res17 bio examiners tips

7/27/2019 RES17 Bio Examiners Tips

1/191 Pearson Education Ltd 2009This document may have been altered from the original

At A2 you will go further and deeper into the study of biology, building on the work

done at AS. As at AS, the work at A2 is divided into units and modules. Each unitcorresponds to one of your examination papers.

hese examiner!s tips have been written to help you in your studies. hey start withsome general advice about approaching examinations, then go on to give specificadvice and tips for each module in your A2 course. "e have tried to pick out topicswithin each module that candidates often find difficult # i.e. topics that are fre$uentlymisunderstood or where answers to such topic $uestions aren!t as good as theycould be.

General guidance

here are a number of general areas that often cause problems for students whenanswering examination $uestions. hese problem areas are regularly mentioned inexaminers! reports. his general guidance should help you avoid these commonproblems and build good examination techni$ue.

%ractise $uestions on past examination papers and check the

corresponding mark schemes. hese can be an invaluable learning andrevision resource. &ou can use knowledge of a previous mark scheme toanswer $uestions asked from a different aspect, re$uiring answers that

demonstrate the applicationof your knowledge. 'owever, don!t expectexactlythe same $uestions to come up on your examination paper # beprepared to adaptyour knowledge to suit the $uestion.

"hen revising for your exams consider the variety of ways that a topic

could be tested # be prepared to draw together strands of informationfrom different areas of the specification. (emember to use the informationgiven in the $uestion!s introduction to provide an appropriate answer.

Always read the $uestion fully and carefully )at least twice*+ before

beginning your answer.

onsider your responses carefully and ensure that you express yourself

clearly, using appropriate scientific terminology. his is particularlyimportant in $uestions that have been flagged as -" )-uality of "rittenommunication+.

Always read through your answer. Examiners cannot award marks if it is

not clear what you are trying to say. Avoid repetition and reversestatements. Examiners often allow considerable leeway with the spellingof technical terms, but will not be so generous if answers are unclear.

ake sure you use scientific terms appropriately # incorrect use can lose

you marks. he following terms are often used inappropriately/

Examiners tipsExaminers tips



gene and allele

biotic and abiotic

sympatric and allopatric

glucagon, glucose and glycogen

glucose and sugar

interspecific and intraspecific.

alculations are another area in which mistakes are often made. ake

sure you have a calculator with you during the exam, and that you arefamiliar with the necessary functions.

ake use of the all the data provided, whether it is presented in table,

graph or text form. arks will be allocated for $uoted data.

"hen asked to make comparisons, don!t simply describe one thing and

then the other. &ou must describe the differences or similarities betweenthem.

&our A2 papers will always include $uestions designed to test your

knowledge and understanding of the AS specification. he 021 unit willalso test your synoptic knowledge of the material in 021, so look out for$uestions that may draw on your knowledge from previous work.

3se the information given in the introductory part of the $uestion when

being tested on unfamiliar material. 4t is a good idea to highlight keypieces of information as you read through the $uestion. &ou will often beexpected to make particular use of information provided in bullet pointformat.



Unit F214: Communication, homeostasis and energy

Module 1 Communication and homeostasis

Negative feedac!

he general principle of negative feedback can be difficult to understand,

but it is an essential component of homeostatic mechanisms.

6ne common error is to suggest that the homeostatic mechanism will

reverse the environmental change that caused the stimulus.

his may be true of internal stimuli but is nottrue of external stimuli # the

body cannot change the whole environment around it.

Nerves

"here $uestions address changes in membrane potential associated with

an action potential you will often be provided with diagrams or otherinformation # it is important to make full use of the data you are given.

&our answer should include reference to voltage7gated sodium ion and

potassium ion channels # do not confuse these with thesodium8potassium pump*

"hen describing the transmissionof an action potential along an axon,

remember to explain how the sodium ions move inside the axon to areasof negative charge )resting potential+ a short distance away, therebysetting up a local circuit.

(emember that the myelin sheath acts as an electrical insulator and that

exchange of ions across the membrane can only occur at the nodes of(anvier.

'owever, do not overlook the fact that this results in longer local circuits

which cause saltatory conduction and speed up transmission.

