Cambridge A Level Biology 9700 — 2017 Oct/Nov Paper 2 · Variant 1

1 Fig. 1.1 is a photomicrograph of plant cells showing stages in cell division. Fig. 1.1 (a) On Fig. 1.1, draw a circle around a cell in anaphase. [1] (b) Suggest the advantages of using a light microscope, rather than an electron microscope, to study cell division. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .............................................................................................................................................. [2] (c) Mitosis is important in producing more cells for plant growth. Describe three other ways in which mitosis is important in plants. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .............................................................................................................................................. [3] [Total: 6]

Mark scheme: 1(a) ; 1 1(b) two from can observe living, specimens / cells ; (so) the process of mitosis can be seen happening / AW ; R easier to see mitosis happening I to study cell division ease of use, qualified ; e.g. no need for heavy metal staining, preparation of specimen less time-consuming I ref. to colour I portable 2 1(c) three from production of genetically identical cells ; asexual reproduction ; repair of damaged tissue ; A replace damaged cells R repair damaged cells replace, dead / worn out / old / non-functioning, cells ; gamete production in context ; 3

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2 Fig. 2.1 is a transmission electron micrograph of a section through a blood vessel. 1 μm Fig. 2.1 (a) State the type of blood vessel shown in Fig. 2.1 and give two reasons for your choice. type of blood vessel .................................................................................................................. reason 1 .................................................................................................................................... ................................................................................................................................................... reason 2 .................................................................................................................................... ...............................................................................................................................................[3] Fig. 2.2 is a graph showing how the blood pressure in the pulmonary artery and in the right ventricle changes during one cardiac cycle. 4 Key pulmonary artery 3 blood right ventricle pressure 2 / kPa 1 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 time / s Fig. 2.2 (b) Use Fig. 2.2 to state the time at which: (i) the valve between the right ventricle and the pulmonary artery closes .......................................................................................................................................[1] (ii) the ventricle begins to contract. .......................................................................................................................................[1] (iii) State and explain the similarities and differences between Fig. 2.2 and a graph showing how the blood pressure for the left ventricle changes during the same cardiac cycle. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[4] [Total: 9]

Mark scheme: 2(a) capillary ; two from single celled wall / AW ; A thin wall ref. to wall composed only of one, squamous epithelial / endothelial, cell ; ref. to lumen diameter approx 7 µm ; A 5–8 µm A ref. to similarity to dimension of red blood cell in direct contact with tissue fluid ; if vein named, allow one mark for, thin wall (relative to lumen) or wide / AW, lumen (relative to wall thickness) 3 2(b)(i) 0.24 s / 0.25 s ; 1 2(b)(ii) 0.08 s / 0.09 s ; A range 1 2(b)(iii) four from similarity ref. to increases and decreases in pressure at same time ; A description for part of the graph e.g.starts to rise at same point as RV, returns to minimum at same point as RV idea that events in cardiac cycle occur are coordinated ; A described e.g. impulses pass up both ventricles at the same time, ventricles both contract at same time difference reaches higher, blood pressure / peak, (than RV) ; systolic pressure higher in LV (than RV) left ventricle pumps blood to (whole) body / RV only to lungs) overcome greater resistance / ora for RV any two ;; walls of left ventricle, thicker / more muscular more force exerted by LV max 4

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3 Cells of the immune system function to protect the body against infectious diseases. (a) (i) Name the type of cell that produces antibodies. .......................................................................................................................................[1] (ii) The virus that causes the infectious disease influenza has two antigens, H and N. Antibodies are produced in response to an infection by this virus. The antibodies are specific for either antigen H or for antigen N. Describe how the structure of an antibody molecule allows it to be specific for one antigen, such as H or N. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[3] (b) Cholera is a disease caused by a bacterial pathogen. (i) Name the pathogen that causes cholera. .......................................................................................................................................[1] (ii) Describe how the pathogen that causes cholera is transmitted. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (c) Viruses that infect bacteria are called bacteriophages. Some bacteriophages that infect the cholera pathogen cause lysis of the bacterium. (i) Suggest what happens to the structure of a bacterial cell to cause lysis. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (ii) Some scientists believe that bacteriophages could be used to treat people who are infected with cholera. Suggest the properties of the bacteriophages that would make this possible. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (iii) Antibiotics can be used to treat people with cholera. State why antibiotics are not effective against measles. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[1] [Total: 12]

