unit 4

Question 1

state how the production of pollen grains has enabled flowering plants to adapt to terrestrial life [3]

Answer 1

• pollen grains carry the male gametes to the stigma and are able to deliver the male gametes to the ovule via the pollen tube
• the male gametes do not therefore need to be motile or require water and are therefore adapted to the terrestrial life
• pollen grains have become adapted to be transported by wind or insects so that they can be moved long distances without the need for water
• one of these adaptation is a thick excine layer, which is sculpted to allow the pollen grain to be blown in the wind or stick to insects
• the thick excine layer also reduces the risk of the pollen grain becoming dehydrated

Question 2

questions related to ‘evolution’

Answer 2

• evolution happens when selection pressures happen to a population in a particular environment
• as there is variation in any population of organisms, some of them will have a selective advantage over others
• some of the variation in the population may also be caused by mutations
• those members of the population with the selective advantage are more likely to survive to sexual maturity and therefore breed successfully
• they will pass on their beneficial alleles, which will increase the allele frequency of this beneficial allele which will lead over generations to the vast majority of the population of this organism possessing the beneficial allele and therefore the beneficial phenotype

Question 3

questions related to ‘3n infertility’

Answer 3

• 3 of each type of chromosome would mean that one of the chromosomes would be unpaired
• this would mean that homologous pairs of chromosomes could not pair up at prophase I of meiosis so meiosis could not take place and therefore no gametes would be produced

Question 4

questions related to ‘importance of meiosis’

Answer 4

• meiosis produces haploid gametes that allow the diploid state to be restored at fertilisation
• meiosis also produces genetically different gametes

Question 5

questions related to ‘incomplete linkage’

Answer 5

• genes are far apart on the same chromosome and therefore if crossing over occurs the genes can therefore be separated and appear in different gametes even though they were originally on the same chromosome
• four different gametes will be produced but not in equal numbers, a small number will be recombinants and a large number will be parental types
• the recombinants will be equal in number as will the parental types

Question 6

questions related to ‘complete linkage’

Answer 6

• genes are close together on the same chromosome and therefore even if crossing over occurs the genes will normally not be separated and most will therefore appear in the same gametes
• four different gametes will be produced but not in equal numbers, a very small proportion will be recombinants and a very large proportion will be parental types
• the recombinants will be equal in number as will the parental types

Question 7

questions related to ‘gene therapy’

Answer 7

• replacing a faulty allele with a normal allele

Question 8

questions related to ‘cystic fibrosis is caused by a mutation of the gene producing the protein CFTR. explain how the presence of this altered protein results in the production of thick, sticky mucus and how this accounts for the respiratory symptoms of the disease’ [4]

Answer 8

• CFTR is a carrier protein which normally allows the active transport of chloride ions out of the lung cells and into the mucus
• the mutation of the gene producing the CFTR means that it does not carry out its normal function which means that chloride ions remain within the cell
• this means that water is retained within the cell and far less water osmoses into the mucus surrounding the cell
• the mucus is therefore very thick and difficult to remove from the lungs
• as the thick mucus cannot be easily removed it can harbour microorganisms and the likelihood of infection increases
• more respiratory infections are a symptom of cystic fibrosis
• the thick mucus also narrows bronchioles which will reduce airflow which leads to another symptom of cystic fibrosis: breathing difficulties
• finally, the thick mucus reduces the surface area of the gas exchange surfaces and therefore insufficient oxygen is absorbed which would again lead to the breathing difficulties symptoms of cystic fibrosis

Question 9

questions related to ‘the chromosome number of the dog is 2n 78 and the European red fox is 2n 38. rare cases of mating between dogs and foxes have been recorded (resulting in an animal called a dox) but the offspring are all sterile. give reasons for the sterility’ [4]

Answer 9

• the dox would be unable to form gametes as meiosis could not take place because the chromosomes would not be homologous and therefore homologous pairs (bivalents) could not form during prophase I

Question 10

questions related to ‘genetic engineering involves the introduction of DNA from one species into another’

Answer 10

• the required ‘human’ gene is isolated
• a common method of achieving this is to isolate the ‘human’ mRNA from ‘human’ cells that have the required gene switched on
• a reverse transcripase enzyme is then used to make a ‘human’ DNA strand (of the required gene) from the ‘human’ mRNA molecule
• another enzyme DNA polymerase is then used to make this ‘human’ DNA stand a double stranded ‘human’ DNA molecule
• the ‘human’ DNA molecule is then treated with a restriction endonuclease enzyme so that it forms sticky ends at both ends of the ‘human’ DNA molecule
• plasmids are obtained from bacterial cells and are treated with the SAME restriction endonuclease enzyme as before
• this breaks open the loop of ‘bacterial’ DNA and produces sticky ends on both ends of the bacterial DNA molecule which have complementary bases to those on the sticky ends of the human DNA molecule
• the bacterial DNA and human DNA are mixed together and combine due to the complementary base pairing of the sticky ends
• this reaction is catalysed by the enzyme DNAligase
• this DNA is now called recombinant DNA as it has DNA from two different species in it and this is placed back in the bacterium
• the bacterium will then produce the product of the original human gene isolated
• markers such as antibiotic resistance can be added to the recombinant DNA to make it easier to identify, isolate and grow only those bacteria that contain the recombinant DNA

Question 11

questions related to ‘sperm entering the ovum’ [2]

Answer 11

• the acrosome contains enzymes which breakdown the zona pellucida

Question 12

questions related to ‘animal cloning’

Answer 12

• animal cloning can be attempted in two different ways
• firstly, embryo cloning can be used
• this is when in vitro fertilisation is used and then the resulting zygote is allowed to divide by mitosis until the 8 cell stage
• at this point the embryo is split into 8 separate cells
• each of these cells are genetically identical and as they are at this stage undifferentiated they should each develop normally into an embryo that can be implanted into a surrogate and develop into the adult organism
• the second form of animal cloning involves nucleus transplant
• in this case the haploid nucleus is removed from the ovum and replaced with a diploid nucleus from the donor animal that is to be cloned
• this ovum is then stimulated to divide forming an embryo that can be implanted into a surrogate and develop into the adult organism
• the adult animal will be a clone of the animal that donated the diploid nucleus

Question 13

• sperm duct (no mark)
• vas deferens (mark)

Question 14

• must get spelling right for ‘prostate’ (not prostrate)

Question 15

• correct spelling of urethra and ureter

Question 16

• correct spelling of adenine, thymine, cytosine and guanine

Question 17

• correct spelling of spermatogenesis
• spermiogenesis (no mark)

Question 18

be specific when discussing ‘spermatocytes’
- which ones ‘primary’ or secondary’

Question 19

• sertoli cells (mark)
• nurse cell (no mark)

Question 20

mitosis and meiosis spelt correctly

Question 21

questions related to making sure an experiment is reliable:
- always state that you will repeat and mention specifically some controlled variables that could be used

Question 22

follow instructions carefully:
- if asked for 5 letters representing stages of meiosis, all letters correct 5 marks, all words correct 4 marks

Question 23

match genotype to phenotype in dihybrid inheritance questions:
a) RR RW WW
b) Red Pink White
c) 1 3 1
(3 marks)

a) RR RW WW
b) pink, white, red
c) 3,1,1
(only 1 mark for top line)

Question 24

draw punnett squares when you have the opportunity, examiners can give you marks for genotypes from these

Question 25

understand the difference between a point mutation and a chromosome mutation

Question 26

- ‘polypeptide’ (no mark) - ‘polypeptide chain’ (mark)

Question 27

- remember to be detailed: - e.g point mutations cause ‘a change in amino acids sequence’ or ‘alters primary structure of protein’ or ‘produces a different polypeptide chain’ (mark) - ‘sequence is wrong’, ‘different protein’, ‘the wrong polypeptide would be produced’ - too vague - (no mark)

Question 28

- ‘bond formed between amino acids’ (no mark) - ‘peptide bond formed between amino acids’ (mark)

Question 29

nucleated eggs must be STIMULATED to divide

Question 30

in evolution: - beneficial genes (no mark) - beneficial alleles (mark)

Question 31

in evolution: - use: • selective pressure • selective advantage • produces a useful phenotype • variation in population - produces a useful feature (no mark)

Question 32

in evolution: - organisms breed together (mark) - organisms reproduce together (mark) - organisms mate together (no mark)

Question 33

- use information from stem of question - e.g information regarding cod and question related to evolution - if you do a general evolution answer rather than make it specific to the cod you will not get full marks

Question 34

- use information from stem of question - e.g table, graph or diagram - quote relevant figures or phrases from the source for a mark point

Question 35

- careful with language with evolution questions - ‘because of the use of nets VERY FEW of the large cod survived’ (mark) - ‘because of the nets none of the large cod survived’ (no mark)

Question 36

- careful with language with evolution questions - ‘mutations appear spontaneously in populations at all times, one of these mutations may confer a selective advantage if there is a particular selection pressure’ (mark) - ‘mutations appear that confer a selective advantage if there is a particular selection pressure’ (no mark) because the answer implies that mutations happen because of the selection pressure

Question 37

- 3n organisms cannot breed: - ‘no pairing of homologous chromosomes can happen’ (mark)

Question 38

- sex chromosomes (no mark) - X and Y chromosome (mark)

Question 39

- if asked about probability of a particular phenotype appearing from a genetic cross answer with % - e.g. 25% or 1 in 4 - NOT a ratio - only give ratios if requested

Question 40

- restriction endonuclease cuts DNA (mark) - restriction endonuclease cuts gene (no mark)

Question 41

- DNA ligase joins section of DNA (mark) - DNA ligase join sticky ends (no mark)

Question 42

- remember a DNA molecule consists of two strands of DNA - use the correct terms - after replication the DNA molecule is made up of an old and a new DNA strand

Question 43

- replication of DNA (mark) - copying/doubling of DNA (no mark)

Question 44

- transcription: - DNA is used as a template to produce a mRNA molecule - DNA is not changed/made/converted into mRNA

Question 45

- reverse transcriptase - mRNA is used as a template to produce a DNA molecule - mRNA is not changed/made/converted into DNA

Question 46

- translation - mRNA leaves the nucleus (no mark) - mRNA leaves the nuclear pore (mark)

Question 47

pollination: - pollen from the ANTHER of one flower to the STIGMA of another

Question 48

- pollen tube travels through the stigma, style and ovary wall before entering the micropyle

Question 49

- acrosome enzymes digest the zona pellucida not the egg’s membrane

Question 50

- gene therapy is replacing a faulty ALLELE with the normal/correct version of that ALLELE

Question 51

- use the words DONOR and RECIPIENT cells when describing the transfer of nuclei from one ovum to another

Question 52

- Senecio squalidus (2n fertile) + Senecio vulgaris (4n fertile) —> senecio xbaxteri (3n sterile) —> Senecio cambrensis (6n fertile) - S.xbaxteri (a plant species) has three copies of each chromosome - describe the change that has resulted in the formation of the hybrid S.cambrensis and explain why it’s fertile [5]

Answer 52

- chromosome number doubled / 3n to 6n / triploid to hexaploid / even number of EACH chromosome - ref to endomitosis / cell does not divide / non disjunction / no cytokinesis - homologous pairs / bivalents form - prophase 1 - meiosis - (viable) games can be produced

Question 53

- S.cambrensis appeared independently in Edinburgh in 1974 - originally there were 102 plants in three populations surrounded by parental plants growing on derelict land - suggest one reason why the species became extinct in Edinburgh by 1993 [1]

Answer 53

- outcompeted / not isolated so able to breed with parental plants / loss of habitat or description of

Question 54

- through gene therapy, it is hoped that the functional version of the gene can be isolated and introduced into muscle cells - historically, a virus has been used as the vector - suggest two potential problems of using a virus to treat DMD [2]

Answer 54

- cause immune response against virus / antibodies may be produced against it - problems introducing gene into muscle (cells) / may not reach (target (cell) / muscle (cell)) / may invade (non target / host) cells - virus may (become pathogenic / cause disease / cause infection / destroy cells) - may affect other genes / reference to oncogenes