Even though the specification refers to transmission of an action potential

in a myelinatedneurone, to appreciate the role of the myelin sheath and

how this structure speeds up the rate of transmission, it is advisable toconsider how propagation occurs in a non-myelinatedneurone as well.

"ormones

he role of membrane7bound receptors on target cells is crucial. &ou

must remember the complementary nature of the shape of the hormoneand its receptor.

0or $uestions about the maintenance of blood glucose concentrations,

you will gain marks for stating that glucose can be converted to glycogen

if blood glucose concentration increases, going on to add that the reversewould happen if blood glucose concentration falls below the norm.

(emember that the blood glucose concentration must rise above the

normfor insulin to be released, rather than rising back towardsthe norm



from a low level.

he stimulus for these metabolic reactions is changes to the

concentration of blood glucose,not changes in insulin or glucagonconcentrations. %rovide mechanism details by which such changes arebrought about, including the reactions initiated inside the hepatocyte bythe binding of the appropriate hormone to its receptor on the hepatocytemembrane.

4t is important to describe these processes carefully with statements such

as 94ncreased blood glucose concentration causes moreuptake ofglucose, moreconversion to glycogen, and morerespiration!.

0inally, don!t forget that insulin and glucagon are hormonesnot en:ymes.

;on!t lose marks by stating that 94nsulin convertsglucose to glycogen! #

insulin causesthe conversion of glucose to glycogen.

Module 2 #$cretion

&ou need to be familiar with the detailed structures of the liver and the

kidney. &ou will probably be asked to relate the structure of the organ toits effective function.

&ou may be asked to apply your knowledge of kidney physiology and

structure to unfamiliar situations.

;on!t be too casual when using technical terminology as this can result in

muddled answers # e.g.

Stating that the plasma glucose concentration in the renal arteryand the concentration of glucose in the glomerular filtrate areproportionalrather than directly proportionalor that as one goesup so does the other.

0ailing to state that A;' will cause morewater permeablechannels to be inserted in the cell membranes, therebyincreasing the reabsorption of water from the collecting ducts,making the urine more concentrated.

&ou may be asked $uestions involving tables that compare

concentrations of glucose, amino acids, salts and proteins in variousfluids or graphs showing how these concentrations change in differentparts of the tubules.

(emember to read the correctanswer from a graph # don!t read

the scale on one of the axes incorrectly )a common mistake*+.

Study tabulated and graphical information carefully # try anddecide what the trends are beforeyou look at the actual $uestion



being asked.

Always state the trends that can be seen in the data accurately

and use figures to illustrate your points.

ost candidates realise that protein molecules are too large to be filtered,

however, only a small number refer to the basementmembranebeing theeffective barrier # there are often incorrect references to/

the slit pores between podocytes

and the fenestrations between the endothelial cells of theglomerular capillaries as being the effective filter.

"hen studying kidney physiology, consider animals that live in extremeenvironments and the adaptations to the structure and functioning of theirkidneys, for example the kangaroo rat.

(emember to relate the length of the loops of 'enle to the needto conserve water and relate this to creating a high soluteconcentration in the tissue fluid of the medulla.


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photosynthetic cell

for the fact that different pigments absorb different wavelengths

of light. "hen describing the role of accessory pigments, you should realise that it

is energythat is passed to the primary pigments, not electrons #accessory pigments absorb wavelengths of light not absorbed by primarypigments.

he action of different pigments may be represented in a graph. &ou can

gain credit for/

noting that chlorophyll a has a high absorption of light at twodifferent wavelengths )between >#?> nm and between ==>#@1>nm+

stating that there is low absorption of light at wavelengthsbetween >>#=2>nm # remember to state the units*

(ight)de'endent stage

;escriptions of the light7dependent stage of photosynthesis tend to be

good and many candidates are able to give excellent accounts of non7cyclic photophosphorylation and the 7scheme.

'owever, fewer candidates can accurately describe cyclic

photophosphorylation and link the production of A% to a chemiosmotic

mechanism involving the pumping of protons into the thylakoid lumen. he energy for this proton pumping comes from the electron

transport chain that links photosystem 2 to photosystem 1.

he role of chemiosmosis is often taught as part of respiration #don!t forget that it is also involved in photosynthesis.

