GCSE
ADDITIONAL SCIENCE /
BIOLOGY
BL2FP
Report on the Examination
4408 / 4401
June 2013
Version: 1.0
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REPORT ON THE EXAMINATION – GCSE ADDITIONAL SCIENCE / BIOLOGY – BL2FP – JUNE 2013
General
Particular problems which occurred quite frequently included:
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The inability to express ideas clearly and unambiguously
Paying insufficient attention to information provided in the stem of a question in order to guide a
reasoned response and avoid the inclusion of irrelevant information
Repeating, rather than using, information given in the question, for which no marks are
available
The inclusion of extra, incorrect information in addition to the correct answer
Careless reading of the question resulting in an inappropriate answer
Limited ability to apply what had been learned to a novel situation
Poor understanding of certain topics, such as the digestion of fat and limiting factors in
photosynthesis.
Question 1 (Low Demand)
This question was well answered by most students.
(a)
Most students knew that structure A in the diagrams of the animal and bacterial cells
was the cytoplasm and that structure B was the cell membrane although, inevitably, the
latter was confused with the ‘cell wall’ by many. Around three-quarters of the students
also knew that the genetic material in the animal cell was contained within the nucleus or
in chromosomes, DNA or genes. Nucleus and DNA were the most common answers.
(b)
Over half the students were able to assign all three cell structures (the cell membrane, a
mitochondrion and a ribosome) to their functions.
Question 2 (Low Demand)
(a)
Almost two-thirds of students were able to give a satisfactory definition of a fossil in part
(i). The most common answers were ‘bones in a rock’ and ‘bones from millions of years
ago’. The answer sought by examiners related to the fossil having been derived from a
living organism and some qualification regarding its nature or when it was formed.
Some students spoiled their answer by specifying too short a time period. The evidence
given in part (ii) was frequently inadequate and only a fifth of students could state that
fossils show some sort of change over time – many students stressed similarities rather
than differences. The use of the word ‘evolve’ in the answer was not regarded by
examiners as sufficient to imply change in a question about evolution.
(b)
Two-thirds of students were able to read the range of sizes of fossil snail shells from the
graph and almost the same proportion were able to suggest that the small sample size
cast doubt on this being the full range of sizes.
(c)
Possible causes of extinction were well known, except that a sizable minority referred to
human factors which were not relevant to a species that went extinct 380 million years
ago.
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REPORT ON THE EXAMINATION – GCSE ADDITIONAL SCIENCE / BIOLOGY – BL2FP – JUNE 2013
Question 3 (Low Demand)
(a)
Just under half of the students were able to assign the three given features of cell
division correctly to either mitosis or meiosis, showing that they knew that mitosis was
used for growth and repair and that it produced genetically identical cells, while meiosis
was involved in gamete production. Similarly, in part (ii), half the students knew that
gametes were produced in the testes in the male and in the ovaries in the female.
(b)
Almost two-thirds knew that the male chromosomes were X and Y, while the female
were X and X.
(c)
It was slightly disappointing that less than three-quarters of students knew that the
chance of producing a male child was ½ or 50% or an equivalent expression. The use
of betting odds, ‘50/50’, should be discouraged as, mathematically this is 1.0 and so was
not regarded as a correct answer.
Question 4 (Low Demand)
(a)
The vast majority correctly chose protein as the substance made by the duckweed using
nitrate ions.
(b) (i)
Students were required to describe from the data the effect of magnesium ions on the
growth of the duckweed. While the majority were able to relate a higher concentration of
magnesium ions to an increase in growth, many answers did not include any
comparative points.
(b) (ii)
Evidence that nitrate ions were needed for growth of the duckweed was often described
inadequately and only half the students related the highest growth rate to the highest
nitrate content.
