Draft July 2011 WJEC CBAC PUPIL GUIDE TO DOING CONTROLLED ASSESSMENTS IN GCSE SCIENCE 0|Page ? Draft July 2011 Why are controlled assessments important? Controlled assessments make up 25% of your marks for your GCSE. If you can get a good mark in your controlled assessment, it‟ll be a great start to getting a good GCSE grade. The worst thing would be not to hand in a controlled assessment – that would mean it would be virtually impossible to get a good GCSE grade. Controlled assessments are particularly helpful for people who CONTROLLED ASSESSMENT get really nervous in their exams. 25% You do these assessments in class. If you do really well, it will help you out if you lose a few marks in the exams through nerves. EXAMS 75% You don‟t have to revise anything to do well in controlled assessments, but you DO have to know how scientists work, and, like a scientist, think really carefully about what you are doing, how you are doing it, and what your results mean. This booklet takes you through the skills you will need, and gives tips on how to do really well in your controlled assessments. The controlled assessment is in three parts: 1. Doing research and using the material to write a report and design a survey or an investigation.( the RESEARCH AND USE OF INFORMATION exercise). 2. An experiment, then designing follow-up work (the PRACTICAL exercise). 1|Page Draft July 2011 3. Watching a DVD of an experiment and doing a risk assessment and some evaluation of it (the EXPERIMENTAL TECHNIQUES AND SAFETY exercise). SYMBOLS USED IN THIS BOOKLET: Indicates things connected with the RESEARCH AND USE OF INFORMATION exercise. Indicates things connected with the PRACTICAL exercise. Indicates things connected with the EXPERIMENTAL TECHNIQUES AND SAFETY exercise. 2|Page Draft July 2011 Research skills The first task of your controlled assessment will always be a piece of research. Although there is no mark for the research itself, doing a good job here will make it easier to get a really good mark on the task that follows. The exam board provides some basic research material, but for better marks it‟s important that you find some additional material. LOOKING FOR SOURCES On the Internet, start with a search using Google© or another search engine. Don‟t type too much into the search bar, but do include enough to make sure you don‟t get loads of useless material. For example, suppose you want to look for material about genetically modified crops Don’t search for: GM (you‟ll get sites with any word that contains those letters!). Crops (too vague). The pros and cons of GM crops (too wordy – will cut out a lot of relevant sites) Do search for: GM crops Genetically modified crops Genetic modification 3|Page Draft July 2011 It is worth doing an image search. It can provide you with pictures and graphs you could use in your report, and can also lead you to useful articles. It might also be useful to do a video search. You won‟t be able to use video in your report, but watching a relevant video may help you understand the topic better Video search Image search WHAT YOU SHOULD LOOK FOR: Information backed by evidence. Experimental data (or data from surveys etc.). Details of the experiment/survey that produced the data (if possible). Relevant pictures, charts and graphs. You should probably look for at least 5 sources. Sometimes, sites use material from news agencies, and the information can be basically the same on a number of different sites. Look for different sources of information. ASSESSING THE QUALITY AND BIAS OF DIFFERENT SOURCES Un-biased sources will usually provide both sides of an argument. If a source makes out that their point of view is clearly right without 4|Page Draft July 2011 even mentioning the other side, it is best not to use that site. It‟s not that biased sources necessarily tell lies, but they can be „selective‟ about what information they give, missing out relevant facts that may not fit with their ideas. You should understand that companies and organisations send press releases to newspapers and TV companies, who will often put them into articles without checking all the facts. For this reason, you should always judge bias by looking at the information, not just the source. If you can find where the information came from in the first place, then the source may tell you if the information may be biased. You can see that this report on the BBC website is actually from the UK nuclear inspectorate. In any report about scientific data or opinion, you should always try to find out where the information actually came from. If the report includes figures, you should try to find out if the data comes from a well-run scientific experiment. Good quality experiments will meet the following criteria: If a sample has been used, it will be big enough (never less than 30, but better to have hundreds or thousands). Any differences reported should be big enough to be „significant‟. 