Although photolysis is generally well understood, a common

misconception is that the electrons derived from the photolysis of waterwere directly boosted by light rather than replacing those lost fromphotosystem 2.

(imiting factors

he rate of photosynthesis is governed by the law of limiting factors # you

met this concept at


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most obvious ones # e.g. in photosynthesis the light7independentreactions may be reduced by high temperatures and en:ymes becoming

denatured. 'owever, another explanation might be that the hightemperature increases transpiration # causing the stomata to close andreduce the supply of carbon dioxide.

;o not make the mistake of thinking that if water is in short supply it may

slow the rate of photosynthesis directly. he amount of water used inphotosynthesis is small compared with that lost in transpiration # a plantwould wilt severely before the rate of photosynthesis is affected by ashortage of water.

*rue and a''arent rates of 'hotosynthesis

6ne potential area to gain Stretch and hallenge marks is through

comparing the roles of respiration and photosynthesis in a leaf.

4t is important to grasp the difference between true andapparent rates of photosynthesis.

4t should be clear that some of the oxygen released by aphotosynthesising cell will be used in respiration.

Similarly, the carbon dioxide produced in respiration will beused in photosynthesis.

4n calculations to find the true rate of photosynthesis you should add the

carbon dioxide released in respiration to the carbon dioxide uptake forphotosynthesis # the most common error is to subtract the carbon dioxideproduced in respiration from the net uptake for photosynthesis rather thanadding it*

Module 4 +es'iration

iochemistry

ost students seem to understand the biochemistry of respiration andglycolysis. Accounts of the Crebs cycle should refer to the processes ofdecarboxylation, dehydrogenation and oxidative phosphorylation. Damingthe en:ymes involved also gains credit.

6ne common misconception is to consider the molecule of acetyl

coen:yme A to be a two7carbon molecule. 4n fact/

acetyl coen:yme A is a combination of the two7carbon acetategroup and the coen:yme.

coen:yme A is a carrier molecule, which transports the two7carbon acetate group into Crebs cycle

the molecule of coen:yme A is recycled. Ensure you can account for the number of reduced DA; and 0A;

molecules produced in the Crebs cycle.


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ake sure you have a sound grasp of oxidative phosphorylation and the

events taking place in the inner mitochondrial membrane # remember to

be clear as to whether the carriers transport hydrogen ions, hydrogenatoms or electrons.

ake reference to dehydrogenase en:ymes removing the hydrogen from

the reduced coen:yme )DA;'+ # the hydrogen then becomes split intoprotons and electrons.

ake sure you understand that oxygen is the final hydrogen8electron

acceptor and that water is formed.

-tructure of .*&

A% is closely related to one of the nucleotides that form ;DA. A goodsynoptic topic is to compare the structure of A% with that of nucleotides.

ry to make the link between nucleotides )some of whichcontain the nitrogenous base adenine, a sugar and onephosphate group+ and A% )which contains the base adenine, asugar and three phosphate groups+.

A;% could be considered to be a nucleotide phosphate andA% could be considered to be a nucleotide diphosphate )or anucleoside triphosphate+.

A% is the immediate source of energy for active processes in the cell. hese

processes include active transport and muscle contraction as well as anabolicreactions. 'owever, at A2 it is not enough to suggest that A% is used formoving, keeping warm or growth.



Unit F21/: Control, genomes and environment

Module 1 Cellular control and variation

&rotein synthesis

ake sure you understand the mechanism for protein synthesis.

&ou must know that the genetic code consists of triplets of bases #

remember that three bases code for an amino acid not three amino acidscoding for a base.

"hen considering non7coding triplets, a stoptriplet stops transcription not

translation # try and state an example of a stop triplet.

(emember a stoptriplet does notstop ;DA replication, amino acid synthesis

or ribosomes from reading m(DA )or even ;DA+.

;on!t make the mistake of mixing the coding strand with the codon/

he coding strand is a length of ;DA.

he codon is a base triplet on the m(DA.

Meiosis

he maBority of candidates are able to describe the phases of meiosis

successfully and arrange them in a suitable se$uence.

he process that causes the most difficulty to students is the division of thecentromeres, which occurs duringanaphase 44.