Mark scheme: 3(a)(i) B-lymphocyte / plasma cell ; A B-cell / white blood cell / lymphocyte / leucocyte / R beta / β, cells R T-lymphocyte / macrophage / neutrophil 1 3(a)(ii) three from I ref. to receptor 1 antibody complementary (shape) to antigen ; I matching shape 2 idea that variable regions different for each antibody ; 3 (specific) antigen / H / N, binding sites (on antibody) ; if mp 2 and 3 not gained, allow one mark for antigen binding regions 4 sequence of amino acids / primary structure, varies between antibodies / gives specificity ; 5 ref. to difference in, primary structure / amino acid sequence, leading to different, tertiary structure / 3-D shape ; 6 ref. to R group interactions between antibody and antigen ; 3 3(b)(i) Vibrio cholerae ; I bacterium 1 3(b)(ii) faecal–oral route ;; if mode of transmission not named, allow description infected person faeces / sewage, contaminates, (drinking) water / cooking utensils / vegetable plots / crops / food A diarrhoea for faeces R (human) waste unqualified or ref. to houseflies landing on contaminated faces ; uninfected person eating contaminated food / using contaminated utensils / drinking contaminated water ; A bacteria enters water in context of drinking R infected food or water I handling contaminated food need ref. to contaminated once only 2 Question Answer Marks 3(c)(i) cell wall, breaks / damaged / AW A cell wall becomes thinner or cell wall weakened ; plus one from detail of change to cell wall e.g. cross links break down, quantity of murein / peptidoglycan, decreases or cell membrane, breaks / AW or increase in water in cell (so increase in turgor pressure) / AW ; 2 3(c)(ii) two from infect only, V. cholerae / cholera bacteria AW or do not, infect human cells / infect humans ; A do not harm human cells do not give side effects / allergic responses, (to humans) ; able to replicate inside V. cholerae (to produce more bacteriophage for treatment) ; ref. to remaining, active / infective / AW, with delivery method used / within gut ; 2 3(c)(iii) antibiotics only effective against bacteria / not effective against viruses or do not act on structures possessed by, (measles) virus / Morbillivirus A named structure e.g. protein coat or act on structures that viruses do not have A named structure e.g. murein cell wall or only act on, living / growing, cells or may not be able to reach virus inside (host) cell ; AW 1

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4 Fig. 4.1 shows the structure of the R groups of three amino acids, aspartate (Asp), glutamine (Gln) and isoleucine (Ile). O O– O NH3+ CH3 C C CH2 CH2 CH2 H C CH3 CH2 Asp GIn Ile R group R group R group Fig. 4.1 (a) One of the mRNA codons for the amino acid Gln is CAA. A mutation could change this codon from CAA to UAA. UAA is a STOP codon. State what is meant by a STOP codon. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (b) Many proteins that contain the amino acids shown in Fig. 4.1 are globular. Describe how the three R groups in Fig. 4.1 can contribute to the globular structure of a protein. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[4] (c) An example of a globular protein is the enzyme starch phosphorylase. This enzyme catalyses the conversion of starch to glucose-1-phosphate. Name the type of bond that is broken when starch is converted to glucose-1-phosphate. ...............................................................................................................................................[1] An investigation was carried out to find out how the activity of starch phosphorylase varied with temperature, when free in solution and when immobilised in alginate. The results are shown in Fig. 4.2. 9 Key free enzyme 8 immobilised enzyme 7 6 enzyme 5 activity / arbitrary 4 units 3 2 1 0 20 25 30 35 40 45 50 55 temperature / °C Fig. 4.2 (d) With reference to Fig. 4.2, compare the results for the enzyme activity when free in solution and when immobilised. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[4] (e) State how the Michaelis–Menten constant (Km) is derived from Vmax for an enzyme. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (f) The Km values for starch phosphorylase were determined when free in solution and when immobilised. The Km values were: • free in solution, Km = 0.34 mmol dm–3 • immobilised, Km = 0.84 mmol dm–3. Suggest an explanation for the difference between the two values. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[2] [Total: 13]

