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Prac. 1(a) A protein is formed from 300 amino acids. The diagrams show the primary, secondary and tertiary structures of this protein.1122045157834Explain what causes the secondary structure to differ in length from the primary structure.........................................................................................................................................................................................................................................................................................................................................................(1 mark)Explain what is meant by the tertiary structure of a protein.......................................................................................................................................................................................................................................................................................................................................................(1 mark)Heating may affect the tertiary structure of a protein. Explain how.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)The first step in investigating the primary structure of a protein is to break it into shorter lengths with enzymes. The table shows some of the enzymes used and the position of the peptide bonds they break.69405513906500The diagram shows a polypeptide chain. The sequence of amino acids should be read from left to right.1036320100330How many amino acid fragments will be produced from this polypeptide if it is incubated with a mixture of trypsin and V8 protease?..........................................................................................................................................................................(1 mark)Explain why trypsin and chymotrypsin break peptide bonds between different amino acids..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3 marks)ext.Prac. 2(a) Complete the following table. Use a tick if the feature is present or a cross if it is absent.1181100104775(3 marks)(b) Cells were scraped from the cut surface of a potato tuber. They were stained with iodine solution and examined with an optical microscope. The drawing shows one of these cells.2181225161290Name two polysaccharides found in this cell which would not be found in a red blood cell............................................................................................................................................2. ..................................................................................................................................................(1 mark) (ii) The diameter of this cell, measured from A to B, is 40 ?m.Calculate the magnification of the drawing. Show your working. Answer ............................................(2 marks)The focusing knob of the microscope was adjusted slightly. The drawing below shows how the cell then looked.236474018859500Explain the difference in appearance of the cell contents.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)ext.Prac. 3EXT. Tradescantia is a house plant. There are small hairs on its flowers. These hairs are made of cells. Figure 1 shows the appearance of cells from one of these hairs after 20 minutes in distilled water. Figure 2 shows cells from another hair after 20 minutes in a solution of potassium nitrate.1914525102870(a) What does Figure 2 suggest about the permeability of the plasma membranes surrounding these cells?................................................................................................................................................................................................................................................(1 mark) (b) What is present in the space labelled F? Explain your answer.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)(c) How would the water potential of the sap in the vacuole of cell E differ from the water potential of the sap in the vacuole of cell D? Explain your answer.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3 marks)ext.Prac. 4The diagram shows the outer layers of a cell from each of three different organisms. One ofthe cells is a prokaryotic cell, one is an animal cell and one is a plant cell.12122154127500(a) Which of the three cells, A, B or C, is the prokaryotic cell? Give a reason for your answer.............................................................................................................................................................................................................................................................................(1 mark)(b) Complete the table which shows some of the similarities and differences between the outer layers of these cells. Use a tick if the statement is true or a cross if it is not true.(2 marks) (c) Penicillin is a substance which kills bacterial cells by damaging their cell walls. As a result, they burst when they take in water.The concentration of dissolved substances is higher in the cytoplasm of a bacterial cell than it is in the surrounding solution. Explain why water enters the bacterial cell.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)Penicillin kills bacterial cells but has no effect on plant cells. Suggest why.............................................................................................................................................................................................................................................................................(1 mark)(d) Explain why a plasma membrane can be seen with an electron microscope but not with an optical microscope.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)ext.Prac. 5EXT. The diagram shows a human heart seen from the front.2247900118745(i) Which one or more of vessels A to D contains oxygenated blood?......................................................................................................................................