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Control, Genome and EnvironmentCellular Control

(a) state thatgenes code for polypeptides, including enzymes;

(b) explain the meaning of the term genetic code;The sequence of the bases on a gene is a code with instructions for the construction of proteins. Ithas a number of characteristics

It is a triplet code! three bases code of an amino acid

It is a degenerate code! "ll amino acids bar one have more than one code#ome codes don$t code for amino acids but are %stop$ codons! they indicate the end of the

polypeptide chainIt is widespread but not universal! Codons generally always code for the same amino acid

in every organism, but this is not always the case.

(c) describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acidsequence in a polypeptide;

&'" is copied into m('" by a process called transcription)nly one strand of the &'" is copied by complementary base!pairing *hydrogen bonds+The code is a triplet code which is read in threes *a codon is bases+The base sequence determines the amino acid sequeneThe m('" is released from the &'" and passes out of the nucleus through a pore in the

nuclear envelope to a ribosome

(d) describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct apolypeptide, including the roles of messenger RNA, transfer RNA and ribosomes;

-. " molecule of m('" binds to a ribosome. Two codons are attached to the small subunit of theribosome and eposed to the large subunit. The first eposed m('" codon is always "/G./sing "T0 energy and an enzyme, a t('" molecule with the amino acid methionine and theanticodon /"C forms hydrogen bonds with this codon1. " seconds t('" molecule, bearing a different amino acid, binds to the second eposed codonwith its complementary anticodon. " peptide bonds forms between the two ad2acent amino acids. This is catalysed by an enzyme3. The ribosome now moves along the m('" reading the net codon. " third t('" brings anotheramino acid and a peptide bonds forms between it and the dipeptide. The first t('" leaves and

is able to collect and bring another of its amino acids.4. The polypeptide chain grows until a stop codon is reached, for which there are nocorresponding t('"s and the polypeptide chain is complete

(e) state thatmutations cause changes to the sequence of nucleotides in &'" molecules ;A - base pair deletion has serious consequences as it would cause a frameshift. "s thegenetic code is triplet *read in groups of bases+, it alters all amino acids that are coded forafter the mutation" 1- base pair deletion causes 5 amino acids to be lost" substitution changes one or possibly no amino acids

(f) explain how mutations can have beneficial, neutral or harmful effects on the way a protein functions;eneficial

The mutation changes the sequence of amino acids and therefore the phenotype, but thisgives the organism an advantageous characteristicE.g. 0aler s6in in more temperate climates absorbs more vitamin &

NeutralIt is a mutation in a non!coding region of the &'"It is a silent mutation! although the base triplet has changed, it still codes for the sameamino acid and so the protein is unchanged.

!armfulThe mutation changes the sequence of amino acids and therefore the phenotype, and theresulting characteristic is harmfulE.g. paler s6in in a hotter climate burns more easily

(g) state thatcyclic "70 activates proteins by altering their three!dimensional structure ;

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(h) explain genetic control of protein production in a pro"aryote using the lac operon;This involves both regulatory and structural genes.

(egulatory genes ma6e a repressor protein which is a transcription factor that switches astructural gene on or off#tructural genes ma6e enzymes, polypeptides or proteins#o the regulatory gene controls and affects the epression of structural gene

E. coli grown in a culture medium with no lactose can be placed in a growth medium with lactose."t first they cannot metabolise the lactose because they only have tiny amounts of the enzymes

needed to catalyse the reaction. " few minutes after the lactose is added, E. coli increases the rateof synthesis of these enzymes by about -888 times, so lactose must trigger the production of them. Itis the inducer.

9hen lactose is absent-. The regulator gene is epressed and the repressor protein is synthesised. Ithas two binding sites. )ne binds to lactose and one that binds to the operatorregion1. In binding to the operator region, it covers part of the promoter region where('" polymerase normally attaches. ('" polymerase cannot bind to the promoter region so the structural genes

cannot be transcribed into m('"3. 9ithout m('" the genes cannot be translated and the enzymes cannot besynthesised

9hen lactose is added-. lactose binds to the repressor protein1. It changes the shape *structure+ of the repressor protein. This change stops the repressor protein binding to the operator3. #o ('" polymerase is able to bind to promoter4. : and ; are transcribed and the m('" is made

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7eiosis and ?ariation

(a) describe, with the aid of diagrams and photographs, the behaviour of chromosomes during meiosis, and theassociated behaviour of the nuclear envelope, cell membrane and centrioles$ (Names of the main stages areexpected, but not the subdivisions of prophase);

7eiosis I0rophase I

-. The chromatin condenses and supercoils1. The chromosomes come together in their homologous pairs to form a bivalent.

Each member of the pair has the same genes at the same loci. Each pair consists of one maternal and one paternal chromosome. The non sister chromatids wrap around each other and attach at points called chiasmata3. They may cross over and swap sections of chromatids with each other4. The nucleolus disappears and the nuclear envelope brea6s down

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recessiveCharacteristic in which the allele responsible is only epressed in the phenotype is there isno dominant allele present. It is not epressed when heterozygous and the epression ismas6ed by the dominant allele

(c) explain the termslin"age

Genes for different characteristics that are present at different loci on the same chromosomeare lin6ed

crossing%over9here non!sister chromatids echange alleles during prophase I of meiosis

(d) explain how meiosis and fertilisation can lead to variation through the independent assortment of alleles;&eiosis'

Crossing over %shuffles$ alleles(andom distribution and subsequent segregation of maternal and paternal chromosomesin the homologous pairs during meiosis I leads to genetic reassortment(andom distribution and segregation of the chromatids at meiosis II leads to geneticreassortment(andom mutations

ertilisation(andom combinations of two sets of chromosomes, one from each of two genetically

unrelated individuals

(e) use genetic diagrams to solve problems involving sex lin"age and codominance;ex lin"age

e.g. Aaemophilia

The gene for haemophilia is carried on the B chromosome. 7ale offspring only have one copy of the Bchromosome, so if they have the allele for Aaemophilia, they will be affected

*odominancee.g. @lood type

If both the " and the @ alleles are present in the genotype, the phenotype will be "@! theyare co!dominant. The ) allele is recessive, so it will not be epressed in the phenotypeunless the alleles " or @ are not present

(f) describe the interactions between loci (epistasis)$ (+roduction of genetic diagrams is not required);Epistasis is the interaction of different gene loci so that one gene locus ma6es or suppresses theepression of another gene locus.The gene products are usually enzymes in a multi!enzyme *therefore multi!step+ pathway where the

product of one reaction is the substrate *starting point+ for the net.

