Cambridge A Level Biology 9700 — 2022 May/June Paper 2 · Variant 2

1 Epithelial cells in the small intestine have cell structures known as microvilli. The microvilli of these cells are found only on the surface that borders the gut lumen. Fig. 1.1 shows images of microvilli of intestinal epithelial cells. These images have been obtained using a scanning electron microscope and a transmission electron microscope. Fig. 1.1A is at a different magnification to Fig. 1.1B. A B Fig. 1.1 (a) With reference to Fig. 1.1, state how it is possible to distinguish between a scanning electron micrograph and a transmission electron micrograph. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (b) The approximate length of a microvillus is 1 μm. Outline the method you would use to estimate the magnifications of the images shown in Fig. 1.1. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) One role of an intestinal epithelial cell is the absorption of glucose from the gut lumen into the circulatory system. This involves different membrane transport proteins. The events occurring in an intestinal epithelial cell during the absorption of glucose are summarised in Fig. 1.2. not to scale glucose gut lumen tissue capillary K+ fluid glucose Na+ Na+ Fig. 1.2 • Sodium ions (Na+) are removed from the cell by active transport through a transport protein known as a sodium-potassium (Na+ / K+) pump. • This decreases the concentration of Na+ in the cell compared to the gut lumen. • Glucose molecules are cotransported with Na+ into the cell from the gut lumen. • Glucose molecules are transported out of the cell into the tissue fluid down a concentration gradient. (i) Active transport involves water-soluble substances, such as Na+ and K+, and the use of ATP to provide the energy needed for their transport through carrier proteins. Outline other features of active transport. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Glucose molecules enter the cell through a membrane protein. Suggest why glucose molecules need to be cotransported with Na+ when it enters the cell through the membrane protein. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iii) Explain how microvilli increase the uptake of glucose into an intestinal epithelial cell. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (d) Stem cells are also located in the wall of the small intestine. These cells divide by mitosis continuously. Suggest and explain the importance of mitosis by stem cells in the small intestine. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [4] [Total: 13]

Mark scheme: 1(a) I ref. to resolution any one from: Fig. 1.1A is scanning (EM), qualified ; e.g. shows, surface / contour / 3-D, views shows (only the), the outer / external, view (of microvilli) idea of good focus with different depths does not have stated feature of TEM (see mp2) Fig. 1.1B is transmission (EM), qualified ; e.g. showing, 2D / flat, views (of, microvilli / mitochondria) image in one plane showing section through, mitochondria / microvilli / cell I thin shows, internal view of cell / contents of cell / AW does not have stated feature of SEM (see mp1) scanning (EM) stated plus feature and ; if Fig. 1.1, A / B not identified transmission (EM) stated plus feature 1 1(b) any two from: max 1 if stating to measure one of the sides of the figure (for each image) measure a number of microvilli and calculate a mean ; same units for actual and measured images / example given ; e.g. if microvillus measurement is in mm convert, microvillus measured length to m / actual length to mm R if extra detail given is incorrect e.g. divide by 1000 for mm to m divide, microvillus / image, length by, actual length / AW / 1(m) ; A idea that value for, microvillus / image, length is the magnification 2 1(c)(i) any two from: (movement of substances) against concentration gradient / from low(er) to high(er) concentration ; (protein has) binding site(s) ; specific ; A description e.g. shape complementary to shape of substance can be in context of protein or binding site ref. to (binding causes protein), conformational change / change of shape ; 2 Question Answer Marks 1(c)(ii) any two from: 1 glucose is moving against a (concentration) gradient ; AW e.g. low to high 2 movement powered by inward movement of Na+ ; AW 3 Na+ movement (into cell from gut lumen) down an electrochemical gradient or down a (Na+), concentration / diffusion, gradient or by facilitated diffusion ; A diffusion if response includes ref. to the cotransport protein / cotranporter 4 AVP ; e.g. idea that, cotransport needed so that all glucose will be removed from gut lumen ora facilitated diffusion of glucose will only be to equilibrium / AW cotransporter has (specific) binding site for glucose I cotransporter has a complementary shape idea that there is no specific active uptake protein for glucose 2 1(c)(iii) increases / larger / large, surface area (over which glucose can enter cell per unit time) ; A increases / higher / high, SA:V idea of (so) more, transport / carrier / cotransport, proteins A more cotransporters or more proteins, located in membrane / AW ; R pump proteins A idea of more space / places, where proteins can transport glucose 2 Question Answer Marks 1(d) any four from: suggestion max 3 explanation 1 to replace, old / dead / damaged / injured, cells or to, repair / replace, damaged tissue ; I repair cells I replace old tissues 6 idea of function in context of mp1 or 2 or 3 ; e.g. repair allows tissues to function specialisation / differentiation, allows, cells / tissue, to function genetically identical so cells can function as a tissue look for other approaches e.g. ‘replace damaged cells that no longer function’ is mp1 and mp6 …………………………………………………………………… 7 detail of function (intestines) ; e.g. absorption (of, glucose / nutrients) production of digestive enzymes pass absorbed, nutrients / AW, to blood I nutrition 2 cells are produced that can, differentiate / become specialised (into intestinal cells); I multipotent / AW R if, stated / strongly implied that, all cells produced by mitosis become specialised 3 produce cells that are genetically identical ; A clones A identical / same, DNA / genetic material / genetic information 4 growth ; R growth of cells 8 idea of development during, infancy / childhood ; 5 renew / replenish / restore number of / AW, stem cells ; I increase in stem cells 9 for, continued production / constant supply / AW, of intestinal cells or so that number of stem cells doesn’t decrease ; 4