(c)
Suggested methods of monitoring the growth of the duckweed plants, other than leaf
counting, frequently lacked sufficient detail, for example ‘measure with a ruler’ or
‘measure the size of the root’. Although about half of the students did include sufficient
detail here by suggesting measuring the mass of the plant or the length of the roots, very
few were able to explain why their suggested method was better than leaf counting;
most just thought their method was more ‘accurate’, ‘reliable’ or ‘valid’ without any
explanation.
Question 5 (Low Demand)
(a)
It was disappointing that, given that the alleles for having 5 or 6 toes on the foot were,
respectively, d and D, very few students were able to state that a sperm cell would
contain just one of these alleles. And less than two-thirds could supply the term
fertilisation for the process in which a sperm cell joins with an egg cell. The remainder of
this question consisted of four multiple choice items about the inheritance of polydactyly.
(b)
Students had much greater difficulty in deciding that the man with polydactyly was
heterozygous (Dd) than they did in assigning the homozygous recessive genotype (dd)
to his unaffected wife, despite the fact that the family tree diagram showed that they had
produced both affected and unaffected offspring.
(c)
In each of parts (i) and (ii), less than half the students were able to choose the correct
probability. To some extent the answer to part (i) must have been affected by an
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REPORT ON THE EXAMINATION – GCSE ADDITIONAL SCIENCE / BIOLOGY – BL2FP – JUNE 2013
incorrect choice for the man’s genotype in part (b)(i). However, it should have been
apparent that two unaffected people, thus having the same genotype (dd) as the woman
in part (b)(ii), had zero chance of producing a child with polydactyly.
Question 6 (Low Demand)
This question was about the use of a simple respirometer for measuring the rate of aerobic
respiration in earthworms at different temperatures.
(a)
Over half of the students were able to choose the correct substances for completing the
equation for aerobic respiration.
(b)
The correct reason for leaving the apparatus containing the earthworms in the water
bath at 20oC for 10 minutes with the tap open (i.e. so that the worms’ body temperature
would change to 20oC) was selected by only half of the students.
(c) (i)
This section involved the selection of data from a graph of the results and using them to
calculate the worms’ rate of oxygen consumption, only a small minority were able to read
the two relevant figures (5 and 60) from the graph, at times of zero and 10 minutes, and
subtract them to give the answer 55 for the amount of oxygen consumed in 10 minutes.
‘60’ was a much more common answer.
(c) (ii)
Much greater success was achieved in this part for dividing the answer from part (i) by
10 in order to calculate the rate of oxygen consumption by the worms per minute. The
majority of students also found it difficult to suggest that the reason why the worms took
in less oxygen at 10oC than they did at 20oC was due to them being less active at the
lower temperature and thus having a lower rate of respiration.
A variety of
misconceptions were expressed, such as oxygen being used to cool the body at the
higher temperature, or an incorrect reference to ‘anaerobic’ respiration.
(d)
Over two-thirds of students correctly suggested that the reason for ignoring one of the
plotted points when the line had been drawn on the graph was due to it not fitting the
pattern, or being anomalous. However, only a quarter of the students understood that
the reason for repeating the experiment was to get a more reliable or representative
result; many thought that repetition made the result more ‘accurate’.
Question 7 (Standard Demand)
This was the first of three standard demand questions common to both the Foundation and Higher
Tier papers.
(a)
A little less than half of students recognised the terms xylem and phloem as the names
of the two tissues in the leaf that are used for transport.
(b)
Just over a quarter of the students were able to give a satisfactory definition of diffusion.
Although many knew that a substance would move from high to low concentration by
diffusion, far fewer stressed that it was molecules / particles of the substance that
moved.
(b) (ii)
Most answers were either ‘oxygen’ or ‘carbon dioxide’, less than half of the students
correctly gave the former as the gas that would diffuse out of the leaf on a sunny day.
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REPORT ON THE EXAMINATION – GCSE ADDITIONAL SCIENCE / BIOLOGY – BL2FP – JUNE 2013
Question 8 (Standard Demand)
This was the second of the three common questions.
