Cambridge A Level Biology 9700 — 2019 May/June Paper 2 · Variant 2

1 Fig. 1.1 is a photomicrograph of a low power image of part of the common sunflower, Helianthus annuus. Fig. 1.1 is a transverse section. B A Fig. 1.1 (a) State, with a reason, whether Fig. 1.1 shows a section through the root or the stem of H. annuus. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (b) Cell type A in Fig. 1.1 has a large central vacuole. Suggest, with reasons, the role of the tissue formed by this type of cell. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) Structure B in Fig. 1.1 contains phloem tissue and xylem tissue and other tissues that provide support. (i) Name structure B. ..................................................................................................................................... [1] (ii) The actual length of structure B is 650 µm. State the actual length of structure B in mm. ..................................................................................................................................... [1] (d) When structure B is observed at a higher magnification, more detail of xylem vessel elements and phloem sieve tube elements can be seen. Outline the differences in the structure of a xylem vessel element and a phloem sieve tube element. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] [Total: 8]

Mark scheme: 1(a) stem / not a root, because, transport tissue / vascular bundles / vascular tissue(s) / xylem and phloem / xylem / phloem, around the edges / not in the centre / AW ; A stem because, pith / parenchyma tissue, is in the centre 1 1(b) any two from: (hydrostatic) support / described ; R if incorrect context e.g. support because of thick cell walls A packing tissue (cells), turgid / store water ; storage ; in context of substances other than water e.g. sucrose / starch / waste 2 1(c)(i) vascular bundle ; 1 1(c)(ii) 0.65 (mm) ; 1 Question Answer Marks 1(d) mp1-3 must have statements for both xylem and phloem mp4-7 need statements for either xylem or phloem three from: xylem phloem 1 no cytoplasm / hollow / no contents (peripheral / little / some) cytoplasm ; I protoplasm R full of cytoplasm / AW 2 no organelles / hollow / no contents (a few) organelles ; A examples of organelles mitochondria or ER I has SER / RER / ribosomes R has nucleus 3 lignified R idea of lignin within element no lignin / (only) cellulose ; 4 no end wall(s) / no sieve plate(s) A end walls have broken down or sieve plate(s) / perforated end wall(s) ; A (end walls) have sieve pores 5 (side walls) contain pits or no pits (in side walls) ; 6 no plasmodesmata or plasmodesmata (to companion cells) ; 7 thick(er), cell wall / walled or thin(ner), cell wall / walled ; 3

More questions on Structure of transport tissues

2 Some tissues of the gas exchange system include cells that are able to produce and secrete mucins. Mucins are stored in vesicles in these cells, ready for secretion. Once outside the cell, mucins adsorb water to form mucus. (a) Name the structures in the gas exchange system that produce and secrete mucins. ................................................................................................................................................... ............................................................................................................................................. [2] (b) Mucins are described as glycosylated proteins. The process of glycosylation involves the addition of sugar components after polypeptides are synthesised. Suggest one location in the cell where glycosylation of mucin could occur. ............................................................................................................................................. [1] (c) The processes that occur in the production and secretion of mucins are listed. translation exocytosis glycosylation transcription Complete Table 2.1 by writing the processes in the correct order in which they would take place. Table 2.1 first process second process third process fourth process [2] (d) Chloride ions move out of the mucin-producing cells at the same time as mucin is secreted. Suggest and explain how the exit of chloride ions helps the formation of mucus from mucin. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (e) The gas exchange system includes some cells that are able to divide by mitosis. Explain why it is important to have these cells in the gas exchange system. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] [Total: 11]