Question 55

- DMD can be treated using a drug which acts as a ‘molecular patch’ on an mRNA molecule transcribed from the mutated DNA - the drug contains a short RNA molecule which is complementary to a specific sequence of bases on the mRNA - it prevents translation of the covered mRNA but allows ribosomes to continue translating the strand following the patch state one difference between the structure of the protein dystrophin synthesised after the use of the molecular patch and normal dystrophin [1]

Answer 55

- shorter / different 1° structure / less amino acids / smaller

Question 56

- there is another drug available which is used to removed mutated exons rather than the dystrophin gene - state the advantage of using this drug to treat DMD rather than the molecular patch on mRNA [1]

Answer 56

- do not have to repeat treatment / more permanent treatment / change present in daughter cells / change present after cell replicates / can pass to next generation

Question 57

- scientists are also investigating a means of using a molecular patch for germ line therapy - state one ethical issue of using germ line gene therapy in the treatment of DMD [1]

Answer 57

- unknown long-term effects - possible activation of oncogenes - modified gene passed on to next generation - affect (other genes / later generations)

Question 58

i) the mitochondria in the sperm do not enter the secondary oocyte at fertilisation. what does this suggest about the origin of all mitochondria in an organism? [1] ii) a woman has inherited a mutation in her mitochondrial DNA resulting in mitochondrial disease. her husband and father dont have this disease. write a tick or a cross to indicate which of her relatives will suffer from the SAME mitochondrial disease: son: daughter: daughter’s children: son’s children : [2]

Answer 58

i) all from (secondary oocyte/ female / mother / egg) ii) son: ✓ daughter: ✓ daughter’s children: ✓ son’s children: X

Question 59

- the inheritance of mitochondrial diseases can be prevented using the technique outlined: - donor egg with healthy mitochondria —> nucleus is removed —> mother’s nuclear DNA is removed from her secondary oocyte and inserted into donor —> healthy secondary oocyte is then fertilised oocyte is then fertilised with partner’s sperm —> implanted into mother’s uterus - using all of the info provided explain why a child produced by this method has been referred to as a ‘three parent baby’ [3]

Answer 59

- (nucleus / DNA / nuclear material / genetic information) from mother - (nucleus / DNA / sperm) from father - MITOCHONDRIA (DNA) from donor

Question 60

- the Hardy-Weinberg principle states that allele frequencies in a population remain constant from generation to generation providing certain conditions exist - state three of these conditions [3]

Answer 60

- random mating - non disjunction does not occur / no mutation - large population - no immigration / no emigration / population is isolated - no selection / selective advantage/no selection pressure

Question 61

use your knowledge of hormonal control of the human reproductive cycle, explain the effects of the hormonal changes shown below [3]

Answer 61

hormonal control of ovulation: - FSH stimulates the development of follicles in the ovary - follicle cells produce oestrogen - which inhibits the production of FSH - and stimulates the production of LH - LH stimulates production of more oestrogen - and oestrogen stimulates production of LH - eventually the LH levels cause ovulation - increase in FSH levels also aids ovulation - the corpus luteum produces progesterone - which is needed for the development of endometrium

Question 62

- the body’s response to infection shows both a primary response and a secondary response to the foreign antigens - both responses can be identified by measuring the levels of two antibodies found in the blood, IgM and IgG - IgM is produced mainly by B-cells on initial exposure; IgG antibodies are produced in higher levels during the secondary response - explain why the level of IgG is higher after the secondary exposure to the antigen than the first exposure [1]

Answer 62

- MEMORY CELLS (must make IgG during the secondary response / after second exposure / clonal expansion)

Question 63

- the body’s response to infection shows both a primary response and a secondary response to the foreign antigens - both responses can be identified by measuring the levels of two antibodies found in the blood, IgM and IgG - IgM is produced mainly by B-cells on initial exposure; IgG antibodies are produced in higher levels during the secondary response - lyme disease can persist in patients for many years and the IgM levels remain high. suggest possible reasons why [2]

Answer 63

- the bacteria may have antigenic variation / surface proteins / reference to mutations - (IgM produced again as ) no memory cells to new antigen - primary response each time

Question 64

- an ELISE (enzyme-linked immunosorbent assay) can be carried out to diagnose Lyme disease using a blood sample from the patient around TWO WEEKS after infection - it is detecting the antibodies made in response to being exposed to B.burgdorferi - (using the graph provided) explain why carrying out an ELISE would not detect the IgG antibodies in the days immediately after the tick bite [2]

Answer 64

- delay in detection of bacterial antigen / reference to latent period/clonal selection - IgG not produced straight away - time is needed to produce and secrete antibodies

Question 65

- the ELISA can produce false negative results for Lyme disease - in a false negative result there is no colour change, even if the patient is infected with the bacteria - suggest why, even if there are anti-B.burgdorferi antibodies in the patient’s plasma, the enzyme may not cause a colour change [5]

Answer 65

- antibodies maybe already attached to the bacteria / antigen / a substance within the plasma - different strain of bacteria which is not recognised by the test - more than one type of antigen on the surface of the bacteria - antibodies not at detectable levels / variation amongst peoples’ immune response / colour change not detectable - enzyme not functioning / denatured - lack of control of variables e.g pH / temperature / volume of sample

Question 66

- as maize seeds germinate they produce the enzyme amylase which hydrolyses the starch in the endosperm into maltose - this can be demonstrated in the laboratory using the following method: • maize seeds are soaked in water • seeds are cut in half and placed onto starch agar • after 24hours the seeds are removed and iodine solution added to the starch agar • clear zones around the position of seeds indicate amylase activity • boiled then cooled seeds are set up as a control - describe how you develop and refine this practical procedure to determine whether treatment of seeds with 0.1 mmol dm^-3 solution of gibberellic acid increased production of amylase [4]

Answer 66

- soak some seeds in gibberellic acid - measure clear area / compare size of clear zone - any two from: • same type / variety / age / size / mass of seed • soaked for same time • same conc / depth starch agar • same temperature / light

Question 67

what is the outside layer of the graafian follicle called?

Answer 67

- theca / thecal cells / follicle cells / granulosa cells

Question 68

- an electron micrograph shows a sperm penetrating the surface of structure x to get to the oocyte. - describe how the sperm is able to penetrate the outer layers of this structure [2]

Answer 68

- acrosome - releases (enzymes / named enzymes) which (hydrolyse / digest / break down) (layers)

Question 69

- in vitro fertilisation (IVF) is a technique available to help people with fertility problems - during IVF, secondary oocytes are remove from a women’s ovaries and are fertilises with sperm in a laboratory - there is a risk during fertilisation more than one sperm enters the secondary oocyte - the risk is increased if the secondary oocyte is not fully mature - there is a 6% increased chance of more than one sperm entering the secondary oocyte with IVF - state how the secondary oocyte usually prevents the entry of more than one sperm and suggest a reason why there is an increased risk with IVF [2]

Answer 69

- (cortical granules rupture / cortical reaction) + zona pellucida (thickens/hardens) / fertilisation membrane forms - (secondary oocyte taken from graafian follicle is immature) so cannot form a fertilisation membrane / zona pellucida cannot (harden/thicken) / (fewer/less) developed cortical granules

Question 70

- in vitro fertilisation (IVF) is a technique available to help people with fertility problems - during IVF, secondary oocytes are remove from a women’s ovaries and are fertilises with sperm in a laboratory - there is a risk during fertilisation more than one sperm enters the secondary oocyte - the risk is increased if the secondary oocyte is not fully mature - there is a 6% increased chance of more than one sperm entering the secondary oocyte with IVF - the developing embryo is not transferred into the uterus until three days after IVF - using your knowledge of fertilisation and implantation explain why this delay is needed [3]

Answer 70

- fertilisation normally in fallopian tube - embryo needs to reach uterus / blastocyst to form/allow cleavage to take place - if embryo put into uterus immediately, endometrium would not be fully developed - (trophoblastic/chorionic villi) will not have developed - (embryo / blastocyst) would not implant/survive

Question 71

how can you tell if data shows continuous variation?

Answer 71

- not discrete / there are intermediates / complete graduation

Question 72

- one hundred years ago the sweet vernal grass was unable to survive on the mine sites but now colonises them - use your understanding of natural selection to explain this observation [4]

Answer 72

- (variation due to) MUTATION - so the tolerant plants have a selective advantage m - (survive and) reproduce - pass on alleles (for tolerance to offspring) - repeated over several generations AND allele frequency for toleration increases

Question 73

- sweet vernal grass plants which are tolerant to high copper concentration in the soil flower at a different time of year from the non-tolerant plants in adjacent areas - explain why it is predicted that this could lead to the formation of two different species [4]

Answer 73

- no longer able to (cross pollinate / cross fertilise) - (reproductive / seasonal / temporal / prezygotic) isolation / gene flow prevented - genetic differences accumulate - no longer able to produce fertile offspring - sympatric speciation

Question 74

- a diagram shows the structure of a human placenta - state four differences between the composition of the blood in the umbilical arteries and the umbilical vein [2]

Answer 74

UMBILICAL ARTERY: - less oxygen - more CO2 - more urea - less nutrients/named - less antibodies UMBILICAL VEIN: - more oxygen - less CO2 - less urea - more nutrients/named - more antibodies

Question 75

give two reasons why there must be a barrier between foetal and maternal blood systems [2]

Answer 75

- (barrier) (against hormones/toxic substances/microorganisms/cells/mothers antigens) - protection against differences in pressure - protection against mother’s (immune system / antibodies)

Question 76

suggest how the following features of the placenta enable it to carry out its function: - the arterial blood flow to the placenta is high (700 cm^3 min^-1) and the blood in the intervillus space is exchanged three times per minute [1]

Answer 76

- maintain (concentration/diffusion) gradients/prevents equilibrium being reached

Question 77

suggest how the following features of the placenta enable it to carry out its function: - the pressure in the uterine arteries is ten times greater than the pressure in the intervillous space [1]

Answer 77

- (pressure difference) forces materials through (capillaries)

Question 78

suggest how the following features of the placenta enable it to carry out its function: - the length of the capillaries in the placenta is about 320km [1]

Answer 78

large (surface) area for exchange

Question 79

- in PCR, explain why two different DNA primers are required [1]

Answer 79

- different nucleotide sequence at each end / one primer for each strand of DNA

Question 80

- a sample of blood from a pregnant women is taken - primers specific to a gene on chromosome 21 are used to replicate it - primers specific to anther gene on a different chromosome are used at the same time - these act as a control - both primers have fluorescent markers attached . - suggest why it is important to use primers which are specific to a certain gene on each chromosome [1]

Answer 80

- enables (specific/the gene) to be (amplifier/to be copied/to be replicated)

Question 81

- after the PCR, the DNA fragments are separated using gel electrophoresis and the level of fluorescence for each gene is measured - the level of fluorescence corresponds to the quantity of that gene - the quantity of both genes is expressed in the form of a ratio as shown below quantity of genes from chromosome 21 : quantity of gene from control chromosome - suggest why it’s necessary to express the quantity of the genes as a ratio [2]

Answer 81

- does not matter how (many cycles in PCR / initial quantity / number of copies made) - ratio will be the same

Question 82

state two concerns that some people may have about the ethics of prenatal diagnosis [2]

Answer 82

- (selective) abortion may become more common - moral status of foetus / right to live - may cause harm to foetus - could result in false (positive/negative) results

Question 83

- cholera is caused by the production of cholera toxin by 2 strains of V.cholerae, O1 and O139 - an agglutination test can be carried out to test for the presence of O antigens on the bacterial surface - agglutination is when clumping takes place between antibodies and antigens - a different agglutination test can be carried out to test for each of the strains - explain why a agglutination test would be able to distinguish between the two strains of cholera bacteria [3]

Answer 83

- antibodies are specific to an antigen - different strains would have different antigens - if no agglutination they different strains / if tested using antibodies to O1, O139 would not show agglutination

Question 84

in a cholera outbreak, suggest why some patients with severe symptoms are given antibiotic tablets, but antibiotics alone are not a cure for the disease [3]

