A Level Biological Molecules Practise OCR ExamBuilder
Biology AA level Biological Molecules practiseAmy VickersPlease note that you may see slight differences betweenthis paper and the original.Candidates answer on the Question paper.Duration: Not setOCR supplied materials:Additional resources may be supplied with this paper.Other materials required: Pencil Ruler (cm/mm)INSTRUCTIONS TO CANDIDATES Write your name, centre number and candidate number in the boxes above. Please write clearly and in capital letters.Use black ink. HB pencil may be used for graphs and diagrams only.Answer all the questions, unless your teacher tells you otherwise.Read each question carefully. Make sure you know what you have to do before starting your answer.Where space is provided below the question, please write your answer there.You may use additional paper, or a specific Answer sheet if one is provided, but you must clearly show your candidatenumber, centre number and question number(s).INFORMATION FOR CANDIDATES The quality of written communication is assessed in questions marked with either a pencil or an asterisk. In History andGeography a Quality of extended response question is marked with an asterisk, while a pencil is used for questions inwhich Spelling, punctuation and grammar and the use of specialist terminology is assessed. The number of marks is given in brackets [ ] at the end of each question or part question. The total number of marks for this paper is 72. The total number of marks may take into account some 'either/or' question choices. OCR 2020. You may photocopy this page.1 of 43Created in ExamBuilder
1.Which of the processes, A to D, describes the formation of cellulose?Acondensation polymerisation of amino acid moleculesBcondensation polymerisation of β-glucose moleculesChydrolysis polymerisation of α-glucose moleculesDhydrolysis polymerisation of deoxyribose moleculesYour answer[1]2.Which of the molecules, A to D, is a pentose sugar?Your answer[1] OCR 2020. You may photocopy this page.2 of 43Created in ExamBuilder
3.The diagram below shows part of a plasma membrane.Which of the label lines points to a structure that could contain a sulfur atom?A1, 2 and 3BOnly 1 and 2COnly 2 and 3DOnly 1Your answer OCR 2020. You may photocopy this page.[1]3 of 43Created in ExamBuilder
4.The table below shows four biological molecules and their component elements.Which of the rows, A to D, correctly identifies the elements in each molecule?sucrosecholesterolinsulinATPAC, H, OC, H, O, NC, H, O, N, SC, H, O, N, PBC, H, O, NC, H, OC, H, O, N, SC, H, O, N, SCC, H, OC, H, OC, H, O, N, SC, H, O, N, PDC, H, OC, H, OC, H, O, N, PC, H, O, N, PYour answer5.[1]The following are a series of organic molecules and the chemical processes that occur to convert them intodifferent molecules.Which of the rows, A to D, is correct?Anucleic acidnucleotideBα-glucoseamylopectinCamino lypeptidecellulosemaltoseYour answer OCR 2020. You may photocopy this page.[1]4 of 43Created in ExamBuilder
6.Proteins are important biological molecules.Hydrogen bonds also form between water molecules.(i) Describe the formation of a hydrogen bond between two molecules of water and explain why water can formthese bonds.[3](ii) Hydrogen bonds allow water to act as a solvent.Why is the ability of water to act as a solvent important for the survival of organisms?[3] OCR 2020. You may photocopy this page.5 of 43Created in ExamBuilder
7.Which of the statements, A to D, correctly describes the process of adhesion?Aattraction of water molecules to the impermeable walls of xylem tissueBattraction of water molecules to other water molecules in the xylem tissueCactive transport of water molecules into phloem tissueDattraction of water molecules to other water molecules in the phloem tissueYour answer8.[1]Root vegetables require sulfate ions (SO42-) in order to grow to a normal size. The plant uses the sulfur atoms tosynthesise biological molecules during growth.Sulfur atoms are required for the synthesis of which type of biological molecule?[1] OCR 2020. You may photocopy this page.6 of 43Created in ExamBuilder