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(ecessive EpistasisThe homozygous presence of a recessive allele prevents the epression of anotherallele at a second locus

E.g. flower colour in #alviaThe alleles for purple *@+ and pin6 *b+ can only be epressed inthe presence of the allele ". 9hen the genotype is aa!! thephenotype is white

&ominant Epistasis" dominant allele at one gene locus mas6s the epression of alleles at the second

gene locusE.g. feather colour in poultryIf the dominant allele " is present, the chic6ens will be whiteeven if the dominant allele of the second gene, @Db is present.The genotype must be aa@! for any colour to be epressed

(g) predict phenotypic ratios in problems involving epistasis;(ecessive epistasis in #alvia 3&ominant epistasis in 0oultry -

(h) use the chi%squared (-) test to test the significance of the difference between observed and expectedresults$ (.he formula for the chi%squared test will be provided);

) is observedE is epectedThe smaller the value of chi squared, the more certain we can be that that difference between observed andepected data is due to chance and is therefore not a significant difference.To calculate how significant the chi squared value is, a table is used. /sing n!- *where nF number of classes+degrees of freedom, and a 4 critical value, we can see if the value is due to chance.If the value is smaller than the value on the table, the null hypothesis can be accepted! any difference is dueto chance and therefore not significant. If the value is larger than the value on the table then the nullhypothesis is re2ected! any difference is significant and not due to chance.

(i) describe the differences between continuous and discontinuous variation;

&iscontinuous variation describes qualitative differences between phenotypes! they fall into clearlydistinguishable categories with no intermediates.

E.g. blood type is either ", @, "@ or )Continuous variation is quantitative differences between phenotypes! there is a wide range ofvariation within the population with no distinct catagories

E.g. height

(#) explain the basis of continuous and discontinuous variation by reference to the number of genes whichinfluence the variation;

&iscontinuous variation&ifferent alleles at a single gene locus have large effects on the phenotype.&ifferent gene loci have different effects on the trait

Continuous variation&ifferent alleles at the same gene locus have small effects&ifferent gene loci have the same, often additive effect on the trait" large number of gene loci may have a combined effect on the trait

(") explain that both genotype and environment contribute to phenotypic variation$ (No calculations ofheritability will be expected);

9hile an organism may have the genetic potential to achieve a certain characteristic, e.g. length ofcorn cob, the environment also has an influence. The corn cob may have the genetic potential to be-1cm long, but the plant may be short of water, light or certain minerals, meaning that the cob isshorter, as the environmental factors have limited the epression of the genes.

(l) explain why variation is essential in selection;#o that when the environment changes, there will be individuals that are better adapted, so theywill survive and reproduce passing on the advantageous alleles to their offspring and allowing thespecies to continue

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(m) use the !ardy/0einberg principle to calculate allele frequencies in populations;p is the frequency of the dominant allele "q is the frequency of the recessive allele apHq F - as everyone in the population has the alleles

q1is the frequency of the homozygous recessive genotype aap1is the frequency of the homozygous dominiant genotype ""1pq is the frequency of the heterozygous genotype "a-F p1H1pqHq1as everyone in the population has one of the genotypes

The frequency of aa can be measured. #uppose that the incidence is -.If q1F 8.8- then q F 8.8- F 8.-pH8.-F-pF 8.

#o, p1 F 8.1F 8.>-8.>-H1pqH8.8- F -

#o 1pq F -! *8.8- H 8.>-+F 8.->

#o, -> of the population are heterozygous "a

The Aardy!9einberg principle cannot be used to predict the epected frequencies of albino and non!albinoalleles in the worldwide zoo population of tigers because

the population is too small and there is no random mating as matings are arranged

(n) explain, with examples, how environmental factors can act as stabilising or evolutionary forces of naturalselection;

In unchanging conditions, stabilising selection maintains eisting adaptations and so maintainseisting allele frequencies.In changing conditions, directional selection alters allele frequencies." mutation may be disadvantageous in eisting conditions, and so is removed in stabilisingselection, but if the conditions change, the mutation might be advantageous and selected for,meaning that selection becomes an evolutionary force

(o) explain how genetic drift can cause large changes in small populations;Genetic drift is a change in allele frequency that occurs by chance because only some of the

organisms in each generation reproduce ie selection is happening. It is particularly noticeable when asmall number ofindividuals are separated from the rest of the large population. They form a small sample of theoriginal population and so are unli6ely to be representative of the large population$s gene pool.Genetic drift will alter the allele frequency still further.

(p) explain the role of isolating mechanisms in the evolution of new species, with reference to ecological(geographic), seasonal (temporal) and reproductive mechanisms;

If two sub!populations are separated from each other, they will evolve differently as they havedifferent selection pressures, so different alleles will be eliminated or increased within each subpopulation. Eventually the sub populations will not be able to interbreed and so will be differentspecies.

The sub populations may be split by various isolating mechanisms

Geographical barriers e.g. rivers or mountains#easonal barriers e.g. climate change throughout the year(eproductive mechanisms e.g. their genitals, breeding seasons or courtship ritualsmay be different

Isolating mechanisms involved in dogs evolving from wolves aregeographic ! wolves avoid human settlements but dogs are confined by humansbehavioural J dogs and wolves have different courtship ritualsmechanical ! wolves are large and some dogs are very smallgamete incompatibility J there is a possibility of different chromosome numbersseasonal D temporal J wolves and dogs have different breeding seasons

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(q) explain the significance of the various concepts of the species, with reference to the biological speciesconcept and the phylogenetic (cladistic1evolutionary) species concept;

.he biological species concept" species is %a group of similar organisms that can interbreed and produce fertile offspringand it reproductively isolated from such other groups$

@ut'ot all organisms reproduce seually7embers of the same species can loo6 very different to each other7ales can loo6 different to females

Isolated populations may appear to be very different from each other.he phylogenetic species concept" species is %a group of organisms that have similar morphology, physiology, embryologyand behaviour, and occupy the same ecological niche$. This classification shows theevolutionary relationships, or phylogeny. The phylogenetic linage is called a clade.

