controlled assessments in gcse science

Draft July 2011
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.
particularly helpful for people who
get really nervous in their exams.
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.
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
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).
Indicates things connected with the RESEARCH AND
Indicates things connected with the EXPERIMENTAL
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.
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
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
Image search
Information backed by evidence.
Experimental data (or data from surveys etc.).
Details of the experiment/survey that produced the data (if
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.
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
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
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.
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.
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
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
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
Decide how your results will be processed and what you will be
looking for.
Draft July 2011
Variables, fair testing and ranges
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.
Sometimes this is obvious, but the hints below may help.
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.
This can be controlled with mixtures called buffers. There are
different buffers for different pH values.
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.
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.
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
repeatable than others.
quite a lot, you can still
have some confidence in
your results if you do a
very large number of
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
instruments are not necessarily more accurate than
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
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
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
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
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.
A chemical or piece of apparatus that could cause
An action involving a hazard that might result in
14 | P a g e
Draft July 2011
Something that can be done to reduce or prevent a
risk, while still allowing you to carry out the
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