Biology 9700/23 May/June 2023: question paper and mark scheme

Mark scheme

1(a)(i) B prophase ; I early / mid / late 2 C metaphase ; A early anaphase 1(a)(ii) any three from: 3 A identical chromatids for sister chromatids assume points are related to anaphase, unless stated as telophase sister / identical, chromatids (of each chromosome) separate / AW ; A idea of spindle fibres pulling apart sister chromatids in context of end of metaphase / start of anaphase movement of / AW, daughter chromosomes / chromosomes / (sister) chromatids, to (opposite) poles (of cell) ; R if context is a chromosome composed of two chromatids R if context is movement of sister chromatids to same pole I ends of cell movement (to opposite poles) by spindle fibres, contracting / pulling ; I moved by spindle fibres centromeres, qualified ; e.g. centromeres divide at start of anaphase (to separate sister chromatids) centromeres leading (during movement so arms of chromosome lagging) if telophase stated, mark behaviour of chromosomes in telophase to max 2: (daughter) chromosomes at poles ; A sister chromatids at poles A ref. to two separate groups of (daughter) chromosomes (chromosomes) become diffuse / become long and thin / decondense / uncoil ; A become chromatin ref. to re-forming nucleolus ; 1(a)(iii) any three from: 3 (active during) DNA replication / S phase / synthesis phase ; A during synthesis of DNA / semi-conservative replication joins / AW, Okazaki fragments ; A description of Okazaki fragments on lagging strand ; (by catalysing) formation of phosphodiester bonds (between adjacent nucleotides) ; to complete sugar phosphate backbone / AW ; e.g. produces continuous, DNA / polynucleotide, strand 1(b)(i) at both ends (of interphase chromosomes) ; 1 A on the ends (of, a chromosome 1(b)(ii) any three from: 2 telomeres, maintained / AW, for, longer / greater length of time ; allows increased, number of cell cycles / DNA replication cycles / AW ; A allows, mitosis / cell division, to occur more times AW R speeds up, mitosis / cell division / cell cycle idea of prevents loss of genes (at ends of chromosomes, for a longer time) ; A loss of, genetic information / coding DNA A less, genes / AW, lost I loss of genetic material ref. greater ability to replace, damaged / worn out / old, cells ; in context of active for a longer time idea of cell metabolism remains optimal / cell does not go through apoptosis / AW ;

Mark scheme

2(a)(i) max two if, number of (reported) cases / AW, not stated 3 any three from: 1 overall decrease in number of reported cases from 1980 to 2000 / over the time period / AW ; 2 from, 27 600 / 27 700 / 27 800, to, 16 300 / 16 400, cases ; A manipulated data e.g. decline of, 11 200 / 11 300 / 11 400 / 11 500 cases 3, 4 additional trends ;; e.g. decrease from 1980 to 1984 increase between 1988 and 1992 or (overall) increase between 1984 to 1992 decrease after 1992 (to 2000) little change / slight increase and decrease / AW, between 1984 and 1988 5 use of comparative values from Fig. 2.1 to support mps, 3 / 4 ; 2(a)(ii) HIV-infected people may develop a weak(ened) immune system 2 or people with, HIV/AIDS have a weak(ened) immune system ; A poor immune response A idea of more susceptible to disease caused by, Mycobacterium, tuberculosis / bovis A TB is an opportunistic disease (of people with HIV/AIDS) increased risk of latent TB becoming active in (many) people, living with HIV / with HIV/AIDS ; AW detail of weak immune system ; e.g. decrease in number of ,T-lymphocytes / T helper cells poor, humoral / B-lymphocyte, response AVP ; idea of more cases of TB owing to more people infected with HIV increases risk of spreading to uninfected people 2(b) any two from: 2 1 prescribe / take, antibiotics, only when (absolutely) necessary ; A examples e.g. do not use for viral infections do not use as preventative medicine 2 make sure, correct / effective, antibiotic(s), prescribed / used AW A ref. to, broad spectrum / narrow spectrum, antibiotics, qualified or make sure people take the correct dose or complete course / follow instructions for use, of antibiotics A ref. to DOTS ; 3 develop new, antibiotics / antibacterials ; 4 use other antibacterials ; if mp3 and 4 not gained, allow one mark for vary antibiotic treatment or use a number of different antibiotics at the same time 5 (named) measures to, prevent infection / break transmission cycle (to reduce the need for antibiotic use) ; e.g. vaccines good hygiene in hospitals quarantine people who have multi-drug resistant bacterial infections 6 report, cases / patterns, of antibiotic resistance ; 7 reduce / control, antibiotics in, agriculture / animals used for food ; 8 ref. to education for, healthcare professionals / public, to reduce impact of antibiotic resistance ; 9 AVP ; e.g. ref. to monitoring situation to check if antibiotic is effective WHO Global Plan to End TB 2(c)(i) (bronchi) may, collapse / lose (structural) support ; 1 2(c)(ii) one mark each correct column = 3 marks ;;; 3 if 0 or 1 mark gained, check for correct row to max 2 In the whole table: if only ticks are used, assume blanks are crosses if only crosses are used, assume blanks are ticks If there are ticks and crosses and blanks in the whole table, R the columns or rows with the blank(s) cell type alveolus bronchus trachea ciliated epithelial cell × goblet cell × smooth muscle cell × squamous epithelial cell × ×