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2 Cholera is a life-threatening and infectious disease caused by the bacterium Vibrio cholerae. One of the symptoms of the disease is severe diarrhoea. V. cholerae O1 and V. cholerae O139 are the two forms of the pathogen that are associated with cholera epidemics (large outbreaks). These two forms have different antigens that can be detected. (a) If an outbreak of cholera is suspected but not confirmed, a standard home treatment for diarrhoeal diseases can be used immediately to help prevent severe illness as a result of dehydration. If cholera is the cause of the disease, this standard treatment also helps to prevent a larger outbreak of the disease. (i) Outline the standard treatment that can be used for suspected cholera cases. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Suggest and explain why this treatment can help to prevent a larger outbreak of cholera. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) Rapid diagnostic testing (RDT) can be used to diagnose cholera by detecting the presence of V. cholerae. One type of RDT involves using a dipstick that contains mobile and immobilised monoclonal antibodies. Monoclonal antibodies (mAbs) are specific in their action. Fig. 2.1 shows a simplified diagram of an RDT dipstick that can be used to distinguish between V. cholerae O1 and V. cholerae O139. A faecal sample from a person with suspected cholera is collected and added to a reagent solution to form the test mixture. area where dipstick can be held 4 control area 3 test area containing immobilised monoclonal antibody that binds antigen-antibody complex O1 2 test area containing immobilised monoclonal antibody that binds antigen-antibody complex O139 direction of flow of 1 area containing two different mobile monoclonal antibodies: test • anti-O1 antibody mixture • anti-O139 antibody area where dipstick is inserted into the test mixture Fig. 2.1 The test mixture moves up the dipstick through area 1. The mobile monoclonal antibodies are attached to tiny gold particles. If these antibodies collect in test area 2 or 3, a coloured band becomes visible. A coloured band that becomes visible in area 4 confirms that the test strip is working and that the results are valid. (i) Explain how the structure of the monoclonal antibodies in the dipstick allows them to be specific in their action. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Fig. 2.2 shows the results for samples taken from two different people, A and B, who are suspected of having cholera. 4 4 3 3 2 2 1 1 person A person B Fig. 2.2 With reference to Fig. 2.2, state and explain the conclusions that can be drawn from the results of the RDT dipsticks for each person. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (c) Table 2.1 shows the results of an investigation to evaluate the effectiveness of an RDT dipstick in diagnosing cholera. Samples taken from 156 people were tested using a dipstick and compared to the results obtained by culturing the pathogen in a laboratory for accurate identification. Table 2.1 number of test results using culture techniques using dipstick (to obtain accurate identification) correct diagnosis incorrect diagnosis positive results for cholera 102 97 5 negative results for cholera 54 32 22 (i) With reference to Table 2.1, calculate the percentage chance of an RDT dipstick correctly confirming that a person with cholera has the disease. [1] (ii) Using an RDT dipstick to diagnose cholera is much cheaper than culturing the pathogen and requires less technical skill. Suggest one additional advantage of using an RDT dipstick, rather than culture techniques, to diagnose cholera. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 11]

