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

I thought that whenever the baroreceptors are stretched (hence detecting an increase in pressure?) they will send impulses to the CVC which will then send impulses down the PARASYMPATHETIC nerve to lower the heart rate.
Sorry if I am being really dumb here.

And I thought it's chemoreceptors that play more of a role. They detect a drop in pH due to an increase in CO2 as there is more aerobic resp taking place. That's what it says in the CGP book and in the purple edexcel revision guide anyway.

i would still mention chemoreceptors because ultimately chemoreceptors do detect the fall in pH associated with increased respiration (and subsequntly increased blood CO2 levels)

but i agree with what you've said before...

i think the distinction was in why baroreceptors in the vessels lead to an INCREASED heart rate in response to lower pressure, and why the baroreceptors in the atrial walls lead to an INCREASED heart rate in response to an INCREASED pressure

Ok yeah, I agree..mentioning both would be good

Yup..kind of confusing that the receptors in the heart walls seem to have a positive feedback system but ultimately, it's to reduce the overall volume of blood..so would you say that's negative or positive feedback? cause the direct effect is to magnify the change so it seems like positive but...

sorry I havent finished.. I had to stop doing biology for a while and focus solely on chemistry... there was so much in chemistry that I hadnt revise and my exam is today.. I'll start again today.
sorry for the delay

Hey,

You're right but those are the baroreceptors located in carotid arteries. However, the stretch receptors in the heart muscle walls respond to increased stretching (more than usual due to greater venous return) by stimulating the sympathetic nerve to increase heart rate. Essentially, this is also a negative feedback system which I think chemdweeb mentioned somewhere before about the heart trying to reduce the volume received to the normal volume by contracting more and harder.

Yup, both are important. I think they both work together in the end so might as well write both if you have time but knowing edexcel, we're not likely to have much spare time :P

how is everyone finding the article? im finding it really confusing!

Can someone explain respiration?

I get the whole proton pumping thing, but I don't get the ETC. In the book it has nothing about what actually happens when the ETC accepts the electron. I am guessing they go through a series of redox reactions, but is there energy released when this occurs? Is this used to phosporylate ADP? I don't get it.
In the book it just mentions the ETC and then talks about chemiosmosis, completely ignoring the ETC giving the impression that ATP is only formed by chemiosmosis.

thanks

Does anyone know what the importance of synaptic divergence and synaptic convergence is?

divergence allows the wave of depolarisation to distributed from one neurone to multiple nuerones, therefore these impulses are distibuted around the body.
Convergence causes multiple neurone's electrical impluses to be amplified into one neurone, making the action potential more likely to occur.

When the electrons gets accepted by the primary electron acceptor, they get passed down the ETC, through a series of redox reactions like you said.

As they are passed down the ETC. the electrons keep going from a higher energy level to a lower energy level and this releases energy. The energy is then used to pump protons (H+) into the space between the inner membrane and outer mitochondrial membrane.

This creates an electrochemical gradient and protons move down this gradient via ATPsynthase, and when this happens ADP gets phosphorylated to ATP

http://www.youtube.com/watch?v=mfgCcFXUZRk&feature=relmfu
this video is really good^

I used that video as well earlier in the year, it's really good and his accent sucks you in :P If you get what I mean...haha

Could someone shed light on what we need to know on how plants react to stimuli?

LOL... shed light

haha... erm...
You should know about phytochromes and how they respond to light ... they detect light ... where they are found? possible mechanism? the two types.... and certain functions / consequences of phytochromes like germination... etiolation.... etc.

and then there is shedding unilateral light on plants... phototropism and how this is controlled by IAA