1. 1. A diagram was provided that showed part of a system designed to meet all basic needs of a
family of four living in the tropics. The system was based in part on the generation of fuel gas
by bacterial fermentation of urine and faeces.
(a) Candidates were asked to describe how processes which naturally formed part of the
nitrogen cycle could make nitrogen contained in urine and faeces available to crop plants.
There were many competent answers that showed detailed knowledge of the relevant
parts of the nitrogen cycle and scored full marks. There were also very weak accounts,
however, that included unselective descriptions of the whole of the nitrogen cycle
including inappropriate references to denitrification and nitrogen fixation. The average
type of response tended to include one or other of the following faults: the assertion that
ammonia was present in urine or faeces; use of the term “nitrogen” in a very loose way
with little reference to specific forms; errors in the sequence of nitrite and nitrate
production; confusion in the nomenclature of the microorganisms involved; lack of
precision concerning uptake of nitrate by plants.
(b) In the system, solid waste from the fermenter was used as fertiliser for crop plants and
candidates were asked to explain the advantage of growing leguminous plants such as
groundnuts or beans. It was evident that many candidates were unfamiliar with
leguminous plants. Answers were often quite weak, with scoring limited to mention of
root nodules (root “noodles” were held to be nutritious, but unacceptable here) and
nitrogen fixing bacteria (with the latter frequently misidentified). There was widespread
belief that nitrate was the product of nitrogen fixation and, in some cases, that the plant
itself fixed the nitrogen. Few candidates appreciated that remains of the legumes would
need to be decomposed before releasing material that could be converted to nitrates and
consequently there were many vague answers such as “legumes return goodness to the
soil”. Ironically, some of those who had discussed nitrogen fixation entirely out of
context in part (a) did not repeat this material which was now relevant.
The question concluded by asking candidates to explain the advantage in the system of
stocking the pond with fish that feed on algae rather than with carnivorous fish. Most
candidates chose to refer, sometimes at undue length, to prevention of eutrophication.
Very few, however, discussed trophic levels in relation to relative energy loss but some
did suggest that stocking with fish that feed on algae would produce a greater yield of
fish. A large number of obscure answers suggested that carnivorous fish would need to be
fed by “bringing meat in” and there was even the occasional idea that the cattle and
chickens would be fed to these fish.
2. There was a great deal of confusion between nitrogen fixing and denitrifying bacteria in part
(a). Candidates are still not clear about the sequence of changes in the nitrogen cycle. Some
failed to read the question carefully and began with nitrogen gas in the atmosphere rather than
nitrogen compounds in dead spruce seeds. Weaker candidates still fail to define the compound
containing the atom of nitrogen.
Hyde Clarendon Sixth Form College 1

2. Decomposition or ammonification releasing ammonia from organic sources of nitrogen still
seems to be the weak link. Candidates frequently misread part (b), and often suggested that
moss must contain nitrogen fixing bacteria in their roots. Many spotted that competition was
involved but were unsure of the factor for which the organisms were competing. Again,
competing for nitrogen was a common error.
3. The essays indicated that most candidates had given thought to organising material into a logical
and coherent account. The Quality of Language was considerably better and there was
substantially less of the colloquial expression that marred many essays in previous years. The
main criticism in this area was the widespread failure to present new ideas in discrete
paragraphs. However, as was the case last year, the scientific content of the essays proved to be
disappointing. Work was often extremely superficial and not infrequently failed to reflect the
detail expected of candidates following an A Level course of study.
Relationships between animals and plants
This was the least popular of the essays and was often chosen by the weaker candidates. As a
result, many responses offered no more than a brief discussion of animal dependence on food
and oxygen from plant photosynthesis before embarking on lengthy and often anecdotal
accounts of the provision of habitats, shelter and building materials. Only rarely did such
accounts offer an appropriately detailed discussion of trophic levels, energy transfer and carbon
dioxide/oxygen balance. Where nutrient cycling was introduced, the better candidates
successfully established the link between animal excretion, decomposition and the uptake of
mineral ions by plants. Many less able candidates lost sight of the question at this point and
essays digressed into discussions of the roles of various micro-organisms. Other areas which led
to the introduction of much peripheral matter were references to pharmaceutical compounds
derived from plants and to habitat destruction. Some accounts were totally irrelevant and
suggested that candidates had misinterpreted the question as requiring a discussion of the
similarities and differences between animals and plants.
4. In part (a) it was obvious that some candidates had actually done this sort of exercise as they
described in detail how random numbers are generated and used with a grid on the ground to
place the quadrats. A minority of students still described throwing random quadrats but this
method is prone to bias and is not random. The most common error was to omit the method of
generating random numbers.
Many wrote at length in part (b)without focusing on the stages of heather growth given in the
diagram, or failed even to offer an indication of the heather’s age, and vaguely used the terms
‘early’ and ‘late’. The diversity of heather and not of the whole community was a popular
misunderstanding. Some candidates agreed that the diversity would change but failed to say
whether it would get greater or less. Although many did use the information in the table to
explain that increased cover offered by the heather, blocked light and affected diversity. Many
offered other factors such as more nutrients in the soil, but could not easily rationalise how that
occurred.
Hyde Clarendon Sixth Form College 2

3. In part (c)(i) some candidates did manage to calculate the rate but this caused problems for
many. Some demonstrated misunderstandings with the correct notation of SI units. Few read the
question in part (c)(ii)so many did not relate age of the heather to the changing distribution of
green shoots and older woody ones. The most common incorrect response involved a discussion
of the death of parts of the plant. In part (iii) the availability of extra food for grouse was
frequently given, but few related the fact that burning heather eventually increased cover, which
provided the grouse with somewhere to hide. In part (d)(i) many students failed to show an
understanding of the term ‘organic’. This can be the only explanation for responses such as
ammonia, soil, humus, bone and root. Some however did offer protein and few even gave DNA.
Candidates really had a problem with (d)(ii) as phosphate, sodium, and hydrogen ions were
given, this suggested that the candidates read the question as “name an ion” rather than “name
an ion containing nitrogen”. Ammonia and the correct named ion, but with an incorrect
chemical formula, were common mistakes.
In part (e) there was still a great deal of confusion over the role of the bacteria and the sequence
of the nitrogen-containing compounds. The relative positions of ammonium, nitrite and nitrate
ions were regularly switched. Many candidates did, however, correctly name the bacteria
involved in the nitrogen cycle and gave complete and accurate accounts. Saprobiotic bacteria
were rarely mentioned and often the pathway began with the ammonium ions, but with no
mention as to how they were created from organic nitrogenous compounds. Inappropriate
bacteria such as the nitrogen-fixing bacteria were often mentioned, candidates being unable to
identify the relevant parts of the nitrogen cycle and so found it necessary to include everything
they knew.
In part (f) most candidates realised that the table showed changing amounts of nitrogen in the
soil and heather plants, but they were at a loss to explain the reason for burning heather after 8
rather than after 15 years. Few realised the significance of creating gaseous oxides of nitrogen
during burning and thought that burning would place nitrogen directly into the soil.
5. (a) There was a strong centre bias to this part of the question. Candidates were either familiar
with the ways in which organisms were classified or their answers appeared t6 be based
largely on guesses.
(b) In part (i) most candidates appeared to be of the opinion that digestive enzymes were
present in worm casts so that digestion could continue in the soil. Some were of the
opinion that, as worms were primitive animals, they had short guts. They therefore
ingested the casts and passed them through the gut a second time. There were relatively
few references to the key points that the enzymes were not themselves digested and being
proteins they were too large to be absorbed through the gut wall. Some of the answers to
part (ii)showed a good understanding of the basic principles of experimental design, but
far too many simply assumed that demonstration of the presence of reducing sugar or the
absence of starch in worm casts proved the presence of amylase.
Hyde Clarendon Sixth Form College 3

