UNIT 1

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  • Created by: gifty
  • Created on: 17-12-12 20:26

EXAMINERS COMMENTS

CARD 2: Candidates need to know that they can be asked to draw out the structures of the molecules named in the specification. Although these diagrams need to be biochemically accurate in terms of the positioning of the  H or OH groups, they can be sketched and don’t need to have the quality of a computer print out. The structure of starch was generally well-described in

 CARD 3 :but only the more able candidates extended their account to describe why the structure made starch a suitable energy-storage molecule. Candidates need to understand that a question needs to be answered in its entirety in order to access full marks; in this case, the full four marks could not be awarded if the candidates had only described the structure of starch. A common error was to refer to energy and not glucose in marking points 4 and 6.


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CARD 4:but only the more able candidates extended their account to describe why the structure made starch a suitable energy-storage molecule. Candidates need to understand that a question needs to be answered in its entirety in order to access full marks; in this case, the full four marks could not be awarded if the candidates had only described the structure of starch. A common error was to refer to energy and not glucose in marking points 4 and 6.

CARD 5:Part (a) generally scored well - except for those candidates who used the expressions waterhating and water-loving. These are excellent  aides memoires but do not score marks unsupported. Grade E candidates would generally comment on the polar heads and non-polar tails and the better candidates would then link these properties of the molecule to their orientation in the membrane.

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CARD 6:In (a), many of the diagrams were sloppily drawn and the label lines carelessly positioned. Although we did not expect three-dimensional drawings, we did expect the drawings to be representative of the biology so that, for example, the vessel wall would be wider than the diameter of the lumen and the diagram would indicate the number of layers present

CARD 7: Part (b) was poorly done by many candidates who failed to appreciate that each component of the vessel wall is present for a different reason. Every structure and function came across as being interchangeable. For example, there were many descriptions of the elastic fibres and smooth muscle cells ‘contracting and relaxing’ to increase and maintain the pressure of the blood. Candidates need to learn to write one fact in one statement to avoid such ambiguities

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CARD 8:  . In (c), many responses did not actually state differences between the vessels but instead stated facts about one vessel or the other. A surprisingly high number of responses compared veins with arteries. Only the more able candidates scored well in this part and the previous part of the question.

CARD 8: were not so high scoring, except by the more able candidates; the topic of these question parts is new material in the specification

CARD 9: correlation was confused with causation (not surprisingly)

CARD 10: A surprisingly high number of candidates named RNA polymerase as the enzyme

CARD 11 : Candidates who chose to describe amniocentesis in (a) generally scored well. However, embryos were found in some odd places (such as the stomach), amniotic fl uid was withdrawn from the embryo and DNA was free floating in the fl uid! Candidates describing chorionic villus sampling did less well, even at the A grade boundary. A very common mistake was to refer to the method as chronic villus sampling and there was little understanding of the actual location of the fetal tissue. Weaker candidates described preimplantation techniques

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CARD 12:There was good understanding of the benefits of prenatal testing. The majority of candidates understood that there were risks and ethical issues surrounding the technique, but failed to score well for one of two reasons. Firstly, especially at the E boundary, there was confusion over what constituted a risk and what an ethical issue. Secondly, across the ability range, answers were poorly worded or too vague. Hopefully, with the publication of the mark scheme, candidates in the future will be able to phrase their answers to similar questions more eloquently.

CARD 13 : 'rights to live, very typica; response'

CARD 14 : In (b), a large number of high scoring responses was seen, although few candidates appreciated that the valves were open during diastole. Marks were lost by the weaker candidates who failed to specify clearly at which stages in the cardiac cycle events were occurring

CARD 15 : The defi nitions given in (a) for causation and correlation were very disappointing, despite the fact that we asked for the defi nition of correlation in January. There was the expected confusion between the two terms and there were a lot of defi nitions where the candidates were using the words themselves in the defi nitions. Other frequently seen mistakes included using the words thing or data instead of variable or factor and not mentioning that there is a change in variables involved. A number of candidates gave specific examples, some of which were very imaginative, but did not give a generic definition

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CARD 16 :Candidates have a good knowledge of the development of atherosclerosis. The grade E candidates generally scored two or three marks and the grade A candidates 4 max. Mistakes that were made included reference to fatty deposits for mp 4, the build up of plaque (as on teeth) for mp 6 and reference to the hardening of the arteries for mp 7.

CARD 17 :It was clear that some candidates had not covered the vitamin C practical in very much detail. Weaker candidates, who had covered the practical, scored marks for details of the vitamin C assay but could not apply their knowledge to the actual question scenario.

CARD 18 : Defi ning the terms again caused problems to candidates, especially gene and allele. Genes were frequently described as something that codes for our characteristics and alleles as types of gene.

CARD 19 : okay

CARD 20 : The fi nal part of this question must have appeared too straightforward to some candidates as there were some very long and complicated answers. The weaker candidates simply rewrote the information shown in the equation.

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CADRD 21 :If (a) had been well answered we could have made the comment that candidates knew the meaning of the term, but had no understanding of the process. However, very few candidates could clearly explain the meaning of the term, giving vague statements that did not clearly indicate what concentrations they were referring to. This is illustrated in the response below that could only be awarded mp 1.

CARD 22 : marks  were generally scored in this question

CARD 23 : very few candidates who tried to discuss the use of a rule could actually explain why it would be less accurate than a balance

CARD 24 : N/A

CARD 25 : N/A

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Comments

gifty

I'll upload the flash cards that go with this 

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