Mark scheme: 4(a) codon that terminates / AW, translation / polypeptide synthesis R stops production of amino acids or does not specify any amino acid or has no complementary, tRNA / anticodon or causes the release of the (completed) polypeptide chain ; 1 4(b) four from Asp and Gln R groups, hydrophilic / AW, and Ile R group, hydrophobic / AW ; ref. to R group interactions and, folding / coiling, of polypeptide chain (to give globular structure) ; ref. to (charged / polar R groups) forming, ionic / hydrogen, bonds ; (amino acids with), hydrophobic / non-polar, R groups, on the inside / AW ; A hydrophobic amino acids (amino acids with), hydrophilic / charged / polar, groups on outside / AW ; A hydrophilic amino acids detail ; e.g. ionic R groups can interact with water, hydrogen bonds form with water ref. to promotes stability / helps to maintain globular structure ; in context of interaction with water / formation of (compact) hydrophobic core 4 4(c) glycosidic ; 1 Question Answer Marks 4(d) four from 1 both, increase and decrease / peak ; 2 both active, over range of temperature tested / between 20 to 55°C ; 3 free enzyme lower, optimum temperature / temperature for maximum activity ; ora 4 (free) 37°C v (immobilised optimum) 46°C; 5 free enzyme higher, maximum activity / activity at optimum temperature ; ora 6 (free) 8.2 / 8.3, a.u. v 7.5 a.u. ; 7 between 20°C and 39°C the activity of free is higher ; ora 8 between 39°C and 55°C the activity of free is lower ; ora if mp 7 and 8 not gained, allow 1 mark for free activity higher at lower temperatures and lower at higher temperatures (than immobilised) ora 9 comparative data to support mp 7 or 8 ; A comparison at one temperature (stated or use of numerical data) 10 AVP ; e.g. both have same activity at 39°C, similar activity between 20°C and 30°C 4 4(e) substrate concentration that gives half Vmax / AW ; A description of how to use a graph to derive (must refer to substrate concentration) 1 4(f) two from look for ora throughout free / low(er) Km , has higher affinity for substrate ; free needs a lower concentration of substrate to reach, Vmax / maximum activity / ½ Vmax ; takes lower substrate concentration to saturate active sites in free ; free active site more, likely to be saturated with substrate / accessible ; active site (may be) distorted by immobilising ; ref. to substrate passing through matrix when immobilised ; ref. to some product retained within matrix ; 2

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5 Fig. 5.1 is a transmission electron micrograph of part of a cell. X 2 μm Fig. 5.1 (a) (i) Name the organelle labelled X. .......................................................................................................................................[1] (ii) Put a tick (3) in the box beside the type, or types, of cell that contain this organelle. animal cell plant cell bacterial cell [1] (b) Use the scale bar to calculate the magnification of Fig. 5.1. Write down the formula and use it to make your calculation. Show your working. formula ◊ magnification ......................[3] (c) The organelle in Fig. 5.1 is made from structures surrounded by a single membrane. Name two organelles that are surrounded by double membranes. ...............................................................................................................................................[2] (d) (i) The structure of the cell surface membrane is described as a fluid mosaic. Explain what is meant by the term fluid mosaic. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (ii) Outline the roles of the cell surface membrane. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[4] [Total: 13]