Mark scheme: 2(a) mucous gland cells / mucous gland(s) ; I mucosa goblet cell(s) ; list containing trachea and / or bronchus and / or bronchioles I and allow to two max BUT if alveoli stated or incorrect cell types (e.g. ciliated cells) max 1 2 2(b) any one from: Golgi (body / complex / apparatus) ; rough endoplasmic reticulum ; A rough ER / RER R SER I ER 1 2(c) two marks to complete table first process transcription second process translation third process glycosylation fourth process exocytosis allow one mark if transcription first process and exocytosis last process but other two wrong way round allow one mark if transcription and translation wrong way round and other two correct 2 2(d) accept symbol Ψ for water potential three from: 1 chloride presence outside cell causes water potential (outside cells) to, decrease / become more negative / become lower or chloride leaving cell causes water potential (in cell) to increase / AW ; 2 water potential gradient, created / present (between inside and outside of cell) ; 3 water leaves cell by osmosis (to be taken up by mucin to form mucus) ; 4 from higher to lower water potential / AW ; R if term gradient included 3 Question Answer Marks 2(e) any three from: to produce, new / daughter, cells« 1 that are genetically identical ; 2 to replace, old / damaged / dead, cells ; A named cells 3 to repair (damaged / injured / diseased) tissue ; A named tissue if mp 2 and 3 not gained, allow 1 mark for replacing damaged tissue 4 ref.to function ; in context 5 AVP ; idea of increase in number of cells / growth, to accommodate increase in size of gas exchange system in growing infants / AW 3

More questions on Protein synthesis

3 Fig. 3.1 is a photomicrograph of human blood cells from a healthy individual who lives at sea level. The cells labelled C, D and E are white blood cells. E C D red blood cell Fig. 3.1 (a) Name cells C, D and E. C ............................................................................... D ............................................................................... E ............................................................................... [3] (b) In humans, an increase in the white blood cell count can be associated with leukaemias and with infectious diseases, such as measles. Chronic lymphocytic leukaemia (CLL) is a type of cancer that starts in the bone marrow. In the early stages, many people with CLL feel well. The disease is sometimes diagnosed by chance during a routine blood analysis, when a high white blood cell count is noticed. Many of these white blood cells are only partially mature. (i) Suggest why CLL starts in the bone marrow and not in any other location in the body. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Explain why a high white blood cell count is a feature of measles and of CLL. measles ............................................................................................................................. ........................................................................................................................................... ........................................................................................................................................... CLL .................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (c) Most of the oxygen that enters the mammalian circulatory system is transported by red blood cells. (i) Describe and explain the passage of oxygen across the cell surface membrane of the red blood cell. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) At a high altitude, the partial pressure of oxygen in the atmosphere is lower than at sea level. If a person travels from low altitude to high altitude and remains there for a few weeks, the red blood cell count increases. Explain why the body needs to respond to high altitude by increasing the number of red blood cells. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (d) Polypeptide synthesis occurs before a red blood cell is released into the circulation. The HBB gene codes for the β-globin polypeptide of haemoglobin. There are two alleles of HBB, known as HbA and HbS. Describe the difference between the HbA allele and the HbS allele and state how this difference affects: • the β-globin polypeptide • the haemoglobin molecule. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [4] [Total: 17]

