the article is scary stuff! sounds like my class should be going through it with our teacher soon though (thank god) and the teacher I never learn anything from has gone on paternity leave for two weeks so my teacher from last year is subbing =] yay! might actually learn something, finally.

Reply 1427

iracle

Original post by libra08

i've got a question here that i hope someone can help me!! :smile:

paragraph 7 and 8, page 7 of the scientific article

can someone explain to me about this:-

the last sentence in paragraph 7 says 'knock out either and muscle wasting all but stops'.. does this means that when you knock out the genes, muscle wasting do not stop?

and in paragraph 8, 'when Glass knocked out each of the 2 atrogenes in rats, he found they suffered less atrophy after both disuse and disease'

i thought paragraph 7 implies that if you knock out the genes, you will suffer atrophy but then paragraph 8 seems to imply that when the genes are knocked out, there is less atrophy..

hope someone can help me! :smile:

thank a lot!!!!

In paragraph 7, 'all but' is a phrase that means 'almost'. Check up the dictionary or simply google it and you can get the meaning there. That's the problem when they want to play with language instead of using something everyone understands.
So nothing is wrong, para 7 - knock out the genes muscle wasting 'almost' stops, and in para8 - knock out the genes, less atrophy.

Reply 1428

photosystem1

I'm sitting the the unit 5 exam and re-sitting the unit 4 exam in the summer.
So scared of what they could ask for the scientific article because they can draw questions from AS modules too. :frown:

Reply 1429

IGotAQuestion

Can anyone please explain nerve impulses to me? At the beginning of topic 8 !

thank you - the book gives me a headache and we havent covered it fully in class

Reply 1430

chemdweeb1234

Original post by IGotAQuestion

Can anyone please explain nerve impulses to me? At the beginning of topic 8 !

thank you - the book gives me a headache and we havent covered it fully in class

can you be a bit more specific? thats a broad topic!

is it the resting membrane potential? the generation of action potential? or the propagation of the nerve impulse?

Reply 1431

IGotAQuestion

Original post by chemdweeb1234

can you be a bit more specific? thats a broad topic!

is it the resting membrane potential? the generation of action potential? or the propagation of the nerve impulse?

202 to 203 and 206 to 208 :colondollar:

the wording just sends me in a daze - please dont feel obliged to do it all lol

just the crossing of ions and AP, RP on page 202 will be great - :biggrin:

Reply 1432

chemdweeb1234

Original post by IGotAQuestion

202 to 203 and 206 to 208 :colondollar:

the wording just sends me in a daze - please dont feel obliged to do it all lol

just the crossing of ions and AP, RP on page 202 will be great - :biggrin:

Well

I'll start with the resting membrane potential

RESTING MEMBRANE POTENTIAL
A neurone that is not conducting an impulse is said to be at rest. However, this is slightly wrong because the neurone is not "actually resting". It is actively maintaining a potential difference across it...(actively meaning by the use of ATP)

so the key points for when the membrane is at rest:

1) there are MORE sodium ions outside neurone than inside
2) there are MORE potassium ions inside neurone than outside
3) there are also negative proteins and chloride ions inside the neurone
4) this causes the inside to be negative with respect to the outside
5) There is a potential difference across the membrane... this is said as "the membrane is polarised"
6) this potential difference is maintained because of the uneven distribution of ions across the membrane... which is maintained by the Na/K pump
7) This, consequently depends on the PERMEABILITY of the membrane to ions
8) At rest, the membrane is permeable to potassium ions and impermeable to sodium ions...
9) The Na/K pump actively pumps out 3 Na ions and brings in 2 K ions against their concentration gradients...
10) Since the membrane is more permeable to K, these can move back out down their concentration gradient through Potassium Ion Channels
11) Some potassium will also be attracted back into the neurone (to balance the charge)... this is said as the K ions move down the electrochemical gradient...
12) Eventually, a dynamic equilibrium is reached between the conc. gradient and electrochemical gradients...

When this equilibrium is reached... the potential difference is -70mV ... and it stays like that because the dynamic equilibrium means no net movement of ions

Reply 1433

chemdweeb1234

Original post by IGotAQuestion

x

The Action Potential

Neurones being at rest would be pointless...

Action potentials are just temporary reversals in the potential difference that was maintained at rest in the neurone... when this happens we say the membrane is DEPOLARISED ( this is etymologically wrong... but hey, whos gonna argue with science :P )

The key points are as follows...