Mark scheme: 5(a)(i) Golgi (body / apparatus / complex) ; 1 5(a)(ii) animal cell 9 plant cell 9 bacterial cell ; 1 5(b) magnification = scale bar length / actual length ; A M = I / A M = I / O or magnification triangle 14 500 ;; for 29 mm scale bar length A 14 000 (for 28 mm) or 15 000 (for 30 mm) allow one mark only for incorrect answer but correct calculation using scale bar e.g. 29 000 ÷ 2 correct answer but units given correct measurement and correct calculation but incorrect conversion 3 5(c) mark first two only nucleus ; mitochondria ; chloroplasts ; 2 5(d)(i) fluid idea of phospholipid (and protein) molecules, move about / diffuse (within their monolayer) ; mosaic protein (molecules), interspersed / scattered / AW ; A different / AW, proteins ; 2 Question Answer Marks 5(d)(ii) any four from 1 barrier between cytoplasm and, external environment / AW ; e.g. tissue fluid A protects, organelles from damage / from pathogens, I keeps cell contents in / membrane surrounds the organelles 2 cell signalling or has receptors for, cell signalling substance / hormone / neurotransmitter / AW 3 cell recognition / acts as cell surface antigen ; 4 cell-to-cell adhesion ; 5 site for, enzymes / catalysing reactions ; 6 anchoring the cytoskeleton / AW ; 7 selection of substances that enter or leave a cell ; AW 8 formation of hydrogen bonds with water for stability ; 9 AVP ; e.g. ref. to, changing shape of cell / flexibility of cells e.g. phagocytosis 4

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6 Plants have two transport tissues, xylem and phloem. (a) Describe and explain two ways in which the structure of xylem vessels is adapted to their function. description 1 ............................................................................................................................. ................................................................................................................................................... explanation 1 ............................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... description 2 ............................................................................................................................. ................................................................................................................................................... explanation 2 ............................................................................................................................ ................................................................................................................................................... ...............................................................................................................................................[2] (b) Describe two differences between the vessels that transport phloem sap in flowering plants and the vessels that transport blood in mammals. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[2] Fig. 6.1 shows root hair cells. root hair cells Fig. 6.1 (c) Explain why the root hair cells in Fig. 6.1 have more mitochondria than the other root cells shown. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[3] [Total: 7]

Mark scheme: 6(a) mark first two statements given cellulose, cell wall / lining, allows adhesion of water ; thick (cellulose) cell wall prevents collapse / idea of providing support (under tension) ; (cell wall impregnated with) lignin, for waterproofing / prevents water loss ; lignin, rings / spirals / thickening / AW (of walls), prevents collapse / idea of providing support (under tension) ; A lignified walls no cytoplasm / lack of contents / hollow / empty (lumen), gives, less resistance to / unimpeded / uninterrupted / unhindered / ease of, flow ; A greater volume per unit time / faster rate R continuous, smooth R dead ack of end walls / continuous tube, so, less resistance to / unimpeded / uninterrupted / unhindered / ease of, flow ; AW R continuous, smooth pits / pores, for lateral movement / for movement around air bubbles / supplies (water) to (surrounding), cells / tissues ; R holes wide / large diameter / large lumen, so large volume of water can be transported ; if max 2 not gained, allow one mark for two correct explanations or descriptions where accompanying descriptions and explanations are in context 2 Question Answer Marks 6(b) two from accept phloem vessels for sieve tubes only sieve tubes / one type, v, arteries, veins and capillaries (any two) A three types; sieve tubes are composed of cells v blood vessels composed of tissues ; A ref. to named tissues sieve tubes, have cytoplasm or blood vessels are, hollow / AW; sieve tubes have sieve plates ; ora sieve tubes have companion cells (to fully function) ; veins have valves ; ora ref. to blood vessels and vasoconstriction ; ora idea of transport open (phloem) v closed (blood vessels) ; A sieve tubes have plasmodesmata ref. to unidirectional flow in blood vessels ; ora 2 6(c) three from mitochondria, synthesise ATP / carry out aerobic respiration ; more ATP needs to be synthesised / increased ATP synthesis ; A need to produce large quantities of ATP to provide more (metabolic) energy ; R in context of water uptake for active transport / active uptake ; in context of mineral ions A to move mineral ions against the concentration gradient 3

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