Mark scheme: 3(a) C =neutrophil ; A polymorphonuclear leucocyte A basophil A eosinophil D = lymphocyte ; B / T is neutral E = monocyte ; A macrophage I leucocyte / white blood cell, throughout 3 3(b)(i) any two from: lymphocytes / blood cells, produced in / originate from, bone marrow ; ref. to stem cell(s) ; ref. to cell division ; e.g. bone marrow has cells that can carry out, mitosis / cell division A (stem cells are) multipotent 2 Question Answer Marks 3(b)(ii) any three from: measles immune response stimulated ; detail ; e.g. either antigen recognition / presence / binding or lymphocyte / white blood cell, stimulated / triggered or clonal selection / AW plus clonal, expansion / proliferation / cell division / mitosis R incorrect pathogen name R bacteria CLL result of, uncontrolled mitosis ; A uncontrolled, division / cell cycle I rapid mitosis detail ; owing to, mutation / named mutation or cell cycle checkpoints not working or cells don’t respond to signals to control division 3 3(c)(i) any two from: (passive / simple) diffusion (of oxygen) across the phospholipid bilayer ; A movement from a higher to a lower concentration for diffusion A between phospholipids / between fatty acid chains / across hydrophobic core / across bilayer / AW, for phospholipid bilayer small size ; non-polar / uncharged ; 2 Question Answer Marks 3(c)(ii) any three from: less oxygen in inhaled air / AW ; A less oxygen taken up from alveoli low(er) saturation of haemoglobin (with oxygen) ; A Hb for haemoglobin A haemoglobin carries less oxygen must be the context of oxygen R saturation, with air / carbon dioxide haemoglobin has lower affinity for oxygen ; (so) more haemoglobin required (so more red blood cells) / (more red blood cells) so more haemoglobin ; AW compensation / compensates ; A so same, volume / quantity / amount, of oxygen reaches body cells (compared to lower altitude) 3 Question Answer Marks 3(d) any four from: 1 (alleles have) different nucleotide sequences ; A different base sequences 2 base substitution / substitution of a base ; A T replaced by A 3 (alleles have) different mRNA codons ; A altered mRNA codon R altered genetic code 4 (results in) one amino acid change or change from, glutamic acid / glutamate / glu, to, valine / val or changed primary structure ; A changed sequence of amino acids R if implies whole sequence changes 5 AVP ; e.g. HbA = CTC and HbS = CAC (on template strand) A HbA = GAG and HbS = GTG (on non-template strand) or HbA = CTT and HbS = CAT (on template strand) A HbA = GAA and HbS = GTA (on non-template strand) this is not also mp2 ref. to amino acid substitution at position 6 (this is not also mp4) A 6th, codon / triplet, changed 6 changed, (β-globin / Hb) tertiary structure ; A polypeptide / (Hb molecule) quaternary structure R β-globin / polypeptide 7 ref. to loss of globular structure / hydrophobic amino acid faces outside (instead of towards centre) ; A described e.g. (val) amino acid with hydrophobic R-group instead of (glu) amino acid with hydrophilic R-group accept hydrophilic / polar, amino acid accept hydrophobic / non polar, amino acid 4 Question Answer Marks 3(d) 8 sticky (haemoglobin) molecule formed / forms fibres with other haemoglobin molecules ; 9 oxygen taken up less easily / less oxygen carried by haemoglobin / AW ; A β-globin takes up oxygen less easily / AW 10 AVP ; (sickle cell) haemoglobin / β-globin, less soluble / AW I insoluble

More questions on The immune system

4 The bacterium Vibrio cholerae is the causative organism of the infectious disease cholera. V. cholerae has structural features typical of all bacterial cells. It also has a flagellum for movement. (a) Fig. 4.1 is an outline drawing of V. cholerae. Complete Fig. 4.1 by drawing and labelling the structures found in V. cholerae. flagellum Fig. 4.1 [4] (b) The World Health Organization (WHO) collects data about cholera from the 194 countries that are members of the World Health Assembly (WHA). In 2015: • there were cases of cholera in 42 of the member countries of the WHA • the total number of cases of cholera reported was 172 454 • there were deaths as a result of cholera in 23 of these countries • the total number of deaths from cholera reported was 1304. The case fatality rate for cholera is the proportion of cases of cholera that results in death within a particular time period. A country with cases of cholera that are properly treated should have a case fatality rate of less than 1%. (i) Calculate the case fatality rate for the 42 member countries of the WHA for 2015. Give your answer to the nearest 0.1%. case fatality rate = ..................................................... % [1] (ii) Many of the 23 countries reporting deaths from cholera in 2015 had a case fatality rate of less than 1%. However, two of the 23 countries had case fatality rates greater than 5%. Suggest two explanations for the higher case fatality rate in these two countries. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (c) In 2010, the country of Haiti experienced a major earthquake. This led to an outbreak of cholera. (i) Explain why an earthquake may lead to a cholera outbreak. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Fig. 4.2 shows data about cholera collected by WHO over a period of 8 years, from 2008 to 2015. These data include: • the total number of cases of cholera for each year • the number of countries in each year that had cases of cholera. 700 000 70 600 000 60 500 000 50number number of of cases countries 400 000 40 300 000 30 200 000 20 Key number of 100 000 10 cases number of countries 0 0 2008 2009 2010 2011 2012 2013 2014 2015 year Fig. 4.2 Comment on the trends shown in Fig. 4.2. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] [Total: 11]