9.When interpreting the results of an experiment to investigate the effect of detergent on plasma membranes, astudent looked for a diagram to show what the phospholipids may look like in the presence of detergent.Which of the diagrams, A to D, should the student use?Your answer[1] OCR 2020. You may photocopy this page.7 of 43Created in ExamBuilder
10.An unknown solution of a single sugar was tested. The results were recorded in Table 9.1.Colours observed after testingBenedict's test for reducing sugarsBenedict's test for non-reducing sugarsbluebrick redTable 9.1Identify the unknown sugar.AfructoseBlactoseCsucroseDglucoseYour answer[1] OCR 2020. You may photocopy this page.8 of 43Created in ExamBuilder
11.A student mixed an unknown substance with water and ethanol. A white suspension formed in the tube.Which of the explanations, A to D, is correct?Alipid is presentBnon-reducing sugar is presentCprotein is presentDreducing sugar is presentYour answer[1]12.Which of the following processes involves the formation of ester bonds?1synthesis of polynucleotides2 synthesis of triglycerides3 synthesis of polypeptidesA1, 2 and 3BOnly 1 and 2COnly 2 and 3DOnly 1Your answer OCR 2020. You may photocopy this page.[1]9 of 43Created in ExamBuilder
13.Which of the statements, A to D, about amylopectin is correct?Ait contains 1-4 and 1-6 glycosidic bonds between α-glucose monomersBit is an unbranched chain of α-glucose monomersCit contains α 1-4 and β 1-6 glycosidic bondsDit is made up of β-glucose monomers and is uncoiledYour answer14.[1]The hormone ecdysone is synthesised in the prothoracic glands found in the upper thorax of some invertebratesand is released into haemolymph. It is then transported to cells near the surface of the body and causes the lossof the exoskeleton so that a new exoskeleton can form.Which of the following statements explains how ecdysone is able to act on cells near the surface of the body?1Ecdysone is synthesised by specialised neurosecretory cells.2Ecdysone is soluble in haemolymph because it is a polar molecule.3Ecdysone is complementary to cell surface receptors on cells throughout the body of someinvertebrates.A1, 2 and 3BOnly 1 and 2COnly 2 and 3DOnly 1Your answer OCR 2020. You may photocopy this page.[1]10 of 43Created in ExamBuilder
15.Which option, A to D, describes the role of cholesterol in cell surface membranes in the human body?ACholesterol binds to phospholipid phosphate heads, increasing the packing of the membrane, thereforereducing the fluidity of the membrane.BCholesterol binds to phospholipid fatty-acid tails, reducing the packing of the membrane, thereforeincreasing the fluidity of the membrane.CCholesterol absorbs ATP, preventing active transport across the membrane.DCholesterol binds to phospholipid fatty-acid tails, increasing the packing of the membrane, thereforereducing the fluidity of the membrane.Your answer OCR 2020. You may photocopy this page.[1]11 of 43Created in ExamBuilder
16.In cells, glucose can exist as α-glucose or as β-glucose.The figure represents the structural formula of a molecule of α-glucose.(i) In the figure, some atoms or groups have been replaced by the letters X, Y and Z.Identify the correct atom or group that has been replaced by each letter.XYZ[3](ii) Describe how the structure drawn in the figure above would be different if it represented a molecule of βglucose. OCR 2020. You may photocopy this page.12 of 43Created in ExamBuilder
[2](iii) Two α-glucose molecules can be joined to form a disaccharide molecule.State the precise name of the covalent bond that forms between the two glucose molecules and the name ofthe disaccharide that is formed.bonddisaccharide[2] OCR 2020. You may photocopy this page.13 of 43Created in ExamBuilder