5|Page Draft July 2011 The people doing the study should be professional scientists from a respected organisation. The experiment/study should have been published in a „peerread‟ journal (i.e. someone has looked at the experiment to make sure it‟s of good quality). Ideally, other studies should have been done which confirm the findings – it is always best to be suspicious of reports that find something completely new or different from other reports. Writing reports When you‟ve done your research, you will be asked to write a report using the information you have collected. A good quality report will meet the following criteria: It will focus on the topic or question given and will not include irrelevant information. This may mean that you don‟t use all the information you researched. It will start with an introduction, stating the purpose of the report. Make it clear, detailed but not too long! It will present evidence without bias, presenting both sides of any argument. At least some of the evidence will be actual data. Any explanations will be clear and detailed, but not too wordy (don‟t “waffle”). Relevant graphics will be used where they will help to explain a point. 6|Page Draft July 2011 Any opinion will be backed up with evidence. There will be a list of websites, books or any other materials that you have used in your research. Designing investigations and surveys After doing your research, you will be asked to design some sort of investigation based on the research topic. This is likely to be a survey or an investigation using second hand data, not a simple experiment. You will need to think about the following points: Will the questions in the survey, or the information collected, actually answer the question asked or solve the problem? Will the sample size be big enough? In this sort of exercise, no sample should ever be under thirty, and sometimes the sample may need to be a thousand or more. The more variation your sample is likely to show, the bigger the sample should be. Is the sample chosen typical of the whole group you wish to study? For example, if you want to study binge drinking in males and females under 30, it would be no good if your samples of males and females all came from large cities, because lots of people live in smaller towns and villages, so your conclusions may not be true for the whole country. 7|Page Draft July 2011 EXAMINER TIPS – Research task Don’t bring in a huge amount of research material – it will take too long to read through it before you start writing your report (and you will only have around 45 minutes in total). The research report should be around 3 sides of writing, including diagrams and charts. Doing more is unlikely to get you any more marks, and you could end up doing worse because you rush, or don’t finish. What we are looking for is whether you can select relevant information and graphics, and leave out everything else. A short report that gets straight to the point and explains the issues clearly will get the best marks. You are assessed on your spelling, grammar and presentation – take care to produce a well laid out, neat piece of work. Designing experiments In the practical exercise, you will have to design an experiment. This needs a number of different skills. You may need to: Identify variables and choose which ones to control for a fair test. Design a control experiment. Choose a range for the variable being tested. Decide how many repeats will be needed. Choose a measurement technique that is likely to be accurate. Make sure that your experiment is „valid‟ (i.e. actually tests the hypothesis). Decide how your results will be processed and what you will be looking for. 8|Page Draft July 2011 Variables, fair testing and ranges TYPES OF VARIABLES Independent variable What you change – this usually goes on the x axis of any graph. Dependent variable What you measure – this usually goes on the y axis of any graph. Control variable Any factor (there may be several) which is likely to affect the outcome of the experiment but which you are not investigating. Not every variable needs to be controlled – only those that might affect the experiment. If you‟re not sure if it will affect the experiment or not, keep it the same. WAYS OF CONTROLLING VARIABLES Sometimes this is obvious, but the hints below may help. Temperature This is best done with a water bath if the experiment can be put in water. It is best to use a thermostatically controlled water bath. pH This can be controlled with mixtures called buffers. There are different buffers for different pH values. Light If a lamp is being used, the important features are the distance the lamp is away from the experiment and the wattage of the bulb. 9|Page Draft July 2011 Lamps also give out heat, so a heat shield (a sheet of glass or perspex or a container of water) should be used. CHOOSING A RANGE It is difficult to give general rules, as the choice of range will vary with the experiment. The range must be neither too big nor too small. You should choose at least 5 points within the range to take readings – more if the range is large. The sampling points should be fairly evenly distributed within the range. Repeats and repeatability If you are going to have confidence in your results, they ideally need to show „repeatability‟ (i.e. when repeated, the results are similar). You cannot possibly tell if the results are repeatable if you don‟t repeat them a number of times. In school, experiments are often repeated three times, but that is because of the time available – „real‟ science experiments would often be repeated many more times. Some results are more Real scientists may repeat their experiments 50 or 100 times! repeatable than others. If the readings vary quite a lot, you can still have some confidence in your results if you do a very large number of repeats and take an average. 