Mark scheme

3(a)(i) X neutrophil ; 2 Y monocyte ; A lymphocyte I B– / T– 3(a)(ii) image / line Z, length / width 2 (magnification) = ; A (M) = I / A actual width A magnification triangle (x) 1500 ; A 1375 (for 11 mm) / 1438 (for 11.5 mm) 3(b)(i) any four from: 4 1 (carbonic anhydrase) catalyses the reaction between CO2 and H2O ; AW 2 to form, carbonic acid / H2CO3 ; 3 H+ forms (together with HCO3- from dissociation of H2CO3) ; 4 H+ binds to haemoglobin to form haemoglobinic acid ; 5 displacing / releasing, oxygen from haemoglobin ; 6 allosteric effect / change in tertiary structure / AW, in (oxy)haemoglobin (causes release of oxygen) ; 3(b)(ii) curve below the original line ; 2 curve, merging / will merge, with the original line after it begins to plateau ;

Mark scheme

4(a)(i) 3 description level of protein structure a gliadin protein is a single polypeptide that tertiary forms a compact structure 20% of the amino acids in a glutenin primary molecule are glycine gliadin and glutenin molecules contain secondary regions of β-pleated sheets 1 mark per correct row ;;; 4(a)(ii) any one relevant: e.g. 1 RNA / gene, splicing, not needed / does not occur ; R DNA splicing ref. to all primary transcript is a coding sequence ; A primary transcript has the same sequence as the mRNA no nucleotides removed, from the primary transcript / after transcription ; no process of exon joining / AW ; no non-coding sequences, so introns to not need to be removed ; no alternative RNA splicing / exons not joined in different combinations ; A only one type of mRNA formed / mRNA formed always the same idea that only other post transcriptional processing occurs ; e.g. 5’ G (guanine) cap / poly A tail 4(b)(i) endocytosis ; A pinocytosis 2 A described detail ; e.g. invagination of membrane / AW use of ATP A active process / energy needed formation of (endocytotic / pinocytotic) vesicle if mp1 gained from description, mp2 must be another detail accept other named transport mechanism, with detail 4(b)(ii) any four from: 4 1 ref. presence of, non-self / foreign, antigen or gliadin acts as antigen or ref. to antigen presentation (by macrophages) ; 2 recognition / activation / AW, of (specific) B- / T-lymphocytes ; A clonal selection 3 clonal expansion of B-lymphocytes (and T-lymphocytes) ; AW e.g. form a clone of cells (by mitosis) / divide many times by mitosis 4 T-helper cells, secrete / release, cytokine ; 5 cytokine stimulates, humoral / B-lymphocyte, response ; if mp4 and mp5 not gained allow one mark for T-helper cells stimulate B-lymphocyte response 6 B-lymphocytes (differentiate to) form plasma cells ; 7 plasma cells, produce / secrete, (anti-gliadin) antibodies ;