1) When there is a change in stimulus, the energy is used to open Voltage-gated Na ion channels...
2) This increases the permeability of the membrane to Na ions...
3) Since initially there was a higher concentration of Na outisde the cell, and the inside was more negative, the Na ions move down the concnetration and electrochemical gradients into the neurone...
4) As this happens... the inside begins to get more and more positive...
5) There is a reversal in PD... the membrane is depolarised..
6) (Extra point: in fact, as more and more Na ions enter the neurone, there is a positive feedback cycle... more and more Voltage gated Na channels open)
7) If the threshold potential is reached an action potential will propagate along the neurone...
8) After the threshold potential there is a sudden change in the permeability of the membrane .... the voltage gated Na ion channels suddenly close and the voltage gated K ion channels open...the membrane becomes more permeable to K and practically impermeable to Na...
9) There is a now a phase of repolarisation where the high conc of K ions inside the neurone decide to move back out of the cell via facilitated diffusion...
10) as this happens the inside gets more and more negative - REPOLARISATION
11) There is actually a slight overshoot due to a delay in the closing of the K channels..
12) The PD is more negative than normal.... this is hyperpolarisation

13) To return to resting membrane potential, K ions move back into the cell down concentration and electrochemical gradients.... eventually another dynamic equilibrium will be reached and you maintain the membrane potential at - 70mV again...

Reply 1434

IGotAQuestion

Original post by chemdweeb1234

Well

I'll start with the resting membrane potential

RESTING MEMBRANE POTENTIAL
A neurone that is not conducting an impulse is said to be at rest. However, this is slightly wrong because the neurone is not "actually resting". It is actively maintaining a potential difference across it...(actively meaning by the use of ATP)

so the key points for when the membrane is at rest:

1) there are MORE sodium ions outside neurone than inside
2) there are MORE potassium ions inside neurone than outside
3) there are also negative proteins and chloride ions inside the neurone
4) this causes the inside to be negative with respect to the outside
5) There is a potential difference across the membrane... this is said as "the membrane is polarised"
6) this potential difference is maintained because of the uneven distribution of ions across the membrane... which is maintained by the Na/K pump
7) This, consequently depends on the PERMEABILITY of the membrane to ions
8) At rest, the membrane is permeable to potassium ions and impermeable to sodium ions...
9) The Na/K pump actively pumps out 3 Na ions and brings in 2 K ions against their concentration gradients...
10) Since the membrane is more permeable to K, these can move back out down their concentration gradient through Potassium Ion Channels
11) Some potassium will also be attracted back into the neurone (to balance the charge)... this is said as the K ions move down the electrochemical gradient...
12) Eventually, a dynamic equilibrium is reached between the conc. gradient and electrochemical gradients...

When this equilibrium is reached... the potential difference is -70mV ... and it stays like that because the dynamic equilibrium means no net movement of ions

thank you so much! :biggrin:

Hope others who see will also be as grateful :smile:

really helped to make sense of the book, really appreciate it

Reply 1435

chemdweeb1234

Original post by IGotAQuestion

thank you so much! :biggrin:

Hope others who see will also be as grateful :smile:

really helped to make sense of the book, really appreciate it

no worries :smile:

ill do the rest tomorrow :P

have to do physics tonight :frown:

Reply 1436

darkiee

10

Help Please,

Explain how variation in ventilation and cardiac output enable rapid delivery of tissues and the removal of carbondioxide from them, Including how the heart rate and ventilation rate are controlled and the roles of cardiovascular centre and the ventilation centre

This is on the syllabus and i dont understand it,

Can someone please explain it in depth.

Thanks

Reply 1437

InItToWinItGetIt?

11

Hi

''Explain how genes can be switched on and off by DNA transcription factors including hormones.''

Info on this spec point is nowhere to be found in the green textbook or the revision guide? :s-smilie:

Reply 1438

jklm123

Original post by dush_2

fool ?? ok fine u will never get any thing form me keep that in ur mind !!

u dont have the paper anyway

Reply 1439

chemdweeb1234

Original post by InItToWinItGetIt?

Hi

''Explain how genes can be switched on and off by DNA transcription factors including hormones.''

Info on this spec point is nowhere to be found in the green textbook or the revision guide? :s-smilie:

Hmm.. they have cheekily omitted it in the green book... they have mentioned a bit on Page 180 and 181... but it the context of steroids... there is literally like one or so paragraphs on it :smile:

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

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