Mark scheme: 4(a) max 3 if any membrane-bound organelles drawn inside cell e.g. nucleus, Golgi body, mitochondrion, lysosome, ER, a large vacuole BUT I vesicle / small vacuoles I detail of cell wall / cell surface membrane around flagellar area four from: cell wall ; must add another line to diagram R cellulose cell wall cell (surface) membrane ; A plasma membrane label line to the inside of cell wall I if outer line labelled as cell membrane DNA ; A bacterial chromosome / nucleoid as label allow one or two circular molecules (circle, loop, ball of string, tangled) R if obviously linear R if label includes, histones / histone proteins / chromatin R if nuclear, envelope / membrane, shown R if nucleolus shown or labelled ribosomes ; R 80S ribosomes shown as, dots / small spheres cytoplasm / cytosol ; plasmid ; smaller than DNA, circular AVP ; e.g. 70S / smaller / 17–20 nm, for ribosome murein / peptidoglycan (for cell wall – allow even if cell wall label not added) pilus /pili drawn as external hair-like structure(s) basal granule at base of flagellum capsule drawn to outside (some do have a capsule) 4 4(b)(i) 0.8 % ; R 0.80 % 1 Question Answer Marks 4(b)(ii) any two from: delay in / no, diagnosis ; delay in / no, treatment / therapy ; A feature of, oral rehydration, treatment /solution A ORT / ORS e.g. lack of supply of ORT unwillingness by health workers to give ORT greater belief in herbal remedies thinking drug treatment is sufficient lack of clean water to make up ORT solution no rehydration programmes I improper treatment / treatment not effective ref. to no / lack of, antibiotic therapy ; e.g. lack of supply of / less efficacious (AW) antibiotics used / less supervision in taking full dose ref. to antibiotic resistant strains ; idea that already have a weak immune system / malnourished ; A may have HIV/AIDS (hence weak immune system) 2 4(c)(i) any one from: damaged sanitation system / poor sanitation following earthquake ; I poor sanitation unqualified damage to, sewage treatment plants / water purification plants ; AW (contaminated) sewage contaminates drinking water ; I pollution A water becomes contaminated lack of purified drinking water; A lack of, clean / treated / safe / bottled, water AVP ; no, proper / safe, disposal of sewage 1 Question Answer Marks 4(c)(ii) any three from: 1 2011, peak in / highest / AW, number of, cases / countries / countries and cases ; A decrease, increase in 2011, decrease for countries A increase to 2011 and decrease for cases 2 (2010 outbreak in) ref. to Haiti and epidemic (so high number of 2011 cases) ; 3 ref. to spread of disease to countries neighbouring Haiti (hence increase in countries in 2011) ; 4 overall / generally / AW, decrease in number of countries with cases of cholera or 2008 54–56 countries and 2015 41–43 countries, with ref. to decrease ; decrease, peak at 2011 / increase in 2011, decrease is mp1 only 5 suggestion for trend in decrease in number of countries ; e.g. improved infrastructure for sewage / water treatment improved health education to prevent spread providing piped (treated) water 6 2008–2010 number of cases increased and number of countries decreased ; 7 AVP ; e.g. lowest / AW, number of cases in 2013 R if also state that 2013 is lowest for countries similar number of countries in 2008 and 2011 but, approx 3× / much higher / stated values, number of cases in 2011 3