Mark scheme

5(a) phloem (identified) ; 2 xylem (identified) ; e.g. two marks for: 5(b)(i) any four from: 4 1 (transport is by) mass flow ; 2 entry of sucrose into phloem sieve tube, from companion cell / through plasmodesmata ; 3 sucrose, is dissolved in water / is part of phloem sap / lowers water potential ; 4 (transport is) down a hydrostatic pressure gradient / from high hydrostatic pressure to low hydrostatic pressure ; high hydrostatic pressure 5 water moves into phloem sieve tube, by osmosis / down water potential gradient / from xylem (at source) ; 6 increased volume increases hydrostatic pressure ; hydrostatic needed once only low hydrostatic pressure 7 (at sink / in other parts of plant) sucrose unloaded, water follows osmotically ; AW 5(b)(ii) any two from: 2 respiration 1 less / no, ATP produced from aerobic respiration ; A ETC / oxidative phosphorylation 2 less ATP / energy, for sucrose synthesis (in mesophyll cell) ; in context of companion cell 3 less / no, ATP / energy, for, proton gradient / active transport of protons (out of companion cell) / AW ; A hydrogen ions / H+ for protons 4 less sucrose cotransported (with, protons / hydrogen ions / H+) into companion cells ; 5 (less sucrose in companion cells means) decreased diffusion of sucrose (via plasmodesmata) into phloem sieve tubes ; if no marks gained, allow 1 mark for less ATP for, active loading / active transport of protons 5(c) Benedict’s solution does not react with, non-reducing sugar / sucrose 2 or Benedict’s solution only reacts with, reducing sugar / glucose ; AW A Benedict’s is, a test for reducing sugars / not a test for non-reducing sugars solution A because sugar present in, cytoplasm / solution A, (mainly) reducing sugars / glucose and sugar in, phloem sap / solution B, is mainly, sucrose / non-reducing sugar or solution B because phloem sap / solution B, contains, a higher concentration of / AW, reducing sugar / glucose, (than, cytoplasm / solution A) ; A in cytoplasm glucose stored as, polysaccharide / starch

Mark scheme

6(a) any three from: 3 nystose is not branched / glycogen is branched ; different glycosidic bonds, qualified ; e.g. nystose has one type of glycosidic bond and glycogen has two types 1-4 and 1-6 (glycosidic) bonds in glycogen (v 1-2 glycosidic bonds in nystose) two types of monomer / AW, in nystose v only glucose in glycogen ; nystose contains one glucose (residue / monomer) ; ref. to ring shape, glycogen monomers have six-sided rings and nystose has (a) six-sided ring and five-sided rings ; AVP ; e.g. fructose in nystose and no fructose in glycogen I numbers of C,H and O 6(b) any four from: 4 must attempt both to gain max 4 rough endoplasmic reticulum translation (of mRNA) / polypeptide synthesis, at ribosomes ; A protein synthesis polypeptide folding (in lumen) ; A protein folding packaged in / formation of, transport vesicles / vesicles for transport, to Golgi body ; Golgi body packaging into, Golgi / secretory, vesicles ; A formation of, Golgi / secretory vesicle, containing glycoprotein A packaging into vesicles for transport to cell surface membrane rough endoplasmic reticulum or Golgi body (modification by) glycosylation (of protein) / described ; e.g attachment of, sugars / oligosaccharide / polysaccharide / carbohydrate ref. to checking for, misfolded / incorrectly synthesised, proteins ; additional detail of post-translational modification ; e.g. suggestion of forming quaternary structure addition of non-protein groups 6(c) any one from: 1 cell signalling or receptor(s) / binding site(s) , for , chemicals / hormones / molecules ; cell recognition or (cell surface) antigens or cell-cell interactions ;