WJEC Biology for A2 Level: Revision Workbook

Understanding AO3: Analysing, interpreting and evaluating scientific information This is the last and most difficult skill. You will need to analyse, interpret and evaluate scientific information, ideas and evidence, to: ⦁ Make judgements and reach conclusions ⦁ Develop and refine practical design and procedures. Approximately 28% of the available marks on the A2 exam papers are for analysing, interpreting and evaluating scientific information. Common command words used here are: evaluate, suggest, justify and analyse. This could involve: ⦁ Commenting on experimental design and evaluating scientific methods ⦁ Evaluating results and drawing conclusions with reference to measurement, uncertainties and errors. What is accuracy? Accuracy relates to the apparatus used: How precise is it? What is the percentage error? For example, a 5ml measuring cylinder is accurate to ±0.1ml, so measuring 5ml could yield 4.9−5.1ml. Measuring the same volume in a 25ml measuring cylinder which is accurate to ±1ml would yield 4−6ml. Calculating % error It’s a simple equation: accuracy/starting amount × 100. For example, in the 25ml measuring cylinder the accuracy is ±1ml so the error is 1/25 × 100 = 4%, whereas in the 5ml cylinder the accuracy is ±0.1ml so the error is 0.1/5 × 100 = 2%. Therefore, for measuring 5ml it is better to use the smaller cylinder as the % error is lower. What is reliability? Reliability relates to your repeats. In other words, if you repeat the experiment three times and the values obtained are very similar, then it indicates that your individual readings are reliable. You can increase reliability by ensuring that all variables that could influence the experiment are controlled, and that the method is consistent. Describing improvements If you were asked to describe what improvements could be made to the reliability of the results obtained from an experiment extracting apple juice, you would need to look closely at the method and apparatus used. Q: Pectin is a structural polysaccharide found in the cell walls of plant cells and in the middle lamella between cells, where it helps to bind cells together. Pectinases are enzymes that are routinely used in industry to increase the volume and clarity of fruit juice extracted from apples. The enzyme is immobilised onto the surface of a gel membrane, which is then placed inside a column. Apple pulp is added at the top, and juice is collected at the bottom. The process is shown in the diagram. Describe what improvements could be made. apple pulp added juice collected tap to control ow rate gel membrane with immobilised pectinase 8 | WJEC Biology for A2 Level: Revision Workbook | Introduction Copyright: Sample material