(emember that ;DA replication and synthesis of organelles occurs during

interphaserather than in prophase 4.

"hen genotypes are included on the chromosomes, most candidates can

successfully identify the possible gametes that could be formed at the end ofmeiosis.

Genetics 'rolems

"hen answering $uestions on genetic problems, try to use genetic diagrams,taking care over the layout # remember there is a standardlayout for suchdiagrams.

;on!t insist on using your own symbols # suitable symbols are usually given

at the start of the $uestion.

(emember to always match the phenotypes to the correct genotypes at the

end of the genetic diagram.

he same rules apply to genetic problems involving sex7linkage. (ead the

instructions carefully and use the correct symbols for both the sexchromosomes and the alleles # the most common mistake is to show alleles

on the & chromosome when told they are on the F chromosome. (emember that to be a carrier, the individual must be heterozygous# in sex7

linkage this is only possible for females as they have two copies of the Fchromosome.


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6ne common error in genetic problems is to put too many alleles )different

forms of genes+ into the gametes. (emember that gametes have halfthe

genes of the parent cell, so will only have oneallele from each pair of allelesfound in the parent cell.

any candidates can successfully tackle comparing supplied results with

expected results using chi7s$uared )2+ statistical analysis. 'owever, somecandidates seem unsure as to what their calculated value of chi7s$uaredactually means # examiners look for statements that the calculated value iseither above or below the critical value as well as comments on whether thisdoes or does not support the hypothesis.

4n problems that involve crossing7over, candidates should be aware of the

distinction between crossing7over and chiasmata.

&ou should also be able to describe sister chromatids as having identicalbase sequencesor identical allelesrather than simply saying they aregenetically identical.

"ardy)0einerg

ost candidates are able to use the 'ardy7"einberg principle to calculate thefre$uency of alleles in a population. &ou need to recall that if the fre$uency of arecessive allele is q then the fre$uency of the associated phenotype is q2, i.e. theindividual must possess tworecessive genes and the chance of ac$uiring eachone is q. 'owever, it is important to remember that these e$uations rely on a

number of assumptions about the population. hese are that/

the population is large

mating is random

there is no selective advantage to any particular phenotype

there is no mutation

there is no migration

there is no genetic drift.

#volution

4n $uestions about evolution and selection, most candidates are able to state

how some environmental factor )e.g. predators+ could reduce the numbers of apopulation )i.e. their prey+. his may impose selective forces by removing moreof one phenotype, so that another phenotype is at a selective advantage.

;on!t fall into a generalisedaccount of the ;arwinian theory # most $uestions

are likely to be based on a specificexample which you should use whereverpossible in your response.

At A2, examiners are also looking for a link to changes in allele fre$uencies.

ry to use technical terms such as stabilising selectionor

directional evolution.

;on!t discuss fre$uencies of alleles when you really meanfre$uencies ofphenotypes.



Module 2 iotechnology and gene technologies

Cloning

his is a very descriptive section, so be prepared to sit down and learn the

details for your exams.

Datural cloning is a common event in the plant kingdom but less so in

animals.

ake sure you know the main steps in cloning plants using tissue culture.

ake sure you know the difference between embryo cloning and adult cell

cloning.

iotechnology

he use of fermenters is fairly well understood, although some candidates

seem to believe that an autoclave could be used instead or that fermentersneed to be heated to high temperatures # don!t make the same mistakes*

ost students understand the need for oxygen for aerobic respiration and the

need for mixing the cells with nutrients.

oo many candidates offer incomplete or imprecise answers such as/

mixes the contents

as oxygen is essential for survival

air creates aerobic conditions.

4nade$uate checking of responses provides incorrect answers such as/

mixes cells withproducts

oxygen for anaerobic respiration

air provides energy

air inspires growth

respirating organisms.

ry to avoid muddled and imprecise answers to $uestions about the

conse$uences of contamination with unwanted bacteria in a fermenter #don!t Bust describe how contamination occurs or how it can be preventedas this suggests a lack of understanding of the term consequences. &ouwill not gain marks for vague answers such as/

productG.not produced properly8not as wanted

stops it from doing its Bob

pathogens form

nutrients8products die.

o gain marks at A2, your responses need to be specific, detailed and any

scientific terms must be used correctly. A common error when describing the use of fermenters is to suggest that

thermometers and p' probes are used to controlthe conditions inside thefermenter/



hermometers monitorthe temperature.

p' probes monitorthe p'.

