A2 Biology OCR June 2015 Revision Thread

Thanks, do you know which papers would be the best ones to look over or do before the exam to prepare??

Maybe do those two? Since they're the harder ones you should be okay if you're doing well on those try and fit in three at least I'd say

Sequencing the genome involves PCR and Electrophoresis, so as long as you describe and explain these two processes you should get the marks.

I did them and just managed to scrape A's in both by one or two marks, so I will do a bit more revision, and then try some of the other papers, thanks though

So no mentioning of BACs ??

do you want everything explained? i might just type it out since its good for my revision
so, selective reabsorption takes place in the PCT. The cells lining the PCT are well adapted for uptake of all glucose and all amino acids, some salts and most of the water. This is what happens:
- Na/K ion pump actively transport sodium ion out of cell and potassium ion into cell. This reduces the conc of Na+ in the cell
- Sodium ions are then reabsorbed through co-transporter proteins by facilitated diffusion along with glucose and amino acids
- As glucose and amino acids travel along the cell, they are removed by diffusion and active removal from the opposite side of the cell into the tissue fluid and then into the blood where they are carried away
- The conc of glucose and amino acids inside the cell lowers the water potential inside the cell so the tubule fluid has a higher water potential so water enters by osmosis.
- The larger molecules like small proteins enter by endocytosis

do you want stuff on loop of henle/dct etc?

Hey guys, I retook unit 1 and 2 this year, so if I get a B in unit 1 and 2 and for the CAT i got an A, and then for f214 if I get an A and for F215 if I get a low B, wwhat grade would I get?

Consireding I've gotten A in both controlled assesment and hoping for high A in f214...

How would i answer "outline the sequencing of a genome " i have no clue how to and people are banging on about BACs which ive never heard of , Help me Please !!!!!!

BACs is used when overlapping regions are analysed and put back together to form a complete code. Genome maps allow identification of the location that the BAC (Bacterial Artifical Chromosome) has come from

Cant i just use the chain termination method ??

Just to further ease your mind we don't actually need to know an example, just the definition <img src="images/smilies/smile.png" border="0" alt="" title="" smilieid="1" class="inlineimg" />

So no mentioning of BACs ??

Well it make a physical map of the whole genome before sequencing the DNA. Constructing a map requires cutting the chromosomes into large pieces and figuring out the order of there large chunks of DNA before taking a closer look and sequencing all the fragements. So it's more or less you would do it before chain termination I assume

Ahh finally makes sense , so I firstly go on about mapping the genome + role of BACs and then extracting DNA , use if R enzymws to cut DNA , then electropheresis to seperate DNA fragments by size and THEN the chain termination method and then use of computer to read the base sequence etc ... Sorry for the many Qs, this is my most diffucult topic

Yes we do? There was an example of it in a paper once about low oxygen levels causing higher breathing rate.

Easiest example of positive feedback is blood clots

Yes because the genome has to be fragmented before sequencing because its too large and theres more or less better accuracy with smaller fragments! haha dont worry we've all been there

Ahh finally makes sense , so I firstly go on about mapping the genome + role of BACs and then extracting DNA , use if R enzymws to cut DNA , then electropheresis to seperate DNA fragments by size and THEN the chain termination method and then use of computer to read the base sequence etc ... Sorry for the many Qs, this is my most diffucult topic

Which paper? You need to be able to recognize if something is an example of positive feedback but you'd not be asked to name an example.