17.Proteins are important biological molecules.Protein structure can be represented at four levels: primary, secondary, tertiary and quaternary.Below is a set of features that may be used when describing the structure of a protein such as haemoglobin.FeaturesLetterhydrogen bondsApeptide bondsBα and β subunitsCthe sequence of amino acidsDthe initial folding of the polypeptide chainEthe overall 3D shapeFionic bondsG(i) Select the letters of the features that describe the primary level of protein structure.[1](ii) Select the letter or letters of the feature(s) found in the secondary level of protein structure that are notpresent in the primary structure.[1](iii) Select the letter or letters of the feature(s) that are found in the tertiary level of protein structure that are notpresent in the primary and secondary structures.[1](iv) Select the letter or letters of the feature(s) found only in the quaternary level of protein structure.[1] OCR 2020. You may photocopy this page.14 of 43Created in ExamBuilder
18.Complete the following statements about proteins using the most appropriate terms.The secondary structure of a protein may contain many regions folded in zig-zag patterns known as.The secondary structure of a protein is determined by the arrangement of bonds,which stabilise the structure.The structure of collagen is described as a left-handed helix because of thedirection in which the polypeptide twists.Polypeptides known as alpha (α) and beta (β) form part of thestructure of haemoglobin.[5] OCR 2020. You may photocopy this page.15 of 43Created in ExamBuilder
19.*Describe and explain how the structure and properties of different carbohydrate and lipid molecules suit them totheir role as energy storage molecules in plants and animals.[9] OCR 2020. You may photocopy this page.16 of 43Created in ExamBuilder
20.Which of the following could not be an amino acid?[1]Your answer OCR 2020. You may photocopy this page.17 of 43Created in ExamBuilder
21.The following table describes the approximate percentage mass of different chemical elements in c 1.00.0Which of the rows, A to D, is correct?Your answer22.[1]Enzymes are important molecules in living organisms.(i) A student decided to use the biuret test to detect the presence of enzyme in a solution.Outline the procedure the student should follow in order to detect the presence of enzyme in a solution usingthe biuret test.[2](ii) State why the structure of enzyme molecules allows them to be detected in solution using the biuret test.[1] OCR 2020. You may photocopy this page.18 of 43Created in ExamBuilder
23.In 1913, scientist Peter Boysen-Jensen investigated phototropism in plants.He inserted mica plates into growing shoots illuminated from one side only. Mica allows electrical impulses topass through, but does not allow soluble molecules to pass through.The diagram below summarises Boysen-Jensen's results.Which of the following statements correctly explains these results?1The factor causing phototropism moves away from the tip.2The factor causing phototropism is not an electrical impulse.3The factor causing phototropism moves away from light.A1, 2 and 3BOnly 1 and 2COnly 2 and 3DOnly 1Your answer[1] OCR 2020. You may photocopy this page.19 of 43Created in ExamBuilder
24.One of the main functions of the liver cells is the formation of urea by the ornithine cycle, an outline of which isshown in Fig. 17.2.(i) Step 1 of the cycle takes place in the organelle represented by D.Identify organelle D.[1](ii) During the cycle ornithine moves into organelle D and citrulline moves out of the organelle.Suggest the method by which these molecules move into and out of the organelle during the cycle. Givereasons for your choice.[2](iii) How has the ammonia that is used in step 1 been formed?[1](iv) Identify the compound labelled X in Fig. 17.2. OCR 2020. You may photocopy this page.20 of 43Created in ExamBuilder
[1] OCR 2020. You may photocopy this page.21 of 43Created in ExamBuilder
25.Energy can be stored in living organisms in the form of carbohydrates or lipids.Name the carbohydrate molecules used to store energy in plants and animals.plantsanimals26.[1]Cellulose is a polysaccharide that is present in some living organisms.(i) Complete the following table to show three other differences in the structures of starch (amylose) andcellulose molecules.AmyloseCellulosecoiledno coiling[3](ii) Which properties of cellulose make it suitable for forming cell walls?[2] OCR 2020. You may photocopy this page.22 of 43Created in ExamBuilder