(a)
While approximately half of the students knew that, to investigate the distribution of
clover plants in a field, the quadrats should be placed randomly, very few could explain
satisfactorily how this randomness could be achieved. Some gave reasons why it was
necessary to place the quadrat randomly rather than how it should be done.
(b)
In this section, students had to estimate, from a diagram, the percentage cover of clover
plants within a quadrat. The first step involved an estimate of the number of squares
covered from the 25 into which the quadrat was subdivided. Just under half of students
were able to do this and explain how they had counted the squares completely covered
and added on an estimate from those partially covered. It was evident that some
schools had taught their students that squares with coverage of half or more counted as
a whole square while less than half coverage could be ignored; other students tried to
piece together the partially-covered squares the best they could. Either of these
methods was considered satisfactory and each should have resulted in an answer of
either 7 or 8 squares out of the 25. A common error was to include all the squares in
which the clover was simply present rather than to give the cover specified in the
question. Many students struggled to describe how they had worked out their answer.
The final stage was to scale this figure up to a percentage which resulted in answers
between 28 and 32 per cent, although allowance was made for calculations based upon
incorrect estimates of the number of squares covered. Around a third of students were
successful in this exercise.
(c)
Less than half of the students were able to suggest an environmental factor that might
have affected the distribution of the clover plants, the most common being light, water
and nutrients in the soil. Some suggestions, such as carbon dioxide or oxygen levels,
were considered unlikely to have varied sufficiently over short distances to have made
any difference in the given situation. Vague answers such as ‘the soil’, ‘pollution’ or ‘the
weather’ were not credited.
Question 9 (Standard Demand)
This was the third of the three common questions.
(a)
A little over half of students were able to read enzyme Z’s optimum pH from the graph as
8.6. However, only a fifth of the students knew that hydrochloric acid was the substance
that generated the correct pH for enzyme action in the human stomach, with a little
under one-third identifying enzyme X (showing an optimum pH of 1.9 in the graph) as
the one that would work best in the stomach.
(b)
In this question, students were required to describe how the human digestive system
was able to break down molecules of fat so that they could be absorbed by the body.
The quality of written communication was also taken into account in the awarding of
marks. Many students found this question very difficult with only a minority displaying a
good knowledge of fat digestion. Many knew that lipase was involved, although the term
was often confused with ‘lipid’, and that fat was converted into fatty acids. Relatively few
knew that the lipase was produced in the pancreas and / or the small intestine (the
mouth and stomach were common errors). A fair proportion knew that bile was involved
but there was much confusion about where it was made, its storage in the gall bladder
being better known. Only a few were able to explain that the bile was alkaline and
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REPORT ON THE EXAMINATION – GCSE ADDITIONAL SCIENCE / BIOLOGY – BL2FP – JUNE 2013
hence helped to neutralise the acid coming into the small intestine from the stomach (a
common error was to suggest that bile entered the stomach to neutralise the acidity);
and few knew that the bile emulsified the fat, or were able to describe this process as the
production of tiny droplets of fat (the breakdown of fat molecules was a common error
here). Some students also explained how initially the food could be broken down
mechanically by the teeth and how eventually the products of digestion could be
absorbed by the small intestine. Many students were confused about which processes
occurred where, about the name of the enzyme (‘amylase’ was a common error) and
about the products of digestion (e.g. ‘amino acids’ were sometimes suggested). One
major mistake, made by a large proportion of students, was to misinterpret the question
and not limit themselves to the remit of fat digestion. Consequently, these students
wasted a great deal of time giving details of carbohydrate and protein digestion which
were not required and for which no marks were available. The only penalty incurred was
that of wasting valuable time which could have been better devoted to gaining marks
elsewhere.
Mark Ranges and Award of Grades
Grade boundaries and cumulative percentage grades are available on the Results Statistics
page of the AQA Website.
Converting Marks into UMS marks
Convert raw marks into Uniform Mark Scale (UMS) marks by using the link below.
UMS conversion calculator www.aqa.org.uk/umsconversion
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