GCE. Biology. Mark Scheme for January Advanced Subsidiary GCE Unit F212: Molecules, Biodiversity, Food and Health PMT

Transcription

1 GCE Biology Advanced Subsidiary GCE Unit F: Molecules, Biodiversity, Food and Health Mark Scheme for January 0 Oxford Cambridge and RSA Examinations

2 OCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range of qualifications to meet the needs of pupils of all ages and abilities. OCR qualifications include AS/A Levels, Diplomas, GCSEs, OCR Nationals, Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications in areas such as IT, business, languages, teaching/training, administration and secretarial skills. It is also responsible for developing new specifications to meet national requirements and the needs of students and teachers. OCR is a not-for-profit organisation; any surplus made is invested back into the establishment to help towards the development of qualifications and support which keep pace with the changing needs of today s society. This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by Examiners. It does not indicate the details of the discussions which took place at an Examiners meeting before marking commenced. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes should be read in conjunction with the published question papers and the Report on the Examination. OCR will not enter into any discussion or correspondence in connection with this mark scheme. OCR 0 Any enquiries about publications should be addressed to: OCR Publications PO Box 00 Annesley NOTTINGHAM NG 0DL Telephone: Facsimile: publications@ocr.org.uk

3 F Mark Scheme January 0 (a) (i) human immunodeficiency virus / HIV ; DO NOT CREDIT if there is any ref to AIDS (a) (ii) (infective agent), in blood / body fluids ; ACCEPT any infective agent even if incorrect as question asks for mode of transmission idea of: used needles are contaminated ; ora ACCEPT e.g. used needles are infected ACCEPT e.g. new needles are sterile DO NOT CREDIT dirty / clean needles (b) (i) reduces chance of sharing needles ; ora amino acid(s) ; max IGNORE prevents / stops Answers must be on correct line ACCEPT phonetic spelling for both (b) (ii) nucleotide(s) ; reverse transcriptase in (host) nucleus ; DO NOT CREDIT if ref to DNA / nucleosides ACCEPT ribonucleotides viral DNA, (inserted) in (host), chromosome / DNA ; idea of: (viral) RNA / mrna produced / transcribed ; (to) code for / make / translate, viral proteins ; max IGNORE different protein

4 F Mark Scheme January 0 (c) (i) Mark the first three answers only regardless of which line they are on not vaccinated against TB ; IGNORE general refs to lack of medical care weakened immune system ; (lifestyle) e.g. poor diet / lack of protein / malnourished / smoking / alcoholism ; homelessness ; poor ventilation (of housing) / AW ; overcrowding ; close contact with people from / visiting, area where TB is common ; close / prolonged, contact with individual(s) with TB ; DO NOT CREDIT alcohol unqualified IGNORE poor health 7 ACCEPT area where those with TB are not quarantined 9 consumption of milk or beef, from infected cattle / in developing countries ; max

5 F Mark Scheme January 0 (c) (ii) cytokine / interleukin / receptor has, specific / unique, DO NOT CREDIT cytokine is specific to receptor as shape ; this is implied in question (cytokine / interleukin), binds / attaches / bonds to / fits into, receptor ; receptor on (cell surface) membrane (of B lymphocyte) ; (receptor and cytokine have) complementary shapes ; DO NOT CREDIT antibodies (on cell surface) activates / stimulates, clonal expansion / mitosis ; max Total ACCEPT activates / releases nd messenger

6 F Mark Scheme January 0 (a) (i) blue-black / black / dark blue ; ACCEPT dark purple / purplish-blue DO NOT CREDIT blue or purple unqualified by darkness ACCEPT acceptable colour change (a) (ii) CREDIT marking points from clearly labelled diagram max if incorrect charges are on atoms between oxygen and hydrogen (atoms) ; DO NOT CREDIT molecules / ions (a) (iii) (between) electronegative / δ -, and electropositive / δ + ; hydrogen / H, bonds break ; DO NOT CREDIT ions / + and ACCEPT slight / partial (negative / positive), charge IGNORE refs to denaturation helix, lost / unravels / AW ; ACCEPT spiral / coil iodine, released / no longer in complex / AW ; max ACCEPT no longer contained in helix