;on!t confuse the difference between batchand continuousculture.

4n batchculture, the fermenters are set up and allowed to runfor a certain time before being closed down and emptied #thereby producing a batch.

4n continuousculture, the nutrients are continually supplied andthe products continually removed # providing an ongoingprocess.

Hiotechnology has numerous applications in medicine and you should

expect $uestions that link to knowledge from earlier units. Such areas forsynoptic links are with/

the 0ood and 'ealth unit at AS

parts of 3nit 021 at A2 where biotechnology can be used totest both blood and urine for imbalances of various components.

(emember glucose biosensors use immobilised enzymeswhile

pregnancy7testing kits use immobilised antibodies. ommon errorsinclude describing/

glucose biosensors being used to test urine in order to measureblood glucose

glucose biosensors detecting diabetes

pregnancy7testing kits using immobilised en:ymes.

Gene technology

any candidates become confused when describing sticky ends. he

action of restriction en:ymes is to make staggered cuts that leaveexposed bases on the end of the cut ;DA # these exposed bases are thesticky ends.

he restriction en:ymes produce complementary sticky ends so that the

ends can be Boined by hydrogen bonding between the complementary

bases # these sticky ends are usually the same se$uence of bases. 4t isincorrectto claim that/

because the ends left by the en:ymes are the same they cannotBoin

blunt ends are needed.

"hen describing the action of restriction en:ymes, avoid saying that they

break down;DA # this suggests wholesale destruction rather than a cutat a specific site*

Although the formation of recombinant ;DA is usually well understood, a

common error is to involve ;DA ligase in the hydrogen bonding of

complementary bases rather than in sealing the nicksin the sugar7phosphate backbone of ;DA.

Expect to find $uestions re$uiring knowledge of meiosis and selective

breeding. &ou need to be able to explain why selective breeding is carried



out and understand that it can be used to improve some desired trait. &oumay gain extra marks if you can/

discuss the process in detail mention that it increases the number of desirable alleles

link narrow genetic diversity with inbreeding.

he point of testing selective breeding is to allow a comparison with

genetic engineering. ost candidates can suggest at least twoadvantages of genetic engineering over selective breeding. he mostcommon being/

a $uicker outcome compared with the numbers of generationsinvolved in selective breeding

the ability to add one trait rather than dealing with the wholegenotype.

"hen asked about disadvantages, candidates tend to concentrate onethical undesirability and rarely describe what might be undesirable.

any $uestions are likely to be set in a real7life context. ertain gene

therapies have undergone clinical trials # including as a possibletreatment for cystic fibrosis. &ou should be familiar with such examples aswell as othersI however, you are unlikely to be asked in detail about thesymptoms of cystic fibrosis or other conditions.

;o not confuse gene therapy with genetic counselling or with genetic

engineering.

Module % #cosystems and sustainaility

#cosystems

here is some confusion amongst candidates about the dynamic aspects

of ecosystems. ake sure you understand the difference between/

biotic and abiotic changes

biological and non7living components of an ecosystem. 4t is not always the case that there would be an increase in biodiversity as

succession proceeds.

Systems that are prevented from reaching their climaxcommunity, such as through the introduction of gra:ing, retainmuch higher species diversity.

he usual dip in the species diversity as an ecosystem reachesits climax can be attributed to increased competition )principallyfrom trees+, leading to smaller plant species dying out.

;isturbance usually leads to the creation of a variety of niches and hence

the potential for greater species diversity.

An important aspect of any ecosystem is the recycling of nutrients.

ost accounts are limited to the fact that minerals are released



from dead and decaying organic matter and are taken up by theroots of living plants. Hut remember that decomposers respire

and grow # these processes add to the complexity of recycling. he most common mineral mentioned is nitrate but you should

remember that there are many others that are also recycled e.g.phosphorus and potassium.

