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A2 Biology OCR June 2015 Revision Thread

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Well good luck for monday! I'm not as stressed for these bio exams as I need a low B to get an A overall. I'm most worried about chemistry though, I only just skimmed an A at AS last year, and need AAB for my uni offer...so need to nail these exams <img src="images/smilies/s-smilie.gif" border="0" alt="" title=" :s-smilie:

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Same! AAB for York, so technically, I don't need an A in biology but then my hopes depend on me getting anA in PE and ugh, if you know anyone who does PE, you'll understand where I'm coming from.

Haha must be nice to be a bit more relaxed in these bio exams. Good luck with chemistry next week then! And biology, of course.

Reply 1561

Shostakovish

Okay everyone, I'm going for the cram, wish me luck.

I hope you all do well.

Good luck my warriors.

Reply 1562

AnnekaChan173

Original post by tewas

yes! thank you that helps so much! yes i saw a question about the NaHCO3 solution changing due to different filters with increasing and decreasing pH and that's what confused me :frown:

so are you only expected to know that:
- chlorophyll a absorbs red light, reflects green
- chlorophyll a can also absorb blue light
- chlorophyll b appears blue-green in colour
- carotene and xanthophyll absorb blue light and reflect yellow-orange?
also, sometimes in mark schemes they talk about short/long wavelengths absorbed/reflected - how are we meant to know this? are we supposed to know the wavelengths?

Original post by Student23478

Is that all you need to know regarding wavelntgjd pigments and accessory pigments?

Loooool sorry this is late, I literally typed up a good 200 words and my iPad just f'ed up a few minutes before I had to leave...

Honestly just knowing Chlorophyll a is fine imo. They don't want you to know much, they just want you to know that the accessory pigments widen the range of light wavelengths that can be absorbed and used in the light dependent reaction. Reflecting maybe, but in the mark scheme they accepted the plant, the leaf and chlorophyll a reflect green light, so I don't think you need to be too specific. Do you take Chemistry? I try to look at it as if it were an equilibrium.

Forward reaction: respiration. Plant releases CO2, CO2 forms acid, pH decreases.
H2O+CO2 -> H+ + HCO3- (H2CO3 dissociated)
Reverse reaction: photosynthesis. Plant needs CO2, so more is available if you reverse the reaction. (not technically but pls)

In other words, when the rate of respiration exceeds photosynthesis, the pH decreases, and the solution will become more yellow. When the rate of photosynthesis is faster than the rate of respiration, the pH will increase, as there are fewer H+ When I did this Q I wrote the intermediate colours down to help me work out just how pH had changed (ie writing orange-yellow between yellow and orange-red)

In the case of green light, it becomes more yellow, so we know that the rate of respiration must be faster than the rate of photosynthesis. This is because green light is reflected by chlorophyll a and all that lovely jazz, so green light isn't used in photosynthesis. You could mention accessory pigments for an AVP I think too...? I think that was to say that some photosynthesis takes place. Yeaaaaaaah, this was a little longer than expected.

Original post by bakedbeans247

I've been looking around for one for a while, but no luck. So please let me know if you find one.

But for f214, I just looked through the last 7/8 papers in a few mins, and I haven't seen much of or there hasn't been any detailed questions on: how ADH works, a QWC type q. about action potentials, a QWC type q. about the transmission across the synpase, Calvin cycle, cyclic/non-cyclic photo phosphorylation (only 1-3 marker questions), how the structure of mitochondria enables them to carry out their function pg86, how chloroplasts are adapted for their role pg60, the bit about cofactors on pg87, oxidation phosphorylation, link and krebs cycle, how insulin is secreted from the beta cells in terms of K+ and Ca2+ ions, q.s about pages 28-29, q.s about pages 50-51 esp. the bit about testing for anabolic steroids, pages 96-97 esp. that section about lipids and the B-oxidation pathway.

now that above is what ive seen that hasn't come up, though im probs wrong with some of them as i flicked through 7/8 papers in a few mins.