4. (c) Many candidates were content to take the lack of earthworms at face value and made no
attempt to link it in any sensible way to the use of fungicide. Some realised that the
information in the passage about breaking the leaves into smaller pieces was relevant, but
few went on to develop this point further and describe the effect of increased surface area
on the rate of microbial decomposition.
(d) The answers to this part of the question were generally poor. Although there were some
references in part (i) to nitrate and ammonium ions, mineralised nitrogen was rarely
described as being more than “nitrogen in mineral form”. The tendency to repeat the
question also characterised many of the answers to part (ii) with excretory nitrogen
generally described as being “nitrogen in excreted products”. Where the answer was
amplified, excretory nitrogen was usually identified as the nitrogen found in faeces.
Evidence from the answers to this part of the question, and elsewhere in the paper, point
to few candidates understanding the differences between the processes of secretion,
excretion and egestion.
(e) The number of times that ammonia appeared in the answer to part (i) suggested that either
few candidates understood the meaning of the word “organic” or that ammonia was
genuinely regarded as an example of an organic compound. Where both of the examples
offered were organic, lipids and carbohydrates often featured. There were, in addition,
many inappropriate references to cells and tissues. Although there were some excellent
answers to part (ii), others reflected a fundamental lack of knowledge on the part of the
candidates concerned or were totally unselective in the material they presented. The
production of ammonia was often omitted, the terms “nitrifying” and “nitrogen-fixing”
were frequently confused and nitrates were too often described as being converted into
nitrites.
(f) In part (i) most candidates showed understanding that the behaviour of earthworms in dry
conditions led to a smaller surface area over which water could be lost. Some,
unfortunately, linked this behaviour to saving energy through a lower rate of respiration,
while others referred to reduced rates of sweating. There were also many sound answers
to part (ii).
(g) Many candidates understood the difficult concept that lowering the C : N ratio could be
achieved either by removing carbon or by adding nitrogen. Unfortunately, the
explanations of how these effects were achieved Were often insufficiently clear to gain
credit. Once again, far too much use was made of unqualified pronouns and many
members of the examining team commented on difficulties in deciding to what “it” was
referring.
6. Many candidates did not study the diagram of energy flow through the ecosystem with
sufficient care.
(a) This was concerned with the possible fates of energy already absorbed by the producers
but not yet transferred to organic molecules. Hence reference to energy loss by reflection
was irrelevant, and respiratory loss was inappropriate, especially as the diagram showed
this at a later stage.
Hyde Clarendon Sixth Form College 4

5. (b) In calculating the energy transfer to the primary consumers, many candidates failed to
subtract the value for material in the producers which was not actually consumed, hence
8760 was a more common answer than the correct 2920 kJ m –2.
(c) Many candidates displayed a sound grasp of the topic of nitrification by soil bacteria.
Some spoiled their answers by giving supplementary, incorrect chemical formulae (e.g.
“nitrate / NH3”). Some candidates included irrelevant extra material about nitrogen
fixation and denitrification, and some had these different aspects of the nitrogen cycle
totally confused.
7. This question required the use of extended prose throughout. Full marks were only available to
those able to express the appropriate concepts clearly and unambiguously in scientific terms.
Many candidates produced good answers, using both information from the passage and their
own biological knowledge. Lack of detail, misconceptions and careless expression all
contributed to the loss of marks for other candidates.
(a) The main points given by candidates here were related to deforestation causing loss of
habitat, loss of food, and potential extinction or the need to migrate elsewhere. Some
gave details relating to exposure of the soil and hence erosion and leaching of ions. Very
few mentioned changes in climate or in light levels as a result of removal of the trees.
(b) Many understood that trees could act as carbon sinks by absorbing carbon dioxide (but
not ‘carbon’ as a high proportion of weak candidates stated) for use in photosynthesis and
conversion of organic molecules within the tree. Careless omission of any of these details
resulted in the loss of marks – the third point being the one most commonly left out. Far
too many candidates believed that carbon dioxide was converted into oxygen or that it
was used in ‘respiration’ rather than photosynthesis.
(c) Some candidates did not make it clear whether the scenario they were describing related
to the situation where ploughing took place or, as the question stated, to where ploughing
was reduced. Such ambiguity in the answer cost marks. Once more, ‘carbon’ was often
the substance used rather than dead organic matter and this carbon was often thought to
combine directly with oxygen to form carbon dioxide. Ploughing sometimes introduced
‘air’ into the soil, with oxygen not being specified. Similarly, the process of respiration, if
mentioned in the context of saprotrophic organisms in the soil, was rarely qualified as
being aerobic. Some candidates even imagined a peculiar situation whereby carbon
dioxide was still formed in the soil but it was trapped due to a lack of ploughing.
Hyde Clarendon Sixth Form College 5

