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AS EVALUATIVE ADVANCED SUBSIDIARY GCE F213/ Mark Scheme Ta sk BIOLOGY Practical Skills in Biology 1 Evaluative Task: Investigating the Fat Content of Milk For practice use only, not for assessment Further guidance is available in the Practical Skills Handbook. tic e Once the work has been collected in, it must be kept secure and marked by the teacher as it stands. Marked work must not be returned to the candidate. Under no circumstances can a candidate be allowed to change or elaborate on an answer. Teachers are reminded that it is possible for a candidate to be assessed on another occasion using a different Task and that the best mark achieved for each task type should be submitted. It is appropriate for the teacher to provide feedback to explain in general terms how the work could have been improved, but details of the Mark Scheme and of which marking points were and were not awarded must not be communicated to the candidate. Mark Tasks clearly, in red ink, in accordance with the Mark Scheme. Annotation can help the Moderator and staff in the Centre who are checking the marking as part of internal standardisation. Useful annotations consist of: ticks and crosses against responses to show where marks have been earned or not earned; specific words or phrases to confirm why a mark has been earned or indicate why a mark has not been earned (e.g. indicate an omission). ac • • Where a candidate has given an answer not covered by the Mark Scheme, the teacher should use their professional judgement to decide whether the answer is worthy of credit. If it is, then the script should be annotated accordingly and the mark(s) awarded. Half marks must not be awarded. This document consists of 6 printed pages. Any blank pages are indicated From time to time OCR may need to publish clarification for a Task or Mark Scheme. Please ensure that you check Interchange before using a Task for assessment to ensure that no modifications have been posted, and check again before the final submission of marks to OCR. Any changes made will be flagged in the Notices area of the GCE Biology page on Interchange via OCR’s e-mail updates service. Pr * O C E / 3 1 2 5 2 * Note For Practice Tasks and Specimen Assessment Tasks, teachers may give detailed feedback to candidates. To subscribe to the e-mail updates service, please send an e-mail to [email protected] including your Centre number, Centre name and a contact name. Include the title GCE Biology in the subject line. © OCR 2010 DC (AC) 31252/2 OCR is an exempt Charity Turn over For practice use only, not for assessment 2 Question Expected answers Mark Additional guidance All marks to be assessed from the candidate’s completed Task sheet. 1 Award 2 marks for correct standard deviation • 1.3 2 AWARD 1 mark if the standard deviation is incorrect but all of the following are correct: total of x2 = 289 289 – 280.2 = 8.8 8.8 ÷ 5 = 1.76 OR AWARD 1 mark if standard deviation is calculated correctly but is not rounded correctly to 1 decimal place (e.g. given to 2 d.p. as 1.33) © OCR 2010 For practice use only, not for assessment 3 Question Expected answers 2 (a) 3 correct error bars = 2 marks 2 correct error bars = 1 mark 1 or 0 correct error bars = 0 marks Mark Additional guidance 2 max CREDIT error bars plotted to the nearest grid line. ALLOW error carried forward from Table 2 and/or incorrect calculation. • error bar plotted correctly from 11.1 to 14.9 for full-fat cow’s milk • error bar plotted correctly from 5.5 to 8.1 for skimmed cow’s milk • error bar plotted correctly from 8.4 to 9.6 for full-fat soya milk. (b) Award 1 mark per bullet point up to a maximum of 4 marks 4 max Word(s) in brackets are not essential for the mark to be awarded. IGNORE references to soya milk. • there is a marked difference between skimmed (cow’s) and full-fat (cow’s) milk • drop of skimmed (cow’s) milk falls more quickly than drop of full-fat (cow’s) milk • skimmed (cow’s) milk is more dense than full-fat (cow’s) milk • error bars are relatively small so we can be confident of reliability of means OR small (value of) standard deviation so we can be confident of reliability of means © OCR 2010 DO NOT CREDIT ‘there is a difference’ without qualification; CREDIT correct data quotes CREDIT ‘significant’ or any other term that qualifies the difference. CREDIT reverse argument. CREDIT reverse argument. Both statement and consequence required for the mark. • ranges of the error bars do not