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A2 Biology OCR June 2015 Revision Thread

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Hiya!
Is anyone able to explain the movement of Na+ and K+ at each point on this graph, please?
Resting potential
Threshold
Depolarisation
Repolarisation
Refractory

Thank you
Action_potential.svg.png54.2KB
Original post by Molly_xox
Just done it, does that make sense?


you star, many thanks!! x
Original post by MeeraP07
Hiya!
Is anyone able to explain the movement of Na+ and K+ at each point on this graph, please?
Resting potential
Threshold
Depolarisation
Repolarisation
Refractory

Thank you


Hey, not quite relevant but just never say refractory period when describing this graph. It's hyperpolarisation
Guys which paper do you think was the hardest? So I can have a go at doing it :smile:
Reply 1624
Avatar for Qui
Qui
2
Difference between NAD and NADP?
Edit: In terms of where they're used and how they function.
(edited 8 years ago)
Original post by Beni24
Guys which paper do you think was the hardest? So I can have a go at doing it :smile:


June 11

Original post by Qui
Difference between NAD and NADP?


Produced by different organelles and specific for respiration and photosynthesis respectively
Original post by LA_95
Guys what is photorespiration? its mentioned in the revision guide that increasing temperature will make the rate of photorespiration greater than rate of photosynthesis but it doesn't actually say what it is???

Posted from TSR Mobile


It's when the temperature increases to the point where oxygen out competes carbon dioxide for the active site of rubisco, meaning that carbon dioxide fixation will not occur. I think that's all you need to know, it's mentioned in a bit more detail in the big OCR textbook
Reply 1627
Avatar for Qui
Qui
2
Original post by ChoccyPhilly


Produced by different organelles and specific for respiration and photosynthesis respectively


Thanks!
Original post by tewas
yes that is right but could you explain how you worked that out from the info given in the question? thanks


If the leaf is red/black then that means it is absorbing all of the green spectrum of light in addition to the others.
Original post by LauraS88049
Hi, does anyone know where I can find the OCR June 2014 F214 paper? Looked for it everywhere I can't find it!


http://www.thebiotutor.com/uploads/2/7/2/8/27287711/f214-01_jun14.pdf
Original post by Maham88


Thank you so much!!
Original post by domcandrews
biotutor


Thank you!!
Original post by MeeraP07
Hiya!
Is anyone able to explain the movement of Na+ and K+ at each point on this graph, please?
Resting potential
Threshold
Depolarisation
Repolarisation
Refractory

Thank you



from 0-1 seconds the neurone is at resting potential where 3 Na+ ions are actively transported out of the cell using sodium-potassium ion pumps for every 2K+ ions in . However membrane is more permeable to K+ ions so K+ essentially leak out , so there are more positive ions outside compared to inside so P.D = -70mv

If the P.D. doesn't exceed -55mv (threshold value ) and A.P. will not occur this is the all or nothing law

At 1 second a stimulus causes Na+channels to open ,so Na+ ions flow into the cell leading depolarisation where P.D. = +40mv

At 2 seconds , the Na+ channels close and K+ channels open

After this K+ flows out of the cell as their is a very high conc. gradient this leads to repolarisation .

However K+ "overshoot" so P.D. = -75mv leading to hyper-polarisation

Now the refractory period occurs where resting potential is being reestablished and Na+ channels are closed therefore no A.P. cannot occur in this period until resting potential is restored


Hope that helps
How much do we need to know about the evidence for chemiosmosis? I've just learnt what was in the CGP revision guide about PH difference, artificial vesicles, alkaline mitochondria and uncouplers? is that ok, and do you think much is likely to come up about it?
[QUOTE=flygerianmc;56691569]Using the CGP book for this, let me get this straight, cell membrane and plasma membrane is interchangeable right? Keeps using cell membranes sometimes than switching to plasma membrane, what is that about?
You should say cell surface membrane not just cell membrane and yes they are
Anyone want to ask each other Q's ?
Original post by 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!

Hello mr biotom. Do you think it's necessary to revise AS material in preparation for synoptic questions?
Original post by shannolivia
Hey please may someone tell me the difference between a primary pigment and accessory pigment? Thank you!!


Posted from TSR Mobile


Primary: location of the reaction centre, this is where light energy is absorbed to excite electrons so that they can pass into the electron transport chain.
It's found in the centre of photosystems.
Contains Chlorophyll A, P680,P700

Accessory: absorbs light energy of a wide range of wavelengths, absorbs any light energy that the primary pigment can't. Then transfers this light energy to the primary pigment.
Surrounds the primary pigment in the photosystem.
Contains chlorophyll B, Xanthophyll and Carotenoid.

Hope that helps! :smile:
Original post by TheLegalDealer
Anyone want to ask each other Q's ?


where does glycolysis occur?
does anyone know what they mean by polygenic genes in the continuous and discontinous variation spread to me it sounded a bit like epistasis or codominance but it said that those are only for discontinuous variation.so confused

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