A2 Biology OCR June 2015 Revision Thread

Which Unit/Topic is the most effort/worst to learn?

Reply 362

ChoccyPhilly

13

Original post by frozo123

Which Unit/Topic is the most effort/worst to learn?

Anything and everything on ecology.It's just so boring and monotonous and I can't seem to do the apply questions at all. At least the harder topics are interesting.

Reply 363

Original post by ChoccyPhilly

Anything and everything on ecology.It's just so boring and monotonous and I can't seem to do the apply questions at all. At least the harder topics are interesting.

what are the "harder" topics you are talking about?

Reply 364

AnnekaChan173

18

Original post by smozsolution

That was so me last night when I finished my cellular control notes which took me forever and then I realised I still have the rest of unit 5 to go.

I'm going on a gap year but for what I want to do I need at minimum AAA-AAB. I need an A, but the only way for me to get that A (without retakes) is by getting two A*s in the exams :s-smilie:

I'm going on a gap year too! Did you get a B last year? I'm sure it's not that bad is it? What was your UMS?

Original post by frozo123

Which Unit/Topic is the most effort/worst to learn?

Biotech and DNA tech etc for me. Awful. I put it off for a while because I didn't want to look at it

Reply 365

sarahelizabeth18

Original post by Hmht

Mainly did revision for the first exam ready for mocks last January and a lot has stuck in my mind :smile:

Posted from TSR Mobile

You're so lucky! I'd forgotten so much, as I'd pretty much crammed for the mock - probably not advisable to cram for the real thing :tongue:

Reply 366

ChoccyPhilly

13

Original post by AnnekaChan173

Biotech and DNA tech etc for me. Awful. I put it off for a while because I didn't want to look at it

Aww that bits the best bit! I have no idea how Im going to answer the questions but it's the most interesting stuff we've done thus far, IMO
What subject are you doing at uni?

Original post by frozo123

what are the "harder" topics you are talking about?

Not necessarily harder but the more in depth and detailed chapters, such as gene tech and any of the 3 from unit 4

Reply 367

Original post by ChoccyPhilly

Aww that bits the best bit! I have no idea how Im going to answer the questions but it's the most interesting stuff we've done thus far, IMO
What subject are you doing at uni?

Not necessarily harder but the more in depth and detailed chapters, such as gene tech and any of the 3 from unit 4

Ah cool gonna be doing genetech tomorrow
I love every topic in Unit 4haha

Reply 368

Original post by AnnekaChan173

I'm going on a gap year too! Did you get a B last year? I'm sure it's not that bad is it? What was your UMS?

Finally someone else who is! Got any plans for your gap year?

I did yeah, it was 229 UMS. This was what I was saying a while ago, I only need just A*s in terms of marks, as opposed to full UMS. So it's somewhat doable, it'll just be really hard work.

Reply 369

Original post by smozsolution

Finally someone else who is! Got any plans for your gap year?

I did yeah, it was 229 UMS. This was what I was saying a while ago, I only need just A*s in terms of marks, as opposed to full UMS. So it's somewhat doable, it'll just be really hard work.

You can help me outtt
what is sex linkage? how would you work out sex linkage genetic questions out?

Reply 370

Original post by frozo123

You can help me outtt
what is sex linkage? how would you work out sex linkage genetic questions out?

Haha, can I?

Sex linkage is where a genetic disorder will be dependent on the gender of the individual and will be associated with the sex chromosomes. An example of this that is in the textbook is haemophilia. Haemophilia only affects males as it's on the X chromosome and as you know, males are XY. Women are XX so are either normal (not having haemophilia) or are carriers of haemophilia.

To work out a sex linkage genetic question you can draw a dihybrid cross of the female and male you cross to work out the offspring's genotypes and phenotypes.

Hope this helps :smile:

Reply 371

AnnekaChan173

18

Original post by smozsolution

Finally someone else who is! Got any plans for your gap year?

I did yeah, it was 229 UMS. This was what I was saying a while ago, I only need just A*s in terms of marks, as opposed to full UMS. So it's somewhat doable, it'll just be really hard work.

You were really close, don't worry! Pretty sure you don't need A*s in the papers to come out with an A with your UMS being that high. As long as you get mid high As you should be fine :') I'm volunteering and working in mine (hopefully as a porter or Hca, not sure yet) and then hopefully I'll go travelling after. You?

Original post by frozo123

You can help me outtt
what is sex linkage? how would you work out sex linkage genetic questions out?

Original post by smozsolution

Haha, can I?

Sex linkage is where a genetic disorder will be dependent on the gender of the individual and will be associated with the sex chromosomes. An example of this that is in the textbook is haemophilia. Haemophilia only affects males as it's on the X chromosome and as you know, males are XY. Women are XX so are either normal (not having haemophilia) or are carriers of haemophilia.

