The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

A2 Biology OCR June 2015 Revision Thread

Scroll to see replies

Original post by AnnekaChan173
I just started doing practice questions and I'm suddenly ****ting myself
I know nothing


for unit 4 or 5?
Reply 221
Avatar for Hmht
Hmht
2
Original post by AnnekaChan173
I just started doing practice questions and I'm suddenly ****ting myself
I know nothing


Hahaha I know they exactly how I feel with the second exam xD I think 'yes I know this, let's do this!!!' Then open and exam paper up.... and cry a little :P
Original post by Hmht
If i do a simple version with a lack of detail for you just to sum up the key points:

PCR- only amplifies (produces many copies) of DNA. They can only be short pieces though. For example DNA found at a crime scene need to be sequenced by there is not enough to do that, so PCR is ran and now we have enough to sequence it.

Electrophoresis - Once some genetic material has been broken up to study (and maybe amplified by PCR if there is not enough to break up and study by its self) then this is used to separate out the fragments of DNA by size. This is because the DNA fragments have a slight negative charge and move towards the positive electrode.

If you want more detail then I'm happy to provide it but that just covers the key ideas/basics of what they do :smile:


Thank you!! :biggrin:

What about interrupted PCR? How does that differ from normal PCR?
Original post by Hmht
Hahaha I know they exactly how I feel with the second exam xD I think 'yes I know this, let's do this!!!' Then open and exam paper up.... and cry a little :P

ME EVERY YEAR, especially C2 sweet Jesus that was a ****ty exam for me


Original post by games211
That's because, as you said, you haven't finished everything yet :tongue:

But I've finished cellular control... :frown: I haven't fully revised it but we've done it at school

Original post by corey7695
for unit 4 or 5?

Unit 5, which is seriously bugging me because we have so little time left and eugh I'm so done
On the biotechnology page, 158-159, are we expected to know all the examples in that table or just a few? Thanks!
Reply 225
Avatar for Hmht
Hmht
2
Original post by 96akhan
Thank you!! :biggrin:

What about interrupted PCR? How does that differ from normal PCR?


Interrupted PCR combined with electrophoresis is the new modern way to sequence DNA :smile: Lets say you had a piece of DNA that was 100 base pairs long and you wanted to sequence it. You will do PCR however some of the free nucleotides you add are modified to a) contain a fluorescent marker (different colours for each base - A T C G) and b) have an extra bit added on to knock the DNA polymerase off (hence the name 'interrupted PCR'), stopping it from adding anymore nucleotides to the chain. This means when PCR is done the entire piece will be amplified accept for one key difference. One of these modified bases will join at base 1 of one piece of DNA, the next joins at say base 23 and the next at base 40 and so on... This happens until there is a modified on each of the 100 bases but only 1 modified bases can join to one piece of DNA (a minimum of 100 pieces of DNA will be needed to sequence a piece of DNA that is 100 bases long if that make sense). If the modified base joins at base 40 then the interrupted PCR will amplify the first 40 bases pairs until the DNA polymerase is knocked off. If it was joined at base 75 then the first 75 bases would be amplified - you get the idea :smile:
Now the Mixture contains different lengths of DNA all with a modified fluorescent marker at the end. Electrophoresis can then be used to separate them out into size order. These are then passed through a computer and it reads the colours that pass through (the shortest piece of DNA will pass through first because of the electrophoresis) and because each bases is a different colour it can match them up and say what each base is :biggrin:
say A=red, G=green, T=blue and C=black and the sequence went -

blue blue blue red green blue black black green

then the computer can tell you the sequence is
T T T A G T C C G .
This would happen for all of he 100 hundred bases and it will provide the full sequence for you :smile: There is a really good picture showing this in the A2 heinemann text book on page 173 if you have it :smile:

Hopefully it makes sense, its really hard to describe it by typing and not talking/ with diagrams :P
Reply 226
Avatar for Hmht
Hmht
2
Original post by CamilleClarke
On the biotechnology page, 158-159, are we expected to know all the examples in that table or just a few? Thanks!


