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JAJC
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#941
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#941
Anyone know if ISAs count for the A* boundary? got 49/50 on my ISA so was just wondering if that would let me drop and extra few marks in unit 5 and still get it
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Gnome :)
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(Original post by JAJC)
Anyone know if ISAs count for the A* boundary? got 49/50 on my ISA so was just wondering if that would let me drop and extra few marks in unit 5 and still get it
All A2 units count, so as long as you get 90% in units 4,5 and 6 combined and get over 480UMS total you'll get an A*
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DavidYorkshireFTW
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I haven't looked at a past paper yet as i have nearly finished learning the content, i have just learnt PCR. Could someone please tell me how much HSW there is in this exam, is it like unit 4 ?
Thanks!
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DELETED ACCOUNT
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#944
(Original post by JAJC)
Anyone know if ISAs count for the A* boundary? got 49/50 on my ISA so was just wondering if that would let me drop and extra few marks in unit 5 and still get it
Yes it does count. .
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Anniestasia
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(Original post by erniiee)
Oh okay. Yes that last sentence has really helped me, thank you!

So repolarisation doesn't return the concentrations to what they were before, thats done by the sodium potassium pump?
But repolarisation IS the return of concentrations to what they were before, e.g resting potential! Its just a name for the whole process, not a particular part of it
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Anniestasia
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#946
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(Original post by JAJC)
Yes, as the outflux of potassium due to the opening of the potassium voltage gates on repolarisation causes the voltage to drop, the concentrations of ions will be on the opposite sides compared to what we had on the resting potencial, here the sodium potassium pumps actually do what they are important for (along with just maintaining the resting potencial) and restore the concentrations to their respective sides from pre depolarisation. During this time it is much harder for another action potencial to occur due to there already being alot of sodium still in the axon from the previous one, then over time, this will be restored by the pumps ready for it to be stimulated above the threshold value once again
Although potassium just moving through the gated channels back into the axon helps to repolarise too! Right?
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feelinginfinite
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(Original post by erniiee)
LEAKAGE CHANNELS?! :lolwut: :lol: what are those?
Oh God, I should think about what I'm writing before putting it on this thread haha, sorry! I watch videos on youtube to help me understand things and half of them are american so I'm not sure if we even use it...

They're basically the potassium channels; except when watching revision videos they call them "potassium leakage channels" since they "leak" (diffuse) the potassium out quickly down the potential gradient (at repolarisation I believe). Apologies for any confusion/errors, I need to focus on biology revision more
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F1's Finest
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(Original post by Anniestasia)
But repolarisation IS the return of concentrations to what they were before, e.g resting potential! Its just a name for the whole process, not a particular part of it
This.
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JAJC
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(Original post by Anniestasia)
Although potassium just moving through the gated channels back into the axon helps to repolarise too! Right?
Potassium most likely always diffuse out of the axon during repolarsing and I am not aware of potassium diffusing back into the axon even during refractory period as i think it's just actively transported back in. maybe im just misinterpreting it though
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JoshL123
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(Original post by JAJC)
Potassium most likely always diffuse out of the axon during repolarsing and I am not aware of potassium diffusing back into the axon even during refractory period as i think it's just actively transported back in. maybe im just misinterpreting it though
I beleive that it is intially actively transported into the axon via the Na K ion pump. If we are talking about the diffusion of K ion then I think that it does occurs following the stage of hyperpolarisation. Given that the Na K ion pump actively transports 3 K ions into the axon for every 2 Na ions into the surrounding tissue fluid an electrochemical gradient is created. Hence the respective ions move down their electrochemical gradient, so k ions moves to the surrounding tissue fluid. The membrane is approx 100 times more permeable to k ions than Na ions. So as the k ions move an electrical gradient is created that pulls the k ions back into the axon of the nuerone. So yeah diffusion does occur when trying to bring the potential difference to resting potential however I believe that active transport occurs before. Sorry for poor spelling and granner. Trying to speed type on my phone :L

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Rebeelouise
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It is finally done... 5.8 AKA gene technology.
Took ages.
Hope this helps!
Attached files
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feelinginfinite
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(Original post by Rebeelouise)
It is finally done... 5.8 AKA gene technology.
Took ages.
Hope this helps!
Couldn't appreciate this more, thank you very much!! +1ing
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Rebeelouise
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#953
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#953
(Original post by feelinginfinite)
Couldn't appreciate this more, thank you very much!! +1ing
Thanks.. I really hate this unit!!! But past paper questions on this seem generic.. so keep practising! And best of luck!!!
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F1's Finest
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(Original post by Rebeelouise)
It is finally done... 5.8 AKA gene technology.
Took ages.
Hope this helps!
Nicely condensed, this should help me to consolidate on my knowledge!

I'll rep you when I have rep remaining.
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Rebeelouise
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#955
(Original post by James A)
Nicely condensed, this should help me to consolidate on my knowledge!

I'll rep you when I have rep remaining.
I'm glad you think so!
Think I'll make some essay plan topics next.
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Anniestasia
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#956
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#956
God this whole action potential, resting potential Na and K stuff is so confusing... Think we're getting too hung up on it really, sure they won't ask to the amount of detail we're questioning it!
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erniiee
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(Original post by JAJC)
Yes, as the outflux of potassium due to the opening of the potassium voltage gates on repolarisation causes the voltage to drop, the concentrations of ions will be on the opposite sides compared to what we had on the resting potencial, here the sodium potassium pumps actually do what they are important for (along with just maintaining the resting potencial) and restore the concentrations to their respective sides from pre depolarisation. During this time it is much harder for another action potencial to occur due to there already being alot of sodium still in the axon from the previous one, then over time, this will be restored by the pumps ready for it to be stimulated above the threshold value once again
Thank you so much for clearing that up for me, makes a lot more sense!

(Original post by Anniestasia)
But repolarisation IS the return of concentrations to what they were before, e.g resting potential! Its just a name for the whole process, not a particular part of it
Oh I thought repolarisation was that part of the graph where the voltage/PD falls from the peak?

So repolarisation includes the drop of the graph and the action of the sodium potassium pump even after the refractory period?

(Original post by feelinginfinite)
Oh God, I should think about what I'm writing before putting it on this thread haha, sorry! I watch videos on youtube to help me understand things and half of them are american so I'm not sure if we even use it...

They're basically the potassium channels; except when watching revision videos they call them "potassium leakage channels" since they "leak" (diffuse) the potassium out quickly down the potential gradient (at repolarisation I believe). Apologies for any confusion/errors, I need to focus on biology revision more
Ah okay thanks for explaining aha!
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erniiee
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(Original post by Anniestasia)
God this whole action potential, resting potential Na and K stuff is so confusing... Think we're getting too hung up on it really, sure they won't ask to the amount of detail we're questioning it!
Yea it is quite tricky :/ I suppose its good to understand it through and through though incase AQA decide to throw in an awful question involving application of it :lol:
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erniiee
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(Original post by James A)
Before the action potential, there are lots of sodium ions outside the axon, yes.

The sodium potassium pump restores the resting potential. That's it's job and that is how we return back to having more sodium ions outside the axon and more potassium ions in the axon.....

If that makes sense
Yea that does make more sense, thanks!
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F1's Finest
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I'm just wondering.... why don't fast twitch muscle fibres contain many mitochondria. I do know that they are adapted for anaerobic respiration, but surely having mitochondria around would help this type of muscle fibre if the supply of ATP gets really low. But then again, phosphocreatine is present which can regenerate ATP , kinda confused
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