OCR Biology New A-level H420 Paper 1,2,3 (2019) Predictions + Exam Discussion Thread

does anyone have the link for the practice papers set one and two. These are protected on the OCR website not the ones you can access. Thanks

can anyone explain the events that occur during an action potential pls? I've confusing myself cause I keep looking at other resources and they're saying different things...

How depolarisation happens? Or after depolarisation?

https://drive.google.com/folderview?id=1ATeygzkeCeDDbs9UEeusQMhkSKMki9cv

I believe this has some of the papers you’re after but not all. Have a look.

Well this is what I'm learning but I feel like its wrong somewhere; is it ok?
also at what stage is the refractory period?

1. Neurone has resting potential - some K+ channels open (mainly non VGC) but Na+ channels closed
2. Energy of stimulus causes some Na+ VGC to open so membrane is permeable to Na+ ions and so Na+ ions diffuse down EC gradient into axon making neurone less negative (depolarisation)
3. If the increase of Na+ in the axon meets the threshold potenital, more Na+ VGC will open
4. When potential difference reaches +40mV, Na+ VGC start to close and VG K+ channels open; they diffuse down EC gradient out the neurone, making neurone more negative (repolarisation)
5. Initially, lots of K+ diffuse out making inside of axon more negative than resting state (hyperpolarisation)
6. K+ VGC start to close & the sodium potassium pump causes Na+ to be move out and K+ to move in, and causes axon to return to resting potential

Well this is what I'm learning but I feel like its wrong somewhere; is it ok?
also at what stage is the refractory period?
and I don't really get how a wave of depolarisation occurs either!
sorry to be a pain haha

1. Neurone has resting potential - some K+ channels open (mainly non VGC) but Na+ channels closed
2. Energy of stimulus causes some Na+ VGC to open so membrane is permeable to Na+ ions and so Na+ ions diffuse down EC gradient into axon making neurone less negative (depolarisation)
3. If the increase of Na+ in the axon meets the threshold potenital, more Na+ VGC will open
4. When potential difference reaches +40mV, Na+ VGC start to close and VG K+ channels open; they diffuse down EC gradient out the neurone, making neurone more negative (repolarisation)
5. Initially, lots of K+ diffuse out making inside of axon more negative than resting state (hyperpolarisation)
6. K+ VGC start to close & the sodium potassium pump causes Na+ to be move out and K+ to move in, and causes axon to return to resting potential

Well this is what I'm learning but I feel like its wrong somewhere; is it ok?
also at what stage is the refractory period?

1. Neurone has resting potential - some K+ channels open (mainly non VGC) but Na+ channels closed
2. Energy of stimulus causes some Na+ VGC to open so membrane is permeable to Na+ ions and so Na+ ions diffuse down EC gradient into axon making neurone less negative (depolarisation)
3. If the increase of Na+ in the axon meets the threshold potenital, more Na+ VGC will open
4. When potential difference reaches +40mV, Na+ VGC start to close and VG K+ channels open; they diffuse down EC gradient out the neurone, making neurone more negative (repolarisation)
5. Initially, lots of K+ diffuse out making inside of axon more negative than resting state (hyperpolarisation)
6. K+ VGC start to close & the sodium potassium pump causes Na+ to be move out and K+ to move in, and causes axon to return to resting potential

1. Resting membrane potential of -70mv is maintained by Na+K+ pumps which actively transports 3 Na+ out of neurone & 2 K+ into neurone.
2. When a stimulus occurs, Na+ channels open allowing the Na+ ions to move into the neurone. If this caused the potential difference to reach threshold (-55mv) depolarisation occurs where an action potential is generated. VG na+ channels open and Na+ enter into the neurone by diffusion.
3. When the p.d reached +30mv VG Na+ channels close. VG K+ channels open and k+ ions diffuse out of the neurone during repolarisation
4. The membrane potential drops below threshold potential because the k+ channels are slow to close (hyperpolarisation)
5. The Na+K+ pump restores the potential difference back to resting membrane potential of -70mv.

refractory period - the time phase during hyperpolarisation when its not possible to stimulate another action potential.

i hope this is it.

Just make sure
You mention how the resting potential is maintained
like the sodium potassium pump as well as -70mv as the resting potential

Thats right. Refractory period is just a short period of time when the axon cannot be depolarised again to ensure impulses are unidirectional. this happens after the hyperpolarisation phase i think.

Paper 1 spec Paper was so hard.

For evaluating questions in the new spec this is the best way to get full marks. An argument supporting the statement with evidence and describe the trend. An argument against statement with evidence and saying correlation does not mean causation. An argument about the validity of the experiment saying this was not controlled, an experiment was not repeated, no mean was taken, no statistical tests.

ahh thank you !! what occurs during a wave of depolarisation?

Wow, this is actually amazing. Now that you've said that, I recall the mark schemes on those questions looking exactly like that. There's always a mark for saying not enough repeats so we cannot say for sure haha.

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Depolarisation - there’s is an influx of sodium ions as voltage gated ion channels open that’s all ik I haven’t revised that in detail yet tbh I love neurones and synapses 😂