7 F Mark Scheme January 0 (b) take samples at a range of times / AW ; B B B B same volumes (of solutions) added / removed (each time) ; heat with, Benedict s (solution) / CuSO and NaOH ; (use of ) excess Benedict s ; changes to, green / yellow / orange / brown / (brick) red ; B must be in context of Benedict s test rather than reaction mixture B DO NOT CREDIT boil / warm B DO NOT CREDIT if Benedict s added to the mixture at the beginning C6 C7 remove precipitate / obtain filtrate ; colorimeter ; C6 CREDIT description of method e.g. filtering / centrifuging / decanting 8 9 calibrate / zero, using, a blank / water / (unreacted) Benedict s ; use (red / orange) filter ; 8 IGNORE control 9 DO NOT CREDIT if colour of filter is incorrect T0 reading of, transmission / absorbance OR mass of precipitate ; T0 ACCEPT measure how much light, does / does not, pass through more transmission / less absorbance, of filtrate, OR greater mass ppt, = more maltose present ; ora using, standard / known, concentrations (of maltose) ; (obtain) calibration curve ; plot, transmission / absorbance / mass of ppt, against (reducing sugar) concentration ; use graph to read off concentration of maltose / AW ; 6 max if unfiltered Benedict s / precipitate is clearly indicated as being present in sample, ACCEPT less transmission / more absorbance, = more maltose present DO NOT CREDIT if precipitate is added to colorimeter CREDIT serial dilutions QWC correct sequence ; of mps B to B, then mp C6 or C7, then mp T0

8 F Mark Scheme January 0 (c) (i) ACCEPT any time between. and. min. increases / greater / faster ; reaction completed in / plateaus after / concentration is 00% after,. minutes ; figures with units to support mp ; max two maltose concentrations (+ or chloride) for a given time or two times (+ or chloride) for given maltose concentration. ACCEPT calculated difference DO NOT CREDIT if % and min. not given ACCEPT any concentration within ± % and time within ± 0.0 min. Presence or absence of chloride ions The percentage concentration of maltose (%) present every half a minute 0.0 min 0. min.0 min. min.0 min. min.0 min. min.0 min Chloride ions present Chloride ions absent Difference in maltose concentration When chloride ions are either present or absent Allow a + /- % for any concentration of maltose and a +/- % for the difference in maltose concentrations (c) (ii) (acts as a) cofactor ; IGNORE coenzyme (Cl - ) binds to, enzyme / amylase / amylose / substrate ; ACCEPT binds to, active site enzyme substrate complex / ESC, forms more, easily / quickly ; max ACCEPT description 6

9 F Mark Scheme January 0 (c) (iii) Mark the first three answers only regardless of which line they are on DO NOT CREDIT refs to, time 6 temperature ; ph ; enzyme / amylase / chloride, concentration ; substrate / starch / amylose, concentration ; constant / regular, stirring ; (fixed) volume of solution (removed each time for sampling) ; max Total 9 IGNORE amount or volume DO NOT CREDIT concentration unqualified IGNORE amount or volume DO NOT CREDIT concentration unqualified 7

10 F Mark Scheme January 0 (a) (i) (all), sub-arctic / all named sub-arctic, species / birds, show decrease ; ACCEPT reference to numbers rather than breeding success throughout sub-arctic species = snow bunting + Lapland bunting + ptarmigan + dotterel (all / most), other / non sub-arctic / all named non subarctic, species / birds, show, increase / no change ; non sub-arctic species = red grouse + wheatear + meadow pipit + ring ouzel greater change / AW (in breeding success), in sub-arctic than in non sub-arctic species ; comparative figs (in 970 AND 000) ; number of young for one sub-arctic and one non sub-arctic species in 970 and 000 (or calculated subtraction between the two years) DO NOT CREDIT if figures are not from 970 and 000 number of young raised per year species difference in number of young raised between 970 and 000 Snow bunting* 78 Down 76 Lapland bunting* 7 0 Down 7 Ptarmigan* Down 0 Red grouse Up 7 Wheatear 09 Up Meadow pipit 8 Up 9 Ring ouzel 6 Up Dotterel* Down 0 8

11 F Mark Scheme January 0 (a) (ii) climate change / global warming ; IGNORE greenhouse effect DO NOT CREDIT it is too warm or it is not cold enough without reference since 970 (environmental) change too rapid for adaptation ; change in, flora / plants / food supply / insects / prey / predators / human activity ; ACCEPT camouflage no longer appropriate / reduction in size of habitats disease (that affects sub-arctic species more than others) ; sub-arctic species, less well-adapted than / have been outcompeted by, non sub-arctic species / AW ; max ACCEPT ora (b) (i) the number of species present (in a habitat) ; DO NOT CREDIT range / amount 9

12 F Mark Scheme January 0 (b) (ii) Mark the first three suggestions idea of: unbiased method to selecting sampling area ; ACCEPT e.g. random selection of, areas / coordinates OR use of transect IGNORE random sampling unqualified sample many times / AW, and calculate mean / average ; standardised sweeping procedure ; e.g. same type of movement / same length of time same number of sweeps ACCEPT sample at same time of day IGNORE same collector IGNORE refs to using alternative collecting techniques in order to collect more insect species ensure insects do not escape (before being identified) ; ACCEPT use of pooter 6 method to prevent recounting ; sample at different times of, day / month / year / weather conditions ; max if ref to mark-release-recapture, IGNORE release and recapture and look for idea for preventing recounting 0