Answer 84

- antibiotics will pass through the gut before all bacteria killed - V.cholerae is gram-negative and some bacteria (less/not) effective / narrow spectrum - kill bacteria but toxin remains - antibiotic resistance

Question 85

- oral cholera vaccines can be used to prevent the disease if there is a risk of an epidemic - two doses of the vaccine are required - Shancol is a vaccine which has been used successfully in areas of endemic cholera but was not used during the Haiti epidemic as it had not then been authorised for use by the UN/world health organisation - explain why the oral vaccine must be administered in two doses [2]

Answer 85

- (first dose) - for a primary (immune) response AND - (second dose) - for a secondary (immune) response - second dose acting as a booster/to increase antibody levels / increase memory cells

Question 86

state one reason why a higher concentration of the cholera vaccine must be used when given orally [1]

Answer 86

- the vaccine would pass through the digestive system / the vaccine would be in the intestine long enough / not (enough/all) absorbed / vaccine could be broken down / stomach acid stops vaccine working

Question 87

what considerations would need to be made by the UN/WHO before allowing the use of a vaccine in Haiti? [2]

Answer 87

- safety of the patients / side effects - effectiveness / the vaccine may not work - costs / logistics of storage issues (needing cold conditions)

Question 88

- the allele for normal haemoglobin is HbA and the abnormal haemoglobin is HbS - malaria is the most serious and wide-spread parasitic disease in humans; the vast majority of global malaria cases are in Africa - sickle red blood cells are less likely to be infected by the malarial parasite - the frequency of heterozygotes (HbA HbS) in some parts of Africa is approximately 42% - the frequency of heterozygotes in African-Americans is lower than in native African populations - use the information provided and your own knowledge, explain the differences in the % frequency of African-American heterozygotes compared to those in Africa [5]

Answer 88

- (HbS Hbs / or description) are not likely to survive AFRICAN-AMERICANS: - no (selective) advantage to being heterozygote - disadvantage to being (HbS HbA / heteroxygotes / sickle trait / (HbS HbA / heterozygotes / sickle trait) are selected against - there is an advantage to being (HbA HbA / homozygous HbA) AFRICA: - HbA HbA more likely to die of malaria / selected against - (heterozygotes / HbA HbS / having one HbS) are selected for

Question 89

- malaria is caused by a parasite of the genus Plasmodium and it is transmitted from one person to another by Anopheles mosquitoes - in 2002, after seven years, the Plasmodium Genome Project and the Anopheles Project were both completed . a) state what information has been obtained from the Anopheles and Plasmodium genome project [2] b) state two uses of the information obtained from these genome projects in the control of malaria [2]

Answer 89

a) - (nucleotide / base / DNA) (SEQUENCE/CODE) (1) - location of genes (1) - on chromosomes (1) - complete DNA sequence = 2 marks b) - make mosquitos susceptible to insecticides - make mosquitoes less fertile - prevent transmission - modification of Plasmodium to reduce pathogenicity - development (of more effective) drugs or vaccines

Question 90

define what is meant by proto-oncogene [1]

Answer 90

- genes which can mutate to (oncogenes which) cause (uncontrollable cell division / mitosis / cancer)

Question 91

define what is meant by epigenetics [1]

Answer 91

- control of (gene expression / transcribed and translated / switched on or off) by (factors / names factors) other than changes in DNA sequence

Question 92

- in some humans, tumour suppressor genes can become permanently switched off in ALL CELLS in the body - explain the consequences of such a change [1]

Answer 92

- INCREASED (risk of) cancer / INCREASED (risk of) tumour formation - passed onto next generation

Question 93

- the human reproductive cycle is controlled by several hormones - clonifene as a medication used to treat some forms of infertility - it leads to increased release of FSH and LH - suggest how clomifene increases the chance of conception [2]

Answer 93

- FSH causes follicle development - LH causes (ovulation / secondary oocyte to be released)

Question 94

- prolactin and oxytocin are hormones which play a role in birth and feeding of the child after birth - prolactin concentrations stay higher in women who are breasfeeding - prolactin inhibits the production of FSH - describe the role of prolactin in women who are breastfeeding and explain why they have a reduced chance of conception [3]

Answer 94

- (stimulates cells in mammary glands) to (secrete / produce) milk (into ducts) - (lack of FSH) prevents (maturation / development) of the follicle - (no / less) ovulation / or description of

Question 95

explain why oxytocin production during birth is an example of positive feedback [3]

Answer 95

- stimulates contraction of (uterine (wall) / myometrium) - (which stimulates release of) more oxytocin - which increases the contractions

Question 96

- plant, such as maize (Zea sp.) can be genetically modified to provide resistance to insect pests - the bacterium, Bacillus thuringiensis, naturally produces a protein toxic to insects - the Bt gene that codes for this protein can be introduced into plant cells using a genetically engineered plasmid - one way of achieving this is to prepare a cDNA fragment containing the Bt gene and then incorporating it into a suitable plasmid . - describe how a cDNA fragment containing the Bt gene can be prepared and the processes by which genetically engineered plasmids can be produced - explain why there are concerns over the use of such a technique to increase resistance to insect pests in plants [9QER]

Answer 96

- EXTRACT mRNA from the bacterium (which is synthesising the proteins) - use REVERSE TRANSCRIPTASE to synthesise a (single strand of DNA / cDNA) using the mRNA (as a template) - use DNA POLYMERASE to produce double stranded DNA - STICKY ENDS are added to the end of each DNA strand of the DNA - the DNA is copied many times using PCR . - plasmids from bacteria are isolated - RESTRICTION (ENDONUCLEASE/ENZYMES) is used to open the plasmid (at a specific point) - producing STICKY ENDS COMPLEMENTARY to the DNA - DNA LIGASE is used to bind the DNA into the plasmid - ANTIBIOTIC RESISTANCE GENES/MARKERS / LacZ are used to select bacteria containing the recombinant plasmids . concerns: - dispersal of pollen from engineered crops to wild relative/contamination of organic crops - unknown effects of eating new protein which is toxic to insects/health concerns from eating GM crops - a reduction in biodiversity e.g. beneficial insects killed/affect on food chains - could result in resistance to protein in insects/selection pressure

Question 97

immunology and disease section: - explain why the body is sometimes described as a host to other living organisms [1]

Answer 97

- (many organisms / named organisms) live (in/on) the (human) body

Question 98

- Rhinovirus uses the metabolic pathways of a host cell to produce many copies of the virus - explain how infection with rhinovirus could cause cell death [1]

Answer 98

cell lysis / cell bursts

Question 99

- in cells infected with rhinovirus, the cell-mediated immune response involves the activation of B and T lymphocytes, and phagocytes - explain how phagocytes and T lymphocytes bring about the cell-mediated response against rhinovirus [3]

Answer 99

- (macrophages / phagocytes) (engulf virus infected cell / carry out phagocytosis) / antigen presentation - clonal expansion / T cells (proliferate / divide many times) - cytokines stimulate phagocytosis - killer T cells cause cell lysis

Question 100

explain why antibiotics can be used to treat cold caused by S.pyogenes, a bacteria, but not those caused by rhinovirus [3]

Answer 100

- antibiotics can act on (cell wall of bacteria / or description of / hydrolyse peptidoglycan) - antibiotics affect (metabolism / protein synthesis) by bacterial cell - viruses dont have a (cell wall / metabolism) so not affected by antibiotics

Question 101

explain why S.pyogenes was cultured at 35°C [1]

Answer 101

- human pathogen / (close to human) body temperature

Question 102

- vaccination programmes for the common cold caused by rhinovirus have so far proved unsuccessful - using your own knowledge of immunisation, suggest and explain why it is unlikely that a vaccine for the common cold will ever be developed [3]

Answer 102

- may be (rapid / high) mutation rate in rhinovirus / antigens change / viruses are antigenically labile - many (strains / serotypes / antigenic types) of rhinovirus - vaccines would need to contain antigen from all strains (to provide complete immunity) - each antigen must produce a strong immune response / be highly antigenic / be immunogenic

Question 103

- the flu virus causes many similar symptoms to the common cold - there is a vaccine against the flu virus which can provide protection - it’s offered to certain ‘at risk’ groups - these immunisations are not compulsory - suggest why it would be considered unethical to make the flu vaccine compulsory for all [1]

Answer 103

- religious objections - safety fears / side effects - individual rights - some people may be too ill for vaccination e.g due to HIV-AIDS or chemotherapy

Question 104

- in April 2003, the complete genetic code of a human being - their genome - could now be made freely available on-line - The human genome project aimed to read the human genome using a technique called sequencing - in 2012, the 10,000 genome project was launched and by 2017 had sequence the genomes of 100,000 NHS patients. the project focused on patients with a rare disease and their families, and on patients with cancer Scenario: - it’s 2025 and Sharon has a painful skin infection that she can’t get rid of. her doctor would like to prescribe an antibiotic called phenyloxacillin, since it’s especially effective against the bacteria causing the infection. however her doctor knows that in a small number of cases phenyloxacillin can cause serious liver damage so suggest a genome test. she tells Sharon that there is a law giving people the right not to disclose the results of genetic tests to insurers . - explain what is meant by ‘sequencing’ the human genome and describe the type of data that might be made available online - explain how the extra information provided by the ‘100,000 genomes project’ might be useful in medicine, and describe how the scenario above illustrates one possible beneficial application and an ethical dilemma of genome sequencing. [9QER]

Answer 104

SEQUENCE AND DATA: - the order of NUCLEOTIDES/BASES in the DNA - sanger sequencing - description of methods used - data/information would give (loci/sequences) of individual genes - coding for specific amino acid/proteins - description of introns and exons 10000 GENOMES PROJECT: - next generation sequencing (NGS) - locate genes responsible for (rare genetic disorders/cancers) / mutated sequences - by comparing genomes of sufferers with (normal genome/large number of individuals) - predisposition to disease/(diagnosis / understanding causes) of diseases - developing treatments/gene therapy - used in prenatal diagnosis BENEFITS AND ETHICS: - sharon would find out of the drug would give her liver damage/benefit is matching drugs to genetic make up of person / personalised medication - ethical dilemma is over RIGHTS OF ACCESS to genomic information - (misuse of genetic information) by employers/insurers - wider implication on family health - anxiety/stress caused by knowledge - social discrimination

Question 105

AATTCAATCGTACG GTTAGCATGCTTAA - explain why the ends are known as ‘sticky ends’ [1]

Answer 105

- they have unpaired bases / they have exposed bases / they are single stranded DNA sections

Question 106

define the term plasmid [1]

Answer 106

- {ring of / circle of / loop of} DNA (found in bacteria)

Question 107

- in recombinant DNA technology, the piece of DNA which has been cut out is inserted into a plasmid which has been cut open using the same enzyme - why is it important to use the same enzyme? [1]

Answer 107

- so that the cut ends (of the fragment and the plasmid) are COMPLEMENTARY

Question 108

- in recombinant DNA technology, the piece of DNA which has been cut out is inserted into a plasmid which has been cut open using the same enzyme - name the type of enzyme used to join the cut fragment into the plasmid [1]

Answer 108

DNA Ligase

Question 109

- restriction enzymes are also used to cut up DNA during DNA fingerprinting/profiling - labelled DNA probes are then used to identify the positions of the fragments on an electrolysis gel - the fragments used are sections cut from introns rather than exons - explain why introns are more useful for genetic fingerprinting than exons [2]

Answer 109

- introns are {non-coding/blocks of repeated nucleotides} /exons code (for proteins) - so there is more variability/more unique to individual/{number of times that the blocks are repeated varies/STRs vary)

Question 110

- a DNA profile of a sample of DNA taken from a crime scene and samples prepared from blood of three suspects are shown below - give 2 features of the DNA profiles which would lead to the identification of suspect B as being present at the scene of the crime [1]

Answer 110

same position AND thickness of bands

Question 111

- the enzyme used in PCR has an important function during interphase in both mitosis and meiosis. - name the enzyme used: - the enzyme’s function in interphase [2]

Answer 111

- DNA polymerase - (DNA) REPLICATION

Question 112

in PCR, suggest why two different primers are required [1]

