Assessment: written papers
Notes about the 2005 specification provided by Edexcel.
For information about assessment of the new course starting September 2008 see Edexcel Biology 2008
Six written papers
There are 6 written papers taken under formal examination conditions, units SN1, SN2, and SN3/02 (practical review) at AS, and SN4, SN5/01, and SN6 (synoptic) at A2.
The remaining two units, SN3/01 (visit or issue report) and SN5/02 (investigation) are Coursework.
The importance of accurate recall
Accurate factual knowledge and sound understanding of the specification is just as important in SNAB as in any other A level Biology specification. In accordance with QCA requirements, 46% of the marks at AS and 35.5% at A2 are from recall. Some candidates who do well in context questions lose easy marks through inaccurate straight forward knowledge. But in SNAB knowledge is only the beginning of wisdom, a tool which oils the wheels of thinking. Accurate knowledge provides the starting point for context questions, and also a secure platform from which to make intelligent suggestions and deductions with confidence.
Putting ideas into words
Being able to do this is an important study skill that needs developing throughout a course and some candidates lose marks by being unable to do this in the examination. A question in 2007 (6132) which asked for an explanation of the difference between 'global warming' and the 'greenhouse effect' revealed that most candidates (rather vaguely) thought that the two terms meant the same thing. In January 2008 a question requiring an explanation of the term 'fluid mosaic' model revealed that many were not able to visualise what the diagram, which they knew how to draw, represented in reality. Another place where lack of ideas put into words may cost marks is in genetics questions. Many can do the punnet checkerboard (perhaps as a mechanical exercise) but a sentence at the end summing up in words and in the context of the question often secures at least one mark. A few other words explaining the steps in the conventional notice at strategic places can be useful in making for secure responses.
Questions based on core practicals
These questions reward what students have acquired through hands-on experience. They include the kind of down-to-earth practical details one remembers from actually having carried out the activity personally. The questions also test understanding by inviting the candidates to extend the core practical or to apply the techniques involved in a different context.
Contexts
The Salters-Nuffield Advanced Biology course lays emphasis on placing scientific knowledge in an ethical, social and technological context. The well-informed citizen continually updates knowledge of scientific issues from TV, newspapers or more specialist sources throughout his or her life. He or she makes sense of new information by relating it to an existing framework of knowledge, and uses this to re-evaluate where they stand on biologically-related issues. SNAB aims to develop these skills.
It is often helpful for students presented with an unfamiliar context to 'spot the spec' - to recognize the knowledge and understanding from the specification which underlies the question and then apply it to the unfamiliar. Any further knowledge the candidate actually needs to answer the question will be in the stem of the question. In a recent paper (6131, January 2008) there was a question about pectin, pectinase, cellulase and peeling oranges on an industrial scale. Cell walls and cellulose are dealt with in unit 2 - but the knowledge from unit 2 was not actually needed in this question. Pectin was introduced as a polysaccharide which was hydrolysed with the help of an enzyme pectinase. Polysaccharides and their hydrolysis, as well as enzyme action, are very much in the specification and this was what the question was really about. Having done the core practical on the properties of enzymes (which is in the unit) would have been a great help.
Demonstrating understanding through 'issues' questions.
All current A level biology specifications have to have a minimum of 15% the examination marks allocated to 'personal, environmental, economic, ethical, social and technological applications. In SNAB these kinds of 'issues' are clearly identified in the specification. Unit 1, for example, is very much concerned with risk, correlation and causality in relating diet to the incidence of heart disease and with respect to genetic screening. Unit 2 focuses on ethical issues related to stem cell research and environmental issues related to global warming and climate change. A2 units include issues surrounding zoos, evolution, the use of performance enhancing drugs, and the use of animals in medical research.
Candidates have the opportunity in the written examination to demonstrate not only relevant knowledge but understanding and ethical thinking skills. This is done by looking at issues in unfamiliar as well as familiar contexts which go beyond the traditional (and largely recall) - 'Give two advantages and two disadvantages of GM crops' or 'for and against stem cell research'.