6. (d) This section was specifically about the role of nitrifying bacteria. These were frequently
confused with saprotrophic and with nitrogen fixing bacteria. For those thinking the latter,
ploughing introduced nitrogen gas into the soil ready for fixation. Only correct, relevant
details were rewarded, such as the conversion of ammonium ions to nitrite and then to
nitrate, using the extra oxygen introduced by ploughing. Many candidates knew that
nitrate ions were taken up by crop plants and some explained how these could be
converted into named organic compounds, such as DNA or protein, which could be used
in turn by the plant to increase its growth or yield (hence being of benefit to the crop
plants, as required by the question). Such completeness of detail was the domain of the
better candidates who frequently scored full marks.
8. (a) Weak answers followed the stem of the question and only referred to carbon rather than
considering the form it would take in the atmosphere, namely carbon dioxide. Unclear
responses proposed that ‘slash and burn’ would increase its concentration without
explaining whether it was the ‘slash’, the removal of trees, or ‘burn’, the combustion of
trees, that was responsible for the change. Not all candidates used the allocation of marks
to construct their answer and generally included only the increase due to release of carbon
dioxide from burning. Better candidates identified the reduced uptake of carbon dioxide
since there would be fewer photosynthesising organisms.
(b) The concept tested in this question was secondary succession. Where the role of pioneer
species was identified, clarification was needed since soil already existed from the earlier
presence of organisms. Weak responses produced unnecessary descriptions of primary
succession. Better candidates recognised that recolonisation would occur with seeds and
spores from neighbouring areas although this was not always well expressed. Many
achieved credit by explaining the process of succession and the resultant re-establishment
of a climax community, but there were also many who appeared unfamiliar with the
concept or who could not communicate the main ideas adequately.
(c) This question allowed candidates to demonstrate their ability to interpret information and
apply their knowledge. Thus, good candidates could identify the source of ammonium
compounds in manure, which soil bacteria would be relevant, and what was meant by
crop yield. Many showed a good knowledge of the nitrogen cycle but only the better
candidates considered the role of nitrogen-fixing bacteria. It was not necessary to name a
specific nitrifying bacterium, but where this was done, the bacterium had to be linked to
the appropriate reaction to secure credit.
(d) It was pleasing to see so many candidates familiar with environmental concerns and
conservation, although candidates often failed to express themselves clearly. A large
proportion considered the view of what would be lacking if a forest ecosystem was
removed, rather than the advantages of conserving one, but examiners sought to credit the
concepts. There was a limited appreciation of forests as sustainable resources but frequent
reference to habitats, carbon sinks, species diversity and food chains allowed maximum
credit to be obtained by many.
Hyde Clarendon Sixth Form College 6

7. 9. (a) Some candidates were able to gain maximum credit by linking contraction of the
diaphragm and intercostal muscles to an increase in volume of the chest and a decrease in
pressure, but there were many who gained little credit for their responses. Of these, some
failed to take note of the requirements of the question and emphasised the role of
chemoreceptors, some clearly confused inspiration with expiration, and others wrote in
extremely simplistic terms about unspecified muscles “working” and the chest “getting
bigger”.
(b) Candidates who identified part (i) as a question relating to experimental technique
produced sound answers, commenting on the need to allow breathing rate and tidal
volume to stabilise.
Others responded inappropriately with such answers as “allowing the average to be
worked out” or “warming up”. The mathematical problem in part (ii) created relatively
few difficulties, although there were those who were uncertain of the required approach,
or incorrectly converted the figures to cm3. The examiners had little sympathy with those
candidates who confessed at this point that they did not have calculators. Answers to
part (iii) were almost universally disappointing. Although candidates clearly experienced
little difficulty with the wording of the question, they did not take sufficient care in
picking out the underlying trends, a feature which also frequently marks their approach to
coursework. Thus many did no more than describe an “increase in breathing rate and tidal
volume”. Good answers needed to refer to the change in gradient.
10. Only the better candidates were able to give satisfactory answers to the sections requiring
understanding of the chemical aspects of the process of photosynthesis.
(a) Many were confused concerning the identity of the carbon dioxide acceptor substance in
the Calvin cycle. Not many of those that did know this to be RuBP went on to stress that
two molecules of GP would be formed per molecule of carbon dioxide fixed. The concept
of equilibrium existing between the rates of formation and breakdown of GP was foreign
to all but the best candidates. Many were beguiled by the superficial resemblance of the
relevant part of the graph to a typical ‘limiting factors’ curve. Some others argued in
favour of some sort of saturation phenomenon.
(b) In order to explain that the concentration of GP was increasing in the dark, many
candidates concentrated, incorrectly, on the formation of GP rather than on its lack of
conversion to other substances. Some even invoked GP production in glycolysis
(forgetting that it would also have to be broken down before any ATP were produced).
Only the most able candidates realised that conversion of GP to TP required ATP and
reduced NADP from the lightdependent reactions and that these would, of course, soon
be depleted in the dark.
Hyde Clarendon Sixth Form College 7

8. (c) Most candidates tended to be successful in their interpretation of the data in the table and
understood that, in the light (between 8 am and 4 pm) photosynthesis would occur, hence
removing carbon dioxide from the air and leaving a lower concentration, as shown in the
data.
Many also appreciated that the absence of leaves, or reduced light levels, or even the
production of carbon dioxide by soil organisms, would result in a higher concentration of
carbon dioxide at ground level than that found higher up among the leaves of the plants.
(d) Many candidates realised that the wind could alter the concentration of carbon dioxide in
the air, but not all of these explained that this would be due to the wind bringing in fresh
supplies or, alternatively, removing carbon dioxide. Very few candidates went on to
explain that the wind would therefore have introduced another experimental variable and
hence made any measurements of carbon dioxide concentration in the air (which was the
basis of the experiment) unreliable. There was also much irrelevant discussion of the
effect of the wind on the rate of transpiration.
(e) While many candidates appreciated that saprotrophic microorganisms would cause dead
leaves to decay and hence release carbon dioxide which could then be taken up by the
plants, fewer gave more specific details relating to the involvement of digestion and
respiration. Many thought that ‘carbon’ would be released into soil for uptake by plant
roots. Some could not resist the temptation to include irrelevant comments about the
nitrogen cycle, despite carbon having been stated quite explicitly as the subject of the
question.
11. This question required the use of extended prose throughout. Full marks were only available to
those able to express the appropriate concepts clearly and unambiguously in scientific terms.
Many candidates produced good answers. Lack of detail, misconceptions and careless
expression all contributed to the loss of marks for other candidates.
(a) Many candidates were very careless and gave few practical details of how sticky traps
could be used to compare the diversity of flying insects in the two environments.
Elementary procedures such as the use of multiple traps and details of how these would
be placed at random were frequently overlooked. Most suggested that the number of
individuals of each species caught by the traps should be counted and used to calculate an
index of diversity, but many others were confused and thought that the mark-release-
recapture technique should have been used in order to find the Lincoln Index.
While most candidates appreciated that the diversity of insects in the forest would be
greater than that in a cultivated field, some gave very little detail in their explanation of
the reason for this. Better candidates included details regarding the relative harshness of
the two environments (often giving the use of pesticides in cultivation as a factor
detrimental to insects), and the abundance of different habitats and greater variety and
quantity of food available in the forest. Many wasted both time and space by reiterating
the converse argument for the second habitat rather than expressing themselves in
comparative terms once only.
(b) The explanation offered for why crops could only be grown for a few years in a field
produced by clearing part of the forest were frequently vague. References were made to
‘nitrogen’ ‘running out’ with no detail such as the removal of material in the crops at
Hyde Clarendon Sixth Form College 8