In terms of different breeds od dog and wolvesbiological species concept

members of same species need can interbreed to produce fertile offspringnot all dog breeds can do this therefore not same speciesdog and wolf can so they should be same species

phylogenetic species conceptdogs and wolves are a monophyletic group

genetic differences between dogs and wolves are smallgene flow between wolves big dogs little dogs

(s) compare and contrast natural selection and artificial selection;Natural selection

The organisms best adapted for their environment are more li6ely to survive and pass onthe favourable characteristics to their offspring)ver time, the frequency of this new allele will increase in the gene pool

Artificial selectionAumans select the organisms with the useful characteristicsAumans allow those with useful characteristics to breed and prevent the ones without thecharacteristics from breedingThus, humans have a significant impact on the evolution of these populations or species

In selective breeding. more females than males may be used because males can father many offspringand mate several females whereas females produce only a few offspring. This means that morefemales *than males+ are needed to maintain the numbers in each generation

(s) describe how artificial selection has been used to produce the modern dairy cow and to produce breedwheat (.riticum aestivum)

2airy cowCharacteristics selected for

large yield *volume+ of mil6long lactation periodhigh mil6 quality large udders or the correct udder shape *for mil6ing machine+

resistance to disease *eg mastitis+ or effective immune systemcalm temperament

0rocess of selectionEach cow$s mil6 yield is measured and recordedThe progeny of bulls is tested to find out which bulls have produced daughters with highmil6 yields)nly a few good!quality bulls need to be 6ept are the semen from one bull can be used toartificially inseminate many cows#ome elite cows are given hormones so they produce many eggsThe eggs are fertilized in vitro and the embryos are implanted into surrogate mothersThese embryos could also be clones and divided into many more identical embryos

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read wheat9heat can undergo polyplody! the nuclei can contain more than one diploid set ofchromosomes. 7odern bread wheat is heaploid, having 31 chromosomes in the nucleusof each cell, meaning that the cells are bigger.

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Biotechnology and Gene TechnologiesCloning in Plants and Animals

(a) outline the differences between reproductive and non%reproductive cloning;(eproductive cloning is the production of offspring which are genetically identical to either themother *nuclear transfer+, or the other offspring *splitting embryos+'on!reproductive cloning is the use of stem cells in order to generate replacement cells, tissues ororgans which may be used to treat particular diseases or conditions of humans

(b) describe the production of natural clones in plants using the example of vegetative propagation in elm trees;7olecular evidence has shown that all specimens of the English Elm tree, /lmus procera, forma genetically isolated clone. English Elms developed from a variety of elm brought to @ritain from(ome in the first century ".&. "lthough English Elm trees ma6e pollen, they rarely produce seeds.Instead they spread by developing structures 6nown as suc6ers from their roots. Each suc6er cangrow into a new tree. This tendency of elms to create suc6ers has been eploited by humans, whohave separated the suc6ers, with roots attached, and used them to plant hedges and establish newwoodlands.The English Elm clone is genetically isolated from other varieties of elm because they do not produceseeds and they only reproduce aseuallyThe production of the suc6ers is an eample of vegetative propagation.In -

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(e) describe how artificial clones of animals can be produced;'uclear transfer

" nucleus from an adult differentiated cell is placed in an enucleated egg cell. The egg thengoes through the stages of development using the genetic information from the insertednucleus

#plitting embryosCells from a developing embryo are separated out, with each one going on to produce aseparate, genetically identical organism

(f) discuss the advantages and disadvantages of cloning animals

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Biotechnology

a) state thatbiotechnology is the industrial use of living organisms *or parts of living organisms+ to producefood, drugs or other products

(b) explain why microorganisms are often used in biotechnological processes;Grow rapidly in favourable conditions, with a generation time of as little as 8 minutes)ften produce proteins or chemicals that are given out into the surrounding medium and can beharvested

Can be genetically engineered to produce specific productsGrow well are relatively low temperatures, much lower than those required in the chemicalengineering of similar processesCan be grown anywhere in the world and are not dependent on climateTend to generate products that are in a more pure form than those generated via chemicalprocessesCan often be grown using nutrient materials that would otherwise be useless or even toic tohumans

(c) describe, with the aid of diagrams, and explain the standard growth curve of a microorganism in a closedculture;

Kag phase

)rganisms are ad2usting to the surrounding conditions. This may mean ta6ing in water, cellepansion, activating specific genes and synthesising specific enzymes. The cells are active

but not reproducing so population remains fairly constant. The length of this perioddepends on the growing conditionsKog phase

The population size doubles each generation as each individual has enough space andnutrients to reproduce. In some bacteria the population can double every 18!8 mins. Thelength of this phase depends on how quic6ly the organisms reproduce and ta6e up theavailable space and nutrients

#tationary phase'utrient levels decrease and waste products li6e Carbon &ioide and other metabolitesbuild up. Individual organisms die at the same rate at which new individuals are beingproduced. In an open system this would be the carrying capacity

&eath phase'utrient ehaustion and increased levels of toic waste products and metabolites leads to

the death rate increasing above the reproduction rate. Eventually all of the organisms willdie in a close system

(d) describe how en3ymes can be immobilised;"dsorption

Enzyme molecules are mied with the immobilising support and bind to it due to acombination of hydrophobic interactions and ionic lin6s.

Covalent bondingEnzyme molecules are covalently bonded to a support, often by covalently lin6ing enzymestogether and to an insoluble material using a cross!lin6ing agent

EntrapmentEnzymes are trapped, for eample in a gel bead or networ6 of cellulose fibres. #ubstrateand product molecules can pass through the material to the enzyme, but the enzyme

cannot pass through to the solution7embrane separation

Enzymes are physically separated from the substrate miture by a partially permeablemembrane. The substrate and product molecules can pass through the membrane, but theenzymes cannot

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(e) explain why immobilised en3ymes are used in large%scale production;Enzyme can be removed to be used againEnzyme leaves a pure*r+ product ie cheaper D easier, downstream processingEnzyme is more stable, efficient and wor6s better because it is less susceptible to pA andtemperature changes or etremes

(f) compare and contrast the processes of continuous culture and batch culture;

(g) describe the differences between primary and secondary metabolites;0rimary metabolites are substances produced by an organism as part of its normal growth. Theproduction of primary metabolites matches the growth in population of the organism#econdary metabolites are substances produced by an organism that are not part of its normalgrowth. The production of secondary metabolites usually begins after the main growth period of

the organism and so does not match the growth in population of the organism

(h) explain the importance of manipulating the growing conditions in a fermentation vessel in order to maximise theyield of product required;