13 F Mark Scheme January 0 (b) (iii) (measures), abundance / numbers, of individuals in each species ; species evenness is more quantitative than species richness ; ora high(er) species evenness indicates high(er) biodiversity ; ora low species evenness indicates, dominance by / high abundance of, one / few, species ; ora used to calculate (Simpson s) Index of Diversity ; 6 example used to illustrate explanation of mp or ; max Total 6 e.g. Two areas have the same number of species. One with 90% of species has less biodiversity than one where all species have an abundance of -0%

14 F Mark Scheme January 0 (a) free from, disease / illness ; ALLOW infection CREDIT not just the absence of disease physical and mental and social wellbeing / AW ; DO NOT CREDIT state / condition good nutrition ; ACCEPT balanced diet suitably housed ; max ACCEPT ref to economic wellbeing

15 F Mark Scheme January 0 (b) Mark first F mark on line and assume explanation relates to that ACCEPT named example(s) of pathogen or parasite CREDIT E marks if a reasonable, but noncreditworthy, attempt at an F mark has been made, e.g. lining of nasal passages for F F E F E F E skin ; idea of: physical barrier to prevent entry of microorganisms ; mucous membrane(s) / goblet cells ; (produce) mucus to trap, pathogens / parasite ; OR mucus ; traps pathogens ; E ACCEPT pathogens cannot pass through cells E ACCEPT antibacterial effects of sebum or sweat E DO NOT CREDIT physical barrier unqualified F E cilia / ciliated epithelium ; remove, pathogen / parasite, laden / AW, mucus ; F E blood clotting ; prevents, pathogens / parasite, entering bloodstream ; F E ear wax / nasal hairs ; traps, pathogens / parasite ; F6 E6 lysozyme / tears / nasal secretions / saliva ; kills bacteria / contains antibacterial agent ; F6 IGNORE lysosome(s) E6 ACCEPT contains antibodies F7 E7 gastric juice / stomach acid ; kills, pathogens / parasite ; max F7 ACCEPT enzymes in the stomach or acid in vagina

16 F Mark Scheme January 0 (c) (i) lives, on / in / in contact with, and harms host ; living on / in must be stated, cannot be implied from feeding IGNORE live off takes nutrition from / feeds on (host) ; warmth ; ACCEPT incubate protection / safe place / AW ; (c) (ii) allows transmission / spread, to a new host / AW ; wash / clean / disinfect / sterilize, hands ; max ACCEPT distributed / passed on as implies new host not, scratching / touching, of anus ; ACCEPT method to prevent scratching e.g. cutting nails IGNORE wash anus drugs to, kill / remove, parasite / eggs ; max Total DO NOT CREDIT antibiotics IGNORE anti-bacterial

17 F Mark Scheme January 0 (a) statement DNA only (D) or RNA only (R) or both DNA and RNA (B) Award mark for each correct row DO NOT CREDIT if more than one letter in a box contains thymine D contains ribose consists of chains connected to each other with hydrogen bonds has a sugar-phosphate backbone has different nitrogenous bases contains a pentose sugar R ; D ; B ; B ; B ; is found in the nucleus and cytoplasm R ; 6

18 F Mark Scheme January 0 (b) (i) (information used to) decide which, group / taxon, organism answers must refer to the information provided by / species / named example, fits in ; the study of DNA, rather than simply the job of taxonomists, e.g. ACCEPT it can be used to put organisms into groups IGNORE for classification unqualified look for idea of: groups CREDIT ref to belonging to same taxonomic group, e.g. to see if it belongs in the genus Homo compare the proportion of (different) bases ; IGNORE examine proportion of bases CREDIT idea for looking at similarities / differences compare the DNA / genes / sequence of bases ; IGNORE examine sequence of bases CREDIT idea for looking at similarities / differences (b) (ii) idea of: the more similar the, DNA / genes, the closer the relationship / AW ; fossil record ; max Must contain reference to similarity of DNA Mark the first two suggestions IGNORE ref to genetics as DNA is biochemical anatomy / physiology / behaviour ; embryology / AW ; (c) J ; T ; max ACCEPT AW for anatomy, e.g. observable / physical features / cell structure ACCEPT AW for physiology, e.g. method of reproduction DO NOT CREDIT names 6

19 F Mark Scheme January 0 (d) (i) no DNA from living specimens in Wales analysed ; (d) (ii) population (may have) evolved / mutations have occurred / genetic variation, (since 98) ; (introduced) pine martens might not be adapted to local conditions / AW ; max ACCEPT description of evolved DO NOT CREDIT evolution unqualified by context of pine marten population ACCEPT animals as AW for pine martens throughout answer ACCEPT not adapted to the habitat DO NOT CREDIT used to (local) habitat, might have changed / is no longer suitable (for any pine martens) / AW ; introduced, pine martens, might outcompete native, population / pine martens ; introduced pine martens might bring disease ; ACCEPT introduced pine martens might kill native / Welsh pine martens IGNORE compete unqualified Welsh pine marten would lose its, distinctiveness / identity, because of interbreeding ; max Total 7