Answer 112

different nucleotide sequence at each end / one primer for each strand of DNA

Question 113

- a sample of blood from a pregnant woman is taken - primers specific to a gene on chromosome 21 are used to replicate it - primers specific to another gene on a different chromosome are used at the same time - these act as a control - both primers have fluorescent markers attached - suggest why it’s important to use primers which are specific to a certain gene on each chromosome [1]

Answer 113

enables (specific/the gene) to be (amplified/to be copied/to be replicated)

Question 114

- the techniques of recombinant DNA technology and micro-propagation are used to produce genetically modified crops - the following summary is adapted from an account given on the food standards agency website: 1. a plant with the desired characteristic is identified 2. the specific gene that produces this characteristic is found in the plant’s DNA and cut out 3. to get the gene into the cells of the plant being modified, the gene needs to be attached to a carrier. A piece of bacterial DNA called a plasmid is joined to the gene to act as the carrier 4. once the new gene is attached to the plasmid, a marker gene is also added to identify which plant cells take up the new gene 5. the ‘gene package’ is put in a bacterium, which multiplies, to create many copies of the ‘gene package’ - explain how different types of enzymes are used in stage 2 and 3 to produce the ‘gene package’ [4]

Answer 114

- restriction (endonuclease/enzymes) used to cut (out the desired gene) - the SAME (endonucleus/enzyme) is used to open the plasmids - producing (complementary/corresponding) sticky ends - ligase is used to (join/attach/adhere/anneal) gene into plasmid

Question 115

describe 3 ways in which a DNA molecule differs from an RNA molecule [2]

Answer 115

- double stranded not single stranded / double helix vs single stranded - deoxyribose not ribose - thymine not uracil - longer molecule

Question 116

Cas9 enzyme is a restriction endonuclease. state what is meant by a restriction endonuclease [2]

Answer 116

- it cuts DNA / or description - at a specific (base) SEQUENCE

Question 117

- scientists have discovered a way to modify mosquito eggs to produce sterile adult mosquitoes - explain how releasing these sterilised mosquitoes into the wild might benefit humankind and suggest an ethical reason for not doing so [3]

Answer 117

- reference to reduced fertility in mosquitoes - less mosquitoes = less malaria - reference to rights of humans to make another species extinct/ - effect on (removal from food chain/ecosystems/biodiversity) - unknown effects of GM mosquitoes in the environment

Question 118

describe what happens to pollen on the first flower a bee visits, and the second flower [2]

Answer 118

- pollen deposited on insect - pollen transferred to stigm

Question 119

name the hormone produced by the developing embryo which prevents the breakdown of the corupus luteum? [1]

Answer 119

HCG / human chorionic gonadotrophin

Question 120

draw diagrams showing TWO PAIRS of homologous chromosomes as they would appear in the primary oocyte (prophase I) and the appearance of the chromosomes following cell division to form the secondary oocyte (metaphase II) [3]

Answer 120

- correct number of chromosomes in each: primary oocyte = 4, secondary oocyte = 2 - cell prophase I drawn correctly; chromosomes inside nuclear membrane, not on equator - cell metaphase II drawn correctly; must be clearly on equator

Question 121

suggest why only one functional female gamete is produced as a result of meiosis [2]

Answer 121

- polar body produced / reduction in genetic material at each stage of meiosis - functional gamete retains (most of) cytoplasm - (cytoplasm) acts as a food store for zygote / provide mitochondria for zygote - needed until implantation takes place / obtained from placenta

Question 122

explain cell cleavage [1]

Answer 122

(splitting / dividing) of (ZYGOTE/EARLY EMBRYO) cells to form new cells

Question 123

explain blastocyst [1]

Answer 123

hollow ball of cells / ball of (undifferentiated / partly differentiated) cells

Question 124

explain implantation [1]

Answer 124

the (burying/embedding/implanting) of the (blastocyst/embryo) into the (uterine lining/endometrium)

Question 125

define the term ‘gene pool’ [1]

Answer 125

all the alleles (of all the genes) in a population

Question 126

- one theory for the evolution of the different species of Darwin’s finches is that a small population of sharp-beaked finches were blown onto one of the islands from mainland South America - over many generations they became adapted to feed on the different food sources available - give one reason why, in the early generations of the island colony, the frequencies of the alleles might have differed from the frequency in the mainland population [1]

Answer 126

genetic drift / founder effect / description of (accept mutation)

Question 127

- the Large Cactus Finch (Geospiza conirostris) from the isoand Genovesa has a beak that closely resembles fhat of the Cactus Finch (Geospiza scandens) from the island champion - state why these two finches are considered to be separate species [1]

Answer 127

- they are not able to interbreed/ breed or reproduce WITH EACH OTHER and produce fertile offspring

Question 128

- the Large Cactus Finch (Geospiza conirostris) from the isoand Genovesa has a beak that closely resembles fhat of the Cactus Finch (Geospiza scandens) from the island champion - explain why they evolved into separate species [2]

Answer 128

- geographical isolation / correct reference to allopatric speciation - over time develop adaptations which prevent successful breeding with original population/there is no flow of genes between the two populations

Question 129

what are pieces of evidence that could be used to confirm that two organisms were members of the same species?

Answer 129

- if they could interbreed to form fertile offspring - share same gene pool - similar physiology - similar behaviour - similar genetic makeup - similar proteins - similar morphology - similar genetic profile

Question 130

suggest a possible isolating mechanism that could cause speciation

Answer 130

- reproductive cycles different - changes in chromosome number / ploidy - different activity times - mechanical isolation

Question 131

- the chromosome number of the dog is 2n 78 and the European Red Fox is 2n 38 - rare cases of mating between dogs and foxes have been recorded (resulting in an animal called a dox) but the offspring are all sterile - give reasons for this sterility [4]

Answer 131

- chromosomes not HOMOLOGOUS - cannot pair / from bivalents - during prophase I (of meiosis) - meiosis does not take place - no gametes produced

Question 132

- a map shows a distribution of different coloured mice along a beach and into forest - under what circumstance could the difference between the allele frequencies in the different populations be explained by genetic drift, despite both living on beaches [1]

Answer 132

small population (of mice)

Question 133

distinguish between continuous and discontinuous variation [2]

Question 134

distinguish between continuous and discontinuous variation [2]

Answer 134

- discontinuous - when characters are clear-cut / controlled by a single gene - continuous - shows a graduation from one extreme to another / controlled by more than one gene

Question 135

what is meant by the term ‘sex linkage’ [1]

Answer 135

- (genes) on the (X/Y) chromosomes - reject sex chromosomes - accept (genes) on sex chromosomes not on the autosomes

Question 136

- an organism has two genes A and B which are found on the same chromosome - complete the following genetic diagram for a cross between two individuals with genotype AaBb but where no crossing over occurs (complete linkage) - genotype: AaBb AaBb - genotype of gametes: __ __ __ __ - genotype of offspring: __ __ __ __ - ratio of phenotype

Answer 136

- AB ab AB ab - AABB AaBb AaBb aabb - 3:1

Question 137

- in another cross between two individuals with the genotype DdEe, where the genes D and E are on the same chromosome, the offspring showed four different types of phenotype - the phenotype of some of the offspring were far more common than expected and some phenotypes were very rare - explain these observations [2]

Answer 137

- incomplete linkage - genes (further / far) apart on same chromosome - (crossing over / chiasmata) can occur - four types of gametes produced (but not in equal numbers) - small number of recombinants / large numbers parental type - recombinants equal in numbers / parental equal in numbers

Question 138

- zika is an RNA virus, which can be spread by the Aedes mosquito - state the term given to the Aedes mosquito in the lifecycle of the Zika virus [1]

Answer 138

vector

Question 139

- some prevention methods to avoid risk of transmission of malaria by mosquitoes: • use insect repellent and wear loose clothing that covers the body • keep windows closed at night and sleep under a mosquito net • avoid areas with poor sanitation and stagnant water - explain how the preventative method described above would help reduce the chance of infection with malaria [2]

Answer 139

- (insect repellent/loose clothing/keep windows closed and mosquito net) prevent mosquitoes BITING - (avoiding stagnant water means) avoiding areas where mosquitoes BREED

Question 140

- (with reference to a diagram) suggest why viruses are difficult to treat with drugs and state the challenges faced when attempting to develop a vaccine against a virus [3]

Answer 140

- viruses are not cellular so do not have metabolic pathways - a vaccine would need to target (virus infected cells/viruses directly when in tissue fluid/blood/outside cells) - viruses enter host cells so they avoid recognition by host immune systems/drugs may not be able to get virus - drugs would interfere with host cells metabolism or damage the host cells - antigenic variation/description of/drug resistance

Question 141

state two features of a successful vaccine [1]

Answer 141

- must be (safe / not cause harm) / not have side effects - must be effective / trigger an immune response

Question 142

- urgent research has been carried out to provide protection against a virus (Zika) to pregnant women, as quickly as possible as well as providing a long-term prevention strategy - 2 research projects currently in progress are: • the use of an infection containing anti-Zika antibodies for use in pregnant women. this has had some success in animal trials with mice - the development of a vaccine to confer immunity against the virus - evaluate the relative advantages and disadvantages of these strategies in the prevention of Zika cases - state which one would be most effective in the long-term and explain your reasoning [5]

Answer 142

- strategy 2 more effective in the long-term number one: - advantage: antibodies would act quickly/confers immediate protection - PLACENTAL transfer will protect the baby - disadvantage: no memory cells would be produced/no long-term immunity number two: - advantage: the production of memory cells - reference to herd immunity - disadvantage: would take longer to act

Question 143

- methicillin works in a similar way to penicillin and is said to be bactericidal - it is no longer produced for medical use because of the rapid increase in bacterial resistance to it - Methicillin resistant Staphylococcus aureus (MRSA) is endemic in the general human population - infections caused by MRSA are common in hospital patients . - state what is meant by the term endemic and suggests why MRSA is not a major cause for concern amongt the general population [2]

Answer 143

- endemic: a disease that’s always present (at low levels) (in an area) - surgical patients - skin open to bacteria - sick/elderly patients - low levels of immunity

Question 144

- erythromycin can be bactericidal or bacteriostatic depending on the dose - it binds to the large ribosomal subunit in bacterial cells - suggest how erythromycin may work to treat bacterial infection and why it does not affect the patient’s cell metabolism [2]

Answer 144

- (inhibition of / prevent / stop) (protein synthesis / translation) - humans have different ribosomes to bacteria

Question 145

- antibiotic resistance is a global crisis and measures are needed to control the use of antibiotics as well as developing new antibiotics - clinical trials needs to be done on any new antibiotic - a trial was carried out to test the safety of a new antibiotic using 20 healthy male volunteers from the same ethnic background - evaluate the validity of this trial in terms of its use in the whole population [2]

Answer 145

- not enough people - only males - only done on one ethnic group - needs to be tested in infected individuals - use of control group / placebo

Question 146

define the term epidemic [1]

Answer 146

- (significant/large) increase in the usual number of cases / rapid spread of infectious disease to a large number of people within a short period of time

Question 147

( cholera in Haiti question after earthquake): - explain how cholera spread in Haiti [2]

Answer 147

- sewage entered water supply - cholera spread by drinking contaminated water / feco-oral route

Question 148

explain why the time taken to produce the antibody level required for immunity was much shorter following the booster injection [2]

Answer 148

- memory cells already present - less antigen needed to stimulate immune reponse - more plasma cells produced in a shorter period of time

Question 149

- a graph shows the blood antibody concentration after a vaccine - explain why the blood antibody concentration against measles would change in this way after a vaccine [2]

Answer 149

- no prior exposure to the ANTIGEN - produces a primary immune response/no memory cells - has to go through a latent period - needs time to recognise foreign antigen/for colonal expansion/clonal selection/development of humoral response

Question 150

- complete the following sentences giving the correct name: - a disease which is always present at low levels in an area is referred to as _____ - a person who shows no symptoms when infected by a disease but can still pass the disease on to another individual, is referred to as a _____ - organisms which carry pathogens from one individual to another are called _____ - antibiotics that prevent bacterial growth are referred to as _____ - the term used to describe a disease which may be passed or transmitted from one individual to another is _____

