Aqa Biol2 Wre Jun13

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GCE

BIOLOGYBIOL2 The variety of living organisms

Report on the Examination

2410

June 2013

Version: 1.0


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Further copies of this Report are available from aqa.org.uk

Copyright 2013 AQA and its licensors. All rights reserved.AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from thisbooklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy anymaterial that is acknowledged to a third party even for internal use within the centre.


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REPORT ON THE EXAMINATION GCE BIOLOGY BIOL2 JUNE 2013

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produces haploid cells. Similarly, some students drew chromosomes consisting of two chromatidsjoined by a centromere.

(b) (iii) Most students gained this mark for crossing over or genetic recombination. The mostcommon response that failed to score was random fertilisation.

Question 2

This question was targeted at grade E. It is again surprising that all parts proved to be gooddiscriminators.

(a) Two-thirds of students gained full marks. This was usually for mentioning that organisms ofthe same species can produce fertile offspring. However, some students failed to gain the mark forreplacing the word fertile with viable.

(b) (i) Seventy percent of students correctly calculated the index of diversity within the range of6.97 to 7. Of the other thirty percent, most gained one mark for calculating a correct numerator ordenominator.

(b) (ii) Nearly all students gained at least one mark, typically for fewer habitats. Similarly,reference to pesticides or machinery decreasing species diversity was common. Compared withthe previous series, it was pleasing to see a greater percentage of students refer to less foodsources or less variety of food, rather than simply less food. Relatively few students linkedclearing the forest to a reduction in the number of plant species.

Question 3

Parts (a)(i), (a)(ii) and (b)(i) proved to be good discriminators.

(a) (i) One-third of students were aware that a hierarchy contains groups within groups, with nooverlap. However, the no overlap concept was often missed. Similarly, it was disappointing thatnearly forty percent of students failed to score, considering that a simple definition from thespecification was required. Weaker responses often referred to the idea of ranking, dominance orimportance. There were also some very confused responses, which focused on predators andprey in the context of a pyramid of numbers.

(a) (ii) Half of students were aware that a phylogenetic group is based on evolutionary links or

history. Students who failed to score often focused on one syllable of the word phylogenetic.Consequently, the responses a group within a hierarchy and has similar genes were often seen.

(b) (i) Almost all students scored at least one mark for recognising that animalAhas the leastnumber of differences in the amino acid sequence. However, the ability to go back one step andrelate this to a similar DNA sequence discriminated well. Weaker responses often lacked detail, egsimilar DNA and similar genes. Similarly, a minority referred to the amino acid base sequenceor thought that DNA is made of amino acids.

(b) (ii) Most students gained the mark for recognising that the amino acid sequences werecompared with humans or not with each other. Fewer mentioned that different amino acids may beaffected in each sequence. Similarly, responses that referred to the degeneracy of the genetic

code were rare. Weaker responses usually relied on vague, stock How Science Works phrases inrelation to possible flaws in the methodology. They usually referred to a lack of repeats, the


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inability to control certain variables or the absence of a control group. Again, a minority of studentsconfused DNA and protein structures.

(b) (iii) One-third of students were aware that all organisms respire, or that fewer organisms havehaemoglobin. Some were given benefit of the doubt in terms of haemoglobin structure varyingmore due to the environment. This was accepted in terms of evolutionary change, rather than theeffects of pH or pCO2. Students who made a direct reference to these factors causing thestructure of haemoglobin to vary more did not gain credit. Weaker responses often stated thathaemoglobin would vary less than cytochrome c, or that cytochrome c was the same in allorganisms.

Question 4

(a) This proved to be a good discriminator. Most students were aware that DNA helicase

separates strands or breaks hydrogen bonds. However, only better responses went on to statethat this allows nucleotides to attach or the strands to act as templates. Unfortunately, poorexpression or a lack of precision let down some students. This was usually for DNA splitting, orbases, rather than nucleotides, attaching.

(b) Just under half of students gained full credit.

(c) (i) This proved to be a good discriminator. A quarter of students scored full marks. Most wereaware that cytarabine has a similar structure to cytosine. However, weaker responses were oftenvague regarding the subsequent effect of this, eg prevents DNA replication or inhibits helicase.Similarly, there were many unqualified references to cytarabine acting as a competitive inhibitor. Itwas only the best responses that suggested cytarabine may prevent base pairing, prevent the

formation of a new strand or act as an inhibitor of DNA polymerase.

