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Edexcel A2 Biology Unit 5 (6BIO5) - 22/06/2011- OFFICIAL THREAD !

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tkoki1993

so K+ ions just diffuse back in through K channels down their conc. and electrochemical gradient once more, right?

thanks btw :smile:

Yup

Reply 2421

tkoki1993

Original post by sheep_go_baa

Through the action of Na/K pumps

I still don't understand.... :/

Reply 2422

Choca Mocha

Original post by tkoki1993

How is the normal resting potential restored after hyper polarisation?

The resting potential is restored by the cation pump- pumps Na+ out of the membane and K+ back in.

Reply 2423

bertstare

Original post by tkoki1993

How is the normal resting potential restored after hyper polarisation?

in the book it simply says, once the voltage gated K+ channels close, the K+ ions diffuse back in via the regular K+ channels? it doesnt make much sense though lol

Reply 2424

sheep_go_baa

Original post by tkoki1993

Yup

Hyperpolaristion means the potential difference falls to about -80mV,
The difference has to be restored to -70mV.
Na/K pumps actively pump K ions into the axon and Na ions out of the axon.
There overall potential difference has decreased to -70mV.

Reply 2425

tkoki1993

Original post by Choca Mocha

The resting potential is restored by the cation pump- pumps Na+ out of the membane and K+ back in.

Original post by bertstare

in the book it simply says, once the voltage gated K+ channels close, the K+ ions diffuse back in via the regular K+ channels? it doesnt make much sense though lol

Original post by sheep_go_baa

Oh right. Thanks
So sodium pump pumps out of. Potassium pump pump inside. I understand now
I thought they both pumped out

Reply 2426

bertstare

the orange snab book explains it really well

there are basically two things going on

1) the K+ ions are pumped in via the sodium potassium pumps/. the membraine is permeable to them so they diffuse back out of the cell vie their diffusion gradient

2)this causes the inside of the cell to be more negative, and creates an electrical gradient. this causes some of the K+ (positive ions) to diffuse back in due to attraction to the negative charge

eventually the diffusion gradient out of the cell and the electrical gradient into the cell balance out at -70mv

Reply 2427

Jammers123

Q. What are side effects of prolonged steroid use?
A.HIV, liver failure, cardiovascular problems, stunted growth, ligament + joint injury, weight problems, neurological issues.

Haha, this is the answer to question 35 of the questions + answers for the scientific article which the silly teacher thinks is irrelevant for the syllabus, but I tend to disagree :P

Reply 2428

avig613

Original post by sheep_go_baa

Through the action of Na/K pumps

Original post by Choca Mocha

The resting potential is restored by the cation pump- pumps Na+ out of the membane and K+ back in.

Original post by tkoki1993

How is the normal resting potential restored after hyper polarisation?

Hi, I just double checked in the mark scheme for june 2010, and you are both wrong! Actually, it is the idea that the potassium ions re-enter the axon through the membrane which is still permeable to them. this removes the + from the outside- restores the equilibrium between the diffusion gradient and the potential difference.

Reply 2429

haydyb123

Original post by brendan.

Hi.

Question 3(b)(ii) in the June 2010 paper.
It asks why when in the respirometer, when all oxygen has been removed and replaced instead with nitrogen.. why there is no movement of the coloured liquid..
The markscheme says:
1. no oxygen available/no oxygen uptake ;
2. reference to anaerobic respiration ;
3. carbon dioxide produced is absorbed / eq ;
4. no (net) change of {volume / pressure} of gas ;

Okay, so I get points 1,2 and 4. But surely if it is anaerobic respiration, no carbon dioxide would be produced anyway? Because in anaerobic, glucose is converted into pyruvate, then lactate. Right? And carbon dioxide is only mentioned as a product from the link reaction onwards, which requires oxygen.
I just don't get the 3rd marking point.. or is my thinking wrong?
Thanks to anyone that can clear this up! :colondollar:

Yeah I agree, this point does seem strange, you're correct.

Reply 2430

avig613

Original post by bertstare

in the book it simply says, once the voltage gated K+ channels close, the K+ ions diffuse back in via the regular K+ channels? it doesnt make much sense though lol

the bookisexactly right! Don't liisten to the answer about the pump- see lasst year's examiner report- the pumpis wrong! Your answer is right.

Reply 2431

math grim reaper

Anyone has a revision/notes for topic 8? I checked the attachements I found one for topic 7 and it was good, im looking for anything for topic 8.

Reply 2432

chemdweeb1234

i love the fact that the mark schemes are taken as being always right... edexcel obviously messed that one up.... sodium potassium pump has to be involved in restoring the resting membrane potential.... most sources say that... i have no idea why they didnt credit that

Reply 2433

gildartz

Original post by brendan.

Hi.

Maybe because there is still a bit of oxygen left in the lungs as residual air from before the oxygen was taken out? There would still be no oxygen uptake but a bit of aerobic respiration will occur which will produce the CO2 which is absorbed. Not sure though :/

Reply 2434

voices1

HOw gene therapy works?
Viruses are inactivated and inserted into the body. The viruses contain the DNA for the gene to be inserted. Firstly they then attach onto the particles of the receptor cells and the DNA combines with the host cell DNA to form the recombinant DNA which is transcribed and translated producing the appropriate protein.

is this correct?

how is this different from recombinant bacteria?

Reply 2435

dance0403

Hello everyone!! hope you are all stressing out as much as i am!
quick question (sorry if this has already been answered) but is it true that the grade boundary for an A is like 60%? and if so, do you get full ums just for getting 60%?? thank you!

Reply 2436

StudentToday

U no tachycardia - what causes it? like is it failure to recieve a signal?? Is the SAN or AVN affected? aslo is it the ECG with the reversed QRS complex???

Reply 2437

AGM

The sodium potassium pumps pump 3Na+ ions out and 2K+ ions in by active transport whatever is happening to the membrane potential difference wise.

What determines the potential difference is the number of sodium or potassium channels(which allow the ions to diffuse) which are open.

Reply 2438

sheep_go_baa

Original post by dance0403

Grade boundaries are only set once everyone has done the exam and they have all been marked, so no that isn't true. It may have been true for a previous year, but not this year.