Mark scheme: 2(a)(i) any two from: oral rehydration (salts / solution / therapy) ; A ORS / ORT A rehydration therapy if ref. to ‘drinking’ stated within response solution of / water with, glucose and salts ; A named example for salts e.g. sodium / potassium / citrate / chloride AVP ; e.g. antibiotics / doxycycline / tetracycline / furazolidone / choramphenicol / sulfaguanidine (standard treatment in some countries) zinc treatment (standard treatment for children in some countries) ref. to isolation 2(a)(ii) any two from: decreases, recovery time ; A cured more quickly I helps recovery / reduces severity of disease reduces time of / stops, diarrhoea production (containing pathogen) ; less likely to / AW, contaminate water ; reduced transmission of pathogen ; AW e.g. breaks transmission cycle 2 2(b)(i) allow antibody or mAb or Mab for monoclonal antibody I ref. to receptor I active site I combines / bonds any two from: specific / different, (Vibrio / pathogen) antigen-binding sites / binding sites for antigen ; R if antibody described as enzyme A (each) mAb binds to a, specific / particular, (Vibrio / pathogen) antigen (each mAb has) specific / different, tertiary structure / variable region(s) / primary structure / sequence of amino acids ; binding site and antigen have complementary shapes ; 2 Question Answer Marks 2(b)(ii) allow antibody or mAb or Mab for monoclonal antibody any three from: 1 person A, has cholera O1 / is infected with V. cholerae O1 and person B, does not have cholera ; A ref. to person A testing positive for cholera O1 and person B testing negative to cholera 2 tests are, valid / working, because, controls / bands 4, shows bands ; person A, band / colour in area 3 because 3 anti-O1 (mobile) antibody binds (specific antigen on) Vibrio O1 ; A antigen-antibody (complex) 01 formed 4 antigen-antibody (complex) O1 binds to immobilised antibody ref. to area 3 ; R if stated as, band / colour, in area 2 5 person B (in test area 2 and 3) no bands form / no colour / no change, because no antibody binds with antigen / no antigen-antibody complexes formed ; 3 2(c)(i) 95 / 95.1 (%) ; R 95.0% 1 2(c)(ii) I ref. to, cheaper / no need for (highly) trained personnel / easier to use / easier to obtain results / accurate R more accurate any one from: quicker to, obtain result / to do the test ; A less time consuming can carry out test in a greater variety of places / AW ; e.g. can be done at home less labour intensive ; AW e.g. only needs one person / can do it yourself easier to test more people at one time / AW ; portable ; AVP ; e.g. idea of easier to transport or distribute (to reach more people) ref. to, safer / less risk, from pathogen available to more people (consequence of cheaper) suggestion that dipsticks are able to identify different, forms / strains 1

More questions on Infectious diseases

3 Hummingbirds are the smallest of birds and are found in the Americas. Some species migrate hundreds of kilometres between warmer overwintering areas and summer breeding grounds. Like mammals, birds maintain a constant body temperature. Hummingbirds have a high requirement for sugars because they have a very high metabolic rate. Fig. 3.1 shows a hummingbird feeding on nectar, one of their main food sources. Fig. 3.1 (a) Nectar is a sugary liquid containing mainly sucrose, fructose and glucose. Sucrose has the molecular formula C12H22O11. Fructose and glucose each have the molecular formula C6H12O6. State two differences between sucrose and fructose, other than the number of carbon, hydrogen and oxygen atoms present. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (b) In preparation for migration, sugars need to be converted to triglycerides to function as energy reserves. Hummingbirds can double their body mass during this time. (i) Fig. 3.2 shows the structural formula of one type of storage triglyceride. The triglyceride has two types of fatty acid residue, palmitate and oleate. H H H H C C C H O O O C O C O C O H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H C H C H H C H C H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H H C H H C H H C H H C H H H palmitate oleate Fig. 3.2 Outline the features of the molecular structure of the triglyceride shown in Fig. 3.2. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (ii) In hummingbirds, glycogen is the long-term carbohydrate energy store. Suggest one reason why hummingbirds build up a greater energy store in the form of triglyceride, rather than a greater energy store of glycogen, in preparation for migration. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (c) In birds such as hummingbirds: • blood is kept within vessels • for each complete circuit of the body, blood passes through the heart twice. State the term used to describe this type of circulatory system. ............................................................................................................................................. [1] (d) The heart of birds has the same structure as the heart of mammals. Compared with the heart of mammals, the heart of birds is larger in proportion to their body size. Suggest why the heart of birds is larger in proportion to their body size. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (e) Complete Table 3.1 to show the names and functions of the main blood vessels associated with the heart of mammals. Table 3.1 function of blood vessel name of blood vessel carries blood from the heart to the lungs carries blood to the heart from the lungs carries blood from the heart to the rest of the body carries blood to the heart from the rest of the body [3] [Total: 12]

