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

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Reply 3820

vampirerahim

AVENGE YOUR SELVES
UNIT 4
JOIN THE PROTEST

https://www.facebook.com/6bio4

Reply 3821

rohitbd

Original post by M Kh

Here you are: http://www.scribd.com/doc/89838095/S...Stafford-Final

Amazing notes thank you so much, was so worried about what to do with pre release but these are amazing :smile:

Reply 3822

iesians

Original post by rudizzy123

Thank you both. So I am I correct in saying the myelin sheath prevents the transfer of all ions including sodium (na+) and potassium (k+) and the phopholipid bilayer which is present all along the neuron, allows the transfer of na and k but prevents large molecules from passing through?

No!!!
even the phospholipid bilayer doesnt allow na and k to pass cuz they both are CHARGED groups !!
thats why we have Na PUMPS and K channels !! these span throught the membrane and thus allow a way for these CHARGED particles to travel in or out.
they cant DIRECTLY pass thru the membrane !!

Reply 3823

nadzzdan

Original post by iesians

there arent any TYPES of synapses, its just the way impulses are collected over a synapse thats different.

one is spatial summation in this two or three presynaptic memebrane synapse with only a single post synaptic membrane , so impulses from all the three pre ones are merged and thus the chances of action potential formation in the post synaptic memebrane increases (this is what happens when 2 or 3 rod cells converge with a single bipolar neurone)

and then there temporal summation, in this the situation is simple : one post and pre synaptic membrane, but the frequency of action potential in pre synaptic neurone is so high that a lot of neurotransmitter may be released in less amount of time so this also increases chances of adequate depolarisation in the post synaptic membrane.
thats it :smile:

Thanks pal

Reply 3824

nadzzdan

Original post by iesians

ok a question ?! does the hormone bind to a transcrption factor or binds to a receptor and this complex ACTS as a transcription factor ??! WA...?!

two types of hormones
STEROID and PEPTIDE

Steroid hormones can pass into the cell through the membrane because it is non-polar and made up of lipids. it binds to a receptor in the cell cytoplasm and the hormone-receptor complex acts as a transcription factor itself.

Peptide hormones cannot pass through the cell membrane because they are polar. instead they bind to a receptor on the cell membrane and this combination of hormone and receptor activates a second messenger within the cell. this second messenger affects the transcription process directly as a transcription factor or indirectly. it depends which messenger is activated.

Reply 3825

nadzzdan

Original post by ishtarbb

Thanks! you're so kind :smile:

No problem, feel free to quote me for questions. :wink:

Reply 3826

iesians

i threw a wish in the well.....

Reply 3827

VickyDoodle

I have a silly question.. that link for the pre-release article looks really helpful, but who is this Sir V. guy? Is he famous or something, or just happens to be a guy that had some smart stuff? :P

Just finished my (new) Topic 8 notes, gotta do Topic 7 now and then some synoptic/pre-release based ones. Doing a question based day tomorrow.. hopefully I get enough to get me into uni! :frown:

Reply 3828

ghogho

pple got a question!

Explain why a training programme that concentrates only on increasing muscle mass and glycogen content of muscle many not led to significant improvment in endurance events such as cyclng / [ 3 marsks so at least 3 points :s-smilie:

]

Reply 3829

VickyDoodle

Original post by ghogho

]

I'm assuming that it'll have something to do with the fact that the training programme would only increase levels of fast twitch muscle fibres (which have high glycogen content), which fatigue quickly and so would not be useful in endurance sports. Instead a training programme based on buildng up slow twitch fibres would be more useful for cycling..?

Reply 3830

iesians

Original post by ghogho

]

a training programme such as you qouted would increase the proportion of fast twitch muscle fibres, as increasing muscle mass would involve lifting weights which requires short outbursts of energy for which fast twitch fibre is perfect,

while on the other hand cycling and other endurance events involve the use of muscle for a long period of time so they cannot run on fast twitch fibres as they get fatigued quickly, due to high anaerobic respiration rate and increased levels of lactate.

Reply 3831

Kylewalker346234

Original post by iesians

i threw a wish in the well.....

Don't ask me I'll never tell?

Reply 3832

19941994

Original post by ConnorB

Don't ask me I'll never tell?

I looked to you as it fell

This was posted from The Student Room's iPhone/iPad

Reply 3833

fudgesundae

Can someone explain fMRI to me please?

From what I understand:

Oxygenated blood does not absorb the signal as well as deoxygenated blood. Active areas of the brain have more oxygenated blood as they need it for respiration. So the active areas light up because the signal is not being absorbed?

Reply 3834

19941994

So scared for this exam dont know what to do :frown:

This was posted from The Student Room's iPhone/iPad

Reply 3835

bertiejess

Original post by fudgesundae

That's pretty much what I know, also that fMRI measures then brain in action, rather than just taking several images of the tissues, therefore you can watch how the brain is working when listening/completing sums etc.

Reply 3836

Omar1994

Peptide hormones: Relatively small molecules, cannot pass through cell membrane because they are charged. They bind to receptor on cell membrane - activates a second messenger. Second messenger brings about chemical changes in the cell directly or indirectly affecting transcription.

Steroid hormones: formed from lipids, have complex ring structures. passes through cell surface membrane and binds directly to a receptor molecule within cytoplasm. brings about characteristic response resulting from its effect on transcription.

Transcription factors: genes are switched on and off by successful formation and attachement of the transcription initiation complex to the promoter region. transcription initiation complex consists of RNA polymerase bound to transcription factor of some sort. genes remain switched off by failure of the transcription initiation complex to form and attach to the promoter region section of the DNA. This is due to the absence of protein transcription factors or the action of repressor molecules.

signal proteins or regulator proteins related to the secondary messenger in peptide hormones. transcription factors have to be in active form for genes to be switched on. repressor molecules stop genes from being switched on by binding to promoter region or by attaching to transcription factors preventing transcription initiation complex formation. signal hormone proteins may not be present so genes not switched on?