Answer 150

- endemic - carrier - vector - bacteriostatic - infectious

Question 151

- following an earthquake in Haiti, over 60000 cases of cholera were reported - describe how the spread of cholera could have been prevented following the earthquake [2]

Answer 151

- sanitation / safe disposal of sewage / good hygiene - provision of (clean/safe) drinking water / bottled water - vaccine

Question 152

- a diagram shows part of the cell wall taken from Vibrio cholerae - the bacterium causing cholera - has an outer layer and smaller layer labelled X a) name TWO components found in the outer layer [2] b) name the component found in layer X [1]

Answer 152

a) - lipoprotein - lipopolysaccharide b) peptidoglycan / murein

Question 153

explain why penicillin is ineffective in treating cholera [3]

Answer 153

- penicillin prevents FORMATION of (cross linkages/peptidoglycan) in cell wall - cholera is a gram-negative bacterium - therefore has VERY LITTLE peptidoglycan - lipopolysaccharide layer protects cell from penicillin action

Question 154

- although micro-organisms can cause diseases in humans, scientists believe that up to 10^16 symbiotic microbial cells live in or on the human body - up to 90% of all diseases can be traced back in some way to the composition of this microbiome - an average adult has 10^13 cells in our body - suggest why it is often said that we are more microbe than human in terms of our genomes and describe how the microorganisms living inside our bodies and on the skin surface help protect us from infectious disease [3]

Answer 154

- cells : there are (more than 1000 times/many more) microbial cells on/in our bodies than human cells - genomes: there are (many different/variety) bacterial (genomes / species) within the human body - protection: they prevent (harmful microbes / pathogens) colonising the human body and causing disease/ outcompete pathogenic bacteria

Question 155

explain the role of the macrophage in the T-cell response [3]

Answer 155

- (engulfs the foreign microbe / ref to phagocytosis) - antigenic presentation - the T-cell recognises the foreign antigen - T cells are then activated / undergo clonal expansion

Question 156

describe the role of each of the T-cell types as part of the immune response: a) killer T cell b) helper T cells c) memory T cells

Answer 156

a) • killer T cells - (causes lysis of/destroys) (target cells / named cells) b) • helper T cells - co-operate with B cells to initiate antibody response / secretes cytokines / B cell activation c) • memory T cells - remain (dormant/in circulation) until host is exposed to antigen again / initiate secondary immune response

Question 157

- B cells are activated in a similar way t T cells but synthesise antibodies that are specific protein molecules that can bind to foreign antigens - these antibodies can be of different types as shown in a diagram - IgM is made of five antibody molecules bonded together. - a more detailed diagram of IgG is shown in another diagram (diagram of an antibody) - the hinged section of the IgG molecule give it some structural flexibility. suggest an advantage of this [2]

Answer 157

- it allows the antibody to (bend/flex/distort/change shape) in order (for both arms) to bind to different antigens - because antigens are different distances apart on the target cell - antigens on different cells/cause clumping/agglutination of bacterial cells

Question 158

- B cells are activated in a similar way t T cells but synthesise antibodies that are specific protein molecules that can bind to foreign antigens - these antibodies can be of different types as shown in a diagram - IgM is made of five antibody molecules bonded together. - a more detailed diagram of IgG is shown in another diagram (diagram of an antibody) . - suggest an advantage of the IgM molecule over IgG [1]

Answer 158

- IgM can bind to more antigen than IgG / so it can agglutinate more antigen / bind to more antigen / form larger clumps of antigen

Question 159

- a plate of bacteria was prepared by mixing 0.02 cm³ of a 10^-5 dilution of bacteriophages with a bacterial culture and spreading it on an agar plate - this plate was incubated for 24 hours at 37°C - on the plate shown there are 25 plaques - calculate the number of bacteriophages per cm^3 in the original sample [2]

Answer 159

25 x10^6 = 25,000,000 per 0.02 = 125,000,000 per cm^3

Question 160

describe two techniques that could have been used to maintain sterile conditions when inoculating the plates [2]

Answer 160

- flame mouth of test tube / flask - work near updraft of Bunsen burner - use sterile (pipette / equipment) / flame (loop/spreader) - tilt lid of petri dish

Question 161

- antibiotics have no effect on viruses - chickenpox is a highly infectious airborne disease caused by the varicella-zoster virus - the virus spreads easily in the air when an infected person coughs or sneezes - airborne viruses have antigens that can attach to the surface membrane of cell lining the trachea - explain why the varicella-zoster virus needs to enter the cells of the trachea and the effect this has on the cells [2]

Answer 161

one of: - needs host cell (for reproduction / for metabolic processes) - virus has no organelles / metabolic pathways of its own - uses cell metabolic pathways for reproduction one of: - kills the cell by (cell lysis / production of toxic substances)

Question 162

using your knowledge of the humoral response, explain the concentration of antibodies after the vaccination [3]

Answer 162

- clonal selection B cell / antigenic recognition / antigenic presentation activating B cells - B cell undergoes clonal expansion / mitosis of B cells / cloning - DIFFERENTIATED into plasma cells - that (secrete/produce) the specific antibody

Question 163

- to assess the effectiveness of a vaccine a technique of measuring antibody levels was repeated with several blood samples taken from a number of volunteers - a statistical test was used to assess the significance of the differences in the antibody levels before and after vaccination a) state the null hypothesis [1] b) the test gave a value greater than the critical value at a probability of 0.05. state whether you would accept or reject the null hypothesis and explain why [1]

Answer 163

a) there is no significant difference in the concentration of antibodies in the blood samples before and after vaccination b) the hypothesis should be rejected. there is a significant difference in concentration of antibodies

Question 164

if it asks about mode of action of antibiotic its either bactericidal or bacteriostatic

Question 165

identify the type of bacterium to which Vibrio cholerae belongs (bacterium causing cholera) [1]

Answer 165

gram negative

Question 166

describe how cholera may be transmitted [1]

Answer 166

- via faecal-oral route / faeces of infected person to mouth of uninfected person / via contaminated water / food / flies

Question 167

- the bacterium, Vibrio cholerae, is the causative agent of cholera - it produces a toxin which causes water and ions, such as sodium, chloride, and potassium to be released from the blood into the intestine - this can result in death within 24 hours . - use the information in the passage to suggest how the toxin can lead to the death of a cholera patient [3]

Answer 167

- water not absorbed / reabsorbed / water lost from body - low conc of solutes / in blood - low blood volume - dehydration - poor nerve conduction - poor heart activity / failure

Question 168

- a new strain of cholera arose in the Far east in the 1960s and gradually replaced existing strains throughout much of the world but not in Western Europe - suggest 2 reasons why the new strain of cholera has not become established in western europe [2]

Answer 168

- sewage treatment / better sanitation - clean water supply / chlorination - good food hygiene - transmission cycle broken

Question 169

- the antibiotic tetracycline is sometimes given to cholera patients - describe one way in which the antibiotic can affect the Vibrio cholerae [1]

Answer 169

stops growth / division / protein synthesis

Question 170

explain why tetracycline is not routinely used to treat all cases of cholera [2]

Answer 170

- resistance of bacteria

Question 171

- large numbers of children continue to die from measles - children may now be vaccinated against measles - the effectiveness of the vaccine varies according to diet - a graph shows the level of antibody in a well fed child and a malnourished child over a period of eight weeks from the point of vaccination - state why there is a difference in the response for a malnourished child [2]

Answer 171

- antibodies made of protein - required to make new antibodies / lack of protein / no or fewer antibodies - process is energy dependent

Question 172

how do T lymphocytes affect the activity of phagocytes [1]

Answer 172

STIMULATE phagocytosis / produces more phagocytes (not triggers)

Question 173

what is the function of the vas deferens? [1]

Answer 173

transport/carry/travel sperm/spermatozoa

Question 174

what is the function of the scrotum? [1]

Answer 174

- maintains a (cool/optimum/34°C) environment (for spermatogenesis) - holds tested outside abdomen

Question 175

what is the function of the testes?

Answer 175

- to produce sperm / spermatogenesis / produce testosterone

Question 176

what is the function of the epididymis? [1]

Answer 176

(sperm) (undergo maturation / are concentrated)

Question 177

what is the function of the prostate gland [1]

Answer 177

secrete a (slightly) alkaline fluid

Question 178

state two reasons why it’s important that the radicle emerges prior to the plumule [2]

Answer 178

- (anchors / roots / stabilises) in (SOIL/EARTH/GROUND) - for (water / minerals / nutrients)

Question 179

briefly describe the stages of germination in a NON-ENDOSPERMIC SEED such as the pea [3]

Answer 179

- water is taken up through the micropyle - the testa (splits) - (which allows) oxygen (to enter / used in respiration) - (food reserves / starch / proteins) (from the cotyledons) are (hydrolysed / digested / broken down)/

Question 180

- gibberellin is required for maize kernel (seed) germination - what is the function of gibberellin?

Answer 180

- gibberellin diffuses to the aleurone layer - gibberellins (induce / cause the production / cause the release) of (hydrolytic enzymes / amylase) - glucose/other nutrients are used in (aerobic respiration/growth) - roots/radicle/plumule grow

Question 181

- the human genome project determined the base pairs that make up human DNA - explain how the results from the human genome project have allowed the synthesis of the artificial genome to become possible [1]

Answer 181

the sequence/order of the (DNA) bases (is known)

Question 182

- state the advantages of using an artificially synthesised gene rather than extracting the gene from the human genome [3]

Answer 182

- don’t need to (locate/isolate/find) the gene/do not need to use gene probes - no need to (use restriction enzymes to cut up DNA/find functional mRNA) - (restriction enzymes) may cut within a gene/extracting the gene may damage it - no (introns/non-coding DNA) present / only (exons /coding DNA) present

Question 183

- name the two types of enzymes needed for the successful insertion of the human growth hormone gene and state their function in the process [2]

Answer 183

- RESTRICTION (endonuclease / enzyme) cuts DNA (in the plasmid) at a specific (sequence of bases / point) - (DNA) ligase (anneals/joins/binds) the (plasmid/vector) and (gene/DNA)

Question 184

- an image shows how the skeleton of the modern horse has evolved from a horse-like mammal over the last 38 million years - explain how the information in the image supports Darwin‘s theory of evolution [3]

Answer 184

- the image shows that bone structures follow a similar pattern (through millions of years) - (so) have arisen from (a common ancestor) - example of a change to (jaw/head/skeleton) - by natural selection/selection pressures/selective advantage

Question 185

- the population consisted of randomly mating horses in semidesert conditions. - use all the information given to give two reasons why this population may not be in Hardy-Weinberg equilibrium [2]

Answer 185

- there may be (selection/better survival rate) for the lighter coloured horses / better camouflage/blend in better - reference to mutations - reference to immigration AND emigration / migration in AND out

Question 186

- mutation in the DNA of an organism may have a profound effect on the phenotype - there are two main types of mutations: gene and chromosome - explain what is meant by the term mutation and describe some factors which increase the rate of mutations - describe the different types of gene and chromosome mutations and, using suitable examples, explain the different effects that gene and chromosome mutations may have on the phenotype [9QER]

Answer 186

MUTATION - mutations are (spontaneous/random events/very low frequency) - the change in structure of (gene/chromosome) or change in (sequence of bases/DNA) - are the source of genetic variation - ionising radiation/e.g. gamma radiation/UV/x-rays - cigarette smoke/smoking/cigarettes/polycyclic hydrocarbons - carcinogen/mutagen/chemicals causing cancer/benzene GENE MUTATION - reference to point mutation (/deletion/addition/substitution/inversion) of bases / reference to frame shift - gene mutations can affect protein synthesis - changing the sequence of amino acid/code for different amino acid - can change the phenotype of an organism - some mutations have no effect on the phenotype/description of degenerate code/mutations in intron/silent mutations - example of gene mutation: cystic fibrosis/sickle cell CHROMOSOME MUTATION: - chromosome mutation affect many genes/different sequences of genes (on chromosomes) - (different types of chromosome mutations) e.g (invasion/ translocation/deletion) of part of a chromosome / non-dysjunction (in meiosis) - most chromosome mutations occur during crossing over (in prophase-1) - could result in (trisomy/ aneuploidy / change in chromosome number) - may be fatal - example of chromosome mutation: downs syndrome

Question 187

- a graph of time on x-axis against concentration of antibodies on y-axis, after vaccine, and then exposure to the disease - describe and explain the shape of the graph which shows the primary immune response [4]

Answer 187

- description of graph: antibody levels constant/zero, then increase, then decrease explanation: - latent period/macrophages carry out phagocytosis/antigen presentation takes place - clone selection/activation of B cells/ T helpers release cytokines to stimulate B cells/B cells undergo clonal (expansion/proliferation ) - increases as plasma cells release antibodies - decreases as antibodies are broken down

Question 188

- a graph of time on x-axis against concentration of antibodies on y-axis, after vaccine, and then exposure to the disease - explain how vaccination prevents development of the disease when exposed to the disease [4]

Answer 188

- short/no latent period - due to memory cells - RAPID production of plasma cells/memory cell undergo clonal expansion faster - antibody concentrations increase (faster/sooner / to higher concentrations) (than primary response) - antibody concentrations stay higher for longer/remain in the bloodstream for longer

Question 189

- the methods of treating TB can also be used to treat malarial infections - explain why these methods are less effective when they are used in the treatment of malarial infections [2]

Answer 189

- PLASMODIUM not affected by antibiotics - drugs not effective when PLASMODIUM in red blood cells - resistance to (drug/named treatments) - reference to antigenic variation/high mutation rate

Question 190

what is the function of the fallopian tubes (oviducts)?