But there is this predictions list from last year for f215 (scroll down, 2nd to last page highlighted in blue):

https://www.dropbox.com/s/c846q4mj16g26ek/f215%20stretch%20and%20challenge%20ideas.docx?dl=0

So, i guess anything that didn't come from that list in last years paper could be used to predict what will come up this yr? Although most of them did come up. :/

Last year had quite a bit of communication though, so I'm thinking more Photosynthesis/Respiration? I have seen ADH and transmission across a synapse questions! There was an 8 mark fill in the blanks Q in the Jan 2011 paper. Pretty sure one of the mocks I did in school had an ethical anabolic steroids Qs too, not sure which year that was. I actually don't think we'll get much Excretion too but eh. Still haven't done enough papers :/ operation no sleep today lol kill me now

(edited 8 years ago)

Reply 1563

Shostakovish

There is something I find really confusing: In the book (OCR Heinemann) it says that NAD accepts two hydrogen atoms and is then reduced - but represent it molecularly as NADH - not NADH2. I'm very confused, could anyone explain? Am I missing something?

Reply 1564

loperdoper

Original post by Shostakovish

Which page is this?
edit: found it. I looked at the molecular structure and, I'm not a chemist, but NAD appears to already have one hydrogen atom, and to become NADH is accepts a second hydrogen atom, so the 2H doesn't apply as one of the H's is already accounted for. That's my best guess, at least.

(edited 8 years ago)

Reply 1565

Mousyy

Original post by whenthecatcalls

Hi guys
Did everyone do the past paper questions from the old spec?. Im not sure if they are useful or not

use the question packs on mrs millers blog theyre really good

Reply 1566

Shostakovish

Original post by loperdoper

Aaah, that does make more sense. Thank you very much!

Reply 1567

Mousyy

everyone pray that we don't get too many suggest questions

Reply 1568

sunshinebeem

Original post by Klesia

As advice from someone who is resiting this exam, balls to grade boundries. Be confident in all content and then you can only get higher UMS

Loooool okay thanks, I'm going to try :smile:

Reply 1569

sunshinebeem

Original post by maisie__x

What grades did you get in the individual units last year? Then i'll work it out properly :smile:

47/60 in coursework (but I've retaken for hopefully a higher grade)
Unit 1: 70/90 ums (this was a high B I think)
Unit 2: 144/150 ums (this was an A)

Thanks lol

Reply 1570

Mousyy

Original post by sunshinebeem

Hi everyone does anyone know what I'll need for an A or an A* this year.
Last year I got 161 UMS which I think is a solid A?

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I assume you mean 261 UMS cause 161 Isn't an A, but basically to get an A* overall you need an A at AS which you have and 270/300 UMS for A2 which is basically means you can only drop 15-20 marks across F214 F215 and your coursework to get an A overall you'll need you need 219UMS across your A2s which is like an A in CW and B's in your exams (assuming your AS UMS was 261) hope this helps

Reply 1571

Munrot07

For anyone wanting to do some final revision before tomorrows exam here is my F214 revision playlist:

https://www.youtube.com/playlist?list=PLiJa1PAsFO7ovxSXepr3J6xNjJc-Hlwsz

Good luck!

Reply 1572

maisie__x

Original post by sunshinebeem

47/60 in coursework (but I've retaken for hopefully a higher grade)
Unit 1: 70/90 ums (this was a high B I think)
Unit 2: 144/150 ums (this was an A)

Thanks lol

To get an A overall this year you need to make 192 ums over both exams. So you could get two low B's and get an A :smile:

Reply 1573

Munrot07

Original post by Shostakovish

It's slightly annoying this. Basically you are lied to at A level. NAD doesn't really accept two hydrogens.

The oxidised form is NAD+ (or just NAD). A molecule loses two hydrogen atoms. NAD then accepts one hydrogen atom (proton + electrons) and one election (which means 1 proton and 2 elections overall) from the molecule. The second electron comes from the second hydrogen atom (H --> H+ + e-). This just leaves a proton. It is charged and isn't bound to NAD.

This is why people often use the notation NADH + H+. NADH is how the molecule looks but doesn't take in to account the second proton that isn't bound. NADH2 tells you there is a second hydrogen but doesn't tell you it is charged and not bound. So using NADH + H+ is the most correct. All are valid though.

Reply 1574

TheLegalDealer

Do we have to lnow the exaxt no. Of Reduced NAD and ATP made during each stage of respiration ? And do we have to know the ornithine cycle step by step ??

Reply 1575

maisie__x

Original post by TheLegalDealer

Do we have to lnow the exaxt no. Of Reduced NAD and ATP made during each stage of respiration ? And do we have to know the ornithine cycle step by step ??