Firstly a big well done to Year 13 Human Biology. I thought the test was quite challenging but there were some great marks and none less than a pass (Grade D) so I was really happy with that. Another thing that struck me about the areas where we had difficulty is that a lot of the time it was just factual recall stuff. For example, using the term ligase instead of restriction enzyme. Here is the question by question by question break down. Follow the hyper links to find videos, revision notes and diagrams to help you understand where you went wrong.
A well answered question. The only marks dropped were factual recall – not being able to name reverse transcriptase as the enzyme that makes single stranded DNA from mRNA (a part ii).
Part (a): most of us could describe the features of a gene which enable it to code for a protein – things like: it has a specific sequence of bases that form codons that code for amino acids and the order of bases gives the order of amino acids in the final protein etc.
Part (b) The question about enzymes and vectors was out of six marks so you had to think of six separate things to say about enzymes and vectors – these should have included something about restriction enzymes, DNA ligase and plasmids – two points about each would have gained you full marks. This is where I noticed that people were getting ligase, polymerase and restriction enzymes mixed up.
Make sure you know what each one is and what it does.
Part (c): a big 7 mark question requiring nothing more than factual recall. If you got this in an exam then you would be thrilled to bits because you don’t need to do any working out – just regurgitate transcription and translation! Most of us got between 3 and 5 marks on this through a mixture of misinterpreting the question or through poorly ordered descriptions which was due probably to a lack of revision. Memorise the details!
3. A question about DNA fingerprinting. We need to do some more work on DNA probes and I don’t think anyone got the question about why the probes need to be radioactively labelled.
4. Most of you found this a difficult question, primarily because it was a scenario that you were unfamiliar with. The use of agrobacterium isn’t something that we’ve studied in the classroom but then it’s not on the specification. So why ask a question about it? Because the exam board test your knowledge of biological principles by providing you with novel situations to test your knowledge on. What’s the biological principle here? It is that you can transfer a gene into a plasmid and that plasmid acts as a vector.
Part (a) was simple factual recall – you had to know what ligase and restriction enzymes do. It is essentially the same question as 2(b). Just describe the process.
4 (b) was a synoptic question where the examiner brings together content from different parts of the course to check that you can make links between what you learn in one topic and what you learn in another. This question was about mitosis. All the plant cells have the same DNA because they’re produced by mitosis – in effect they are clones of each other. So if the foreign gene has been introduced into one cell and all the other cells are formed from mitosis of that one cell – well, they’ll all have the gene!
Part (c i): this was a question about replica plating. The antibiotic genes are genetic markers.
Part (c ii): genetic markers are not needed because the gene that’s being inserted in this question is a pesticide resistance gene. Any plants that don’t incorporate the gene will be killed. So no need to select the transformed ones with an antibiotic marker.
Part (d): we could all name a benefit though some of use neglected to explain what the benefit was. We struggled to suggest problems though. Things like the resistance gene being transferred to weeds because of cross pollination are an example of a problem.
caused problems with the class average as 1 mark out of 4. The mark scheme wanted you to go further than just explaining that the fragments move. You need to be able to say what the next steps of the process are after the fragments have moved. How do you detect where the fragments have moved to?
The other parts of question 5 were well answered including part (b), the long six marker at the end of the test. Well done for not getting thrown by the fact that it mentions a protein we haven’t studied.
Here’s the test and markscheme.
I am editing this in Starbucks in Sheffield and have forgotten to bring my power pack. Will update the post with more links and videos later tonight but you should have enough to keep you busy for a while!