overlap so indicates significant difference Both statement and consequence required for the mark. • difference is due to (presence of) less fat in skimmed milk. CREDIT reverse argument. For practice use only, not for assessment Turn over 4 Question Expected answers 3 (a) • all results very similar OR no ‘outliers’. (b) Award 1 mark per bullet point up to a maximum of 2 marks Mark Additional guidance 1 ACCEPT no results more or less than 10% away from mean. ACCEPT no results more or less than 2 standard deviations from the mean. 2 max Word(s) in brackets are not essential for the mark to be awarded. • different amounts of protein (in same volume) • different (proportions of) amino acids CREDIT reference to more/fewer essential amino acids OR first and second class proteins. • different amino acid sequence OR different primary structure • different (types of) bonding IGNORE reference to peptide bonds. • different 3D structure OR different globular structure OR different tertiary structure • different solubility. (c) © OCR 2010 • heat denatures proteins OR heat disrupts bonds OR heat causes a change in tertiary structure OR heat accelerates/speeds up hydrolysis. 1 For practice use only, not for assessment 5 Question Expected answers 4 (a) Award 1 mark per bullet point Mark 2 • concentration of copper (II) sulfate Additional guidance DO NOT CREDIT keeping the volume of copper sulfate constant. DO NOT CREDIT size of drop. • distance the drop was allowed to fall. (b) Award 1 mark per bullet point 2 Concentration of copper (II) sulfate controlled because: • keeps density of copper (II) sulfate constant OR allows valid comparison of how fast different types of milk drops fall. DO NOT CREDIT ‘fair test’ unqualified. Distance the drop was allowed to fall controlled because: • ensures that the times are comparable. (c) © OCR 2010 Award 1 mark per bullet point 2 • concentration of copper (II) sulfate was always constant CREDIT ‘copper (II) sulfate concentration stayed the same’. • distance the drop was allowed to fall was always from 80 to 30 cm3 on the measuring cylinder. CREDIT ‘drop fell a fixed distance’. For practice use only, not for assessment Turn over 6 Question Expected answers 5 Award maximum 1 mark for the source of error and maximum 1 mark for a linked explanation Mark Additional guidance 2 max Word(s) in brackets are not essential for the mark to be awarded. CREDIT logical/sensible explanations of the named source of error. Source of error • (increasing) contamination of the copper (II) sulfate with milk drops OR same copper (II) sulfate used throughout. Note: an error is not a design fault of the procedure but a single or ‘one off’ incident or event (caused by the person carrying out the experiment or by faulty apparatus) that makes the data unreliable. Explanation • the amount of milk drops present will affect the density of the copper (II) sulfate OR (as milk builds up) difficult to judge when the drop has reached 30 cm3 mark. [Note: factors that have not been controlled or taken into account in the design of the procedure can be referred to as limitations. These can be described as design faults and will affect each run and replicate equally throughout the investigation]. Source of error • droplet size/shape OR (single) drops may join together on the way down. Explanation • will affect the rate/speed of fall of the drop OR surface area:volume ratio will vary OR there will be more resistance due to the shape. Task total 20 Copyright Information OCR is committed to seeking permission to reproduce all third-party content that it uses in its assessment materials. OCR has attempted to identify and contact all copyright holders whose work is used in this paper. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced in the OCR Copyright Acknowledgements Booklet. This is produced for each series of examinations, is given to all schools that receive assessment material and is freely available to download from our public website (www.ocr.org.uk) after the live examination series. If OCR has unwittingly failed to correctly acknowledge or clear any third-party content in this assessment material, OCR will be happy to correct its mistake at the earliest possible opportunity. For queries or further information please contact the Copyright Team, First Floor, 9 Hills Road, Cambridge CB2 1GE. OCR is part of the Cambridge Assessment Group; Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. © OCR 2010 For practice use only, not for assessment