Mark Scheme (Results) January 2019 - Edexcel

Mark Scheme (Results)January 2019Pearson Edexcel International GCSEIn Human Biology (4HB0) Paper 2

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General Marking Guidance Allcandidatesmustreceivethesametreatment.Examiners must mark the first candidate in exactly thesame way as they mark the last. Mark schemes should be applied positively. Candidatesmust be rewarded for what they have shown they can dorather than penalised for omissions. Examiners should mark according to the mark scheme notaccording to their perception of where the gradeboundaries may lie. There is no ceiling on achievement. All marks on the markscheme should be used appropriately. All the marks on the mark scheme are designed to beawarded. Examiners should always award full marks ifdeserved, i.e. if the answer matches the mark scheme.Examiners should also be prepared to award zero marks ifthe candidate’s response is not worthy of credit accordingto the mark scheme. Where some judgement is required, mark schemes willprovide the principles by which marks will be awarded andexemplification may be limited. When examiners are in doubt regarding the application ofthe mark scheme to a candidate’s response, the teamleader must be consulted. Crossed out work should be marked UNLESS the candidatehas replaced it with an alternative response.

QuestionnumberAnswerNotes1typhoidcaused by afungusmalariacaused byschistosomathrushspread byhousefliesgonorrhoeaspread elitisbilharziaMarksAll correct 6 marks5 or 6correct 5marks6lung infectioncaused by a virusTotal 6 marks

Questionnumber2 (a) (i)Answer NotesMarksotherwise would see food/identify food by sight/would not need totasteor smell food/to ensure food is identifiedby taste/smell only;1(ii) 160;200;80%;Full marks forcorrect finalanswer3(iii)(iv)(b)(c)THREE OF more people correctly identified foodwhen nostrils not closed/when only eyescovered/ easier to identify food whennostrils not covered; smell increases ability to identify food; taste increases ability to identify food: variations/differences between people; reference to guesswork;anomalous result for Person 3 size/volume/mass/type of food;time left on tongue/same area of tongue;same people/age/gender;max 3Acceptdescription ofdifferences3TWO OF reduce/eliminate effect of anomalousresult/to identify anomalies; to compare results; calculate mean; more reliable;touch/texture/sight;max 2ACCEPTdescription thatimplies sense orvalid alternative1Total 13 marks

Questionnumber3 (a)(i)(ii)Answer deamination;(excess) amino acids;in liver; not very toxic/medium toxicity;highly soluble;little water needed to remove it/enableswater to be conserved;not much energy/only 4ATP required toremove each molecule/little energy used; (iii)(b) (i)plasma;(ii) (c)urine is a solution/fluid/urea is a solid;urine is a mixture/urea not a mixture;(urine) contains dissolved salts/urea;urea is an excretory substance/nitrogencontaining molecule; NotesAllow 1 mark forbreakdown ofamino acids formarking points 1AND 2Marks3431kidneys keep urea concentrationconstant/at 100 au/remove urea from theblood;concentration keeps on rising whenkidneys not working;2dialysis;transplant;2Total 15marks

Questionnumber4AnswerNotesMarks8 of diffusionmovement from high to lowconcentration/down a concentrationgradient;osmosis;movement of water molecules;from high to low water potential/from adilute to solution to a (more) concentratedsolution;through selectively permeable membrane;Ignore referencesto concentrationsof waterALLOW once withref todiffusion/osmosis(Factors affecting diffusion/osmosis): surface area;temperature;distance to travel;ref to steepness of gradient; active transport/uptake;uses energy/ATP;against a concentration gradient;MP’s 7-10 allowonce with ref toeither diffusionor osmosis8Total 8 marks

Questionnumber5 (a)(i)AnswerFunctionreceives oxygenated bloodsends blood to lungsreceives deoxygenated bloodsends blood to body(ii) (b) NotesLetter of chamberY;W;X;Z;prevents backflow of blood;from left ventricle to left atrium;FOUR OFblood can pass betweenventricles/oxygenated and deoxygenatedblood mix;blood doesn't travel to lungs/bodyeffectively;poor oxygenation/less oxygen in blood/tobody cells;less aerobic respiration/less energy/lessgrowth;reference to anaerobic respiration/buildup of lactic acid;reference to drop in bloodpressure/increase in heart rate;Marks4Accept from Z to Y2Max 4Total 10marks

Questionnumber6 (a)(b)Answertemperature; (c)Notes 1maximum rate of activity between 60-70 /optimum temperature for this enzyme isbetween 60-70 C ;optimum temperature for human enzymes37-40 C;this enzyme would be less active/inactiveat body temperature/37-40 C;human enzymes denature/breakdownabove optimum/over 40 C;enzyme denatures;shape of active site lost/disrupted;no enzyme-substrate complexesformed/no binding of substrate possible;Marks4Reject dies3Total 8 marks

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Mar 07, 2019 · Mark Scheme (Results) January 2019 . Pearson Edexcel International GCSE . In Human Biology (4HB0) Paper 2 . exemplification may be limited. When examiners are in doubt regarding the application of the mark scheme to a