(1 mark)(ii) During a cardiac cycle, the pressure of blood in vessel C is higher than thepressure of blood in vessel B. Explain what causes this difference in pressure.............................................................................................................................................................................................................................................................................(1 mark)(b) What does the diagram suggest about the pressure in the atria compared to the pressurein the ventricles at the stage in the cardiac cycle shown?Explain your answer.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks) (c) The wave of electrical activity which coordinates the heart beat is delayed slightly at part X. It then passes along part Y to the base of the ventricles.Explain the importance ofthe slight delay at part X........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)the electrical activity being passed to the base of the ventricles.......................................................................................................................................………………..............................................................................................................………………....................................................................................................................................................................................................................................................(2 marks)ext.(a) (i) C and D; 1(ii) Left ventricle with thicker wall / more muscle / (muscle in) left ventriclecontracts more forcefully; 1(b) Higher in atria / lower in ventricles;Atrioventricular valves / valves between atria and ventricles open; 2(Q Credit second mark only if valves are named or correctly located.)(c) (i) Allows blood to pass into ventricles / from atria / so that atria canempty;Before ventricles contract; 2(ii) Ventricle contracts from base / upwards;Blood pushed through B and C / arteries / all blood rejected; 2Total 8Prac. 6EXT. 1Hospitals can check to see if a strain of bacteria causing an infection is resistant to a range of antibiotics by using a multodisc. A multodisc contains different antibiotics.?The bacteria are isolated from a patient.?The bacteria are spread on nutrient agar in a Petri dish.?The multodisc is placed on the agar.The figure below shows a Petri dish with the bacteria, in which is placed a multodisc containing six different antibiotics. (i)Explain why there are clear areas of agar in the Petri dish............................................................................................................................................................................................................................................................................................................................................................................[1] (ii)Using the figure above, name the antibiotic that is most effective against the bacteria causing the infection..........................................................................................................................[1](iii)Suggest three reasons why a hospital might use a multodisc to select the most suitable antibiotic for treating a patient.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................[3][Total 5 marks] EXT. 2.Drugs, such as antibiotics, are often first discovered in the natural environment.Explain why it may become increasingly difficult to discover new drugs in the future.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................[Total 2 marks]ext. 1(i)bacteria, killed / destroyed / cannot grow / lyse,in presence of antibiotic;DO NOT CREDIT ‘antibiotic works better’ or ‘there are no bacteria there’ or ‘bacteria are broken down’1 (ii)streptomycin;IGNORE ‘4’ as it is the number rather than the name1 (iii)DO NOT CREDIT responses which simply refer toselecting the best antibiotic1cheap / AW;2(test is) quick to carry out / (deals with several antibiotics)at same time / AW;DO NOT CREDIT speed of antibiotic action3(idea of) allowing early treatment of patient;4(idea of) compares antibiotics under same conditions;5(correct antibiotic first time) to prevent antibioticresistance developing;3 max[5]ext. 2 (new) drugs come from (named) organisms;ACCEPT plants / animals / fungi / species / etc.biodiversity is reducing;habitats / named habitat, destroyed / lost;ACCEPT deforestation / natural environment lostreason for habitat destruction;e.g.global warmingloggingfuelcropsconstruction / industrialisationminingfishingpollutiontourismACCEPT any other valid reason that will destroy natural habitats but not general statements such as ‘human development’ or ‘business’[2]Prac. 7EXT. Red seaweeds are algae which contain, in addition to chlorophyll, a red pigment called phycoerythrin. Green seaweeds do not contain phycoerythrin. Both phycoerythrin and chlorophyll absorb light energy which can be used in photosynthesis. The graphs show the percentage of light of different wavelengths absorbed by sea water, by chlorophyll and by phycoerythrin.15741652286000Use information from the graphs to explain why red seaweeds are usually found in deeper water (further down the shore) than green seaweeds...........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(6 marks)ext.Prac. 8EXT. (a) The diagram shows part of the light-independent reaction of photosynthesis.10407654191000How many carbon atoms are there in one molecule of glycerate 3-phosphate?.......................................................................................................................................................