Mark scheme: 3(a) any two from: I ref. to two units v one unit or bigger v smaller (neutral points) sucrose fructose disaccharide R if incorrect monosaccharides stated v monosaccharide ; non-reducing sugar ora or reducing sugar ; ora A described in terms of reaction with Benedict’s reagent glycosidic bond present R glucosidic or no glycosidic bond present ; AVP ; e.g. always ring structure(s) hydrolysed / broken down before used as, a respiratory substrate / an energy source v v ring structure or straight chain form can be used immediately as, a respiratory substrate / an energy source 2 Question Answer Marks 3(b)(i) I three fatty acids A fatty acid residue for fatty acid any three from: 1 glycerol ; 2 ester, bond / linkage, qualified ; e.g. labelled on Fig. 3.2 / three ester bonds / ester bond between (O of) glycerol and (C of carboxyl of) fatty acid 3 palmitate is saturated or oleate(s) are, unsaturated / monounsaturated or two fatty acid(s) are, unsaturated / monounsaturated, and one is saturated ; 4 (each fatty acid has a) hydrocarbon chain ; 5 AVP ; extra detail e.g. hydrocarbon chain palmitate 15C and oleate 17C palmitate,CH3(CH2)14 and oleate, CH3(CH2)7CH=CH(CH2)7 palmitate 16C and oleate 18C unsaturated fatty acid tail(s) / oleate ref. to, presence of one, C=C / (carbon-carbon) double bond not the maximum number of, hydrogen atoms / hydrogens saturated fatty acid tail(s) / palmitate ref. to no, C=C / (carbon-carbon) double bond maximum number of hydrogen atoms / hydrogens 3 Question Answer Marks 3(b)(ii) any one from: idea that provides greater energy per unit volume ; A higher calorific value / greater energy density R produces more energy less mass needed to provide same energy / low(er) mass to energy ratio ; ora higher energy to mass ratio low(er) mass to volume ratio ; AVP ; e.g. glycogen can only be stored in liver and muscles glycogen is hydrated / uses water for storage, so mass increases suggestion that more, areas / adipocytes / adipose tissue, in body to store triglycerides (proportionately) more C-H bonds (to supply H for respiration) suggestion that triglycerides provides insulation during flight (at heights) more compact 1 3(c) closed, double (circulation / circulatory system) ; 1 Question Answer Marks 3(d) I ref. to metabolism any two from: need more, / large quantities of, oxygen / glucose or more / large quantities, of, oxygen / glucose, delivered / reaches tissues / transported / AW or idea of enough, oxygen / glucose supplied to meet needs ; idea that heart pumps blood (to tissues more) efficiently ; e.g. forcefully / in greater volumes / more / with higher pressure / faster more oxygenated blood is mp2 only suggestion of reason for needing more oxygen or glucose ; I migration e.g. more active fly / wing muscles search for food longer constantly moving / move for longer time generate heat to maintain body temperature, qualified ; e.g. (generally) smaller size / larger SA:V ref. to need to meet demands of carbon dioxide removal (from muscle action / respiration) ; idea that more carbon dioxide produced (so must be removed) 2 Question Answer Marks 3(e) note: only one mark for both pulmonary vessels function of blood vessel name of blood vessel carries blood from the heart to the lungs pulmonary, artery / arteries ; pulmonary, vein / veins carries blood to the heart from the lungs carries blood from the heart to the rest of body aorta ; I artery carries blood to the heart from the rest of body I superior and inferior or anterior and posterior I vein venae cavae / vena cava ; 3