27.Pepsin is an enzyme that digests protein foods in the mammalian stomach.Protein molecules are made from chains of amino acids.(i) Name the covalent bond between two adjacent amino acids in a chain of amino acids.[1](ii) Name the type of reaction involved in breaking this bond and describe what happens in this reaction.[2] OCR 2020. You may photocopy this page.23 of 43Created in ExamBuilder
28.Triglycerides contain three elements.(i) M and N are formulae for two macromolecules,Which of the formulae, M or N, corresponds to a triglyceride?Explain your answer.FormulaBecause[1](ii) Phospholipid molecules are similar to triglycerides but they also contain the element phosphorus as part of aphosphate group.Explain how the structure of phospholipids allows them to form the bilayer of a plasma membrane.[3]29.Which of the options, A to D, is a correct statement about polysaccharides of glucose?ACellulose microfibrils are formed by hydrogen bonding between adjacent chains of α-glucose moleculesbonded with 1,4-glycosidic bonds.BAmylose is a straight chain of α-glucose monomers bound by 1,6-glycosidic bonds to allow for densepacking.CGlycogen has a high proportion of 1,6-glycosidic bonds to produce a highly branchedmolecule for rapid release of α-glucose.DAmylopectin has a mixture of 1,4-glycosidic and 1,6-glycosidic bonds between β-glucosemolecules for rapid release of energy. OCR 2020. You may photocopy this page.24 of 43Created in ExamBuilder
Your answer OCR 2020. You may photocopy this page.[1]25 of 43Created in ExamBuilder
30.Glycogen molecules stored in the liver are branched.Glycogen storage disease type IV occurs when the liver is unable to catalyse the addition of branches ofglucose molecules. People with this disease may develop liver damage over time.Suggest why this disease may result in liver damage.[1]31.Phospholipid bilayers play crucial roles within plant cells.Which of the following statements linked to the importance of membranes in plant cells is / are true?Statement 1:ATP synthase embedded in thylakoid membranes maintains chemiosmotic gradients.Statement 2:Phospholipid bilayers within the chloroplast are impermeable to protons.Statement 3:Thylakoid membranes contain electron transport chain proteins.A1, 2 and 3BOnly 1 and 2COnly 2 and 3DOnly 1Your answer[1]END OF QUESTION PAPER OCR 2020. You may photocopy this page.26 of 43Created in ExamBuilder
Mark SchemeQuestion1234Answer/Indicative contentMarksB 1Total1C 1Total1D 1Total1C 1GuidanceExaminer’s CommentsAround half of candidates were able tosuccessfully apply their knowledge ofbiochemistry to the context of a plasmamembrane.Examiner’s CommentsThis question tested knowledge ofmolecular structure. Candidates should beaware that carbohydrates and lipidscontain only C, H and O. Candidatesshould also know that insulin is a proteinand therefore contains N. ATP beingclosely related to nucleotides must alsocontain N as well as P. It appears thatmany less able candidates becameconfused by the numbers of lettersinvolved in each row and guessed at thecorrect response (C).5Total1B 1Total1 OCR 2020. You may photocopy this page.27 of 43Created in ExamBuilder
Mark SchemeQuestion6iAnswer/Indicative contentMarks1between O and H (of adjacentmolecules);32between, electropositive / δ / delta (H), and, electronegative / δ- / delta(O);3water molecule, is polar / has chargeseparation;Guidance1 DO NOT CREDIT O/H molecules2 ACCEPT slightly, positive / negative2 IGNORE oxygen is negative / hydrogenis positive2 DO NOT CREDIT ionsAWARD mp 1 and 2 for diagram below, i.e.H bond can be drawn as dotted or dashedor labelled, but IGNORE solid lineDO NOT AWARD mark if diagramcontradicts text3 ACCEPT electrons pulled closer tooxygen atom / water is a dipole3 IGNORE electronegative / electropositive3 IGNORE oxygen is negative / hydrogenis positive3 DO NOT CREDIT ionsExaminer's CommentsThis question was well answered.Candidates frequently used the spaceavailable to draw a diagram which wasusually accurately drawn and gained 2marks. Many candidates then gained thethird mark for stating the polar nature of thewater molecule. Candidates who referredto oxygen or hydrogen as molecules orions were not awarded one or more of themarking points. OCR 2020. You may photocopy this page.28 of 43Created in ExamBuilder