9. harvest leaving little organic matter to decay in the soil, or to leaching of soluble
nitrogen-containing ions such as ammonium and nitrate. The better candidates had little
problem however in applying their knowledge and understanding of the nitrogen cycle to
explain how the concentration of nitrates in the soil could be restored with time. Some
mentioned nitrogen fixation (both atmospheric and biological) and most gave detailed
accounts of putrefaction and nitrification. Weaker candidates tended to concentrate on
colonisation and succession and lost sight of any connection with nitrate production.
12. BYA8
Candidates gave the impression of leaving themselves adequate time for attempting the essay
and it was encouraging to note that many were able to write three or more sides on their chosen
topic. Some obviously encountered considerable problems in deciding which of the two essays
to attempt and it was not uncommon to see comprehensive plans relating to both and
sometimes, even, a substantial false start. It is important, however, for candidates to appreciate
that length in itself is not a merit.
Care has to be taken over ensuring that the essay is written clearly enough for it to be read by
the examiner. This was by no means always the case. There was surprisingly little evidence of
planning in the work from some centres, and it is possible that this was the main reason for so
many candidates involving themselves in so much needless repetition.
Many candidates felt the need for a lengthy introduction defining the title. Unfortunately such
introductions were frequently devoid of significant factual content or merely served to indicate
that the candidate had little intention of restricting the essay to relevant processes.
The carbon cycle was generally well understood in principle but accounts frequently extended
over one or more pages and lacked significant detail, merely referring to carbon being
transferred.
Candidates who had a thorough knowledge of the nitrogen cycle often produced excellent
accounts of this topic. Others experienced considerable problems. These often stemmed from
failing to appreciate the underlying principles. Thus it was not uncommon to encounter
candidates who saw the whole process as a mechanism centred on maintaining the atmospheric
concentration of nitrogen constant.
Such candidates inevitably started their accounts with a reference to nitrogen fixation and ended
with denitrification. There was also much confusion between the events of the different stages
in the cycle.
Biochemical cycles featured in many accounts and, in general, the level of factual knowledge
here was impressive. Unfortunately many saw inclusion of this material as an opportunity to
display a broader understanding of the processes of respiration and photosynthesis. As a result,
they included much material which could not be considered as relevant to an essay on cycles.
Hyde Clarendon Sixth Form College 9

10. The oestrous cycle was the best described physiological cycle and, where candidates had paced
themselves sensibly and allowed time to incorporate detail of hormonal control, produced some
excellent detail. Other cycles were less convincing and there were many accounts of
physiological process such as synaptic transmission and digestion which, with the best will in
the world, could not be considered as cyclical. A case could be made for the inclusion of other
physiological processes such as those involving homeostasis, the circulation of blood and the
mechanism controlling breathing, but these processes were also usually described as linear
sequences or they lacked the necessary detail to add to the quality of the essay.
BYA9
The essays varied greatly in length, depth of knowledge and relevance. The most common
failing was the inclusion of a number of cycle names without at least a paragraph about the
cycle at the appropriate depth. Candidates should not hesitate to use small, simple sketches (e.g.
carbon cycle, structure of glucose) to illustrate their work, provided such diagrams are labelled
accurately. The full range of marks was used on both essays, with Essay A being less popular
than Essay B, and there was pleasing evidence of planning, both in the form of a plan and as
demonstrated by a piece of coherent, flowing prose. There is a requirement for technical
language at this level so terms such as ‘kicks in’, and ‘Mother Nature’ devalued the essays in
which they appeared. It is important that candidates realise that erroneous or unsupported
mention of an aspect of the specification may actually detract from the impression their essay
gives.
Candidates found it hard to introduce this topic succinctly. The expectation was that candidates
would select at least one each from a range of cycles from which they could emphasise the
common feature of the continuity of a cyclical process, describing the details in sufficient depth
and in technical language such that they gained maximum marks. Some candidates achieved
this ideal.
The range covered included ecological cycles (usually nitrogen and carbon cycles),
physiological cycles (the menstrual cycle, the cardiac cycle), biochemical cycles (the Krebs and
Calvin cycles) and parasitic life cycles (Plasmodium and Schistosoma).
Excellent candidates described the carbon and, more particularly, the nitrogen cycle in
considerable depth. The range of ways in which plants could obtain the nitrogen-containing ions
they need for protein synthesis was thoroughly explained, sometimes with faultless use of the
names of the microorganisms involved. Weaker candidates muddled the process involved,
confusing names and introducing erroneous ideas (‘carbon is taken up through the roots’,
‘plants take in carbon dioxide for respiration’, ‘when plants and trees are eaten, the nitrate they
contain…’, etc.). In some cases, cycles were named but nothing was offered to explain them at
all.
Again some excellent accounts of the menstrual cycle were seen, including considerable detail
on hormones and on uterine changes, The cardiac cycle was well described by a number of
candidates, but many used this term to mean the circulation of blood from the heart to lungs and
back again. These answers generally offered little detail or accuracy above average GCSE level.
Hyde Clarendon Sixth Form College 10

