AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011

Adrenalin.

I was wondering. If we are asked about the initial cause of the depolarising stiumulus that causes the voltage gated sodium channels to open ....and then an action potential....

what would you say?

'they are the result of the receptor to the stiumulus - for example some chemicals trigger chemoreceptors to open chemical gated sodium channels, likewise pressure gated receptors (i.e. pacinian corpsucle) etc etc ...?'

guys for chap 13 i dont understand it says fsh stimulates oestrogen to be prodcued but then oestrogen inhibits fsh?

for up to day 10 oestrogen stimulaes rise in fsh, wtf though it inhibits it?????



MANY THANKSSSSSSSSSSSSS

help hahaha

Can someone help me with this?

One of my biology books say that "high blood pressure is detected by baroreceptors, then impulses are sent to the medulla oblongata, sending impulses along parasympathetic newurons, which secrete acetylecholine, which then binds to receptors on the SAN"

Whereas my other biology book says that " high blood pressure is detected by baroreceptors, then impulses are sent to the center in the medulla oblongata that decreases heart rate, which then increases the frequency of impulses to the SAN via the parasympathetic nervous system"

What should I say in my exam then?? :/

Yeah, except the heart which is myogenic so self stimulated. Everything else ,its the lovely brain.

I think, tahts what it means by "eye piece scale"

if you read the examiners report on that question its hilarious as i think most people have written it as we were taugth in AS but they wanted all the stuff about graticule !!

does anyone have the examiner's report for the bio unit 5 june 2010 paper?

would someone briefly outline positive feedback? read 2 diff books but i still don't get it. any helpful links?
thanks!

if you read the examiners report on that question its hilarious as i think most people have written it as we were taugth in AS but they wanted all the stuff about graticule !!

They are saying the same thing! chose the shorter one! Oh but mention that barreceptors are in carotid arteries you get a mark for that.

what the hell is a graticle!

would someone briefly outline positive feedback? read 2 diff books but i still don't get it. any helpful links?
thanks!

mechanisms that enhance the output created by a stimulus - they result in even greater depatures from the original level

take temperature as an example..

if the temperature went 37 --> 38

positive feedback would see it go to 39, 40, 41, 42 etc

likewise if it went 37 ---> 36

you would see - 35, 34, 33, 32, 31 etc

A stimulus causes a change in the set-point, but instead of the body trying to bring it back to normal, the stimulus causes a further move away from set point. (not sure if this explanation is clear enough!)

e.g. during depolarisation, opening of sodium channels causes sodium ions to flood into the cell, which then leads to opening of adjacent sodium channels.

eg. breakdown of temperature control during a fever

eg. production of oxytocin, which causes dilation of the cervix during labour - is on a positive feeback loop, so contractions become faster and quicker.

wouldnt acetylcholine increase the heart rate tho? :/ its an excitatory neurotransmitter

If there's anything that increases heart rate, it's definately adrenaline, which binds to SAN receptors, increasing heart rate, so returning xxxx back to normal levels.

The opposite is ACh, which only for heart rate as I've found, is secreted, binds to SAN receptors, and slows down heart rate.

But don't get mixed up with Acetylcholine being transmitted accross a cholinergic synapse, binding to sodium channels/receptors, causing them to open, allowing the influx of Na+.

(ACh is a shorthand way of writing Acetylcholine!

wouldnt acetylcholine increase the heart rate tho? :/ its an excitatory neurotransmitter

Mmmmm just got confused why ACh would decrease heart rate rather than increasing it