A2 Biology OCR June 2015 Revision Thread

Hello just confused about if I'm in the right group, is this thread for ial or gce? I'm doing ial.. if not then is there any thread for it? Thanks in advance :smile:

Reply 1361

Beni24

2

Guys I've got a high B in f211, and D's in both of my coursework, Im retaking f212,f214 and f215. If i get a B in f212 and f214 and maybe a high C in f215, Would that be a B overall? :smile:

Reply 1362

medactuary

2

What does it mean to 'predict the phenotypic ratios in problems involving epistasis'?
Does anyone have an example of a past paper q where we've needed to do this?

(edited 8 years ago)

Reply 1363

maisie__x

2

Original post by Beni24

Guys I've got a high B in f211, and D's in both of my coursework, Im retaking f212,f214 and f215. If i get a B in f212 and f214 and maybe a high C in f215, Would that be a B overall? :smile:

I haven't worked it out exactly but from estimating how high the D's were and estimating how high a C/B you'd get this year I think you'd just be short of a B. I think you need to get a B in f215 this year to be sure :smile:

Reply 1364

E_149

2

Original post by medactuary

What does it mean to 'predict the phenotypic ratios in problems involving homeostasis'?
Does anyone have an example of a past paper q where we've needed to do this?

Do you mean epistasis rather than homeostasis?

Reply 1365

Clueless130

1

Hi can anyone explain to me how light is harvested in the chloroplast membranes? Like involving the photosystems etcI was doing a past paper which had this question, but i didn't quite understand the mark schemeThanks :smile:

Reply 1366

Hilton184

9

Can someone explain to me how stacking thylakoids into grana possibly increases the surface area!?

Surely you are decreasing the surface area as thylakoids in the middle of a granum will have the top part of the membrane and the bottom part of the membrane unexposed... Literally nothing on the Internet explains this. Everyone just goes 'stacking thylakoids into grana increases the surface area for light dependent reactions' .. Doesn't explain how the surface area is increased. By looking at it, you can see the surface area clearly decreases from the diagrams of a chloroplast surely?

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Reply 1367

Hilton184

9

Original post by Hilton184

Can someone explain to me how stacking thylakoids into grana possibly increases the surface area!?

Surely you are decreasing the surface area as thylakoids in the middle of a granum will have the top part of the membrane and the bottom part of the membrane unexposed... Literally nothing on the Internet explains this. Everyone just goes 'stacking thylakoids into grana increases the surface area for light dependent reactions' .. Doesn't explain how the surface area is increased. By looking at it, you can see the surface area clearly decreases from the diagrams of a chloroplast surely?

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If we for a moment visualise these thylakoids as cubes as I think it demonstrates my point effectively. Ignore the fact I can't draw haha

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ImageUploadedByStudent Room1433582521.121426.jpg122.8KB

Reply 1368

kawehi

3

I'm not doing this exam, but I hope it goes amazingly for all of you! I can't wait to do A2 bio next year, it looks really interesting :smile:

Good luck!!

Reply 1369

E_149

2

Original post by Clueless130

Hi can anyone explain to me how light is harvested in the chloroplast membranes? Like involving the photosystems etcI was doing a past paper which had this question, but i didn't quite understand the mark schemeThanks :smile:

I think I know the question you mean - from Jan13 - where it wants you to explain basically how the photosystems work using the diagram.

So what you needed to say was how pigments are arranged in photosystems. These pigments absorb photons/light energy which is used to excite electrons. Also the diagram shows the energy being passed between pigments - the accessory pigments pass the energy they absorb to the 'primary pigment reaction centre' where cholorophyll a is. You could also say how different wavelengths of light are refelected and absorbed by different pigments. Then obviously the QWC terms.

Not sure if that was what you needed but hope that helps a bit.

Reply 1370

Beni24

2

what are the features of the PCT that allows it to perform its function efficiently? :smile:

Reply 1371

E_149

2

Original post by Beni24

what are the features of the PCT that allows it to perform its function efficiently? :smile:

Microvilli on side of tubule fluid. Opposite side near capillaries also folded. Both increase surface area for transport of ions, glucose, amino acids, etc. Co-transporter proteins for sodium ions with glucose/amino acids. Many mitochondria make lots of ATP for active processes.

Reply 1372

Nmak2015

Hi could someone please send me a link to the past papers for Biology F214 (communication, homeostastis and energy) please!

Reply 1373

Beni24

2

Original post by Nmak2015

Hi could someone please send me a link to the past papers for Biology F214 (communication, homeostastis and energy) please!

Here you go, http://www.thebiotutor.com/past-papers3.html :smile:

you can also get them from the ocr website

Thank you so much!!

Why is nitrogenous wastes such as urea toxic? :smile:

Reply 1376

Hilton184

9

Original post by Beni24

Why is nitrogenous wastes such as urea toxic? :smile:

Lone pair of electrons on nitrogen atom accepts a hydrogen ion in solution, hence making amines like urea weak bases. This would cause pH to increase and become alkaline. Hence enzymes denature etc.

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oh yea oops!

Original post by AnnekaChan173

I just typed up a huge answer to this but my tablet just killed it for me ok okok
I'll write it back up when I get home, I have a maths exam today (!) good luck for anyone doing S1, S2 or any other applied modules today!