(1 mark)What is the function of each of the following in the reactions shown in the diagram?Reduced NADP .................................................................................................................................................................................................................................................................................ATP ....................................................................................................................................................................................................................................................................................................(2 marks)(b) Radioactive carbon dioxide was supplied to a culture of photosynthesising single-celledalgae. At 5-second intervals, samples of the culture were dropped into boiling alcohol to stop all chemical reactions. The radioactive substances identified in these samples are given in the table.89789017145000Explain how information in the table provides evidence for the following.Glycerate 3-phosphate is converted into triose phosphate..........................................................................................................................................................(1 mark)The reactions given in part (a) form part of a cycle of reactions.........................................................................................................................................................(1 mark)ext.Prac. 9EXT. The diagram gives an outline of the process of aerobic respiration.82169095250(i) Complete the table by naming stages A and B and giving the location of each stage in a cell such as a liver cell.269240-3175(2 marks)(ii) How many carbon atoms are there in each pyruvate ion? .............................................................(1 mark)What happens to the H+ ions and electrons released in stage C?..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)In aerobic conditions, ATP is produced by substrate-level phosphorylation and by oxidative phosphorylation. Use information in the diagram to find the net yield of molecules of ATP per molecule of glucose bysubstrate-level phosphorylation; ..............................................................................oxidative phosphorylation. .......................................................................................(2 marks)(c) (i) One mole of glucose releases 2880 kJ of energy when burned completely in oxygen. Hydrolysis of one mole of ATP to ADP and phosphate releases 31 kJ of energy. Use your answers from part (b) to calculate the percentage efficiency of energy transfer from glucose to ATP by aerobic respiration. Show your working.Percentage efficiency = ........................................%(2 marks)What happens to the energy which is not transferred to ATP?.................................................................................................................................................................(1 mark)Explain why ATP is better than glucose as an immediate energy source for cell metabolism.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)Give three uses of energy from ATP in a liver cell.1 .............................................................................................................................................................2 .............................................................................................................................................................3 .............................................................................................................................................................(3 marks)ext.596902847340Prac. 10IAA is a substance that affects the growth of plants. It is produced in the tips of shoots and moves downwards in the stem to the rest of the plant. A series of experiments was performed to investigate the effect of the IAA on the growth of cucumber seedlings.(a)Figure 1 shows the results of an investigation into the effect of unidirectional light on IAA.Figure 1 (i)Give one reason for the use of the impermeable glass barriers............................................................................................................................(1) (ii)What do the results of this experiment show about the effect of unilateral light on IAA? Use evidence from Figure 1 to support your answer...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3)(b)Figure 2 shows the ways in which two groups of cucumber seedlings were cut before being used in a second investigationFigure 2 The two types of cut seedlings, P and Q, were grown in different growth media over a four-hour period. The table shows the results.Group of cutGrowth mediumMean increase in length/mmseedlings usedGrown in the darkGrown in blue lightP1% sucrose solution1.20.8PSolution of 1% sucrose and 6 mg dm–3 IAA3.95.2Q1% sucrose solution4.13.3QSolution of 1% sucrose and 6 mg dm–3 IAA4.95.7 (i)The cut seedlings were grown in sucrose solution, rather than in distilled water.Give one reason why............................................................................................................................(1)(ii)When they were both grown in the dark, the two groups of seedlings responded differently to the inclusion of IAA in their growth media. Suggest one explanation for this different response.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2) (iii)Describe the effect of blue light on the growth of seedlings P and Q...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3)(c)Many fungi are parasites on plants. Uptake of IAA from the host plant affects the ability of these parasitic fungi to invade their plant host.The uptake of IAA by a particular fungus was investigated. Two phenotypes of the fungus were used, the wild type and a particular mutant.The bar chart shows the effect of DNP on the uptake of IAA by this fungus. DNP is a drug that affects the gradient of hydrogen ions across mitochondrial membranes. Using evidence from the information given above and your own knowledge,(i)explain how IAA is taken up by the cells of this fungus............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2)(ii)suggest how the mutation affected the cells of this fungus........