Mark SchemeQuestioniiAnswer/Indicative content1medium for (metabolic) reactions;MarksGuidance3 max1 ACCEPT reactions can happen in water1 ACCEPT supports metabolic reactions2(because) allows (named) ioniccompound(s) to separate;3transport;4two named transport, systems / mediaORone example of a transport, medium /system, with a named example of whatis transported;4 IGNORE nutrients5 ACCEPT apoplast / sap / blood /symplast / vacuolar pathway / blood /lymph / xylem / phloem / tissue fluid / CSF5(organisms can) absorb / take in,(named) minerals / ions / (named) gas /food;5 IGNORE nutrients / substances5 IGNORE get / obtainIGNORE refs to osmosis6able to dilute toxic substances;Examiner's CommentsMost responses were awarded 1 or 2marks. Reference to transport was themost commonly seen correct response.Marks were also awarded frequently formention that water is a medium forreactions (processes was not sufficient) orgiving examples of transport systems andwhat is carried in them. Many responsesdiscussed the idea of absorption but usedwords such as ‘get’ or ‘obtain’ or ‘nutrients’,which were not precise enough. It wascommon for answers to imply that uptakeof minerals was a feature of aquaticorganisms only. Further detail of reactionfacilitation was rarely seen and dilution oftoxic substances was equally rare. Asignificant minority of responses did notfocus on the word ‘solvent’ in the questionand discussed other properties of water forno credit. Some responses described theprocess of dissolution despite the questionasking about importance.Total OCR 2020. You may photocopy this page.629 of 43Created in ExamBuilder
Mark SchemeQuestion78Answer/Indicative contentMarksA 1Total1protein / polypeptide 1GuidanceExaminer’s CommentsThe majority of candidates chose thecorrect option for this question.ALLOW cysteineIGNORE (other named) amino acids91011121314Total1B 1Total1C1Total1A1Total1B 1(AO1.2)Total1A 1Total1C 1Total1 OCR 2020. You may photocopy this page.30 of 43Examiner’s CommentsMost candidates got this right. Somethought polypeptides contained esterbonds and some were perhaps unawareeither that phosphodiester bonds containesters, or that they are present inpolynucleotides.Examiner’s CommentsA large majority of candidates achieved themark.Examiner’s CommentsOption A provided a distractor andcommon incorrect response to the correctoption C in this question, as statement 1relating to the cells synthesising ecdysone,would not form part of an explanation forthe site of action of the hormone.Created in ExamBuilder
Mark SchemeQuestion15Answer/Indicative contentMarksD 1GuidanceACCEPT AExaminer’s CommentsCandidates could reasonably suggesteither A or D as correct answers and bothwere credited in order to be fair tocandidates.Total OCR 2020. You may photocopy this page.131 of 43Created in ExamBuilder
Mark SchemeQuestion16Answer/Indicative contentiMarksGuidance3Mark the first answer. If the answer iscorrect and an additional element or groupis given 0 marks. For example X C orCH2 0 marksY DO NOT CREDIT O2Z IGNORE hydroxy / hydroxideZ IGNORE OH–X: C / carbon;Y: O / oxygen;Z: OH / hydroxyl (group);Examiner's Commentswas generally answered well. The mostcommon error was describing Z ashydroxide.ii2Max 1 if any other change is described /shown.CREDIT a correct diagramACCEPT right hand part of molecule onlyIGNORE parts of molecule labelled X, Yand ZIGNORE C number if it contradicts anotherwise correct answerOH and H groups reversed / AW (on singleC atom); on, C1 / right hand C atom / AW; 2 marksExaminer's Commentswas also well answered by the majority ofcandidates. If the maximum 2 marks werenot achieved, it tended to be for reversingOH and H on C4 instead of, or in additionto, on C1. OCR 2020. You may photocopy this page.32 of 43Created in ExamBuilder