The growing conditions can be manipulated and controlled in order to ensure that the microorganismis growing in its optimum conditions, and so the yield can be maimised

TemperatureToo hot and enzymes will be denatured, too cold and growth will be slowed

Type and addition of nutrientThis depends on whether the product is a primary or a secondary metabolite

)ygen concentration7ost organisms are grown under aerobic conditions so there must be a sufficientsupply of oygen for respiration to prevent the unwanted products of anaerobicrespiration and a reduction in growth rate

pAChances in pA can reduce the activity of enzymes and therefore reduce growthrates

salt concentrationaffects osmosis by changing the water potential

waste gases *C)1+must be removed to reduce pressure and prevents eplosion of fermenter

speed of stirrercontrolled to ensure even miing and an even temperature

(i) explain the importance of asepsis in the manipulation of microorganisms$"sepsis is the absence of unwanted microorganisms which could

Compete with the culture microorganisms for nutrients and space(educe the yield of useful products from the culture microorganismsCause spoilage of the product0roduce toic chemicals&estroy the culture microorganisms and their products

0asteurisation 6ills harmful microbes and denatures enzymes

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(a) outline the steps involved in sequencing the genome of an organism;Genomes are mapped to identify which part of the genome that they come from. Information thatis already 6nown is used, such as the location of microsatellites#amples of the genome are mechanically sheared into smaller sections of around -88,888 basepairsThese sections are places in separate @acterial "rtificial Chromosomes *@"Cs+ and transferred to E.coli cells. "s the cells are grown in culture, many copies of the sections are produced! referred to asClone KibrariesCells containing specific @"Cs are ta6ing and cultured. The &'" is etracted from the cells and

restriction enzymes used to cut it into smaller fragments. The use of different restriction enzymeson a number of samples gives different fragment typesThe fragments are separated using electrophoresisThe many copies of the fragments are put in a reaction miture containing &'" polymerase, free&'" nucleotides and primers, with some of the nucleotides containing a florescent mar6er.The primer anneals to the $ end of the template strand, allowing &'" polymerase to attach&'" polymerase adds free nucleotidesIf a modified nucleotide is added, the polymerase enzyme is thrown off and the reaction stops onthat template strand"s the reaction proceeds, many molecules of &'" are made. The fragments generally differ in size,as different numbers of nucleotides will have been added"s the strands run through a machine, a laser reads the colour sequence. The sequence of colours,and therefore the sequence of bases can then be displayed

(b) outline how gene sequencing allows for genome%wide comparisons between individuals and between species;The identification of genes for proteins found in all or many living organisms gives clues to therelative importance of such genes to life

Comparing the &'" of different species shows evolutionary relationships7odelling the effects of changing &'" can be carried outComparing genomes from pathogenic and similar but non!pathogenic organisms can be usedto identify the genes or base!pair sequences that are more important in causing the disease,so more effective drugs can be developedThe &'" of individuals can be analysed to reveal the presence of alleles associated withparticular diseases

(c) define the term recombinant 2NA;

" section of &'", often in the form of a plasmid, which is formed by 2oining &'" sections from twodifferent sources

(d) explain that genetic engineering involves the extraction of genes from one organism, or the manufacture ofgenes, in order to place them in another organism (often of a different species) such that the receivingorganism expresses the gene product;

The required gene is obtained" copy of the gene is placed in a vectorThe vector carries the gene to the recipient cellThe recipient epressed the gene through protein synthesis

(e) describe how sections of 2NA containing a desired gene can be extracted from a donor organism usingrestriction en3ymes;

/se a restriction enzyme *endonuclease+ to cut out the gene *&'"+ coding for the protein requiredor to fragment *digest+ &'" and use a gene probeor )btain m('" and then use reverse transcriptase to ma6e c&'"or #equence the protein and wor6 out base code them ma6ethis &'" sequence

This produces stic6y ends

(f) outline how 2NA fragments can be separated by si3e using electrophoresis;&'" samples are treated with restriction enzymes to cut them into fragmentsThe &'" samples are placed into cells cut into the negative electrode end of the gelThe gel is immersed in a tan6 of buffer solution and an electric current is passed through thesolution for a fied period of time, usually around two hours&'" is negatively charged because of its phosphoryl groups. It is attracted to the positiveelectrode.

#horter lengths of &'" move faster than longer lengths, so move further in the fied time thatcurrent is passed through the gelThe position of the fragments can be shown by using a dye that stains &'" molecules

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(g) describe how 2NA probes can be used to identify fragments containing specific sequences;" &'" probe is a short single!stranded section of &'" that is complementary to the section of &'"being investigated. The probe is labelled in one of two ways/sing a radioactive mar6er so that the location can be revealed by eposure tophotographic film/sing a fluorescent mar6er that emits a colour on eposure to /? lightCopies of the probe are added to a sample of &'" fragments and will anneal to any fragmentwhere a complementary base strand is present

(h) outline how the polymerase chain reaction (+*R) can be used to ma"e multiple copies of 2NA fragments;The &'" sample is mied with a supply of &'" nucleotides and &'" polymeraseThe miture is heated to 4LC. This brea6s the hydrogen bonds holding the strands together, so thesamples are now single stranded0rimers *short lengths of single stranded &'"+ are addedThe temperature is reduced to 44LC to allow the primers to bind and form small sections of doublstranded sections&'" polymerase can bind to these double!stranded sectionsThe temperature is raised to 51LC. The enzyme etends the double stranded section by addingnucleotides to the unwound &'"9hen the &'" polymerase reaches the other end of the &'", a new, double stranded &'"molecule is generatedThe whole process can be repeated many times so the amount of &'" increase eponentially

(i) explain how isolated 2NA fragments can be placed in plasmids, with reference to the role of ligase;Cut open the plasmid using same restriction enzyme *as used to cut out the &'"+"llow the base pairing of stic6y ends *annealing+Then 2oin the sugar!phosphate bac6bones using &'" ligaseThe result is a recombinant

(#) state other vectors into which fragments of 2NA may be incorporated;Kiposomes?iral &'" e.g. bacteriophagesAybrid vectors with the propertied of both plasmids and bacteriophages

(") explain how plasmids may be ta"en up by bacterial cells in order to produce a transgenic microorganism

that can express a desired gene product;7i the plasmid with bacteria and use Ca1H ions or lower the temp to freezing before quic6ly raisingto 38LC.The plasmid now transformed