To work out a sex linkage genetic question you can draw a dihybrid cross of the female and male you cross to work out the offspring's genotypes and phenotypes.

Hope this helps :smile:

Almost. Not necessarily - males are more likely to be affected than females because they lack another X chromosome, but say if you had a carrier mother and an affected father, you can have affected females too. Generally sex linked disorders are X linked - found on the X chromosome since it is larger than the Y. So to be affected, the person needs to have either two affected X alleles(female), or one affected X and a Y(male). Punnet squares are how I get by with genetics.

(edited 9 years ago)

Reply 372

Original post by AnnekaChan173

You were really close, don't worry! Pretty sure you don't need A*s in the papers to come out with an A with your UMS being that high. As long as you get mid high As you should be fine :') I'm volunteering and working in mine (hopefully as a porter or Hca, not sure yet) and then hopefully I'll go travelling after. You?

Almost. Not necessarily - males are more likely to be affected than females because they lack another X chromosome, but say if you had a carrier mother and an affected father, you can have affected females too. Generally sex linked disorders are X linked - found on the X chromosome since it is larger than the Y. So to be affected, the person needs to have either two affected X alleles(female), or one affected X and a Y(male). Punnet squares are how I get by with genetics.

It depends on the UMS in my coursework which isn't looking too good but ah well I'll think of something to do about it and just work incredibly hard so it'll pay off. Hopefully.

Ah sounds cool :smile:

I'm hoping to get a job and then travel for a bit depending on funds.

Oh and thank you for correcting me. I wasn't convinced on that when I wrote it but forgot to check my notes to update it. Appreciate it :smile:

Reply 373

tewas

2

have people started papers/practice questions because I'm still on revision of the Unit 5 modules? So worried that I'm not going to have enough time

Reply 374

Hmht

2

Original post by tewas

have people started papers/practice questions because I'm still on revision of the Unit 5 modules? So worried that I'm not going to have enough time

Am i the only one who opens the books and thinks " i need to do this, there is so much to know some is hard and its my least favourite subject.... i just really can't be arsed...but i need it for uni" and just generally feels like its not going to go well? :P

and i have only done one past paper because there is a lot of content to learn :P

Reply 375

tewas

2

Original post by Hmht

Am i the only one who opens the books and thinks " i need to do this, there is so much to know some is hard and its my least favourite subject.... i just really can't be arsed...but i need it for uni" and just generally feels like its not going to go well? :P

and i have only done one past paper because there is a lot of content to learn :P

same! i am so motivated to get the grades for uni but then i open the book and think how am i ever going to learn this? and especially because the questions are practically all application :bricks:

Reply 376

TheLegalDealer

Hi guys, how would I answer a question based on this spec point "(b) explain the meaning of the terms first messenger and second messenger, with reference to adrenaline and cyclic AMP (cAMP); "it sounds so so simple but I have no clue on how to answer a Q on this

Any help greatly appreciated

Reply 377

Original post by TheLegalDealer

Hi guys, how would I answer a question based on this spec point "(b) explain the meaning of the terms first messenger and second messenger, with reference to adrenaline and cyclic AMP (cAMP); "it sounds so so simple but I have no clue on how to answer a Q on this

Any help greatly appreciated

There's a question on this on the January 2012 paper.

Question 2 e (i) Describe the events that occur after adrenaline reaches the cell surface membrane that then result in changes in metabolism inside the cell cytoplasm.

So your answer should talk about how -
Adrenaline will bind to a complementary receptor on the cell surface membrane
ATP will be converted to cAMP
cAMP will then activate proteins by binding to their allosteric site and altering their 3D structure.

I think that's correct, there's not much on it in the book and the mark scheme for that question is a bit different to what's in the book but I hope this helps :smile:

EDIT: this is only a brief answer as the question was a small 4 marker. Another user below has explained in more detail if you need more help!

(edited 9 years ago)

Reply 378

Hilton184

Biological species concept vs phylogenetic species conept

The books definition of phylogenetic species concept is poor and makes no reference to common ancestors which are required in mark schemes.

Is this right...

Biological species concept
A group of similar organisms able to interbreed to produce fertile offspring.

Phylogenetic species concept
An irreducible group of organisms similar in morphology, physiology, embryology and behaviour (+ same ecological niche...) that all share a more recent common ancestor; they are part of the same monophyletic group.

Phylogenetic species concept uses similarities in DNA/RNA base sequences and similarities in amino acid sequences of proteins in order to classify organisms into species.

Phylogenetic species concept can be used to classify fossils/extinct organisms, and can be used to classify asexually reproducing organisms.

There is no requirement for organisms to be able to interbreed in the phylogenetic species concept.

Any suggestions? The key point is the books definition is bad for phylogenetic species concept - is mine better and clearer?

Reply 379

Hilton184