Mark SchemeQuestioniiiAnswer/Indicative contentMarks(α / alpha / a / A) 1–4 glycosidic;2maltose;GuidanceACCEPT glycosidic 1,4IGNORE covalentExaminer's CommentsDespite the question emphasising the term‘precise’ to naming of the bond, very manycandidates stated ‘glycosidic’ but failed toinclude the ‘1–4’ detail. Most candidatescorrectly gave maltose for the name of thedisaccharide although sucrose wasoccasionally seen, along with a variety ofincorrect molecules.17Total7iprimary B and D;1DO NOT CREDIT if another letter is showniisecondary A and E;1DO NOT CREDIT if another letter is showniiiteritory F and G;1DO NOT CREDIT if another letter is shownivquaternary C;1DO NOT CREDIT if another letter is shownExaminer's CommentsThe ability to apply knowledge of thefundamental aspects of protein structurewas required for this question but manycandidates were clearly uncomfortable withthe topic. Part (i) was the part mostfrequently answered correctly. Only aminority answered (ii) - (iv) correctly andvery few scored all 4 marks. A number ofresponses contained only one letter, when,for parts (i)-(iii), two were required. Themost common response to part (iv) was F.Total OCR 2020. You may photocopy this page.433 of 43Created in ExamBuilder
Mark SchemeQuestion18Answer/Indicative contentMarksbeta– / β- / B / b, pleat(ed sheet) / fold;Guidance5hydrogen / H;DO NOT CREDITH / H2secondary;ACCEPT 2 IGNORE tertiary / fibroussubunits / chains;ACCEPT globinsIGNORE strands / units / peptidesquaternary;ACCEPT4 IGNORE globularExaminer's CommentsFew candidates scored full marks for thisquestion. The most common incorrectanswer was to describe the left‐handedtwisting of the polypeptide chain as anaspect of tertiary, rather than secondary,structure. Collagen has an atypicalstructure that many candidates findconfusing and textbooks often do little toclarify.Total OCR 2020. You may photocopy this page.534 of 43Created in ExamBuilder
Mark SchemeQuestion19Answer/Indicative contentMarksGuidancePlease refer to the marking instructions onpage 3 of this mark scheme for guidanceon how to mark this question. In summary:Read through the whole answer. (Beprepared to recognise and creditunexpected approaches where they showrelevance.) Using a ‘best-fit’ approachbased on the science content of theanswer, first decide which of the leveldescriptors, Level 1, Level 2 or Level 3,best describes the overall quality of theanswer.Then award the higher, middle or lowermark within the level, according to theCommunication Statement (shown initalics):award the higher mark where theCommunication Statement has beenmet.award the middle mark where aspectsof the Communication Statement aremissing.award the lower mark where theCommunication Statement has notbeen met.science content determines the level.Communication Statement determinesthe mark within a level. OCR 2020. You may photocopy this page.35 of 43Created in ExamBuilder
Mark SchemeQuestionAnswer/Indicative contentMarksLevel 3 (7–9 marks)A good range of structural details andproperties are provided including referenceto fats and carbohydrates in both plantsand animals. Explanations are provided foreach structural comment.Max 9GuidanceIndicative scientific points may include:Structures (S), Properties (P) andExplanations (E):Carbohydrates:S1. Polymers of glucoseE1. Glucose can be used in respirationto release energyThe explanations are clearly linked to thestructure of the molecules and the use ofscientific terminology is at an appropriatelevel. All the information presented isrelevant and forms a continuous narrative.S2. Large moleculesP2. InsolubleE2. Do not affect water potential of cellLevel 2 (4–6 marks)Some structural details and properties areprovided including reference to moleculesin both plants and animals. Explanationsare provided for each structural comment.S3. 