(l) describe the advantage to microorganisms of the capacity to ta"e up plasmid 2NA from the environment;Genetic variation

In the case of antibiotic resistance genes, survival in the presence of these chemicals

(m) outline how genetic mar"ers in plasmids can be used to identify the bacteria that have ta"en up arecombinant plasmid;

'ot all bacteria ta6e up the plasmid.#ome of the bacteria ta6e up a plasmid that has 2oined with a copy of the gene, but 2ust

sealed up on itself to reform the original plasmid" plasmid is used which carries genes which ma6e any bacteria receiving them resistance to twodifferent antibiotics. The resistance genes are 6nown as genetic mar6ersThe plasmids are cut by an enzyme which has its restriction site in the middle of one of theresistance genes *G-+, so that if the required gene is ta6en up, the resistance gene for one of theantibiotics does not wor6, but it other *G1+ doesThe &'" is placed in the plasmids, and the plasmids in bacteria cellsThe bacteria are grown on an agar plate to produce a colony#ome cells from the colonies are transferred onto agar that has been made from the antibiotic thatremains intact, meaning that all bacteria that have ta6en up a plasmid will grow.#ome cells are transferred onto agar that has been made from the second antibiotic. )nly thebacteria which have ta6en up a plasmid that is not recombinant will grow.@y 6eeping trac6 of which colonies are which, we now 6now that any bacteria which grow on the

agar containing the first antibiotic, but not on the agar containing the second antibiotic must haveta6en up the recombinant plasmidThe required colonies can now be identified and be grown on a large scale

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(n) outline the process involved in the genetic engineering of bacteria to produce human insulin;-. m('" from human insulin is etracted from pancreas cells1. (everse transcriptase uses m('" as a template to ma6e single stranded c&'", and this is madedouble stranded by &'" polymerase. " single sequence of nucleotides *GGG+ is added to each end of the &'" to ma6e stic6y ends3. 0lasmids are cut open when a restriction enzyme4. Cut plasmids have a single sequence of nucleotides *CCC+ asses to each to ma6e stic6y ends

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0cosystems and ustaina$ility0cosystems

(a) define the term ecosystem;"ll living organisms and all the non!living components in a specific habitat, and their interactionsEcology is the study of the interactions between organisms and their environment

(b) state thatecosystems are dynamic systems;

(c) define the terms biotic factor and abiotic factor, using named examples;@iotic factor

Aow living organisms affect each otherNood supply, predation, disease

"biotic factorThe effect of non!living components of the ecosystem

pA, temperature, soil type

(d) define the termsproducer*

"n organism that converts simple inorganic compounds into comple organic compoundsconsumer

"n organism that gains energy from compl organic matter

decomposer"n organism that feeds on waste from other organisms, or dead organisms

trophic levelEach feeding level in a food chain

(e) describe how energy is transferred though ecosystems;Energy is transferred by organisms consuming each other. This is shown in a food web, with thearrows representing the flow of energy between organisms

(f) outline how energy transfers between trophic levels can be measured;The energy content of samples of organisms from each trophic level is measuredEach sample is dried in an oven

The samples are weighedThe samples are burned in a bomb calorimeter in oygenThe energy produced passes to a 6nown mass of water and the temperature rise of the water ismeasuredAow much energy is released per gram is calculated and converted to 6O

(g) discuss the efficiency of energy transfers between trophic levels;Energy is lost between trophic levels because animals never eat all of the available food and cannotdigest all of the food they eat.They also use energy to respire, lose heat energy to the surroundings and lose energy in urine andfaeces

'et primary productivity is different in different ecosystems because

tropical ecosystems compared to temperate ones have higher temperatures and more sunlight *daysare longer+ so they photosynthesise faster and form more biomass and therefore energywoodland or rainforest ecosystems compared to grassland have a greater compleity with greaterbiodiversity and so more niches. This means competition for space is less limiting

(h) explain how human activities can manipulate the flow of energy through ecosystems;Increasing productivity of producers through

#oil improvementIrrigationNertilisers(emoval of

Competing weeds&amaging pathogens and pests

Increasing productivity of producers and consumers through selective breeding or geneticengineering#heltering organisms from damaging environmental factors

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(i) describe one example of primary succession resulting in a climax community;" sand dune

0ioneer plants such as sea roc6et colonies the sand 2ust above the high water mar6. Thesecan tolerate salt water spray, lac6 of fresh water and unstable sand9ind!blown sand builds up around the base of these plants, forming a %mini$ sand dune. "sthe plants die and decay, nutrients accumulate in this mini dune. "s they dune gets bigger,plants li6e sea couch grass colonise it, which has underground stems to help stabilise thesand9ith more stability and accumulation of more nutrients, plants li6e marram grass start to

grow. 7arram grass shoots trap windblown sand and, as the sand accumulated, the shootsgrow taller to stay above the growing dune, thus trapping more sand."s the sand dune and nutrients build up, other plants colonise the sand. 7any aremembers of the bean family, which have nodules in their roots which contain bacteriawhich convert nitrogen to nitrates. 9ith nitrates available, more species colonise thedunes, stabilising them further

(oc6"lgae and lichens begin to living on the bare roc6Erosion of the roc6 and build up of dead and rotting organisms produces enough soil forlarger plants, such as mosses and fern to growKarger plants succeed the small plants until the clima community is reached

(#) describe how the distribution and abundance of organisms can be measured, using

line transects,)n a line across the habitat and record every species touching the line, and their position. #pecies areidentified using a 6ey and recorded in a pre!prepared table.

belt transectsPuadrats places sequentially along a line transect

quadrats" square frame is placed at random in the habitat. Each species present is identified, andthe cover or "CN)( recorded for each species *abundant, common, frequent, occasional, rare+

point quadrats;Nrames with long pins. Kowered vertically at random. Each species which touches a pin isrecorded, along with the number of times it is touched

Kadybirds would be sampled using sweep netting or beating trees and bushes or using a pooter.

(") describe the role of decomposers in the decomposition of organic material;&ecomposers are organisms that return inorganic minerals from the bodies of dead organisms to theabiotic environment.&ecomposers feed on waste from other organisms. They recycle materials such as Carbon and'itrogen. If they did not brea6 down dead organisms, energy and valuable nutrients would remainin the dead organism

(l) describe how microorganisms recycle nitrogen within ecosystems$ (6nly Nitrosomonas, Nitrobacter andRhi3obium need to be identified by name)$

0lant protein is converted to animal protein when animals eat plants. The animal digests *hydrolyses+the protein to amino acids. These amino acids move into the blood and then cells. They are used inthe synthesis of proteins *translation+.