More questions on Carbohydrates and lipids

4 The enzyme carbonic anhydrase has been found in a wide range of organisms and acts as a catalyst in many tissues. Studies have shown that there are differences in the protein structure of the enzyme and differences in the number and organisation of introns and exons of the gene coding for the enzyme. All carbonic anhydrase enzymes catalyse the same reversible reaction, shown in Fig. 4.1. carbonic anhydrase CO2 + H2O H2CO3 H+ + HCO3– carbon hydrogen water X Y dioxide ions Fig. 4.1 (a) With reference to Fig. 4.1, name X and Y. X ............................................................................................................................................... Y ............................................................................................................................................... [2] (b) Carbonic anhydrase enzymes can have different primary structures. Suggest how all carbonic anhydrase enzymes can catalyse the same reaction, even though they have different primary structures. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (c) Genes coding for proteins in eukaryotes consist of introns and exons. Outline the similarities and differences between the introns and the exons of genes coding for proteins such as carbonic anhydrase. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] All mammals have the same type of carbonic anhydrase, known as α-carbonic anhydrase. Many different forms, or isoforms, of α-carbonic anhydrase have been identified in mammals. There are 15 isoforms of α-carbonic anhydrase (CA) in humans. Cells of different tissues have one or more isoforms. Within cells the isoforms may be in different locations. (d) Red blood cells contain two isoforms, CA1 and CA2. Suggest the location of CA1 and CA2 in red blood cells and give a reason for your answer. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (e) Isoform CA6 forms part of human breast milk. Mammary gland cells package CA6 in Golgi vesicles for release from the cells. Name the transport mechanism associated with CA6 secretion. ............................................................................................................................................. [1] (f) Human CA isoforms in some epithelial cells in the eye have a role in the formation of the clear fluid of the eye known as aqueous humour. Overactivity of the enzyme may lead to a harmful increase of pressure within the eye and cause a condition known as glaucoma. Acetazolamide is a therapeutic drug that can be used in the treatment of glaucoma. It acts as a reversible non-competitive inhibitor. Describe the mechanism of action of acetazolamide as a reversible non-competitive inhibitor of carbonic anhydrase. .................................................................................................................................................................................. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] [Total: 12]

Mark scheme: 4(a) R if choice given and one is incorrect carbonic acid ; hydrogencarbonate (ions) ; A bicarbonate (ions) 4(b) any one from: similar / same, active site ; have the same catalytic amino acids ; similar / same, tertiary structure ; A same quaternary structure 1 Question Answer Marks 4(c) allow pre-RNA for primary transcript either exon or intron statement required for mp2 to 7, one mark each row any three from: exons introns 1 both, are (nucleotide sequences that are) transcribed / form part of the primary transcript ; 2 (DNA/RNA) coding (sequences ) R coding genes I exons have the genetic code (DNA/RNA) non-coding (sequences) R non-coding genes 3 (RNA exons) needed / involved / AW, in translation or for formation of, polypeptides / proteins / carbonic anhydrase not involved in translation / AW if mps 2 and 3 not gained ‘exons code for proteins’ or ora 1 mark 4 not removed, from primary transcript / from RNA / during gene splicing / during RNA splicing removed, from primary transcript / from RNA /during gene splicing / during RNA splicing 5 (join to) form mRNA / contain mRNA codons A remain in mRNA not part of mRNA / in primary transcript only 6 not involved in regulating activity of genes / AW may have regulatory roles A other suggestions for role 7 AVP e.g. (as part of mRNA) leave the nucleus / go to cytoplasm / go to ribosomes AVP e.g. remain in nucleus if all are differences and all statements are reversed (i.e. introns for exons and vice versa) max 2 marks 3 Question Answer Marks 4(d) allow Hb or hb or Hgb for haemoglobin two marks for points in left column or two marks for points in right column cytoplasm / cytosol ; (bound to) cell surface membrane ; close to haemoglobin (for H+ uptake) R in / on / with, hb or idea of being dispersed within cell because haemoglobin is distributed throughout ; close to, anion exchanger / transport protein, for (easy) exit of hydrogen carbonate (ions) ; quick for hydrogen carbonate (ions) to be transported out of cell / AW or H+ (from dissociation) binds rapidly to haemoglobin or cytoplasm provides water for reaction to form carbonic acid ; able to, hydrate / react with, carbon dioxide as it enters cell ; if stated cytoplasm and cell surface membrane, one mark reason can be taken from either column if correctly linked, one mark 2 4(e) exocytosis ; 1 4(f) any three from: 1 acetazolamide / inhibitor, binds / attaches / AW, to, allosteric site / site other than active site ; R alternative active site 2 (which) changes, shape / tertiary structure / 3-D structure, of active site ; A active site distorted I protein structure allow ecf for mp3 and 4 if competitive described (to max 2) 3 substrate(s) / CO2 / HCO3-, cannot, enter / bind to / fit in / AW, active site ; A active site no longer complementary to, substrate / AW A enzyme substrate / ES, complexes cannot form A ESCs cannot form I ‘substrate / CO2 / HCO3– / ‘cannot bind to enzyme’ without a link to active site 4 product, not formed / released ; A named product 5 ref. to acetazolamide / inhibitor, leaves, allosteric site / enzyme ; I reversibly binds 3