1–4 glycosidic bondsE3. Easy to make and break to releaseglucose / monomersS4. Coiled shape / compactE4. Take up less space in cellThe explanations are clearly linked to thestructure of the molecules but may not fullyexplain how the structure suits the role anduse of scientific terminology may notalways be appropriate. The informationpresented is mostly relevant.S5. Amylose unbranched / amylopectinwith few branchesE5. No need for rapid release ofmonomers in plantsS6. Glycogen more branchedE6. Allows more rapid release ofmonomers in animalsLevel 1 (1–3 marks)A limited number of structural details areprovided. The explanations do not clearlyshow how the molecules are suited to theirrole.Lipids (ACCEPT lipids or fats):S7. Fats have more carbon-carbonbonds / carbon-hydrogen bondsP7. Fats are energy rich / contain moreenergy per moleculeE7. More energy stored in less spaceThere is a logical structure to the answer.The explanations, though basic, are clear.0 marksNo response or no response worthy ofcreditP8. Fats are insolubleE8. Do not affect water potential of cellS9. Fatty acids are long carbon chainsE9. Can be broken down to release twocarbon / acetyl groups (which enter Krebscycle)S10. Animal fats saturated / harderE10. Have role in protection / insulationas well as energy storage.Total OCR 2020. You may photocopy this page.936 of 43Created in ExamBuilder
Mark SchemeQuestion2021Answer/Indicative contentMarksGuidanceC 1(AO2.1)Examiner’s CommentsMost candidates were able to correctlyspot that C did not have a terminal –COOHgroup.Total1A 1Examiner’s CommentsMany candidates were able to correctlyidentify nucleic acids (option A) here,demonstrating knowledge of thecomposition of some organic polymers.Some candidates opted for B which,although providing the correct elementspresent in carbohydrates, the approximatepercentage mass for each of theseelements could not be true forcarbohydrates.Total OCR 2020. You may photocopy this page.137 of 43Created in ExamBuilder
Mark SchemeQuestion22iAnswer/Indicative contentMarksGuidanceadd / AW, biuret solution / biuret reagent /biuret mixture / NaOH and CuSO4;2IGNORE ‘biuret’ unqualifiedDO NOT CREDIT heat / warm / neutralise /put in water bathobserve colour;ACCEPT see if it goes, lilac / purple /mauve / violetDO NOT CREDIT if incorrect colourchange describedDO NOT CREDIT precipitateExaminer's CommentsThis question blended familiar recall, thatsuited candidates who had spent timelearning the specification, with some AO3questions that many candidates foundchallenging.was generally done well. Candidates hadlearnt how to carry out a Biuret's test.Where candidates lost marks it was forfailing to recognise that the key additionwas Biuret solution, not just ‘Biuret’. Somecandidates mentioned heating andreceived no credit.ii(enzymes are) globular, proteins /polypeptide;1 maxhydrophilic / water soluble, (R-)groups onoutside (of enzyme);Examiner's CommentsThis question blended familiar recall, thatsuited candidates who had spent timelearning the specification, with some AO3questions that many candidates foundchallenging.This mark was rarely awarded. The words‘in solution’ were emboldened in thequestion in an attempt to get candidates tolink enzyme structure to solubility. Fewcandidates appeared to recognise whichaspect of knowledge they were beingasked to apply.23Total3A 1Total1 OCR 2020. You may photocopy this page.38 of 43Created in ExamBuilder
Mark SchemeQuestion2425Answer/Indicative contentMarksimitochondrion1iieitherfacilitated diffusion (1)conversion of ornithine into citrullinecreates concentration gradientsor(molecules are not lipid soluble so) requireprotein channels to cross membrane (1)oractive transport (1)ornithine and citrulline need to be movedinto and out of Dmore quickly than would be met bydiffusion (1)2iiideamination / removal of NH2 group fromamino acid (1)1ivATP (1)1Total5starchANDglycogen 1Total1 OCR 2020. You may photocopy this page.39 of 43GuidanceALLOW mitochondria.ALLOW amylose , amylopectinCreated in ExamBuilder