0lant and animal protein becomes humus in soil when they die or leaves are lost. They then decay."nimals also ecrete urine and defaecate.'1 'A3H *nitrogen gas converted to ammonium compounds+

'itrogen is fied by bacteria such as (hizobium that live in root nodules of legumes *peas,beans+. They have a mutalistic relationship with the plant! they fi the nitrogen for theplant and the plant provides the bacteria with carbon compounds *glucose+There are proteins which absorb oygen, 6eeping conditions anaerobic, so thatnitrogen reductase can reduce nitrogen gas to ammonium ions

'A3 ')1! *ammonium compounds converted to nitrite ions+"mmonium ions are released by bacteria in the putrefaction of proteins found in dead orwaste organic matter'itrosomonas bacteria obtain their energy by oidising "monium ions to 'itrites underaerobic conditions

')1! ')!*nitrate ions converted to nitrate ions+'itrobacter obtain their energy by oidising 'itrites to 'itrates under aerobic conditions'itrosomonas and nitrobacter are nitrifying bacteria. 0lants absorb the nitrates from the soil toma6e amino acids, proteins, enzymes, &'", ('" and chlorophyll

')! '1 *nitrate ions converted to nitrogen gas+

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Po"ulations and sustaina$ility

(a) explain the significance of limiting factors in determining the final si3e of a population;" habitat cannot support a population large than its carry capacity because of limiting factors whichplace a limit on population size.The limiting factors may include

(esourcesNood9ater

Kight)ygen'esting sites#helterEffects of other species0redators0arasitesIntensity of competition for resources

Etinction is more li6ely if a species is rare initially it has a slower reproductive rate and its prey numbershave reduced.

(b) explain the meaning of the term carrying capacity;The maimum population time that can be maintained over a period of time in a particular habitat

" population does not increase in size indefinitely due to limiting factors determining a carryingcapacity. There will be intraspecific competition for food and nesting sites and interspecificcompetition other species. Karger populations attract more predators as well as parasites anddiseases spreading more easily

(c) describe predator/prey relationships and their possible effects on the population si3es of both the predatorand the prey;

9hen the predator population gets bigger, more prey are eatenThe prey population then gets smaller, leaving less food for the predators9ith less food, fewer predators can survive, and their population size decreases9ith fewer predators, fewer prey are eaten, and their population size increases9ith more prey, the predatory population gets bigger, and the cycle continues

(d) explain, with examples, the terms interspecific and intraspecific competition;7nterspecific competition

Competition between individual of different species can affect both the population sizeand the distribution of a species in an ecosystem as no two species can occupy the sameniche

(ed v Grey squirrels compete for the same food. The red squirrel outcompetes the grey inconifer forests, but the grey squirrel out competes the red in forests with less than 54conifers

7ntraspecific competitionCompetition between individuals of the same species

If food supply becomes a limiting factor, the individuals best adapted to obtainingfood will survive and reproduce, whereas those less well adapted will die out andfail to pass on their genes.

(e) distinguish between the terms conservation and preservation;Conservation is the maintenance of biodiversity, but the area can still be sustainably eploited0reservation protects species by leaving their habitat untouched

(f) explain how the management of an ecosystem can provide resources in a sustainable way, with reference totimber production in a temperate country;

#elective felling#ome mature trees, diseased trees and unwanted species are harvested, leaving othertrees to develop and distribute seeds to fill the gaps. This leads to a variety of heights, branchlengths etc and therefore increases biodiversity.

#trip felling#mall patches, or strips, of forest are cleared completely, leaving other patches untouched.

Karge areas are not felled at the same time, so loss of species and soil erosion are avoidedand shade is maintained. It also limits the disturbance by machinery

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(otational felling&escribes felling of areas or individual trees over time allowing regeneration and thereforesustainability. Nelled trees are replanted. The habitat is preserved and nesting sites are not tooheavily disrupted

CoppicingD0ollardingTrees are cut down, leaving stumps from which new shoot develop. These have a welldeveloped root system and so grow fast. "fter a few years the shoots are cut and yieldpoles or wood for burning as a fuel. Can be repeated indefinitely and is so sustainable.0ollarding is similar but the stumps are much higher 3m or so. This prevents deer from eating

the regrowth and new 2uicy shoots.

(g) explain that conservation is a dynamic process involving management and reclamation;7aintaining biodiversity in dynamic ecosystems requires careful management to maintain a stablecommunity or even reclaim an ecosystem by reversing the effects of human activity#ome management strategies may include

(aising the carrying capacity by providing etra food7oving individuals to enlarge populations, or encouraging natural dispersion of individualsbetween fragmented habitats by developing dispersal corridors of appropriate habitat(estricting dispersal of individuals by fencingControlling predators and poachers?accinating individuals against disease0reserving habitats by preventing pollution or disruption, or intervening to restrict the

progress of succession

(h) discuss the economic, social and ethical reasons for conservation of biological resources;There is anaesthetic or recreational value *they loo6 nice+It may bring in *eco+tourism ! important to the economyIt preserves biodiversity and therefore genetic diversity which may help stop etinctionThere may be interactions between species that are needed to preserve whole habitat9e need to preserve gene pool as a species could be useful in the future for medicine orgenetic engineering *particularly applies to the rainforest+9e should support indigenous peoples and aloe them to continue their lifestyleIt may prevent the effects of deforestation on the atmosphere, climate or soil'atural predators of pests can act as biological control agents9ild insect species pollinate crop plants

(are breeds are maintained on farms becauseThey are a genetic resource as they have different alleles that could be used forgenetic engineering, genetic modification, artificial selection, selective breedingif conditions change in the futureEample of useful traits would be disease resistance or hardiness as well as more orbetter quality wool or meat(are breeds also maintain biodiversity and a large gene pool

(i) outline, with examples, the effects of human activities on the animal and plant populations in the5alapagos 7slands

In ->8 the population of the Galapagos Islands was 4888, and about 3888 tourists visited everyyear. In 1884, the population was 1>,888, and -88,888 tourists visited every year.

&ramatic increase in population size has placed huge demand on water, energy andsanitation services7ore waste and pollution have been producedThe demand for oil has increased188- oil spill had an adverse effect on marine and costal ecosystemsIncreased pollution, building and conversion of land for agriculture has caused destructionand fragmentation of habitats#pecies have been harvested faster than they could replenish themselves.