(c) (ii) Just over seventy percent of students were aware that cancer cells divide faster thanhealthy cells.

Question 5

(a) (i) Just over sixty percent of students could give one way in which antibiotics prevent cellgrowth. This was usually for the idea of preventing cell wall formation or causing cell lysis. Therewere very few references to inhibiting ribosomes or protein synthesis. Students who failed to scoreoften gave vague responses about immunity, enzyme inhibition and mitosis.

(a) (ii) Just over sixty percent of students related vertical gene transmission to cell division orreproduction. Unfortunately, some could not be awarded this mark because they wrote thatbacteria divide by mitosis. Responses that failed to score usually lacked detail or were out ofcontext, eg resistance is passed on genetically and genes are passed on when the hostreproduces.

(b) Two-thirds of students were aware of the need for a representative sample or that there couldbe different types of the bacterium. Again, weaker responses usually lacked detail, eg becauseyou want to kill the bacteria and because this is the hospital being studied.

(c) Most students were aware that hypochlorite produced the highest mean diameter of clear

zone. However, the ability to interpret standard deviations correctly proved to be an excellentdiscriminator. Weaker responses usually went no further than to state that hypochlorite was themost effective due to it having the highest standard deviation. It was only the best responses thatappreciated the importance of the overlapof standard deviations between hypochlorite and


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Question 9

(a) Most students scored at least one mark. This was usually for suggesting that the age orspecies of snake should be kept constant. Weaker responses were often vague and referred tothe environment or health of the snakes.

(b) Nearly all students gained this mark for the idea of reducing bias. Weaker responses usuallyrepeated information given in the question stem or contained stock How Science Worksphrases.References to random results, increased accuracy, increased reliability and the need for a fair testwere common.

(c) Just over forty percent of students were aware that using different male snakes for each trialwould provide a more representative sample, minimise changes to future courtship behaviour orcause less distress to the snakes. Weaker responses usually referred to increased reliability,

increased sample size, calculation of a mean, identifying anomalies and finding out if the resultsare due to chance.

(d) Just under half of students gained this mark for stating that filter paper without lipids would actas a suitable control. Responses that failed to score often mentioned using lipids from malesnakes or from other snakes. A minority of students referred to using plastic snakes or a placebo.

(e) It was disappointing that only one-quarter of students scored at least one mark. Many simplystated the converse of information given in the question stem. Consequently, the response thesnakes showed less courtship behaviour towards short female snakes was widespread. It wasonly the very best responses, which noted that courtship behaviour to whole snakes was similar tothat of lipids alone. However, relatively few then went on to explain this observation in terms of the

snakes responding to lipids, rather than whole snakes or visual clues. Some students simplystated that long females must be more fertile.

(f) Nearly one-third of students gained two marks. This was usually for the idea that longerfemale snakes would be better at protecting their young or produce longer offspring. Very fewstudents mentioned that longer female snakes may be more sexually mature or have more foodstores for offspring.

(g) Just over forty percent of students gained full marks. Many students were aware that longfemales produce more fatty acids or mentioned the positive correlation. However, relatively fewdirectly stated that the snakes respond to fatty acids. Some students simply repeated information

in the question stem and linked longer females to greater courtship behaviour.

(h) Over half of students gained full credit for mentioning drawing a line of best fit andextrapolating from, or extending, this line. A minority of students suggested drawing a line up from75 cm, or working out a value based on the data given.

(i) It is disappointing that many students failed to score. There were many vague comments aboutthe results varying and the line of best fit being an estimate. However, better responses wentfurther in terms of the results varying for a particular body size, or noting that values overlapped.Similarly, some students noticed that the data may plateau or reach a maximum after 75 cm. Thiswas also credited.

(j) It was disappointing that many students failed to score. Some referred to lipids, rather thanfatty acids. However, many did not use the information provided in the question stem. They


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typically stated that courtship is species-specific, or that male snakes are only attracted to certaincolours, banding patterns or smells.

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
http://www.aqa.org.uk/exams-administration/about-results/results-statisticshttp://www.aqa.org.uk/exams-administration/about-results/results-statisticshttp://www.aqa.org.uk/exams-administration/about-results/uniform-mark-scale/convert-marks-to-umshttp://www.aqa.org.uk/exams-administration/about-results/uniform-mark-scale/convert-marks-to-umshttp://www.aqa.org.uk/exams-administration/about-results/results-statistics

Aqa Biol2 Wre Jun13

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