead plants would decompose (as would the untreated sewage by theaction of aerobic bacteria which would use up the o"ygen in the water (increased



!;

biological o"ygen demand& +his lack of o"ygen would cause the death of otherspecies such as fish and corals&

(b +he properties of water relate mainly to hydrogen bonding& Water molecules formhydrogen bonds with each other& +hese bonds are weak) but taken all together theygive water important properties for living organisms& Water has a high specific heatcapacity (a lot of energy is needed to break the hydrogen bonds which means itremains at a fairly constant temperature for organisms such as the coral algae&When cooled) water forms more hydrogen bonds) the molecules spacing out to letthis happen so the water e"pands as it free.es) forming ice which is less dense&+his floats allowing animals) like polar bears) to walk on it&

Water can also act as a transport medium for food particles for filter feeders likemussels that have cilia to create currents for feeding& +hese animals alsoreproduce by shedding gametes into the water so it allows male gametes to swimand prevents gametes from drying out&

Water is transparent) which allows light to penetrate for photosynthesis inseaweeds with the right colour of pigment at the right depth& +his transparency alsoallows eyes to function in predatory animals like fish&

4)aminer5s comments

(a +his is not a very demanding Stretch and 'hallenge #uestion& owever:

it does re#uire that you apply your knowledge from one area (eutrophication to

another area (food chains/webs the ecosystem involved may be unfamiliar to you

you have to correctly use terms such as aerobic respirationand eutrophication

for the food web given in this instance) you would be e"pected to refer to thespecificorganisms(e&g& algae or phytoplankton rather than simply plants&

(b 'ompared with the answer to part (a this is a fairly demanding Stretch and'hallenge #uestion as it re#uires an e"tended piece of writing ! with a markallocated for the #uality of your answer& +he challenge of this #uestion is to applyyour knowledge within a new conte"t&

*our answer should include many different and unfamiliar e"amples of theocean ecosystems (see your A% module &cosystems and sustainability whichmust be linked to the properties of water (from your AS module $iologicalmolecules&

*ou need to e"plain the features of the listed organisms by naming anddescribing/e"plaining the properties of water that allow these organisms to livein the way they do&

Stating correct but irrelevant ideas will not gain much credit ! e&g& referring towater3s surface tension as being important for pond skaters in fresh water is notrelevant here&

;ne way to plan an answer to this #uestion would be to list the bullet pointsfrom the #uestion and match them to a list of the properties of water&

0odule , &esponding to the environment



!1

2uestion 1

(a Lost of the research on the ripeningof fruit has been conducted on tomatoes&?"plain the advantage to tomato plants of having seeds enclosed in a fruit such asthe tomato& =%>

(b 1t has been discovered that as tomato fruits ripen the following changes occur:

the rate of respiration increases

chlorophyll production stops

starch is converted into monosaccharides

ethene production increases and ethene is released into the environment

more of the red pigment lycopene is synthesised

the concentration of polygalacturonase) an en.yme that breaks down the pectinin the cell walls) increases&

?"plain how the changes outlined above allow the tomato fruits to carry out theirfunction& =H>

(c ?"plain how plant growth regulators are used commerciallyto control fruitdevelopment& =B>

Ouality of written communication =7>ote:

Sample answer

(a +he fruit has evolved by natural selection to attract and be eaten by animals whichthen carry seeds in their gut and disperse them during egestion (in faeces&1nhibitors in the fruit prevent seed germination until the seed passes out of theanimal and into the soil&

(b +he increased respiration rate produces more A+G which can be used for thebreakdown of starch to produce sugars in the fruit) which attract animals to feed&'hlorophyll is replaced by lycopene to turn the fruit bright red so it can be seen byanimals&

(c Au"in can be used to produce seedless fruit without the need for fertilisation& +hisis called parthenocarpy and it improves the number of fruits that form) andincreases the si.e of each fruit& Glant hormones can be used to control ripening infruits e&g& au"ins and gibberellins can promote ripening) and reducing etheneconcentration can delay ripening (e&g& in transporting fruit like bananas long

distances without ripening&

4)aminer5s comments

+his is an e"ample of a Stretch and 'hallenge #uestion since it includes much information


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that you should use and refer to in your answer& 1t is also synoptic in bringing togetheryour knowledge about digestion) plant hormones) adaptation and respiration& owever) it

also has some unfamiliar material which you need to incorporate into your answer& ote the terms in italicsin the #uestion&

res6 bio stretch challenge

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