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3)(Total 15 marks)ext.(a)(i)Prevents sideways movement of IAA;1(ii)Light does not destroy/change IAA;Diagram D shows total amount of IAA unchanged (byunilateral light);Light causes IAA to move to shaded side of shoot tip;Diagram C shows movement is in tip/not in agar block;3 max (b)(i)Used in respiration / as energy source;1Q Answers that refer to making energy should not be awarded credit.(ii)Q contains tip/site of IAA production;Addition of further IAA has little effect;2Q Accept clear converse argument for P(iii)Inhibits (growth of) both in sucrose solution;Stimulates (growth of) both in sucrose and IAA solution;Greater effect in P;3 (c)(i)Uptake by active transport;(Evidence is that) heat-killed wild type has low/no uptake;2(ii)Mutation increases number / frequency of proton/hydrogenion pumps;(Which explains) increased uptake of IAA without DNP;DNP reduces uptake by mutant cells (to wild type value);3[15]Prac 11EXT. Lactose is present in milk. It is broken down by lactase into glucose and galactose. This isshown in the equation.2869565120652869565107315 lactose + water glucose + galactose (a) Name the type of reaction shown in the equation..............................................................................................................................................(1 mark)(b) The molecular formula of galactose is C6H12O6. What is the molecular formula oflactose?.............................................................................................................................................(2 marks)(c) Doctors use a lactose tolerance test to find out if a person is lactose intolerant. In thistest, the person is given a solution of lactose to drink. Blood glucose concentration isthen measured over the next two hours.A lactose tolerance test was carried out on a healthy man who was lactose tolerant, andon a man who was lactose intolerant. The results for the first hour are shown in thetable. (i) The blood glucose concentration changed in the healthy man after he had takenthe test. Describe how.............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)(ii) Explain the results for the lactose intolerant man...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3 marks)ext.(a) Hydrolysis; 1(b) C12;H22O11; 2(c) (i) One mark for answer that simply refers to increase and subsequentdecreaseTwo marks for answer that refers to reaching a peak at approximately6.6 mol dm-3/45 minutes. 2(Q Descriptions must refer to concentration of glucose and timeto gain credit. Do not accept vague references to “It . . . “)(ii) No lactase;Therefore lactose not digested/glucose not produced;No glucose absorbed therefore concentration in blood stays the same/does not rise; 3Total 8Prac 12EXT. The community present in a roadside ecosystem was investigated.Explain what is meant by:community; ...........................................................................................................................................................................................................................................................................................ecosystem. ............................................................................................................................................................................................................................................................................................(2 marks)The diagram shows a section through a road which has a sloping bank and hedge on each side.135655518288000177419032067500The following plant species were found growing on 10-metre lengths of the north-facing and south-facing road banks.177419011430000Use the formula:to calculate the index of diversity for the plants growing on the north-facing road bank. Show your working. Index of diversity = ...............................(2 marks)Give one advantage of calculating the index of diversity rather than just recording the number of species present...............................................................................................................................................................................................................................................................................................................(1 mark)Suggest and explain how one abiotic factor might have caused differences in plant growth on the two road banks.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)Explain why the south-facing road bank is likely to show greater ecological stability than the north-facing road bank.....................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(3 marks)The south-facing road bank would also be expected to have a higher diversity of animals. Suggest one reason for this.........................................................................................................................................................................................................................................................................................................(1 mark)(c) In order to estimate the population of woodlice living on the north-facing road bank, four pitfall traps were set in the ground at 2-metre intervals and left for 24 hours. All the woodlice that had fallen into the traps were marked on their underside with quickdrying paint and released back into their habitat. The next day the traps were examined again and the numbers of marked and unmarked woodlice were counted. The results are shown in the table.678815179705Use the data to estimate the woodlouse population in this area. Show your working.Population = ..........................................(2 marks)Suggest two reasons why it is not possible to make a reliable estimate of the woodlouse population size from these data.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................(2 marks)ext.8312153997960 ................
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