(emember to state how the plant uses the nitrate or any othernutrients. ry not to use general statements about increasedgrowth but rather more precise comments on the formation ofamino acids and proteins )for nitrates+, or the formation ofchlorophyll )in the case of magnesium+.

redit may also be given for correct reference to humus

formation and how this improves the soil in a way that isbeneficial to living plants. Although it is correct to state that itimproves the water holding capacity of the soil, you should alsoremember that is improves soil structure and holds the soilparticles together.

Examiners want to see references that display a wider understanding of

biology. 0or instance/

the idea that fungal respiration during decay results in theproduction of carbon dioxide, which would then be taken up bythe living trees for photosynthesis.

Jery few candidates manage to provide this sort of answer # i.e. the typeof links expected of candidates aiming for an AK.

&ou have already come across the measurement of the abundance of

organisms during your AS studies. &ou need to recall this knowledge insufficient detail when describing how to investigate the abundance anddistribution of certain plants.

(emember plants are stationaryso don!t suggest using markand recapture or the use of nets and light traps*

"hen studying the abundance and distribution of plants, it isimportant to grid the area in $uestion and sample it

systematically. his could involve using various transects and$uadrat analysis.

&ou also need to correctly identify the need for using keys.

At A2, the emphasis is on the dynamicaspects of ecology.

easurement and recording techni$ues need to take account ofsuccession and changing populations.

&ou should be able to describe how kite diagrams are used toanalyse the data obtained along a transect.

&o'ulations

-uestions involving population changes can often prove to be more

difficult than expected.

%redator7prey relationships are often tested using a graph and you may



be asked to sketch the population changes in one of the populations.(emember/

put the peaks of the predator curve lowerthan those for theprey.

position the peaks to the rightof the prey curve.

sketch your curve carefully # don!t attempt a symmetrical option)this often fails to gain marks+.

4f you are asked about factors that control population si:e, the examiners

will be looking for correctly qualifiedenvironmental factors such as/

morefood

fewerpredators

lessdisease.;on!t Bust simply write 9food, predators and disease! # you need to $ualifythese factors if you want to gain the marks.

&ou must be able to explain the terms interspecific and intraspecific

competition.

Interspecificis competition for resources between individuals ofdifferentspecies.

Intraspecificis competition for resources between individuals ofthe samespecies.

4f you need to accompany each definition with examples, it is always a

good idea to check that you have the correct definition with the correctexamples.

&ou need to be able to define carrying capacity. (emember not to give the

impression that it is the maximum number of all the animals or organismsin a habitat but is specific to the population of onespecies.

0ew candidates link carrying capacity to limiting factors.

&ou should also ensure that you fully appreciate the difference between

carrying capacity and climax community.

Carrying capacityis the maximum population that a particularhabitat can support.

Climax communityis a balanced e$uilibrium of species with few,if any, new species replacing those that have becomeestablished.

-ustainaility

Sustainable production is production that can be maintained indefinitely.

any candidates can give good accounts of the management techni$ues

involved but few link these techni$ues to continuous production. 0orexample, one forestry techni$ue uses coppicing with standards. &ou must

be able to/ write a detailed account of the process of coppicing

realise that it involves cutting the tree down close to the ground


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and that new growth will form from the stool

accurately express how this process is used in sustainable

management # i.e. the process can be repeated every fewyears or rotational coppicing )examiners will be looking for suchreferences+.

&ou could gain extra credit by/

including additional detail such as naming suitable trees forcoppicing and stating the length of time interval betweencoppicing

explaining how coppicing can lead to increased biodiversity # inwoodland, for example, coppicing increases the light intensityreaching the woodland floor

including references to standards providing large planks or theidea that timber from a standard is going to have a highmonetary value

noting that the coppiced trees would provide a regular income,with the biomass being used for hurdles, fencing, etc.

onservation is an important part of sustainable production. ost

candidates have a good understanding of ways to combine sustainabilitywith conservation. 0or example/

the use of hedgerows as wildlife corridorsthat can act as sites ofrefuge or retreat for species to avoid predation or to find food.

Module 4 +es'onding to the environment

&lant res'onses

&ou need to ensure that you have a good understanding of the range of

plant growth regulators and what they do.

&ou!ll gain marks for referring to plant growth regulators )or even plant

hormones+ and for naming examples. -uestions sometimes refer to flowering plants.

;on!t allow this to limit your thoughts to pollination and flowering.