10 | P a g e Draft July 2011 When you design an experiment, you can only guess how many repeats might be needed. If you have done a similar experiment before you will have some idea of repeatability. Once you actually start taking results, you see how repeatable the results are and you can then decide how many repeats may be needed. Choosing measuring instruments Measuring instruments have different resolutions. The resolution is to do with the smallest measurement they can read, e.g. a thermometer may read to the nearest 5oC, 1oC or 0.5oC. It is always best to use a measuring instrument with the highest resolution available. Electronic instruments are not necessarily more accurate than non-electronic ones. Digital instruments are not necessarily more accurate than analogue ones. IT ALL DEPENDS ON THEIR RESOLUTION. Processing results When you design an experiment, you should say how you will process your results. But, what does “processing” mean? Processing may include (depending on the experiment): 11 | P a g e Draft July 2011 Calculating means. Calculating percentages. Calculating rates. Drawing tables. Drawing graphs (bar, line or pie). Writing your method Your description of the method should be clear and detailed. It is usually best to present it as numbered steps. You should also include a list of apparatus. Analysing results When you get the results of the experiment set in task A, you will need to analyse them. A good quality analysis will include: A description of any pattern, relationship or trend in the results. Identification of any results that don‟t fit the pattern („outliers‟) – although these should be picked up during the experiment and re-done. 12 | P a g e Draft July 2011 A statement about whether you think the results support the hypothesis or not (or if they are inconclusive). A comment about how strong the evidence is. Evidence is strong when: Any differences seen are large enough to be „significant‟. The results are repeatable (i.e. they don‟t show large variations). The results are „reproducible‟, i.e. different experimenters get very similar answers. The number of repeats is adequate. EXAMINER TIPS – Practical task The sheet you are provided with gives you guidance, but not always complete details of the practical method you should use. If it does not provide full instructions, think about the best way to do the experiment. The practical you do will be similar to the method you should use when you have to design an experiment for task B. You will simply have to change some details. When you describe the method you have designed for task B, make sure to include as much detail as possible. Don’t just refer to Task A and say you’ll do it the same way. 13 | P a g e Draft July 2011 Risk assessments The third exercise in the assessment looks at „experimental techniques and safety‟. You will have to do a risk assessment of an experiment that you see on a video clip. A good risk assessment includes: A list of all the hazards and why they are hazardous (e.g. acid is corrosive, iodine is an irritant etc.). A list of the risks (things that you do in the experiment) which might result in danger. Suitable precautions you could take which will reduce or prevent the risk. Sometimes, a hazard may not actually present a risk in the experiment. For instance, something may be flammable, but if there is no naked flame or anything that might cause a spark in the experiment, there will be no risk. A good risk assessment prevents anyone doing the experiment from putting themselves in danger Some experiments have no hazards and/or no significant risks. DEFINITIONS Hazard: A chemical or piece of apparatus that could cause harm. Risk: An action involving a hazard that might result in danger. 14 | P a g e Draft July 2011 Precaution: Something that can be done to reduce or prevent a risk, while still allowing you to carry out the experiment. Evaluating experiments You may be asked to evaluate the method used in the experiment you see, and/or suggest improvements. A good evaluation will: Identify any points in the experiment which might have caused the results to be inaccurate. Consider how repeatable and (if appropriate) reproducible the results were. If there were large variations, are there any changes that might have improved this? If the results were repeatable and reproducible, and there is no indication of inaccuracy, then no improvements are necessary. If not, then changes should be suggested that might improve accuracy, repeatability and/or reproducibility. EXAMINER TIPS – Experimental techniques and safety task Any risks you give must be possible, when someone does the experiment properly and sensibly. You need to describe exactly which action in the experiment would cause a risk, and how. It’s OK to say there are no risks in an experiment, if that is true. Even if something is hazardous, it won’t always provide a risk. Precautions must be practical. Remember to evaluate the experiment, not the person doing it. 15 | P a g e
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