Candidates may be presented with a scenario involving one or more such issues from the specification, together with the odd dilemma and some related unfamiliar information, and asked to express an opinion - for or against. Marks are awarded for the way they use their scientific knowledge to justify their point of view. We find that this approach (rather than give for and against arguments) brings more engagement with the context.
Candidates of a wide ability range who have taken part in class discussion and role-play exercises during their SNAB course not only cope well with this approach but appear to enjoy it! By having a range of alternative answers (both for and against), the mark scheme recognises that there is rarely a simple answer to important ethical, environmental and social questions.
The mark scheme recognises a progression in ethical thinking, particularly in the case of 6132 and the synoptic paper. In a 6132 ethical thinking question some marks can be gained relatively easily from type 1 and 2 responses (below) but to gain full marks it is usually necessary to include one or more of type 3, 4 and 5 reponses (below).
1 Recalls relevant knowledge in a familiar context e.g. some people regard embryonic stem cells as potential human individuals and therefore to use them in medical experiments is showing a lack of respect for human life.
2 Applies relevant knowledge in an unfamiliar context e.g. responds to extra information about using cells from the umbilical cord instead of embryonic stem cells.
3 'It depends' questions, e.g. 'is it ethically acceptable to keep animals in zoos?' - it depends how well the animals are treated.
4 Balancing ethical dilemmas, e.g. is the suffering of a few animals used in medical research justified if it alleviates the suffering of many humans?
5 In-built rebuttal - showing awareness of another point of view 'I agree that the use of animals in a lot of research (e.g. testing new kinds of cosmetics) represents unnecessary suffering but to refuse to sacrifice a few animals to prevent the suffering of millions of people is not ethically justified either'.
6 Too finely balanced to come down on either side. To argue this properly is a very high level skill which most candidates are advised not to not attempt. It is not recommended at AS although it might be very appropriate to gain one or more C marks on a synoptic essay.
A SNAB examination aims to discriminate in a range of skills throughout the ability range. Many of the marks in 'issues' questions are accessible to E grade students. However, to gain full marks, depth, context (of the scenario in the question) and the ability to cope with dilemmas are usually also required.
Marks for depth
Where a question asks for, for example, three differences between an ovum and a sperm for three marks and there are three lines on the examination paper it fairly clearly invites three simple short and snappy (in this case comparative) statements for three marks. But if the question asks for an explanation of, for example, the difference between climate change and greenhouse effect, leaves six lines and offers three marks it is inviting an extended and thoughtful response. It may be easy to get the first mark but to get the third it will need some depth and coherence.
Applying knowledge in a different context and making links
The SNAB course is context-driven. This is also reflected in the examination at AS as well as A2, with marks providing credit at different levels. Candidates are required to transfer knowledge from a familiar to a less familiar context, and to make new links between items of biological knowledge they already have. For students brought up in the SNAB tradition this is fun - new links for old is one of things that makes biology so interesting.
For example, in topic 2 of the SNAB AS course, the fluid mosaic model, membrane function, genetics, and discussion of gene therapy are not presented as separate items, but woven together around the theme of cystic fibrosis.
As an example, hazel nuts
An example of a thematic question (January 2004) was built around hazel nuts. It had sub-sections on seed dispersal, lipid as an energy source for germination, protein synthesis to make enzymes (for germination), and switching on the gene in response to environmental stimuli to make the enzyme (needed for germination).
All the information came from one unit (SN2) and most marks were accessible to students answering each subsection in isolation (as straight-forward recall). But to gain full marks a student had to make some new connections. The squirrel disperses a hazel nut, and the stored lipid provides energy for germination when exposure to cold has switched on the gene to make the RNA to produce the necessary enzymes to mobilise the lipid. A SNAB student would think 'isn't that interesting?' rather than 'not fair - we haven't done hazel nuts' !