More questions on Infectious diseases

5 Cells contain carbohydrates, proteins, lipids and nucleic acids. (a) Fig. 5.1 is a list of biological molecules, some of which are components of larger molecules. cellulose thymine nucleotide α-glucose β-glucose messenger RNA glycogen glycine α-globin Fig. 5.1 Complete Table 5.1 by using only the molecules listed in Fig. 5.1. • Each example can be written under one or more correct headings. • All the examples in Fig. 5.1 should appear at least once in Table 5.1. Table 5.1 examples monomers polymers monosaccharides polysaccharides [5] (b) Explain how the structure of phospholipids allows the formation of the phospholipid bilayer of cell membranes. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] [Total: 8]

Mark scheme: 5(a) glycine in monomer column only ; monomer polymer monosaccharide polysaccharide thymine (nucleotide) α-glucose ; β-glucose cellulose messenger RNA glycogen ; α-globin I glycine β-glucose ; α-glucose I glycine cellulose ; glycogen I glycine I incorrect spellings if α-globin appears once and is in monomer column instead of polymer column, and the monomer and polymer columns are otherwise correct, allow one mark (ecf) 5 5(b) any three from: allow points from an annotated diagram 1 phosphate head = hydrophilic / polar ; 2 fatty acid / hydrocarbon, tail / chains = hydrophobic / non-polar ; if mps 1 and 2 not gained, allow one mark for, hydrophilic / polar, heads and, hydrophobic / non-polar, tails 3 (so) heads face, watery environment / tissue fluid / cytoplasm / cytosol / aqueous environment ; 4 (fatty acid) tails, form hydrophobic core / form area away from water / face each other / AW ; 5 ref. tails and hydrophobic interactions ; 3

More questions on Carbohydrates and lipids

6 Catalase is an enzyme that catalyses the breakdown of hydrogen peroxide, which is a waste product of cell metabolism. The reaction catalysed by catalase is shown in Fig. 6.1. catalase 2H2O2 2H2O + O2 Fig. 6.1 (a) A student carried out two experiments to investigate the progress of the reaction shown in Fig. 6.1. Potato tissue was used as the source of the enzyme. Six pieces of potato were cut, each measuring 20 mm × 10 mm × 10 mm. In the first experiment, hydrogen peroxide solution was added to three of the pieces of potato tissue and the progress of the reaction was measured. Fig. 6.2 shows how the first experiment was set up. syringe containing H2O2 solution potato Fig. 6.2 (i) Suggest how the progress of the reaction could be measured. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) In the second experiment, the student cut each of the three remaining pieces of potato to obtain six pieces, each measuring 10 mm × 10 mm × 10 mm. Using exactly the same conditions, the student measured the progress of the reaction and obtained different results to the first experiment. Explain why the results of the second experiment were different from the results of the first experiment. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) The student then investigated the effect of temperature on the activity of catalase. On Fig. 6.3, sketch a curve to show how temperature affects the activity of an enzyme such as catalase. rate of reaction temperature / °C Fig. 6.3 [1] [Total: 5]

Mark scheme: 6(a)(i) any two from: correct ref. to time ; correct ref. to volume of oxygen ; A gas for oxygen A volume of water displaced by oxygen A measuring height of water level (decreasing) A cm3 instead of volume AVP ; subtract volume of gas displaced by H2O2 addition 2 6(a)(ii) any two from: greater surface area (over which catalase released) ; greater number of cells, damaged / cut open, to release catalase ; higher concentration of, catalase / enzyme ; A more, catalase / enzyme A more active sites available must be linked to idea of more enzyme (i.e. must get mp 2 or 3) so, higher rate of reaction / more enzyme-substrate complexes / more oxygen released ; AW 2 6(b) increase to optimum and steeper decrease ; A if curve does not touch one or both axes 1

More questions on Factors that affect enzyme action