11. The Krebs and Calvin cycles were clearly set in context and briefly related to linked reactions
by the better candidates. Weaker essays muddled the two processes or included lengthy (and
irrelevant) sections on the ETC or the light-dependent reaction. It was, of course, possible to use
cyclic photophosphorylation as a valid example of a cycle but few managed to do this
successfully.
Descriptions of parasitic life cycles were of variable quality. Some near perfect accounts were
seen, but in others, particularly when describing schistosomiasis, the stages of the life cycle
appeared to be a mystery.
13. Many candidates found this to be quite a difficult question. Answers were frequently expressed
with insufficient clarity and data were often used non-selectively.
(a) Most candidates realised that the data for the grass in graphs C and D showed no
significant difference. Weaker candidates imagined that some of the slight differences
were of significance.
(b) For those who selected the appropriate graphs for comparison (i.e. A and C, with neither
having Rhizobium added and only C having the nitrate), there was little difficulty in
finding evidence for the effect of nitrate fertiliser on the soybeans. Less selective
candidates produced very confused arguments.
(c) This section required candidates to both describe and explain the effect of Rhizobium on
the growth of the soybeans. Many candidates did either one or the other. Explanations
were frequently confused regarding the details of nitrogen fixation and answers often
included nitrate production in addition to, or instead of, that of ammonium ions. A
sizeable minority realised that a mutualistic relationship existed between the Rhizobium
and the legume (or that, at least, the bacterium formed nodules on the plant’s roots), and
some went on to explain that the plant would gain organic nitrogen compounds such as
amino acids or proteins as a result of the relationship.
In sections (b) and (c), a sizeable proportion of candidates appeared confused regarding
what had been used in the experiment as a measure of plant growth – there were many
references to the ‘number of seeds’ produced but, since this was plotted on the x-axis, it
should have been realised that the number of seeds was a manipulated variable and not a
result.
Hyde Clarendon Sixth Form College 11

12. 14. (a) Some accounts of the activities of decomposers and nitrifying bacteria in the recycling of
carbon and nitrogen from fallen leaves were truly excellent. Aspects which tended to be
omitted were mainly those associated with the early stages of saprotrophic nutrition, i.e.
the secretion of hydrolytic enzymes for external digestion followed by absorption of the
products by diffusion or active transport. Details of respiration releasing carbon dioxide
to be used by the trees in photosynthesis, of the release of ammonium compounds its
conversion to nitrite and nitrate and the subsequent use of the latter by the trees to
produce organic nitrogen compounds such as amino acids were frequently given.
However, weaker candidates typically knew few of these details and often described how
‘carbon’ was released into the soil, in which state it was apparently taken up by the trees’
roots. Some candidates were determined to display all they knew about the nitrogen cycle
and included irrelevant details of denitrification and nitrogen fixation.
(b) For candidates who kept to the point, this was a very straightforward question: felled
trees no longer removed carbon dioxide from the atmosphere by photosynthesis and
burning them released more carbon dioxide back into the atmosphere – hence a predicted
rise in the carbon dioxide concentration. Some became too involved in telling a story and
often forgot about one or other of the key processes.
(c) Answers to this section were very disappointing. Many candidates merely repeated
information given in the stem of the question but did not use this, nor did they attempt to
apply biological principles to the situation with which they were presented. Others treated
examiners to the answer they had prepared earlier, with sound biological facts irrelevant
to this question. One area which was hardly ever explored was how the protective canopy
of the softwood trees might actually have modified the environment to make it suitable for
the growth of hardwoods beneath it – such aspects as protection from wind and
rainstorms, provision of a humid environment, shedding their leaves making ions
available to the hardwoods, reducing soil erosion and leaching of ions due to their root
systems being already established in the soil. Usually answers contained a reference to
the light penetrating following tree felling so that seeds could germinate and the idea that
succession to a climax community would occur, and little else of any relevance. Hardly
any candidates considered that being exposed to light might possibly be advantageous for
photosynthesis in the seedling trees. Better candidates realised that more seeds could be
transported into the cleared area from the adjacent forest, and that animals might return
because new habitats and food would be available for them as the new trees began to
grow.
15. Once again, the nitrogen cycle proved a weak link in the understanding of a large number of
candidates.
(a) More candidates were able to identify process P as denitrification than were able to
identify process Q as nitrogen fixation. Nitrification was a common wrong answer, as
was ammonification, since this refers to the conversion of nitrogen in organic compounds
to ammonia.
Hyde Clarendon Sixth Form College 12

13. (b) Many candidates misread the questions and did not realise that they had to account for the
apparent discrepancy between the amount of ammonia converted to nitrates and the
amount formed by nitrogen fixation. Good candidates knew that ammonia is also formed
by the decomposition of proteins, amino acids, urea and other organic compounds in the
detritus that contain nitrogen.
(c) Most candidates realised that hydrogen is lost and oxygen is gained in the conversion of
ammonia to nitrate.
16. (a) Nearly all candidates knew that habitats would be lost, and a good number also knew that
this would reduce the number of species in the area.
(b) Better candidates realised that both potassium nitrate and ammonium nitrate would
release nitrate ions into the soil immediately, and that the ammonium ions in ammonium
nitrate could be nitrified by nitrifying bacteria to provide a secondary release of nitrates.
Many candidates, however, just did not apply their knowledge to the problem and merely
recited chunks of the nitrogen cycle, with some confusion between nitrifying and
nitrogen-fixing bacteria.
17. (a) Most candidates knew the mark-release-recapture technique, and were able to describe
the various steps. However, they did not always explain the reasons behind the steps. For
example, they did not always explain that the released insects should be left for a suitable
period of time to allow them to re-integrate with the rest of the population.
(b) (i) Nearly all candidates knew that there would be only one degree of freedom.
(ii) Most candidates knew that the 0.05 level of probability is that most commonly
used in biological analysis to judge statistical significance.
(iii) Responses to this section were generally disappointing. Most candidates were
unable to reason that, because the value for χ2 is greater than the critical value,
then there is a probability of less than one in one thousand that the results are due
to chance. They were uncertain as to whether the difference in values of χ2 implied
that the differences in results are due to chance or due to some biological cause.
They wrote about rejecting a null hypothesis which had not been stated and also
merely that ‘the results are statistically significant’. Candidates should be aware of
2
the logic that, if χ is greater than the critical value, there is only a probability of
(usually one in twenty) that the results are due to chance as the basis for rejecting
any null hypothesis and accepting the experimental hypothesis.
(c) (i) A number of candidates realised that some of the biomass produced in
photosynthesis would be respired by the plant, but very few actually explained that
biomass is lost in the form of carbon dioxide. Most of those who involved
respiration in their answers suggested that energy is lost, which is true, but loss of
energy does not account for the difference in biomass between gross primary
production and net primary production.
(ii) Nearly all knew that a higher net primary production would lead to more dead
plants and so more food for the detritivorous insects.
Hyde Clarendon Sixth Form College 13