Mark SchemeQuestion26Answer/Indicative contentMarksi3GuidanceMark the first 3 responsesAWARD 1 mark for each correct rowirrespective of boxesThree correct rows of responses writtenwithin the same box can be awarded 3points.ACCEPT every second one is flippedACCEPT fibres / microfibrils / fibrils /macrofibrilsDO NOT CREDIT myofibrilsACCEPT grainsACCEPT ‘(cross)links’ as AW for ‘bonds’Examiner's CommentsThis question was not answered well. Mostcandidates gained 1 or 2 marks, usually foridentifying α- and β-glucose as subunits,the fibrous nature of cellulose or thearrangement of hydrogen bonding. Few gotfull marks. A significant minority usedterms associated with protein structure andgained no credit. Similarly, manycandidates gave differences relating tofunction rather than structure and gainedno credit. A large number of candidatesanswered as if one of the molecules theywere describing was glycogen, asreference to 1-6 bonds and branches wasoften seen. Candidates who did notcompare like with like within a given rowwere not credited, nor were responses thatwere written in a 4th or
Biology A A level Biological Molecules practise Amy Vickers Please note that you may see slight differences between this paper and the original. Candidates answer on the Question paper. OCR supplied materials: Additional resources may be supplied with this paper. Other mater
CARBON-BASED MOLECULES Reinforcement KEY CONCEPT Carbon-based molecules are the foundation of life. Carbon atoms are the basis of most molecules that make up living things. Many carbon-based molecules are large molecules called polymers that are made of many smaller, repeating molecules called monomers. There are four main types of
The molecules in water have a small positive and a small negative charge, a bit like the poles on a magnet. We call such molecules with partial charges polar molecules. The molecules in oil have almost no positive or negative charge. We call these molecules non-polar molecules. Different kinds of molecules do not mix well with each other. Polar
Practise 4 Times Tables you wearing your hat by and/or Fitness Practise 11 Times Tables and/or Fitness Practise 3 Times Tables and/or Fitness Practise 7 Times Tables Numeracy Ninjas Session 1 Week 10 Numeracy Ninjas Week 10 Session 2 Numeracy Ninjas Week 10 Session 3 Wellbeing Numeracy Nin
The architecture of a large biological molecule helps ex-plain how that molecule works. Like water and simple or-ganic molecules, large biological molecules exhibit unique emergent properties arising from the orderly arrangement of their atoms. In this chapter, we'll first consider how macro-molecules are built. Then we'll examine the .
Answer: Carbon is versatile Can form many covalent bonds resulting in molecules with complex structures (chains, rings, branching) C C C C Organic: Molecules with a carbon skeleton Inorganic: Molecules without a carbon skeleton Functional Groups: Determine characteristics of molecules
stair pressurization fan condensing units, typ. of (3) elevator overrun stair pressurization fan november 2, 2016. nadaaa perkins will ]mit ]] ]site 4 october 21 2016 10 7'-3" hayward level 1 level 2 level 3 level 4 level 5 level 6 level 7 level 1 level 2 level 3 level 4 level 5 level 6 level 7 level 8 level 9 level 10 level 11 level 12
BIOLOGY I. Chapter 5 - Biological Molecules Class Collaborative Activity The class will be split into small groups of 4-6 students. Each small group should work together to discuss one of the four groups of biological molecules, as assigned by your instructor: Carbohydrates, lipids, proteins, or nucleic acids.
dimensional structure of a protein, RNA species, or DNA regulatory element (e.g. a promoter) can provide clues to the way in which they function but proof that the correct mechanism has been elucid-ated requires the analysis of mutants that have amino acid or nucleotide changes at key residues (see Box 8.2). Classically, mutants are generated by treating the test organism with chemical or .