Giant tortoises were ta6en to be eaten on long voyagesNishing for eotic species of fish has decimated the population&epletion of sea cucumbers has had a drastic effect on under!water ecologyInternational mar6et for #har6!fin has led to the deaths of around -48,888 shar6seach year

Aumans have introduced many non!indigenous speciesThe red quinine tree spread rapidly and outcompetes the native species. Itspresence has changed the landscape from mostly low scrub and grassland to aclosed canopy forest. 7any native animals have lost their nesting sites

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Goatseat species unique to the islands,outcompete giant tortoises for grazing,tramples on tortoise nesting sitestransforms forests into grassland, causing soil erosion

Cats hunt a number of indigenous species

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es"onding to the 0nvionmentPlant es"onses

(a) explain why plants need to respond to their environment in terms of the need to avoid predation and abioticstress;

To cope with changing conditions and avoid abiotic stressTo maimise photosynthesis by obtaining more light, more water and more mineralsTo avoid herbivory and grazingTo ensure the germination of its seeds in suitable conditions

(b) define the term tropism;" directional growth response in which the direction of the response is determined by the directionof the eternal stimulus

(c) explain how plant responses to environmental changes are co%ordinated by hormones, with reference toresponding to changes in light direction;

The presence of auin promotes the active transport of hydrogen ions through the "T0ase enzyme,into the cell wall. This decreases the pA and allows optimum conditions for the wall looseningenzymes to wor6. These enzymes brea6 bonds within the cellulose, so the walls become less rigidand can epand as the cells ta6e in water." shoot bends towards a light source because auin is transported from to the tip of the shoot to thecells in the shade, allowing the cells to ta6e up more water and elongate.

@ecause the cells elongate more on the shaded side than the side in the light, the shoot bendstowards the light source

9hen a plant becomes overcrowded, auin is released and causes phototropism as shoots, bendtowards the light. Etiolation means that the plant grow taller. Climbing plants will climb up and overother plants, a response due to thigmotropism. (oots will grow towards water and therefore minerals.#ome plants *eg dandelion+ will secrete chemicals from their roots that 6ill other plants.

(d) evaluate the experimental evidence for the role of auxins in the control of apical dominance and gibberellinin the control of stem elongation;

Auxins"pical dominance is when the growing apical bud at the tip of the shoot inhibits thegrowth of the lateral buds further down the shoot

"uins are produced in the tip of the main shoot. They inhibit the growth of side shoots9hen the tip of the main shoot is removed *eg by an animal+, the side shoots grow.This shows that auin is produced in the ape of the main shoot and transported to lateralbuds to inhibit their growth. 9hen there are low concentrations of auin in the sideshoots, their growth is not inhibited, and so they can grow.This is also shown where, as the plant grows taller, the lateral buds at the bottom of theplants start to grow larger! they are further away from the main shoot, so there is a lowerconcentration of auin and their growth is less inhibited

5ibberellinsIf genetically dwarf plants are treated with Gibberellic acid, the stems elongateconsiderably

(e) outline the role of hormones in leaf loss in deciduous plants;

Cyto6inins stop the leaves of deciduous trees senescing by ma6ing sure that the leaves act as a sin6for phloem transport, so the leave is guaranteed a good supply of nutrientsIf cyto6inin production drops, the supply of nutrients dwindles and senescence begins#enescence causes auin production at the tip of the leaf to dropThis ma6es the cells in the abscission zone more sensitive to ethene" drop in auin concentration causes an increase in ethene productionThis increases production of cellulase, which digests the walls of the cells in the abscission zone,eventually separating the petiole from the stem

(f) describe how plant hormones are used commercially0roducing seedless fruits *grapes+"s weed6illers"s rooting powder to grow cuttings *used in tissue culture+To control fruit ripeningTo controls fruit dropTo restrict hedge growthTo preserve cut flowers and green vegetables *stop them going yellow+To produce longer stal6s on grapes

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To promote seual maturity in conifersTo promote late flow in rubber plantsTo promoting seual maturity in female cucumber plantsTo produce longer nodes in sugar caneTo restrict growth in chrysanthemums

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Animal es"onses

(a) discuss why animals need to respond to their environment;"nimals need to respond to their environment to stay alive. This is done using nerves andhormones, to control responses ranging from muscle actions to run away from a predator, to finecontrol of balance, posture and temperature regulation.

(b) outline the organisation of the nervous system in terms of central and peripheral systems in humans;'ervous system

Central 0eripheral#omatic "utonomic#ympathetic 0arasympathetic

C'# is the brain and spinal cord made up of intermediate neurones. It has a coordinating role andmany synapses 0eripheral is made up of nerves from sense organs, to muscles and to glands. It is made of sensoryand motor neurones and has a role in sensing stimuli and controlling effectors. It conducts impulsesto and from the C'# and includes both the somatic and autonomic systems *sympathetic andparasympathetic+

(c) outline the organisation and roles of the autonomic nervous system;#ympathetic 'ervous #ystem

7ost active in times of stressThe neurones of a pathway are lin6ed at a ganglion 2ust outside of the spinal cord.0re!ganglion neurones are very short0ost!ganglion neurones secrete noradrenaline at the synapse between neuroneand effectorEffects of action include

Increased heart rate0upil dilationIncreased ventilation rate

0arasympathetic 'ervous #ystem7ost active in sleep and relaationThe neurones of a pathway are lin6ed at a ganglion within the target tissue, so pre!ganglionneurones vary in length

0ost ganglion neurones secrete acetylcholine as the neurotransmitter at the synapse betweenneurone and effectorEffects of action include

&ecreased heart rate0upil dilation&ecreased ventilation rate

(d) describe, with the aid of diagrams, the gross structure of the human brain, and outline the functions of thecerebrum, cerebellum, medulla oblongata and hypothalamus;

*erebrumControl of all higher order processes such as memory, language, emotions, thin6ing andplanning *eg clapping hands+

*erebellum

Control and coordination of movement and posture *eg automatically correcting balance whenriding a bicycle+

&edulla 6blongataControl of breathing, heart rate *rate of contraction of cardiac muscle+ and smooth muscle ofthe gut

!ypothalamusControl of the autonomic nervous system and some endocrine glands

(e) describe the role of the brain and nervous system in the co%ordination of muscular movement;The conscious decision to move voluntarily is initiated in the cerebellum. 'eurones from thecerebellum carry impulses to the motor areas so that motor output to the effectors can be ad2ustedappropriately in these requirements