14. (iii) Most candidates realised that decomposers would respire compounds from the dead
plant remains, releasing carbon dioxide, which could be taken in by plants to be
used in photosynthesis.
However, only better candidates knew that the decomposers were saprobionts and
supplied details of extra-cellular digestion.
18. Essays remain extremely variable in quality. For some candidates they provided the saving
grace and did much to redeem the limited quality of the two structured questions. Others proved
themselves unable to recall basic A-level knowledge, and produced superficial and poorly
constructed accounts. The biggest single factor in limiting the marks awarded was undoubtedly
the ability to base the essay on appropriate, detailed biology. Thus, for example, many of the
essays on bacteria ignored the detail of genetic engineering, nutrient cycles and cellulose
digestion which form a major part of the A-level specification and, instead, centred their essays
around such topics as yoghurt and cheese production. Essays generally met the requirements for
breadth although some devoted so much time to scene setting and significance that they left
themselves little time to consider more fundamental issues. There is little doubt that plans would
have helped here but these were often conspicuous by their absence. Given the pressure of
writing under examination conditions, the quality of written communication was usually sound,
often better than that displayed by the same candidates in Questions 1 and 2. The use of
technical language, however, was less impressive and a lack of understanding of the terms “ion”
and “bacteria” provided an obvious handicap.
Certain topics lent themselves to excellent accounts of how inorganic ions are used
physiologically - nerve impulses, nephron function, absorption in the intestine, root pressure and
guard cell activity. These topics enabled candidates to demonstrate what they knew and how
well they understood the processes concerned. There were many detailed and accurate accounts
concerning the roles of sodium and potassium ions in the transmission of nerve impulses and of
calcium ions in synaptic transmission. Less able candidates sometimes confused the roles of the
ions or the parts played by diffusion and active transport. The movement of ions in the counter-
current mechanism of the loop of Henle also appeared frequently, but here confusion over detail
was more apparent.
The identity of inorganic ions and their names produced problems for some in describing the
role of ions in the synthesis of biologically important molecules. Phosphorus, for example, was
commonly identified as the ion important in the synthesis of ATP and phospholipid. This lack of
understanding occasionally led to much irrelevance, especially where discussing hydrogen
bonding in DNA, or the importance of carbon, oxygen and hydrogen in macromolecules.
The role of hydrogen ions gave scope for some sound biological detail in descriptions of the
role of reduced coenzymes in photosynthesis and respiration. Few candidates considered the
importance of hydrogen ions in changing the pH environment of enzymes, but many discussed
the buffering effect of haemoglobin when describing the transport of carbon dioxide as
hydrogencarbonate in the blood.
Hyde Clarendon Sixth Form College 14

15. 19. Essays remain extremely variable in quality. For some candidates they provided the saving
grace and did much to redeem the limited quality of the two structured questions. Others proved
themselves unable to recall basic A-level knowledge, and produced superficial and poorly
constructed accounts. The biggest single factor in limiting the marks awarded was undoubtedly
the ability to base the essay on appropriate, detailed biology. Thus, for example, many of the
essays on bacteria ignored the detail of genetic engineering, nutrient cycles and cellulose
digestion which form a major part of the A-level specification and, instead, centred their essays
around such topics as yoghurt and cheese production. Essays generally met the requirements for
breadth although some devoted so much time to scene setting and significance that they left
themselves little time to consider more fundamental issues. There is little doubt that plans would
have helped here but these were often conspicuous by their absence. Given the pressure of
writing under examination conditions, the quality of written communication was usually sound,
often better than that displayed by the same candidates in Questions 1 and 2. The use of
technical language, however, was less impressive and a lack of understanding of the terms “ion”
and “bacteria” provided an obvious handicap.
Although this option was frequently chosen by less able candidates, overall it was impressive to
note that many identified the key areas of nutrient cycling, mutualistic relationships and the uses
of bacteria in enzyme production and genetic engineering, and wrote about these topics with
conviction.
Better candidates demonstrated a good understanding of the role of bacteria in the nitrogen
cycle although the origins of ammonia were often omitted from discussion. A number of
frequent misconceptions studded the work of less able candidates; denitrifying bacteria were
considered to play a key role in “restarting” the cycle, nitrifying bacteria commonly converted
nitrates to ammonium compounds and nitrogen fixation involved the conversion of “nitrogen in
lightning” to nitrates.
There were many excellent accounts of the role of bacteria in ruminant digestion. The best of
these not only considered cellulose hydrolysis but also discussed the production of fatty acids,
and the conversion of ammonia to urea and its subsequent secretion in saliva. More limited
candidates confined their answers largely to the bacterial digestion of cellulose. These accounts
were characterised by superficiality rather than by error.
Genetic engineering provided a third line of approach and, again, there were some very good
accounts where candidates showed a secure understanding of basic principles. The less
convincing accounts showed confusion over detail. Not infrequently, the role of restriction
enzymes was held to be to remove sections of DNA from plasmids, and many considered the
role of genetically engineered bacteria to be in producing many copies of the gene coding for
insulin. In addition, some of the terminology was heavily reliant on the use of molecular “glue”
and “scissors” than on the relevant enzymes. Some good accounts were subsequently spoilt by
the introduction of poorly remembered examples from the food industry:
yoghurt, cheese and, not infrequently, yeast in the production of alcohol.
Hyde Clarendon Sixth Form College 15