Answer 190

- have lining of ciliated epithelial cells which move the secondary oocyte to the uterus

Question 191

function of uterus?

Answer 191

holds the developing foetus until birth

Question 192

function of endometrium?

Answer 192

- the inner most layer of the uterus wall - has a good blood supply and builds up every month during gthr menstrual cycle

Question 193

function of cervix?

Answer 193

- a narrow ring of connective tissue and muscle - acts as a barrier betwen the uterus and outside environment during pregnancy - during pregnancy, a mucous plug forms in the cervix which helps prevent entry of pathogens

Question 194

when does the secondary follicle develop?

Answer 194

in response to FSH (a follicle consists of a ball of diploid cells surrounding an oocyte. the cells of the follicle develop and increase in numbers as thr oocyte develops)

Question 195

when does the corpus luteum develop?

Answer 195

- when stimulated by LH (if fertilisation occurs, it starts secreting progesterone and oestrogen

Question 196

fertilisation:

Answer 196

- following sexual intercourse, spermatozoa move into the fallopian tubes - capacitation increases the permeability of the cell membrane in the head of the sperm above the acrosome - acrosome reaction releases hydrolyse enzymes which digest zona pellucida - fusion of sperm and secondary oocyte membranes; genetic material of sperm cell enters the secondary oocyte triggering completion of meiosis II and formation of ovum and second polar body - cortical reaction in which cortical granules fuse with the cell membrane and modify the zona pellucida to from the the fertilisation membrane; this prevents polyspermy - nuclei of the sperm and ovum fuse to form a zygotic nucleus

Question 197

- following implantation, the placenta takes over secretion of human chorionic gonadotrophin from the blasocyst - this maintains the corpus luteum and its secretions of progesterone and oestrogen for the first 16 weeks of pregnancy - as the placenta develops it takes over secretion of progesterone and oestrogen from the corpus luteum

Question 198

how are chorionic villi adapted for increased efficiency of exchange?

Answer 198

- microvilli that increase surface area - thin walls - approximately 5 µm therefore distance for diffusion is short - a countercurrent flow of blood between foetal and maternal blood that maintains the concentration gradient

Question 199

what do the intervillous spaces contain in the placenta?

Answer 199

- contain mother’s blood surrounding chorionic villi - maternal and foetal blood do not mix

Question 200

- pollen grain lands on stigma and absorbs water . - during germination and growth of pollen tube, the generative nucleus (n) divides by mitosis to form 2 male nuclei (n) . - the growth of the pollen tube is a positive chemotrophic response - the pollen tube grows towards chemicals secreted by the embryo sac

Answer 200

- once the pollen tube has entered the embryo sac, the pollen tube nucleus disintegrates

Question 201

FORMATION OF STRUCTURE OF SEED AND FRUIT: - following fertilisation: - the diploid zygote divides by mitosis to form the diploid embryo and then differentiates into a young shoot (the plumule), young root (the radical) and one or two seed leaves (the cotyledons) - the triple endosperm tissue divides by mitosis to form endosperm tissue which forms the food source for the growing embryo - in some species of plants called monocotyledons e.g. maize, the endosperm remains and only one cotyledon present - in other plants, called dicotyledons e.g broad beans, the endosperm is quickly absorbed and stored in two cotyledons

Question 202

DEVELOPMENT OF FRUIT AFTER DOUBLE FERTILISATION: BEFORE FERTILISATION VS AFTER - ovule = seed - integuments = testa (seed coat) - micropyle = pore - ovary wall = fruit wall - content of ovary = fruit - attachment point of funicle to ovary = hilum

Question 203

comparing structure of broad bean vs maize seed: BROAD BEAN: - testa - plumule - hilum - micropyle - radicle - cotyledon (two present) (dicotyledon) MAIZE SEED: - testa and fruit fused - plumule - radicle - funicle - endosperm (stores starch which provides a food source for growing embryo) - cotyledon (one present) (monocotyledon)

Question 204

water content of seed is very low and is the major factor that prevents germination

Question 205

changes in dry mass of embryo, seed and endosperm, cotyledon: - hydrolysis of food reserves in the endosperm/cotyledon and starch is converted to sugars - the dry mass of the endosperm/cotyledon decreases because: • CO2 is lost when the sugars are used in aerobic respiration • sugars are sent to the embryo - mass of embryo increases as it receives sugars from the endosperm/cotyledon - total mass: • decreases at first as CO2 is lost in aerobic respiration • then increases as the first leaves produced (plumule) begin producing biomass during photosynthesis

Question 206

GERMINATION IN A NON-ENDOSPERMIC SEED e.g broad bean

Answer 206

- water is absorbed through the micropyle - the cotyledons swell and the testa splits allowing entry of more water and oxygen for aerobic respiration - starch and proteins reserves in the cotyledons are hydrolysed - products of hydrolysis are used as: • a source of source of energy for respiration • growth of the plume and radicle

Question 207

GERMINATION IN AN ENDOSPERMIC SEED e.g maize

Answer 207

- following the absorption of water, gibberellin, (gibberellic acid) is released by the embryo - the gibberellin diffuses to the aleurone layer (the outer layer of the endosperm) which contains protein - gibberellin induces the production of hydrolytic enzymes e.g amylase - the hydrolytic enzymes diffuse into the inner layer of the endosperm and catalyse the breakdown of stored nutrients e.g starch - glucose and other breakdown products of the stored nutrients diffuse into the embryo where they are used for aerobic respiration and growth

Question 208

mendel’s laws only apply if the genes are on different chromosomes i.e not linked

Question 209

for the monohybrid test cross, if the ratio of dominant to recessive is 1:1, the genotype is heterozygous e.g Tt x tt = T t t t = Tt Tt tt tt

Question 210

- in a dihybrid test cross, if the genotype is homozygous dominant, there will only be one phenotype e.g W = white, w= yellow, D=disc shaped, d= spherical WWDD x wwdd gametes: WD x wd so WwDd

Answer 210

- if heterozygous dominant, will be ratio of 1:1:1:1 e.g WwDd x wwdd WD Wd wD wd x wd = WwDd Wwdd wwDd wwdd 1:1:1:1

Question 211

- if the observed ratios doesnt fit any of the Mendelian ratios, test-cross ratios or ratios for codominance, then there may be gene linkage involved

Question 212

a genetic trait is a characteristic of an organism that is a result of gene expression and/or the environment i.e the phenotype

Question 213

when can a chromosome mutation occur?

Answer 213

- polyploidy = some organisms have additional complete sets of chromosomes e.g three sets of chromosomes - additional chromosomes = sometimes during anaphase I of meiosis a pair of homologous chromosomes fail to separate. this is called non-disjunction and is often lethal

Question 214

non-heritable variation refers to the differences in phenotype due to environmental reasons. this type of variation cant be inherited

Question 215

- if a phenotype gives a selective advantage, the alleles responsible for that phenotype will be selected for and is more likely that they will be passed on to the next generation

Question 216

- evolution, in terms of speciation, will NOT take place if the conditions under which the hardy-weinberg principle apply

Question 217

speciation can occur due to:

Answer 217

- genetic drift in isolated populations - the founder effect of disproportionate allele frequencies in small populations - natural selextron - however for new species to develop from a population, some form of isolating mechanism is essential

Question 218

sequencing other species’s genomes can mean scientists can also look at evolutionary relationships - it provides true phylogenic classification and can be used to correct mistakes made using classification based on phenotypic characteristics - consider how to conserve species in the future by targeting which species need particular protection

Question 219

pcr can be described as semi-conservative replication in a test tube

Question 220

restriction endonucleases can be used to cut DNA extracted from a sample into small fragments for electrophoresis

Question 221

basic steps in genetic engineering:

Answer 221

- identify and obtain the gene - insertion of the gene into a vector, producing recombinant DNA - insertion of vector into the host cell and identification of transgenic organism - production of protein by the host cell / separation and purification of the protein

Question 222

in genetic engineering, how to idenify the gene?

Answer 222

- using a gene probe - this is a specific segment of single-stranded DNA that is complementary to a section of the gene into

Question 223

in genetic engineering, how to isolate the located gene?

Answer 223

using either of 2 enzymes: - reverse transcriptase - restriction endonuclease

Question 224

in genetic engineering, how to isolate located gene using reverse transcriptase:

Answer 224

- cells that produce a specific polypeptide will contain many copies of the functional mRNA transcribed from the target gene - the mRNA can be isolated and complimentary single strands of copy DNA can be produced from the mRNA template using the enzyme reverse transcriptase - DNA polymerase can then be used to make a double standard DNA molecule - this will be an exact copy of the gene

Question 225

advantages of using reverse transcriptase:

Answer 225

- this method avoids the to locate the gene - the DNA produced does not include introns because the cDNA is copied from functional mRNA (the pre-mRNA in the nucleus that has been transcribed from the DNA has been modified to produce mRNA that does not contain introns) - the DNA produced does not contain any non-functional fragments

Question 226

in genetic engineering, how to isolate located gene using restriction endonucleases:

Answer 226

- restriction endonucleases are bacterial enzymes that cut DNA at specific nucleotide sequences - the enzyme will cut the DNA into many small fragments and individual genes can be isolated - some restriction endonucleases cut straight across a DNA double strand, making a blunt cut. but many make a staggered cut, which leaves unpaired bases on both strands - these bases pair with complimentary sequences readily so they are called sticky ends

Question 227

in genetic engineering, how to insert the gene into a vector, producing recombinant DNA:

Answer 227

- cells are unlikely to take in a gene spontaneously, so the gene must be carried into the cell by a vector - viruses can be used as vectors as well as bacterial plasmids - plasmids are much smaller than bacterial chromosomes and contain only a few genes - plasmids can move in and out of cells, which makes them useful for introducing genes into bacteria . - bacteria are treated to destabilise the cell walls and breakdown the cell membrane - plasmids are isolated from the cell debris - the circular plasmids is cut open using the same restriction endonuclease as was used to isolate the gene - this means it has the same nucleotide sequence in its sticky ends - DNA ligase then joins the DNA of the plasmid and gene by catalysing the formation of phosphodiester bonds between the sugar-phosphate backbones

Question 228

in genetic engineering, how to insert the vector into the host cell and identification of transgenic organism:

Answer 228

- when plasmids are mixed with bacterial cells, as few as 1% of the bacteria take up the plasmid and become transformed - to obtain transgenic bacteria which contain recombinant plasmids: 1. the plasmids must successfully incorporate the gene (become recombinant) 2. bacteria must successfully take up the recombinant plasmids . - successful transformation can be confirmed by: - DNA sequencing - marker genes - these vary according to the type of transgenic organism produced