I don't think we have to know many specific examples (might be wrong) but i would remember one from each of those boxes incase you do get asked :smile: If you do then i could see a question worth a couple of marks saying " define the term biotechnology and provide an example" then you could just put cheese making or insulin production from E.coli or something, as well as the definition of course :smile:
Original post by Hmht
I don't think we have to know many specific examples (might be wrong) but i would remember one from each of those boxes incase you do get asked :smile: If you do then i could see a question worth a couple of marks saying " define the term biotechnology and provide an example" then you could just put cheese making or insulin production from E.coli or something, as well as the definition of course :smile:


Thank you very much! Remembering one from each box seems reasonable !
Reply 228
Avatar for Kell_
Kell_
2
It's strange how the spec makes particular reference to ATP synthase in the note about chemiosmosis rather than that of oxidative phosphorylation?

"Outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATP synthase"

I wouldn't have felt it necessary to mention ATP synthase when talking solely about chemiosmosis, it's really just the generation of the pH gradient, right?
Reply 229
Avatar for Hmht
Hmht
2
Original post by Kell_
It's strange how the spec makes particular reference to ATP synthase in the note about chemiosmosis rather than that of oxidative phosphorylation?

"Outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATP synthase"

I wouldn't have felt it necessary to mention ATP synthase when talking solely about chemiosmosis, it's really just the generation of the pH gradient, right?


yes i agree with you however they could ask for an example and the only one we study is with ATP synthase :smile:
Reply 230
Avatar for Kell_
Kell_
2
Original post by Hmht
yes i agree with you however they could ask for an example and the only one we study is with ATP synthase :smile:


Cheers I'm glad I'm not the only one that found it a bit weird.
Have so much to do, who's started past papers?
Also can someone explain genetic drift to me :s-smilie:
Reply 232
Avatar for acd55
acd55
11
Original post by PinkElephant16
Have so much to do, who's started past papers?
Also can someone explain genetic drift to me :s-smilie:


Genetic drift is basically a random change in allele frequency in a small population
Like its the idea that because a population is small if some organisms die randomly, it can drastically change the allele frequency if they have recessive alleles or something because the population is small, you could lose a variant completely
It's why if you use the hardy Weinberg principle thing you need to make sure there isn't genetic drift
Sorry it's hard to explain!



Posted from TSR Mobile
Anybody have good condensed notes for f215 pleassssssssse :frown:
Original post by games211
Anybody have good condensed notes for f215 pleassssssssse :frown:


haha even the condensed notes for this beast of a unit will be thick enough to stop doors
Original post by corey7695
haha even the condensed notes for this beast of a unit will be thick enough to stop doors


-laughter descends into sobs-
It's actually ridiculous how big it is. Grade boundaries have to be low. I'm begging at this point.
Original post by corey7695
haha even the condensed notes for this beast of a unit will be thick enough to stop doors


hahahahaha :smile:
Original post by AnnekaChan173
-laughter descends into sobs-
It's actually ridiculous how big it is. Grade boundaries have to be low. I'm begging at this point.


Well it was only 63/100 for an A last year, not too bad really. Assuming we own the unit 4 exam it should be plain sailing (I'm lying to keep up moral, we're all gonna fail)
Original post by corey7695
Well it was only 63/100 for an A last year, not too bad really. Assuming we own the unit 4 exam it should be plain sailing (I'm lying to keep up moral, we're all gonna fail)


in high c02 concentration why is Rubp conc low?
Original post by corey7695
Well it was only 63/100 for an A last year, not too bad really. Assuming we own the unit 4 exam it should be plain sailing (I'm lying to keep up moral, we're all gonna fail)


Oh wow I feel like I might not fail wow 63 for an A I can do this
Maybe
I think

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you