%lants respond to a range of environmental factors and youshould be aware of all their responses.

"hen describing plants responding to changes in the externalenvironment, try to also describe their responses to the internalenvironment # however, do not forget that growth regulatorscoordinate these responses.

-uestions may often be set in the context of investigations and may

present data from such investigations. ;on!t forget to read the data carefully # use the figures in your

answers and remember to use the units.

he data will often show changes in growth such as stem length


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after application of a growth regulator such as gibberellin.

ake sure that you consider data from the controlplants, as

these can indicate how much effect the gibberellin is having. 6nce you have worked out the effect of the gibberellin, ensure

that you answer the $uestion being asked.

0or example, if you are asked to describethe effect then do sowithout further explanation # i.e. that gibberellin may not beproduced by one plant.

'owever, if you are asked to explainthe effect then you will needto give further detail # i.e. this may be due to the plant!sinability to produce an en:yme for gibberellin synthesis.

"here growth regulators are missing, this could be due to a mutation.

'ere, you should be able to demonstrate your knowledge of links to otherparts of the specification.

(emember to provide further detail such as a mutation has led toan altered protein or en:yme.

4f the investigation involves selection of particular phenotypes,then there is further opportunity for synoptic assessment ofselective breeding.

.nimal res'onses

ost candidates can name the muscles involved in coordinatedmovement of the elbow Boint. 4t is important to remember the antagonisticnature of muscle action in coordinated movement.

0or $uestions referring to muscle, you must be able to/

describe the structure and action of striated muscle

understand how a contraction is controlled

describe the control process in sufficient detail

pay particular attention to the role of calcium ions in the muscle.

&ou must understand that the autonomic nervous system is subdivided

into the/ sympathetic

and parasympathetic components.

&ou must also be able to describe the effects of each system on bodily

functions such as controlling the heart rate by acting on the sino7atrialnode. 'owever, to gain any credit these descriptions need to be clear,unlike un$ualified references such as/ 9he vagus nerve affects the heartrate.!

&ou should be able to name the appropriate neurotransmitters involved in

each system and describe the role of the medulla oblongata in the

coordination of bodily functions under different physiological conditions. 4n comparisons of the sympathetic and parasympathetic systems,

remember to include references to the differences in structure such as thelengths of the preganglionic and postganglionic fibres in either system.


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ry to describe in as much detail as you can the detection of changes in

the internal environment, such as/

changes in carbon dioxide or oxygen concentrations in the bloodby chemoreceptors

the role of baroreceptors in monitoring blood pressure.

.nimal ehaviour

4t is often possible to reason some of the marks from the information given

in $uestions on animal behaviour, so this is often a topic in which manycandidates can excel.

0urthermore, correctly describing examples of types of behaviour can also

gain marks and candidates often find it easier to recall interestingexamples of behaviour # e.g. chimpan:ees Boining two sticks together toreach a banana. andidates who are also studying psychology may findthis topic easier to understand.

'owever, there is a danger of losing marks if you get too carried away*

0or instance, explainingthe results of an investigation when you!ve beenasked to describethem.

here is also a tendency to use vague terms such as/

as time went on

instead of as the number of trialsrepeats increased.

&ou need to appreciate that it is the repetitionnot the duration of time thatis significant in many behaviour experiments.

4n experiments on learning in animals, such as mice, you must appreciate

the significance of a controlexperiment.

4f you are asked to describe a suitable control, don!t describe acompletely different experiment*

&ou must realise that a control will use the sameapparatus andsameconditions.

ry not to make general statements such as 9carry out the same

experiment! or 9use the same method!. ention that a different mouse should be used, as it would not

have learned from the previous experiment.

(ealise that a control will use the same number of trials.

here are many categories of learned behaviour and it is important that

you understand the differences between these types of behaviour.

Insightlearningis very different from habituation or operantconditioning and demonstrates a higher level of mental activity.

&ou may be asked to compare types of learning. (emember touse the appropriate scientific terms # e.g. in classical

conditioning you should use terms such as conditionedresponseor conditioned stimulus.

4n $uestions asking for a comparison, remember to comparetheprocesses # don!t simply describe one or the other.


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res17 bio examiners tips

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