Question 229

use of antibiotic resistance genes in the selection of recombinant bacteria:

Answer 229

- the method below describes how antibiotic resistant genes can be used in the selection of recombinant bacteria . - special plasmids are used which already have two inserted genes, an ampicillin resistant gene and a tetracycline resistant gene. these will be used in identifying the transgenic cell later on - when bacterial plasmids are mixed with the gene fragments in the presence of restriction endonuclease and DNA ligase there are two possible outcomes: • the gene is included in the plasmid, disrupting the tetracycline resistant gene • the plasmid is reformed without the inclusion of the gene - the plasmids are then mixed with the bacteria - there are three possible outcomes: • bacteria that have not taken up the plasmids • bacteria that have taken up unaltered (non-recombinant) plasmids • bacteria that have taken up recombinant plasmids - the transgenic bacteria are identified using a technique called replica plating - bacteria are grown on agar in a petri dish - a ‘stamp’ is used to transfer a sample of each bacterial colony onto an agar plate containing either tetracycline or ampicillin

Question 230

in genetic engineering, production of protein by the host cell and/ separation and purification of the protein:

Answer 230

- bacterial cells with recombinant plasmids are cultured in large volumes in fermenters - the bacteria divide over and over to form clones, each one containing copies of the recombinant plasmid - the bacterial enzymes transcribe the inserted gene in the plasmid and translate the mRNA to produce the desired protein

Question 231

- a drug called drisapersen aims to treat DMD by introducing a ‘molecular patch’ over the exon - mode of action of drisapersen:

Answer 231

- it’s a 50 nucleotide sequence that is complementary to the mutated sequence - it binds to the mRNA over the exon with the mutation - that portion of mRNA becomes double-stranded - the ribosome is unable to translate that portion of the mRNA - the ribosome skips the mutation producing a shorter, partially functional dystrophin protein molecule

Question 232

- the human genome and 100 K project should enable healthcare to be improved by:

Answer 232

- more accurate diagnosis - better prediction of the effect of drugs - improved design of drugs - introduction of new and improved treatments for disease

Question 233

- an image shows the sequence of events which occur in the fallopian tube and uterus before and after fertilisation - state the process which has just recently occurred in the ovary [1]

Answer 233

ovulation

Question 234

briefly describe the process of fertilisation in humans [4]

Answer 234

- (the acrosome reaction) releases (hydrolase enzymes) which (digest/break down) the zona pellucida - the (GENETIC MATERIAL/DNA/CHROMOSOMES) of the sperm cell enters (the secondary oocyte) - this triggers (the cortical reaction/formation of the fertilisation membrane/description of) and prevents polyspermy - (entry of the genetic material also) triggers meiosis II - nuclei of sperm and ovum/gametes fuse to) form a DIPLOID (zygote/nucleus)

Question 235

- state the type of cell division involved in the production of the blastocyst in the endometrium and the term given to the events shown by the secondary oocyte travelling through the fallopian tubes to the uterus [1]

Answer 235

- MITOSIS - and (cleavage/cytokinesis)

Question 236

explain why ciliated epithelium is important in lining of the fallopian tube? [3]

Answer 236

- (cillia) move - the secondary oocyte/zygote/blastocyst - (from the ovary) along the fallopian tube/oviduct) towards the (uterus/endometrium)

Question 237

explain why hCG levels are used in pregnancy tests to determine if a woman is pregnant [2]

Answer 237

- no hCG (prior to pregnancy / not present before week 4) - rapid rise in levels (if pregnancy is present) - easy to detect / not likely to get false positives

Question 238

state the function of hCG in pregnancy and what happens if levels of hCG fall or are too low at the start of the pregnancy [3]

Answer 238

- maintains the corpus luteum any two from: - if hCG levels fall then corpus luteum degenerates/is not maintained - levels of progesterone would fall/corpus luteum does not produce enough progesterone - the (endometrium/uterus lining) breaks down/is shed - embryo would be shed/cause miscarriage

Question 239

explain the functions of the hormones oestrogen AND progesterone during pregnancy [4]

Answer 239

- (placenta secretes) progesterone and oestrogen/ (rise/increase) - FSH AND LH secretion are inhibited - progesterone (suppresses the (uterine wall/myometrium) ability to contract/MAINTAINS (endometrium/uterus lining) - oestrogen stimulates the growth of the uterus to accommodate the growing foetus - oestrogen stimulates the (growth/development) of the mammary glands

Question 240

suggest the advantage of being Tt (t= beta thalessemia) individuals in a region where malaria is present [2]

Answer 240

- (more resistant) to malaria - because parasite cannot REPRODUCE/FEED in (Tt individuals) RBC’s

Question 241

- the frequency of the t allele is 2% in a population - using the formula: p+ q = 1 and p^2 + 2pq + q^2 = 1, calculate the % of the population that will be heterozygous (Tt) for the thalassemia gene [3]

Answer 241

t= 0.02 q = 0.02 p = 1-0.02 =0.98 2pq = 0.0392 = 3.92%

Question 242

- one possible way of treating sickle cell disease is using gene therapy and stem cells - stem cells are removed from the patient and treated with a gene editing technique CRISPR - the repaired gene can then function normally and the treated stem cells are replaced in the patient - state why stem cells must be used in this technique [2]

Answer 242

- (undifferentiated/unspecialised) (can continue to divide) - can (specialise and become/differentiate into) RBCs

Question 243

- state two advantages of using bone marrow stem cells over embryonic stem cells [2]

Answer 243

- less / no chance of rejection - fewer / no ethical concerns

Question 244

- the gene editing relies on the RNA guide recognising a target sequence of DNA so that the editing can be carried out on the correct section of DNA - this RNA is synthesised in laboratories from a template so that it matches the target sequence - suggest how the result of the human genome project has made the use of this gene editing technique possible [2]

Answer 244

- identification of position of gene/all genes - need to know base sequence of (normal/replacement) genes - need to know base sequence to RNA guide

Question 245

use the images of a dandelion and cochlebur to briefly describe how the following seeds are dispersed [2]

Answer 245

- dandelion- (wind dispersal) - seeds have ‘parachutes’ so seed is blown in the wind - cocklebur (animal dispersal) - seeds has hooks which catch in animal (fur)

Question 246

- call it a ‘pizzly’ or a ‘grolar’ bear, this new hybrid may be here to stay, say scientists - but is this the end of the polar bear as we know it or the start of a new bear species? - this is the title of a recent scientific report stating that there was an increase in numbers of hybrid bears, which are polar bear and brown grizzly bear hybrids, and subsequent offspring which are 3/4 brown bear and 1/4 polar bear . - at the start of the last ice age, a population of brown bears in the north became geographically isolated when increased ice stopped the free movement of the briwn bears - following their isolation, these brown bears evolved to become polar bears . - brown bears eat tubers, berries and fish - polar bears rapidly evolved a metabolism that let them live off a blubber-rich diet which would be unhealthy for most mammals - polar bears have genes related to fat transport, fatty acid metabolism and cardiovascular function - all of which helped them survive on a diet of mostly fatty marine mammals like seals - polar bears adjusted to this ultra high fat diet in less than 20 500 generations . - since 2008 brown bears have been spotted further north than their historic range, a possible consequence of climate change - as a result the brown bear habitat now overlaps the polar bear habitats - these two kinds of bears, which are capable of mating and producing viable offspring, are considered to be separate species . - describe how the process of geographical isolation has resulted in the evolution of polar bears from the brown bear. - explain how the polar bear has adapted to live in its habitat - suggest how the existence of hybrid bears affects scientists’ confidence that they are two different species [9QER]

Answer 246

PROCESS OF GEOGRAPHICAL ISOLATION: - description of geographical isolation e.g. when a population is separated by a physical BARRIER - ice as isolating mechanisms - which (prevents/interfere with) gene pool/genetic drift / reference to random mutation - effect of selection pressures changing the frequency of alleles in a population - e.g. of selection pressures for bears e.g. food availability/hunting new prey/camouflage/ability to metabolism a high fat diet POLAR BEAR HAS ADAPTED TO LIVE IN ITS HABITAT - selection of alleles/genes/reference to change in the genetic material allowing a high fat diet - physiological changes had to be (quick/reference to less than 20 500 generations) if they were to substist on a dangerously high fat diet - bears have evolved to eat (primarily) blubber - polar bears must have large fat deposits under their skin to keep warm in arctic conditions/rely on metabolic water, a byproduct of the breakdown of fat - change in fur colour (brown to white) so able to (hunt/camouflage) /the development of a seeker body for hunting/swimming. TWO DIFFERENT SPECIES - not separate species as can interbreed to produce fertile offspring - gene pool still sufficiently similar - subsequent interbreeding of hybrid with brown bears - overlapping territories (due to receding ice) allows the two groups contact for interbreeding - will continue to interbreed so gradual loss of pure polar bears - may outcompete pure brown bears/loss of genetic diversity

Question 247

suggest one reason why it’s important that the number of blood vessels in the ovary increase after ovulation [1]

Answer 247

- provides material for hormone (synthesis/secretion/production) / so the hormones can be transported)

Question 248

describe the function of the acrosome in a spermatozoon [1]

Answer 248

- secretes an enzyme to digest the (zona pellucida / jelly coat / outer layer of secondary oocyteG

Question 249

describe the function of the nucleus/head in a spermatozoon [1]

Answer 249

- carries (genetic material / chromosomes / DNA) / fuzes with (female nucleus / secondary oocyte) to form (2n / zygote)

Question 250

describe the function of the mitrochondria in a spermatozoon [1]

Answer 250

- provides ATP for (mobility/movement)

Question 251

- humans normally have a diploid number 2n = 46 - occasionally a secondary oocyte is fertilised by two sperms - the embryo formed develops abnormally and will not survive - state the number of chromosomes this embryo would have and the term used to describe the number of sets of chromosomes [2]

Answer 251

- 69 - triploid / triploidy

Question 252

- humans normally have a diploid number 2n = 46 - occasionally a secondary oocyte is fertilised by two sperms - the embryo formed develops abnormally and will not survive - this number of sets of chromosomes also occur naturally in a certain plant tissue - state the name of this plant and state its function [2]

Answer 252

- endosperm - as (food/starch/protein/lipid) (source)

Question 253

state two features of a placenta and describe how they are important to the survival of the embryo [2]

Answer 253

- has a large surface area + (diffusion/absorption/gas exchange) - (good blood supply/many arteries/many veins) AND (to carry neutrients/waste) - umbilical cord + carries blood (to/from) the (placenta/embryo/foetus/baby) - acts as a barrier + to (mixing blood/different blood pressures/pathogen filter/mothers immune system) OR secretes hormones + to maintain pregnancy

Question 254

- co-dominance and certain homozygous genotypes can give unusual ratios in the resulting offspring - horticulturalists crossed plants which had red flowers and variegated leaves with plants which had red and white flowers and variegated leaves - using the symbols below show this cross and the resulting offspring by: • completing the parental genotypes and gametes • and drawing a genetic diagram RR red flower RW red and white flower WW white flower GG green leaves GA variegated leaves AA white leaves parental phenotype : red flower, variegated leaves vs red and white flower, variegated leaves parental genotype: gametes:

Answer 254

RRGA vs RWGA RG, RA vs RG, RA, WG, WA = RRGG RWGG RRGA RWGA RRAA RWAA 1, 1, 2, 2, 1, 1

Question 255

- the resulting 420 seeds from the above cross were planted and the phenotypes of all the MATURE plants were counted and the following results observed - 56 red flowers green leaves - 102 red flowers, variegated leaves - 49 red and white flowers green leaves - 110 red and white flowers, variegated leaves . - the following observation was made: - of the 420 seeds produced in the above cross, all the seeds germinated but 103 did not grow and so a different phenotypic ratio was observed than expected. - explain this observation. your answer should include reference to : • germination • plant leaf cell structure • observed and expected phenotypic ratios [5]

