AQA A2 Biology BIOL5 - 17th June 2015

Are all three both conduction AND convection? :/

In terms of homoeostasis, what does the spec mean when it says internal conditions are controlled within certain limits?

We may have seen similar questions. The one I saw had radiation specifically on the mark scheme. There was no sign of conduction/radiation.

is anyone able to explain to me the movement of an action potential in an unmyelinated axon? the textbook (pg 169) is ridiculously confusing

Guess it just means that the body can cope with slight changes in temperature etc but not with extremes
for example if it was too cold, you would freeze to death

basically negative feedback, it can deal with variations around set points but not too far.

You could mention radiation as I have seen it in a couple of questions I have done.

So for heat loss: Vasodilation of the arteriole walls would lead to more radiation of heat and so there will be more heat lost from the blood.

Don't say radiation, it said accept conduction/convection in the mark scheme but reject radiation. Don't know why but its aqa biology for you

Yeah that makes sense to me. I think the question when radiation wasn't accepted might have been the heat suit one (idk if you've done it)... but as you said that's AQA for you!

Thanks for your help, both of you.

Good point - also would it be relevant to talk about ions in terms of being part of structures e.g proteins/carbohydrates??

basically what my teacher sent me

Ok so slowly realising that I am f***ed for this exam. I feel like I might as well give up now, I know NOTHING and NOTHING is going in to my puny little brain

(I'm going to assume you know how an AP starts)

So after an AP occurs, the local depolarisation is detected by other voltage-gated ion channels further along the axon. So more Na+ ions diffuse in further along and another depolarisation occurs, so another AP. An AP will always move along the neurone and never backwards because, the previously depolarised region has entered a refractory period (ion channels closed) and becomes hyperpolarised. So only downstream ion channels can open, therefore AP can only go forward.

In short:

1. Other voltage-gated ion channels detect depolarisation and so open
2. Na+ ions diffuse in and so another AP generated
3. AP only goes forward because previous region is in refractory period

What marks have you all been getting on past papers? My marks have been very varied and I'm slightly worried because my unit 2 and unit 4 past papers marks were a lot higher. I think I'm just going to go over the past papers I've done tonight and make sure I'm not making the same mistakes. Anyone else feel the same?

Membranes and functions
Relationships and interactions between organisms
Importance of shapes fitting together in cells and organisms
Effects of bacteria on the lives of humans and other organisms
DNA in science and technology
Causes of disease in humans
Biological cycles
Ions and organisms
DNA and transfer of information