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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.
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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).
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•
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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.
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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
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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
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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
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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
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© OCR 2010
For practice use only, not for assessment