More questions on Transport of oxygen and carbon dioxide

5 Fig. 5.1 is a photomicrograph of a transverse section through part of the bronchus of the human gas exchange system. The image is of a good resolution for a light microscope. The bronchial epithelium is a single layer of cells lining the lumen of the bronchus. lumen D luminal L surface bronchial epithelium A elastic fibres B magnification ×180 Fig. 5.1 (a) The luminal surface shown in Fig. 5.1 is not clearly defined and appears slightly blurred. State why the luminal surface of the bronchial epithelium appears slightly blurred, even though the resolution of the image is good. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (b) Some cells of the bronchial epithelium shown in Fig. 5.1 appear darker than others. For example, cell D appears darker than cell L. With reference to the bronchial epithelium shown in Fig. 5.1, explain why some cells, such as cell D, appear darker and other cells, such as cell L, appear lighter. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (c) In Fig. 5.1 the tissue in box B is cartilage. The tissue shown in box A is different from the tissue in box B. Outline the differences in the structure and function of tissue A compared with tissue B. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] [Total: 6]

Mark scheme: 5(a) any one from: I too small presence of ciia ; A ciliated, cells / epithelial cells / epithelium AVP ; e.g. suggestion that mucus on surface makes detail not easily seen 1 5(b) epithelium has goblet cells and ciliated epithelial cells ; A ciliated cells A two different cell types present I ref. to cell division ref. to staining ; e.g. use of stains gives different, shades / colours differential staining one cell type more neutral / acidic different parts of cells stain differently idea of cells have different densities ; e.g. idea of more structures / larger nucleus, gives greater density / AW R no cell structures for lighter cell I ref. to number of cilia (sectioning may include) more of nucleus so, affects light penetration / makes cell darker ora AVP ; idea of different components in cells appearing, darker / lighter 2 Question Answer Marks 5(c) any three from: A B / cartilage max two for structure smooth muscle / composed of smooth muscle cells or no chondrocytes or no smooth muscle cells or has chondrocytes ; cells close together or cells, (more) isolated / in gaps / in lacunae ; cells, spindle shaped / elongated / AW or cells (more) rounded / AW ; AVP structure e.g. not surrounded by, perichondrium / AW contains blood vessels or surrounded by, perichondrium / AW no blood vessels ; function contractile / contracts (and relaxes) I recoil A bronchi walls contract R bronchi contract or non-contractile ; changes diameter of airways A controls size of lumen or protective / support ; A described e.g. prevents collapse of, bronchus or keeps bronchus open if incorrectly quotes A as the cartilage, use right hand column to allow one mark max (ecf) 3

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6 The transport tissues of plants are phloem and xylem. The role of xylem is the transport of water and mineral ions from the soil solution to the different parts of the plant body. The role of phloem is the translocation of assimilates and other substances from sources to sinks. (a) The source of mineral ions for the plant is the soil solution. These mineral ions are transported from the roots in the xylem. Mineral ions are also found in the phloem sap within phloem sieve tubes. Suggest why mineral ions are found within phloem sieve tubes and state how they are transported within phloem sieve tubes. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3] (b) Phloem tissue consists of different cell types. Complete the passage using the most appropriate terms to summarise some of the features of phloem tissue. The end walls of sieve tube elements are modified to allow efficient flow of phloem sap by the formation of ....................................................................... . These structures also prevent the cells from bursting under pressure. The cytoplasm of sieve tube elements is very much reduced and is found at the ....................................................................... of the cells. Most of the organelles in the cell are absent. Adjacent to sieve tube elements are ....................................................................... cells that carry out the metabolic processes of the missing organelles, allowing the sieve tube elements to function. [3] [Total: 6] The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries.

Mark scheme: 6(a) any three from: at (phloem) source, mineral ion entry (with water), from xylem / through plasmodesmata from companion cells ; dissolved in water / as solutes in water / in solution / in sap solution ; in context of entry from xylem or within phloem sap (transport) as part of mass flow ; must be in context of phloem flow down a pressure gradient / AW ; R differences in pressure gradient R from high pressure gradient to low pressure gradient AVP ; e.g. suggestion that mineral ions are needed for transport of some assimilates (e.g. complexed with) idea of reallocation of resources / arrive at (phloem) source and are moved to other parts, for use / when needed ; 6(b) sieve, plates / pores ; A perforated end plates / end plates with pores I plasmodesmata periphery / edge / AW ; companion ; A transfer 3

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