20 F Mark Scheme January 0 6 (a) (i) Mark the first answer on each line genes / genetic / mutation ; IGNORE inherited / DNA 6 (a) (ii) environment(al) ; no defined categories ; 6 (a) (iii) B ; 6 (a) (iv) range of values / intermediate values ; influenced by, environment / many genes / genes and environment ; quantitative / has to be measured / cannot be counted ; growth too rapid ; max ACCEPT ref to bell-shaped curve / binomial distribution ACCEPT any ref to or more genes ACCEPT metric DO NOT CREDIT if more than one letter is given increased susceptibility to, disease / named abnormality ; e.g. bone / skeletal abnormalities or low immunity inbreeding ; DO NOT CREDIT if implies inbreeding causes mutations reduces gene pool / genetic variation / genetic diversity ; max IGNORE refs to biodiversity 8

21 F Mark Scheme January 0 6 (a) (v) maintain biodiversity ; aesthetic (reasons) / tourism ; ethical (reasons) ; ACCEPT religious part of a food chain / web ; ACCEPT food source for local population maintain / increase gene pool ; 6 genetic resource / availability to breed with domestic chickens ; max 6 CREDIT description, e.g. source of desirable genes or source of genetic variation 6 ACCEPT specific example of genetic resource e.g. disease resistance / strong bones / longevity / heat tolerance / idea of domesticating wild population 9

22 F Mark Scheme January 0 6 (b) (i) Mark the first two answers only reduces / prevents (infectious) disease ; IGNORE illness prevent, problems / named problem, with gut ; e.g. diarrhoea digest food more, efficiently / easily / quickly ; greater proportion of, food / energy, can contribute to growth ; ACCEPT faster growth as AW for contribute to growth IGNORE larger chickens 6 (b) (ii) reduce risk of transmitting, pathogens / named pathogen, to humans ; (antibiotic) resistant, pathogens / bacteria ; max ACCEPT meat less likely to be infected with bacteria ACCEPT microorganisms / microbes IGNORE germs DO NOT CREDIT immune antibiotics kill useful, bacteria ; DO NOT CREDIT if any ref to viruses idea of: antibiotic passing into human food ; max Total 0

23 F Mark Scheme January 0 7 (a) CREDIT marking points from a clearly labelled diagram IGNORE polypeptide sequence / chain, of amino acids ; (amino acids) joined by peptide bonds ; S S S T T T Q Q Q secondary alpha / α, helix ; small regions of, beta / β, pleated sheet / fold ; hydrogen / H, bonds ; tertiary secondary structure / helix / polypeptide chain, undergoes further, coiling / folding ; bonds / interactions from: disulfide / ionic / hydrogen / hydrophobic or hydrophilic ; hydrophilic R groups on outside (of molecule) / hydrophobic R groups on inside (of molecule) ; quaternary, polypeptides / subunits ;, alpha / α, chains and, beta / β, chains ; haem (group) per polypeptide / haems (per molecule) ; S Must be in context of secondary structure T ACCEPT polypeptide chain folds further T IGNORE if clearly in context of secondary or quaternary structures T H bond must be in context of tertiary structure contains and polypeptides = marks (Q and Q) Q IGNORE protein in ref to haem (group) per polypeptide prosthetic group (is) haem, (which) contains Fe + ; ACCEPT iron ion / Fe + / Fe + DO NOT CREDIT iron / Fe unqualified 6 max QWC - correct refs to secondary, tertiary and quaternary structure ; S mark and T mark and Q mark

24 F Mark Scheme January 0 7 (b) (collagen has) amino acid, chain / sequence ; peptide bonds ; Assume answer refers to collagen unless stated If the answer mentions only collagen, assume that the candidate thinks any features mentioned also apply to haemoglobin. IGNORE polypeptide IGNORE repeating units helical / helix ; bonds / interactions from: disulfide / ionic / hydrogen / hydrophobic or hydrophilic ; quaternary structure ; DO NOT CREDIT if candidate refers to collagen having an helix IGNORE primary /secondary / tertiary 6 more than one polypeptide / subunit ; max Total 6 ACCEPT polypeptides but DO NOT CREDIT polypeptides if number in haemoglobin not specified 8 antibodies ; ACCEPT minor mis-spellings so long as word can not be confused with another word in the list natural ; 6 artificial ; natural ; antigen ; vaccination ; 6 Total 6

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