AQA A2 Biol4 January 2012 pre- exam discussion

peeps, the Unit 4 June 2011 paper is online- thank the guy who posted
it

http://http://www.thestudentroom.co.uk/showthread.php?t=1864988

Hmm, you guys are starting to freak me out! I've found unit 4 overall the easiest of the biology units so far.. I also take environmental studies and basically all of it apart from photosynthesis and respiration I've already done in it...
However i am only going for a B unlike most of you so maybe it's more approachable for me.. Got CCB in as. After resitting my as isa I'm at ABC which is nice, resitting unit 1 in jan hopefully securing my B. luckily got the mark for an A with my a2 Isa first time thank god.. Took 3 tries in as haha! Now just need to nail this exam

Hey.. Just got confused in a question.
It's on the Jan 2010 paper where it asks "1d) What type of natural selection is shown in the graph?'
The answer is 'stabilising' but I havn't been taught anything about that. What other types are there?
Thank you

Stabilising and directional are the ones that we've been taught - stabilising favours the average alleles and directional favours one extreme of the phenotype so that the mean shifts towards the extreme. There's also one other that I came across but I can't remember the name now (something like inverted) where both extremes are favoured, either side of the mean. The ones you need to know should be in your textbook

Stabilising and directional are the ones that we've been taught - stabilising favours the average alleles and directional favours one extreme of the phenotype so that the mean shifts towards the extreme. There's also one other that I came across but I can't remember the name now (something like inverted) where both extremes are favoured, either side of the mean. The ones you need to know should be in your textbook

theres also disruptive or destructive one of the two cant remember exactly which one , but i dont think we need to know about it for this board

june 2010 was a horrible paper

Stabilising and directional are the ones we need for Bio.

Stabilising is where the environmental conditions favour the average phenotypes of the species, for example if wolf fur range from 5-25mm in the arctic and the optimum fur length is 17mm the average fur length would be around 17mm as the selection is stable.

Directional is where a change happens in the environment, to continue my example say the temperature drops by 5*C which shifts the optimum fur length from 17 to 22mm, at first the ones with the shortest fur will die, and then through natural selection the longer furred wolves will reproduce increasing the amount of wolves with 22mm fur as this phenotype is more adapted to survival so the allele for 22mm fur becomes more common and before you know it the average fur length has change to 22mm so the mean has shifted- directional selection.

Typed this out on my phOne, hope it helps!

Dont understand Hardy-Weinberg principle or equation D:

Yes, it's in the specification. What do you mean by official material? I have no idea if there is content which can teach you HSW, maybe someone else might know if there is...

i dont know about hsw stuff, thats kind of juts going through the papers and seeing what comes up. i think there is a little bit in the cgp revision guide about interpreting data which is sort of the hsw things. but for the statistical tests you learn all of that stuff for the isa, this year. i did it a couple of weeks ago and we learnt:
-standard deviation + standard error
-spearmans rank
-chi squared

we covered them a little last year aswell before breaking up in year 12, so maybe there should have been some covering of them in class?

hope that helped good luck in the exam.

can we be asked to calculate kai sqaured and spearman ranked in unit 4? or do we only need 2 know about null hypothosis? thanks

How does everyone think the grade boundaries will be? Ive been doing past papers and getting a B at only 55%, which seems odd, do you think they will be that low this time round?