16. 20. (a) Too many candidates saw two empty boxes in the flowchart in (i) and either wrote the
names of both substances in the boxes or the number of carbon atoms in each substance.
This clearly is the result of not reading the question carefully. Those who did answer the
question set, usually scored both marks. In part (ii) good candidates realised that all ATP
is produced in mitochondria, except that produced in glycolysis. They therefore arrived at
the correct answer of 36 ATP by deducting 2 from the net total yield of 38 ATP per
molecule of glucose, or by deducting 4 from the total production of 40 ATP. Others did
arrive at the correct answer by working out where each molecule of ATP was produced,
but many attempting this method did so in a disorganised way and so made errors in
calculation. In (iii) most candidates knew that, in the absence of oxygen, some of the
reactions of respiration could not take place, but many were unable to describe the extent
of anaerobic respiration. Well prepared candidates were able to state clearly that only
glycolysis would take place and, therefore, the ATP production of the Krebs cycle and
electron transport chain would be lost. They also often
(b) Despite being given specific information in part (i) concerning the features of the
heterocysts (thick walls and the absence of chlorophyll), and the requirements of nitrogen
fixation (anaerobic conditions) candidates too often invented other features and reasons
other than maintaining anaerobic conditions for those features. Disappointingly few
candidates confined themselves to answers based on excluding oxygen and not producing
oxygen, which would inhibit the process of nitrogen fixation. There were some excellent
answers to part (ii) from candidates who appreciated that nitrogen-containing compounds
in the rice plants would be the starting point for the reactions of the nitrogen cycle, and
duly described the roles of decomposition and nitrification accurately and logically. Some
realised that the decomposers would produce carbon dioxide as a result of their
respiration and that this could be used in photosynthesis by the leaves of the rice plants.
However, too many just assumed that the ammonia produced by the heterocysts would be
released into the soil, apparently unused by the fern and, in their answers, took this as the
starting point for the nitrogen cycle. This clearly shows less appreciation of the situation
as described.
21. (a) In (i), almost everybody sketched the pyramid correctly. Some did not draw the pyramid
in the conventional way; in effect they drew it upside down, but still showed the correct
relationships between the trophic levels. A few candidates failed to the gain the mark
because they did not label their diagram. Likewise, in (ii), nearly everyone knew that
energy is lost between trophic levels and could suggest at least one way in which it is lost.
(b) In this question, it was a relatively common failing for candidates to be unable to write
about the relevant part of the nitrogen cycle without also trying to include other aspects.
In (i), some candidates failed to distinguish between the roles of decomposers and
nitrifying bacteria in their answers, phrasing their responses along the lines of “the
decomposers and nitrifying bacteria convert the organic substances into ammonia and
then to nitrates”. It was also disappointing to read the number of answers that included
references to lightning and the Haber process. However, candidates who understood the
nitrogen cycle well usually had little problem with this question. There was a general
understanding in (ii) that nitrogen-fixing bacteria convert nitrogen gas into a form that is
more readily available; however, there was also a widespread misconception that they
convert the gas directly into nitrate ions.
(c) In (i), a disappointing number of candidates did not read the question carefully and
described changes in the populations of both types of bacteria and both types of
Hyde Clarendon Sixth Form College 16

17. protoctistans, usually without really explaining the reasons for any of the changes. Good
candidates recognised the predator-prey relationship between the dispersed bacteria and
the free-swimming protoctistans in the way the numbers increased and then declined
slightly out of phase with each other. In (ii), candidates who understood the process of
succession were generally able to recognise the changes in the environment in the
treatment tank that resulted in changes in the community inhabiting that environment. A
common failing was not to make clear that it is the activities of the organisms that inhabit
an area that change the environment and so make it suitable for colonisation by other
species.
22. Unit 8
It is difficult to comment meaningfully on the standard of the essays this year compared to that
in previous years. Essays ranged from the outstanding to the extremely weak and their quality
appeared at times to be independent of the quality of the responses to the other questions in the
paper. Thus, there were some excellent answers to questions 1 and 2 which were followed by
extremely limited essays and, at the other extreme, papers whose sole redeeming feature was a
competent essay. Particularly apparent this year were the many essays which showed no
evidence whatsoever of a plan. They were often poorly organised and lacked coherence, with
timing often presenting an additional problem. Many candidates still see length in itself as a
virtue. Such candidates often produced scripts with two or three extra sheets attached. They
often started with some promise but frequently incorporated much that at best could only be
regarded as being of marginal relevance.
There were some outstanding essays on this topic where the detail throughout was fully in
keeping with what might be expected of an A-level candidate, and which did not stray from the
theme of the relationship between structure and function. Such essays were a pleasure to read
and mark. Others, although sound and attracting considerable credit, tended to belabour
particular aspects unnecessarily. A frequent example of this was in protein structure where the
concept of shape and fit was illustrated at considerable length with enzymes, hormones, carriers,
and antibodies. All were correct and each was relevant but, taken together, they contributed little
more than could be provided by considering one example. This approach not infrequently led to
candidates discussing one particular polymer at great length at the expense of others, thus
affecting the overall balance of the essay. At the other end of the spectrum, it was apparent that
some candidates were uncertain as to the meaning of the term ‘polymer’. It was not unusual to
see substantial paragraphs written about lipids, and there were also frequent references to “small
polymers such as glucose and maltose”. Apart from this, errors often arose from a poor
understanding of technical terminology. Thus a- and P-glucose were regularly confused;
cellulose molecules were described as consisting of p-pleated sheets, and there was considerable
uncertainty over the relationship between amino acids and DNA, the latter all too frequently
being described as a polymer of the former.
Hyde Clarendon Sixth Form College 17

18. Unit 9
The essays varied greatly in length and biological content, but less so in breadth and relevance.
Many essays showed good evidence of planning in a way which would clearly be useful to the
author, and which kept their work relevant. Some candidates failed to plan at all.
The competence with which the scientific terminology was used was pleasing, with many
technical terms being used in the majority of essays. Weaker candidates tended to relate their
work in everyday language, dwelling on the distribution of large surface areas rather than on the
link with transfer processes.
Many of the candidates who chose to write this essay showed themselves to be competent
biochemists. They understood the nature of a polymer, and frequently opened their essay with a
definition. Some of the best candidates were at pains to point out that lipids were not polymers,
and so would not be discussing them. Sadly, some thought they were, and included as much on
this group of substances as they did on the relevant ones.
The most frequently discussed polymers were proteins and carbohydrates. Extensive and
detailed knowledge of the structure of proteins was included, with descriptions of peptide
bonds, primary to quaternary structures, and the bonds which hold them together. Weaker
candidates were somewhat haphazard in their descriptions, but the better ones were not only
capable of demonstrating a lot of detail but their approach was highly logical. The links with
function were less competent. Some simply offered a selection of proteins, while the best essays
discussed the differences, for example, between those with a simple secondary structure
compared with the globular examples. Frequent choices were enzymes and haemoglobin. Other
interesting additions included keratin, antibodies and hormones; although most felt there was no
need to comment on the fact that not all hormones are proteins. As a consequence a few lipids
were mentioned. The work on the structure was in far more detail than the function in many
cases, leaving candidates missing the opportunity to demonstrate detailed knowledge of the
control of blood glucose, the principles of immunology, and the transport of blood gases. This
was a route which could have been exploited by those capable biologists whose biochemistry is
perhaps a little sketchy.
The work on the structure of carbohydrates was equally detailed by a lot of candidates who
chose this essay. However, it was much more often that the function of the molecule was linked
very closely to its structure. Starch and glycogen were described as large, compact molecules
while the work on cellulose reflected its role in the structure of a plant. There was some
confusion over the solubility of some of these molecules.
Candidates who moved on to discuss the nucleic acids were less frequently seen. Those that did
gave good descriptions of their structure, but a number went on to give huge amounts of detail
about the processes in which they play a part, rather than making the more careful links to their
function. Full details of protein synthesis, DNA replication, and genetic engineering, were
inappropriate. Weaker candidates confused nucleic acids with proteins.
Hyde Clarendon Sixth Form College 18

