AQA BIOL5 ~ 17th June 2013 ~ A2 Biology

Hey! From the mark scheme I was given by my teacher, I got told that there's only 2 extra marks for out of spec stuff, so personally I wouldn't stress about learning reams, just read round a bit and see if there's anything relevant that you could maybe include, but I wouldn't panic if you can't fit it in on the day

Hi everyone, this is a question about unit 4 but I couldn't find the thread for it. I'm guessing you're all doing unit 4 or have done it anyway??? My school has decided to do the whole course at the end of the year ahhhhhhhhhhhhhhhh!


Anyway can anyone answer this question from the Jan 2011 Unit 4 paper?

"Residual food intake RFI is the different between the amount of food an animal actually eats and its expected food intake based on its size and growth rate. Scientists have selectively bred cattle for low RFI.

When RFI is calculated, low values are negative. Explain why there are negative."

WHY??? I've looked on the mark scheme and it says "amount of food take in is less than expected" but this doesn't make sense to me

Please can someone explain?? Many thanks

how are you reading around the subject? What sources are u using?

Well it might help if we add numbers to this. So say that the expected food intake is 15 arbitrary units. However, in reality, the animal only eats 10 arbitrary units. As RFI is Actual intake - Expected intake, this would mean 10 - 15 which is -5. Therefore, because actual is always less than expected you will always get a negative answer.

Hope this helps.

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SPECIFICATION A

SPECIFICATION B

- There may be more which I have not found. We did the specification A ones in college

is IAA a hormone or a growth factor thingy?

what could i write about in the negative feedback essay?

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Control of blood glucose, heart rate, menstrual cycle

That's not much, sorry. I can't think of many more examples :/

what could i write about in the negative feedback essay?

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Hi. I have a quick question. Any help will be much appreciated!!

From my (summarised) understanding of an action potential..

Stimulus > Na+ channels open and diffuse into axon - depolarisation
threshold - more Na+ channels open and even more Na+ ions diffuse in.
Action potential is reached.
Na+ channels close and K+ channels open - K+ ions leave axon
If too many K+ leave - hyper polarisation caused by overshoot
Heres where im slightly confused:
If K+ ions are leaving, why is it called REpolarisation?
When the membrane was polarised K+ ions moved IN making the axon more neg than outside. But not its the opposite?? So I dont understand how the resting potential is restored

So no one can help me?

ok well well just so you know (incase you didn't already) both potassium and sodium are both positively charged. They call it positive and negative as it is all relative, due to sodium potassium pump, there is more sodium out than potassium in, so they call the inside negatively charged and out side positively charged.

ok, so, normally sodium are out but in the case of an action potential---membrane made permeable to sodium, hence there is an influx of sodium ions, along with the potassium ions ALREADY in there, so the charge of the Na and the K build up, past threshold, up to 40mV where then the K gates open, sodium close, so the sodium can't in effect escape, but the K can and by the process of diffusion they leave (from high conc to low conc) so this reduces the potential back down in to the minuses (but this is not normal for the axon membrane to have Na in and K out)----now, the K gates are slow to respond so they do not close in time hence there is a temporary overshoot.....once closed, its back down to the sodium potassium pump to restore normality in the axon, bringing back in the K from the outside and 'booting' out the Na ions which it doesn't want! thus resting potential is restored!

Hi everyone. Just wondering, when we refer to Transcriptional factors, for this specification, are we to assume that they all function as activators or also as repressors. I came across a question n the june'10 paper of oestrogen. The description they provide in the mark scheme is of oestrogen functioning as an activator, though there are no clues in the question to suggest that all it functions is as an activator. Thank you!