Cambridge Pre-U Syllabus - Cambridge International Examinations

48
Cambridge Pre-U Draft
Sub-skill
Decisions about measurements or observations
While carrying out an investigation, candidates should be able to:
• decide how many tests, measurements or observations to perform;
• make measurements or observations that span the largest possible range within the limits either of the
equipment provided or of the instructions given;
• make qualitative observations and/or quantitative measurements that are appropriately distributed within
this range;
• decide how long to leave experiments running before taking readings;
• replicate observations, readings or measurements as necessary;
• make and record sufficient, accurate measurements and observations.
Candidates may need to choose how many tests, measurements and observations can be made in the time
available. In some experiments a regularly-spaced set of measurements will be appropriate. For other
experiments, such as those requiring the peak value of a curved graph to be determined, it may be
appropriate for the measurements to be concentrated in one part of the range investigated. Candidates will
be expected to be able to identify the most appropriate distribution of values. In qualitative experiments,
precise descriptions and comparisons of colour or other observations are expected.
In experiments, such as those involving enzymes:
initial rate of reaction may be measured (in which case measurements should be conducted as quickly
as practicable);
the rate of reaction might be expected to be constant over several minutes, or colour changes may take
several minutes to occur, in which case leaving the experiment to run for as long as possible may be
appropriate;
an end point may be sought, in which case, candidates should expect to run the experiment until the
end point is achieved or the time runs out.
Repeated readings of particular quantities are often necessary in Biology, where experimental errors and
variation in the activity of biological materials are large and an average value would be more representative.
Individual readings or observations should be repeated where they appear to be anomalous. It may be
necessary for the candidate to decide how many times to let something that is repetitious occur before
recording the observation (e.g. in counting the number of bubbles released from a delivery tube).