Answer 255

- seeds can still germinate because of food stores any four from: - AA leads to white leaves/white leaved (plants/phenotypes) do not grow - so no (chlorophyll/chloroplasts) - so no (photosynthesis/synthesis of carbohydrate) - plant dies when food stores (in seed) run out - 1/4 of the plants die/white leaves plants not included in ratio / 2:2:1:1 ratio

Question 256

- polymerous chain reaction (PCR) was carried out to amplify DNA and after 40 cycles over a billion copies of the target sequence was produced - explain the following processes during PCR: • a single stranded DNA primer is added [1] • the DNA is heated to 95° at the start of a cycle [1] • the DNA is then cooled to 50-60°C [1] • explain why a certain type of polymerase, called Taq polymerase, is necessary in the final extension stage of the cycle at 70° C [1]

Answer 256

- (is complimentary to/attaches to) the START of the sequence/allows binding of (taq/DNA) polymerase - breaks hydrogen bonds between strands/separating the two strands/DNA becomes single stranded - to allow the primers (to bind/anneal) (to the DNA strands) - thermally stable/can withstand (high temperatures/resistance to heat)

Question 257

- the human genome project was completed in April 2003 when an accurate and complete human genome sequence was made available to scientists and researchers - as a result of this research, more gene therapy drug trials have taken place - a graph shows the number of gene therapy drug trials increasing between 1997 and 2017 . - explain what is meant by gene therapy and outline ONE of the techniques involved - describe how the data in the graph supports a link between the completion of the sequencing of the human genome and the number of gene therapy trials - use your knowledge of the aims of the human genome project to explain your answer - describe the use of exon skipping gene therapy for the treatment of muscular dystrophy [9QER]

Answer 257

GENE THERAPY TECHNIQUES - insertion of a functional (gene/DNA/allele) (into cells)/replacement of a faulty (gene/DNA/allele) - germ line (where functional gene added to embryo/inherited - somatic gene therapy where functional gene is placed in body cells/not inherited - not permanent/needs re-treatment - example of use of restriction endonuclease /ligases/CRISPR/Cas9/ stem cells/use of vector/viruses/plasmids/liposomes HGP LINK - aims of HGP to: (sequence/identify (position of) (genes/DNA) in the human genome/improve understanding of genetic disorders/improve the diagnosis and treatment of genetic disorders - (prior to 2003/before HCG sequenced) very few GT drug trials - (after 2003/HGP sequenced) increase in GT trials - reasons: before 2003, not all of human genome was sequenced/(position of) faulty gene/mutation/change in bases) was unknown USE IN GENE THERAPY - DMD is caused by a (mutation in the/ faulty) (dystrophin) gene AND (failure to produce dystrophin/protein too short/causes muscle weakness/produces non-functional protein - (exon skipping introduces) a molecular patch over the exon with the (mutation/fault) - complementary RNA binds to the (mutated/fault) section of the (dystrophin) mRNA/which makes the gene readable/transcription can take place - a shorter/different form of DYSTROPHIN/PROTEIN is produced - which is functional

Question 258

- streptococcus and straphylococcus are types of gram positive bacteria - suggest how and why flucolaxacillin has a bactericidal effect on these types of bacteria [4]

Answer 258

- gram-positive have thick peptidoglycan in cell wall/no additional lipopolysaccharide (so more susceptible to antibiotic) - inhibits formation of cross linkages between (peptidoglycan/amino acids) - (peptidoglycan) cell wall is (broken down/digested)/cell wall is weekend - (osmosis/water moves in) causing cells to lyse/burst

Question 259

- fucloxacillin has become ineffective against some species of Staphylococcus - suggest why [3]

Answer 259

- reference to mutation - (means some bacteria) become RESISTANT - (the resistant bacteria) have a selective advantage/ are able to survive antibiotic - resistance passed on (when bacteria divide / reproduce / to next generation)

Question 260

suggest how infection following an insect bite could be prevented [1]

Answer 260

- dont scratch bites / wash area / use of anti-bacterial cream

Question 261

state why there is no current effective vaccine against Plasmodium [2]

Answer 261

- different species (of plasmodium) - different antigen(ic types) - mutates regularly

Question 262

conclude why the number of cases of measles increased between 2016 and 2020 [1]

Answer 262

less vaccination

Question 263

- the MMR vaccine contains antigens of three pathogens - explain why a child who is exposed to the measles virus after being vaccinated does not develop the measles disease [3]

Answer 263

- memory cells already present - due to prior exposure to antigen - memory cells detect antigen - shorter latent period - memory cells divide faster if same antigens are encountered

Question 264

what information does the standard deviation provide regarding the reliability of the results of an experiment?

Answer 264

- sd shows (variation from mean / reliability of mean)

Question 265

- bacteria of the species E. coli were genetically engineered contain the gene for chymosin - due to the presence of multiple introns in the gene, bacteria may not be able to carry out the RNA splicing - therefore they may not be able to produce the functional mRNA molecule needed to synthesise the chymosin protein - outline how an intron free DNA molecule containing the chymosin gene could’ve been produced [3]

Answer 265

- (extract / use) mRNA - because the introns have already been (removed / edited) - use reverse transcriptase to synthesise SINGLE STRANDED DNA (ignore cDNA) - DNA polymerase to synthesise double stranded (c)DNA

Question 266

design an experiment to investigate the effect of pH on the growth of pollen tubes. give a brief description of your method [4]

Answer 266

- place pollen grains in range of (pH (solutions) / pH buffers - measure lengths at set time / time intervals / every 20mins - same (species / type) of plant - same concentration of solution - (same/control) temperature - same (mass/volume / amount / age) of pollen grains - light intensity

Question 267

- describe the role of the vesicle, mitochondria, rough endoplasmic reticulum and golgi body in the passage of the pollen tubes through the style of a flower [4]

Answer 267

- (secretory) vesicle (contains/releases) (digestive/hydrolytic) enzymes /secretory vesicle( contain/releases) (protease/named enzymes) /exocytosis - (the enzymes digest/hydrolyse) a path through the style - mitochondria provides ATP/energy - rough EM/ribosomes synthesise the (enzymes/proteins) - golgi body - formation of vesicle/processing/modifying/packaging of proteins

Question 268

explain why after many generations the frequency of allele D is zero in the population of one species but the frequency of allele d in another will never be zero?

Answer 268

- in first, allele D is selectee against and so removed from the GENE PIOl - although d is a disadvantage, it isnt expressed / masked / passed on in heterozygotes thetefore remains in the GENE POOL

Question 269

- the lizards found at sites 3 and 4 are different species - explain how their dewlap colouration may have resulted in their speciation

Answer 269

- they have the opposite/different colour - males will not attract females - there isa reproductive barrier / behavioural isolation / genetic drift / do not interbreed

Question 270

what is the name given to the study of the control of gene expression by factors other than changes in the DNA sequence [1]

Answer 270

epigenetics

Question 271

- scientists have identified and spliced genes from algae that code for reproducing high levels of omega-3 fatty acids into plants - the genetically modified plants now produce seeds that contain 26% omega-3 fatty acids so more useful for fish farm feed - explain how named enzymes would be used to cut genes from algae and splice them into the plant [3]

Answer 271

- restriction endonuclease enzyme used to cut out DNA/gene - sticky ends or description of - SAME restriction enzyme used to open DNA in (vector/plasmid/virus) - ligase used to (insert/anneal/splice) gene into (vector/plasmid)

Question 272

- a photomicrograph below shows part of an ovary during ovulation - describe what subsequently happens to the following: - secondary oocyte - graafian follicle [2]

Answer 272

- (secondary oocyte) passes into the fallopian tube/oviduct - graafian follicle develops into the corpus luteum

Question 273

- describe how the hormones FSH and oestrogen illustrate the principle of negative feedback in controlling ovulation [4] - explain why oestrogen may therefore be used as a contraceptive [3]

Answer 273

- FSH stimulates the production of oestrogen - oestrogen INHIBITS the production/release of FSH - from anterior pituitary - (so that there is negative feedback) which reduces the production of oestrogen/low levels of FSH inhibit oestrogen release - allowance ovulation . - oestrogen inhibits PRODUCTION/RELEASE of FSH - without FSH the follicles do not develop - without a (mature/ graafian) follicle, ovulation and subsequent fertilisation cant take place

Question 274

describe the function of amniotic fluid [1]

Answer 274

- acts as a shock absorber / protection (from physical damage)

Question 275

explain why the frequency of a disease is higher in isolated populations and predict, with a reason, what is likely to happen to the frequency of the disease allele in the general population [2]

Answer 275

- (hardy-weinberg principal does not apply) (because population is small/genetic drift/founder effect/small gene pool/no migration/no immigration/higher probability of two carriers having children) - decrease because allele will be lost from gene pool when sufferers die in childhood/selective abortion/selected against/selective disadvantage/less likely to reproduce

Question 276

- gel electrophoresis was carried out on samples of DNA - an image shows the results of the analysis - a DNA ladder was included for reference - explain the purpose of the DNA ladder on the image [2]

Answer 276

- contains fragments of KNOWN (number of base pairs / length / size) - determine (number of base pairs / length / size) of DNA being analysed

Question 277

- a graph shows the incidence of TB per 100,000 people in the uk - the incidence is expressed as cases per 100,000 population and not ad the total number of cases in the population. - explain why [2]

Answer 277

- population size may vary / proportional to population size - in order to make a comparison / show a trend

Question 278

state what is meant by the term broad spectrum [1]

Answer 278

- affects (many/most) (species/types) of bacteria / gram +ve and -ve)

Question 279

- Rifampicin works by inhibiting bacterial RNA polymerase enzyme, preventing transcription from taking place - explain how this would affect bacteria [3]

Answer 279

- inhibits the formation of mRNA - prevents translation from taking place/stops protein synthesis/cell cannot synthesise (protein/enzymes) - metabolism stops and cell dies/essential processes cannot occur without enzymes

Question 280

- the most widely used vaccine against TB is the BCG vaccine - the vaccine is prepared with a live, attenuated form of myobacterium bovis - M.bovis is closely related to M.tuberculosis - the vaccine is administrated by an injection below the epidermis of the skin - to be effective, the injection must penetrate the epidermis layer of the skin - explain why [2]

Answer 280

- epidermis acts as a physical barrier to infection/needs to reach (blood/antigen presenting cell/macrophages) - to initiate a (primary) immune response

Question 281

describe how injecting a vaccine will result in antibody production [3]

Answer 281

- macrophages egulf the bacterial cells by phagocytosis/antigen presentation by macrophages - activation of T helper cell/reference to cytokines - B cells activated/clonal selection - clonal expansion/description of - some then differentiated into plasma cells

Question 282

- there may be concerns regarding the use of a live vaccine - suggest what these concerns may be and give a suitable alternative to a live vaccine [2]

Answer 282

- could cause pathogenic response/disease - (antigen/RNA/dead/inactive/related) pathogen

Question 283

State the name given to enzymes which work inside cells [1]

Answer 283

- intacellular

Question 284

apart from enzymes, state which other part of the virus is formed of protein [1]

Answer 284

capsid / protein coat / capsomeres

Question 285

- the process of spermatogenesis takes place in the seminiferous tubules, as shown in an image - the heads of the spermatozoa are clustered around specific cells - name the cells that the sperm are clustered around and state their function [2]

Answer 285

- sertoli cells - providing (nourishment / protection)

Question 286

state the name of the organelle that produces the acrosome [1]

Answer 286

golgi body/apparatus

Question 287

- describe what happens to the volume of the nucleus and the cytoplasm in a spermatozoon during maturation and suggests why this occurs [2]

Answer 287

- they both decrease - makes them more streamlined / more can be fitted into a small space

Question 288

state where fertilisation normally occurs in a mammal [1]

Answer 288

fallopian tube/oviduct

Question 289

state two advantages of germ-line therapy [2]

Answer 289

- can be passed on to future generations - present in all cells of the body - doesnt need to be repeated

Question 290

state what is meant by accuracy and reliability [2]

Answer 290

- accuracy = close to true value - reliability = little variation around mean / results are repeatable / consistency of results