19. It was easy for candidates to use this essay to show their A-level knowledge. Some candidates
tried to use the outline of an essay they may have written earlier on a single polymer. There was
a wide range of marks, with a good number of the better candidates gaining full or close to full
marks.
23. Part (a)(i) appeared to indicate a problem over the term ‘organic’, as the most common incorrect
answers were ammonia and nitrate. In part (ii) the process of death or decay was often given
rather than a source of the material. Nitrifying, nitrogen fixing and denitrifying bacteria caused
confusion in answers to part (b); a substantial number of candidates did not know which type of
bacteria did what. Although this flow diagram was not the usual form of the nitrogen cycle,
enough clues were given to allow candidates to relate it to their own knowledge, and many were
able to do so. 183 was a common incorrect answer to part (c), obtained by deducting the value
for ‘cattle’ from that for inorganic nitrogen’. Many gave 339 which suggested that they had the
principle correct, but missed out the effect of fixation in providing some of the ‘nitrogen’
requirements of clover. While a lot of the candidates knew that clover had nitrogen fixing
bacteria in root nodules, a significant number thought that the clover did its own nitrogen, fixing
in part (d). A common circular argument was that cattle eat the clover, add the nitrogen from the
clover to the soil via dung and urine to benefit the grass which is an advantage to the cattle.
Only a few suggested that growing clover might save the farmer having to buy and apply
fertiliser.
24. ‘Ammonia’ rather than ammonium was a common response in part (b). Although many
candidates made correct references to nitrifying bacteria in part (b), few were unable to give
even a GCSE level response to the processes involved in the production of ammonium ions.
25. Three times as many candidates attempted the essay on cycles in biology as on the structure and
function of carbohydrates. As expected, the carbohydrates essay tended to be shorter but there
was no evidence to suggest that this title attracted less able candidates. Most candidates
provided some form of plan, although these varied greatly in length and detail. Fortunately,
compared to last year, fewer candidates spent a disproportionate amount of their time on a plan
to the detriment of the essay itself. There was some evidence to support the view that candidates
were better prepared for the essays, particularly in terms of providing relevant information and
breadth of knowledge. Most examiners commented on a general improvement from last year
although quality of written communication and poor handwriting remains a problem for a
significant number of candidates.
This essay title enabled candidates to include a wide range of topics from several modules. As
with essay (a), content beyond the specification, and to a greater extent from the option
modules, was also credited. Almost invariably candidates included the carbon and nitrogen
cycles in their answers. The weakest candidates limited their discussions to superficial accounts
of these nutrient cycles and often the water cycle, with few if any factual details of A level
standard. However, most candidates were able to provide a greater breadth of knowledge and
included metabolic, physiological and in some cases life cycles in their essays.
Hyde Clarendon Sixth Form College 19

20. The quality of written communication in relation to nutrient cycles was particularly
disappointing. Many candidates referred to animals obtaining ‘nitrogen’ from plants, and
decomposers releasing ‘carbon’ and ‘nitrogen’. Plants ‘breathing in gases’ and energy being
‘produced’ or ‘recycled’ were not uncommon phrases. Many candidates suggested that nitrifying
bacteria are involved in nitrogen fixation. There was also some confusion over the role of
decomposers with few candidates specifying the nitrogen compounds involved. Many
candidates did not display an understanding of nutrient cycles, with some suggesting that the
importance of the nitrogen cycle is to maintain the nitrogen content in the air.
Most candidates mentioned the Krebs cycle, with many candidates also referring to the light-
independent reaction. Descriptions of the Krebs cycle often failed to complete the recycling of
the four-carbon compound and tended to concentrate on ATP production. Unfortunately, very
few candidates described the cyclical features of the electron transport chain. Similarly, the
cyclic nature of ATP formation and breakdown was rarely considered. Nevertheless, there were
some excellent accounts of the Krebs cycle which outlined the importance of regenerating a
four-carbon compound to react with acetyl coenzyme A. Generally candidates displayed a
clearer understanding of the regeneration of RuBP in the light-independent reaction. However,
there was still the tendency for candidates to provide incomplete cycles.
Discussion of metabolic cycles often led to irrelevancies, particularly glycolysis and non-cyclic
features of the light-dependent reaction.
Where attempted, candidates provided some worthwhile attempts to convey the cyclical nature
of negative feedback, usually in relation to the control of blood glucose. However, a significant
number of candidates referred to insulin and glucagon as enzymes and there was some
confusion between glycogen and glucagon. Many candidates provided details of the ornithine
cycle even though this is not required in this specification. A significant number of candidates,
presumably those taking option 8, included the menstrual cycle in their essays. However, many
of these candidates included irrelevant information such as details of the process of fertilization.
References to synaptic transmission and actomyosin bridge formation as cyclical processes were
infrequent. However, when attempted, these descriptions were detailed and comprehensive. This
was certainly not the case for descriptions of the cardiac cycle. These accounts were often
confused and failed to relate pressure and volume changes in the heart and aorta to events in the
cardiac cycle.
A significant number of candidates included descriptions of mitosis and meiosis, often towards
the end of the essay. These descriptions were often superficial or contained numerous
inaccuracies. Candidates were often confused between chromatids and chromosomes and many
had difficulty explaining the significance of meiosis in a life cycle. A few candidates provided
detailed descriptions of predator / prey cycles or viral replication.
26. (a) In general, this question was not well answered in that too many failed to realise that it
was a three-mark question and just gave one idea, rephrased or extended. Surprisingly
few candidates recognised that monoculture provides a huge food supply and hence
promotes rapid population increase within a pest population. Most recognised that the
pest could have an increased effect on the crop in a monoculture.
Hyde Clarendon Sixth Form College 20

21. (b) (i) The majority of candidates were able to identify that the ‘resistance’ allele is
recessive, that the parents would therefore be heterozygous, and that the resistant
offspring would be homozygous recessive. Too many incorrectly referred to
mutations resulting in resistance.
(ii) Most candidates scored well with bioaccumulation and killing non-target
organisms being the most frequently seen correct responses. It was surprising to
see a significant number of candidates referring to the pesticide leaching into the
water and causing eutrophication.
27. (i) Most candidates gained credit for the fact that the fertiliser had leached into the river, but
only the more able explained that it is excess fertiliser that leaches in this way.
(ii) The vast majority of candidates scored highly by correctly recounting the standard
sequence of events in eutrophication.
28. No Report available for this question.
Hyde Clarendon Sixth Form College 21