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(f) describe how co%ordinated movement requires the action of s"eletal muscles about #oints, with reference tothe movement of the elbow #oint;

Coordinated and appropriate movement requires the controlled action of s6eletal muscles about2oints. This can be seen in the movement of the elbow 2oint

-. Impulses arriving at the neuromuscular 2unction cause vesicles to fuse with the presynapticmembrane and to release acetylcholine into the gap1. "cetylcholine binds to receptors on the muscle fibre membrane *sarcolemma+ causingdepolarisation. &epolarisation wave travels down tubules *T system+

3. T system depolarisation leads to Ca1H release from stores in sarcoplasmic reticulum4. Ca1H binds to proteins in the muscle, which leads to contraction

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(") state that responses to environmental stimuli in mammals are co-ordinated by nervous and endocrinesystems;

(l) explain how, in mammals, the 4fight or flight8 response to environmental stimuli is co%ordinated by thenervous and endocrine systems$

#ensory neurons from the somatic nervous system carry impulses from receptors to thesensory areas of the cerebrum of the brain, giving information about the danger in theenvironment

sympathetic *motor neurones+ nervous system is stimulated causing the neurotransmitter

noradrenaline to be released at neuromuscular 2unctions adrenaline is secreted and released into blood from the adrenal medulla adrenaline and noradrenaline bind to receptors on the target tissue #" node increases rate of firing the heart beats faster the heart beats more forcefully blood flow is altered to increase blood pressure blood flow to the gut and s6in is reduced thus reducing gut secretions and ma6ing the s6in pale smooth muscle in the gut relaes and peristalsis slows down smooth muscle in airways relaes and airways widen pupils dilate intercostal muscles and diaphragm contract faster blood flow to s6eletal muscles increases so s6eletal muscles are primed for action

Night or flight in a dog would cause ears to be laid bac6 and pupils dilated. It would adopt a tensedand lower posture with the hair on its nec6 standing up. Its mouth would be open, showing its teethand its tail standing up.

The following table shows how different organs function differently in a calm and frightened mammal

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Animal Behaviou(a) explain the advantages to organisms of innate behaviour;

It does not need to be learnedIt has immediate survival value for a young, ineperienced animal in a dangerous situationIt is appropriated for invertebrates with a short live span that do not have time to learnIt required few neuronesIt is li6ely to be appropriate for the animal$s habitat, as the alleles controlling it will have beensub2ect to natural selection

(b) describe escape reflexes, taxes and "ineses as examples of genetically%determined innate behaviours;Innate behaviour is instinctive and inherited. It follows a rigid, fied pattern and is so infleible andstereotyped *the same in all members of a species+. It is automatic and does not require thought orlearning

9scape reflexes" particular stimulus brings about an automatic response, the function of which is to avoidpredators. Earthworms withdraw underground in response to vibrations in the ground

.axes" directional movement in response to an eternal stimulus. 9oodlice move away fromlight to be less visible to predators and less liable to desiccation

:ineses

" movement in response to an eternal stimulus. The rate of movement is related to theintensity, but not the direction, of a stimulus. 9hen woodlice are placed in dryDbrightconditions, they will move around rapidly and randomly until they are in more suitableconditions

(c) explain the meaning of the term learned behaviour;@ehaviour that is changed, altered and learnt by eperience. It requires memory, reinforcement andpractice. The behaviour is variable in members of the same species.

(d) describe habituation, imprinting, classical and operant conditioning, latent and insight learning as examplesof learned behaviours;

!abituation"nimals response to certain stimuli lessens over time because repeated eposure to the

stimulus results in neither reward or punishment. It avoids wasting energy in ma6ing escaperesponses to non!harmful stimuli. egs sea anemones respond to touch by withdrawing theirtentacles. )n repeated stimulation the response is less and the enaemone does not withdrawits tentacles.

7mprinting;oung animals being associated with another organism, usually the parent. "fter that, theywill only follow and learn from ob2ects that loo6 li6e the first ob2ects. This helps the younglearn s6ills from the parents

*lassical conditioning" form of adaptive learning in which the innate response is modified. The animal learns torespond to a stimulus that is different from the usual stimulus

6perant conditioning" form of adaptive learning in which an animal learns to carry out a particular action in

order to receive a reward or avoid an unpleasant eperience . eg a dog begs and is rewardedwith food. )ver time the dog will beg more and more

atent learning@ehaviour that is not directed towards a particular outcome. "nimals eplore newsurrounding and learn information that has no apparent value at the time, but may beuseful at some time.

7nsight learning" form of learning in which an animal integrates memories of two or more earlier actionsto produce a new response or gain a reward. The organism has the ability to thin6 andreason in order to solve problems or deal with situations that do not resemble simplefied, refle responses or the need for repeat trial and error

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(e) describe, using one example, the advantages of social behaviour in primates;In chim"an3ees* goillas* oang-utans* monkeys* lemus o a"esbehaviour includes

dominance and hieachy inteactions such as "layallogooming one goilla gooming anothe/communication vocal* facial and "ostual/"assing on of cultual and tool-using kno&ledge"olonged and fequent mothe-infant inteactions

the $enefits ae to $oth the gou" and the individual and include im"oved access to food esouces and

mates as &ell as the eduction of disease and "aasites

(f) discuss how the lin"s between a range of human behaviours and the dopamine receptor 2R2< maycontribute to the understanding of human behaviour

There are a range of dopamine receptors in the brain. &epending on how effective the receptorsare, there will be different levels of dopamine in the brain. The different levels are lin6ed to a rangeof conditions, such as schizophrenia, "&A& and 0ar6inson$s disease. The &(&3 receptor is one ofthe most variable receptors.@y studying the levels of &opamine in the brain and the genotype of the individual, the alleleswhich may influence different conditions can be investigated, and different drugs for the conditionscan be developed.

)ne allele of &(&3 has been found more frequently amongst individuals whose personality is

described as %novelty!see6ing$ and whose behaviour tends to be eploratory and impulsive.This particular allele of the &(&3 receptor could have become common in the human populationbecause of natural selection giving those individuals a selective advantage. The behaviour caused bythe allele increases the chances of survival and therefore breeding because it helped them to findfood D find new resources D ma6e new tools D get mates. The allele was passed on to net generationand over time the allele increased in frequency.