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

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I have a favour to ask you wonderful people...
Does anyone have notes/technique on the core practicals from the A level? Obviously its the unit 5 ones I'm in desperate need of (habitutation/snails, respirometer and spirometer I think?) but any core practical notes would be wonderful.
Thank you so much to anyone who can help.
Original post by InItToWinItGetIt?
Another question:

Explain how an increase in blood volume in the venae cavae and right atrium causes a change in heart rate.

The MS says:
1. Increased blood pressure (in vena cava / right atrium);
2. Baroreceptors stimulated;
3. {Cardiovascular centre / medulla} initiate impulses in {sympathetic / accelerator} nerve;
4. {Stimulation of SAN increased / eq} / decreased delay at AVN;
5. Heart rate increased / eq;

I don't get this. I thought an increase in pressure leads to a decrease in heart rate? :s-smilie:


There are two wonderfully competing reflexes (which we dont need to know about):

The Bainbridge Reflex
1) During Exercise, for example, the volume of blood that returns to the heart (the venous return) is greater.... due to increased skeletal muscle activity
2) This leads to a greatER volume of blood returning to the atria.... causing the walls to stretch more... and the baroreceptors in the wall are activated because they detect an increased pressure accompanied by the increased volume of blood....
3) .... send more frequent impulses to CV control centres... ... sympathetic motor nerve.... ... increase in frequency of spontaneous depolarisation of the SAN... increased heart rate...

That is what the question asked about.... bainbridge reflex depends on the venous return and if you think about its a negative feedback system... there is a normal set point for the volume of venous return... however, during exercise, the venous return increases... and thus the heart needs to reduce the venous pressure again to normal... so it "sucks" blood out of the venae cava faster.... therefore, reducing the pressure (im not too sure about this paragraph... if someone could validate.... im recalling from memory...IIRC, it should be stroke volume that should increase, not rate... but ?)


Second, what you seemed to be asking about is the CAROTID SINUS REFLEX or the AORTIC REFLEX

these involve the baroreceptors in the aortic sinus and carotid sinus..... during exercise, the various responses to the pH drops etc. lead to increased heart rate and stroke volume... which leads to increased cardiac output.... increased cardiac output means there is a greater volume of blood flowing against the blood vessels per unit time... therefore increased blood pressure, which is detected by these baroreceptors.. negative feedback returns blood pressure back to normal...
this is the reason why when you take the pulse you should avoid taking it from the carotid artery... as you might press the baroreceptors, that are falsely tricked into thinking that the pressure has increased... thereby causing a false reading as they decrease the blood pressure
Original post by Phenylethylamine_
Hmmm..yeah that's what I'm thinking! Increase in blood pressure definitely leads to a decrease in heart rate


I was reading in the green edexcel book, and it says the reverse actually happens during exercise. Adrenaline released during exercise actually dilates the blood vessels and this causes the blood pressure to drop a little. This reduces the stretch of the baroreceptors and causes the sympathetic nerve to get activated.

Original post by chemdweeb1234
There are two wonderfully competing reflexes (which we dont need to know about):

The Bainbridge Reflex
1) During Exercise, for example, the volume of blood that returns to the heart (the venous return) is greater.... due to increased skeletal muscle activity
2) This leads to a greatER volume of blood returning to the atria.... causing the walls to stretch more... and the baroreceptors in the wall are activated because they detect an increased pressure accompanied by the increased volume of blood....
3) .... send more frequent impulses to CV control centres... ... sympathetic motor nerve.... ... increase in frequency of spontaneous depolarisation of the SAN... increased heart rate...

That is what the question asked about.... bainbridge reflex depends on the venous return and if you think about its a negative feedback system... there is a normal set point for the volume of venous return... however, during exercise, the venous return increases... and thus the heart needs to reduce the venous pressure again to normal... so it "sucks" blood out of the venae cava faster.... therefore, reducing the pressure (im not too sure about this paragraph... if someone could validate.... im recalling from memory...IIRC, it should be stroke volume that should increase, not rate... but ?)


Second, what you seemed to be asking about is the CAROTID SINUS REFLEX or the AORTIC REFLEX

these involve the baroreceptors in the aortic sinus and carotid sinus..... during exercise, the various responses to the pH drops etc. lead to increased heart rate and stroke volume... which leads to increased cardiac output.... increased cardiac output means there is a greater volume of blood flowing against the blood vessels per unit time... therefore increased blood pressure, which is detected by these baroreceptors.. negative feedback returns blood pressure back to normal...
this is the reason why when you take the pulse you should avoid taking it from the carotid artery... as you might press the baroreceptors, that are falsely tricked into thinking that the pressure has increased... thereby causing a false reading as they decrease the blood pressure


See above. That's what it says in my textbook. :s-smilie:

And like say if there was a question is:

Heart rate increases during exercise. Explain the mechanisms involved in controlling this increase in heart rate.

Do we talk about baroreceptorrs (as there is apparently drop in BP during exercise) or chemoreceptors (due to drop in pH during exercise).

Because like say in the MS above, it talked about baroreceptors but in another one it talks only about chemoreceptors. :confused:
Original post by Phenylethylamine_

Original post by Phenylethylamine_
Yup, sucks. I don't think yesterday's exam helped one bit. :frown: I honestly don't know what to expect. Goodluck with the rest of your exams! :biggrin:


Same for you. Well I guess we just have to move on and totally rape our next exam. Unit 5 biology isn't going to go down like this either.
Original post by InItToWinItGetIt?
I was reading in the green edexcel book, and it says the reverse actually happens during exercise. Adrenaline released during exercise actually dilates the blood vessels and this causes the blood pressure to drop a little. This reduces the stretch of the baroreceptors and causes the sympathetic nerve to get activated.



See above. That's what it says in my textbook. :s-smilie:

And like say if there was a question is:

Heart rate increases during exercise. Explain the mechanisms involved in controlling this increase in heart rate.

Do we talk about baroreceptorrs (as there is apparently drop in BP during exercise) or chemoreceptors (due to drop in pH during exercise).

Because like say in the MS above, it talked about baroreceptors but in another one it talks only about chemoreceptors. :confused:


Hey, this confused me too but after reading the book more carefully, it makes more sense now :smile:
Basically, the difference is that the responses take place BEFORE, DURING and towards the END of exercise.

- At the start of exercise, adrenaline is released which dilates vessels and blood pressure falls. Baroreceptors detect a fall in pressure and stimulates the CVC which sends impulses down the sympathetic nerve to increase heart rate and blood pressure (Negative feedback). This is good before exercise as it INCREASES CARDIAC OUTPUT.

- At the beginning of exercise, more blood returns to the heart from the veins due to sudden increase in movement so more blood flows to the atria and more receptors are stretched which send impulses to the CVC that stimulates the sympathetic nerve to increase heart rate. Also, like 'chemdweeb' said, stroke volume also increases...it's not affected by the CVC however- the cardiac muscle contracts harder due to increased stretching so stroke volume increases and overall cardiac output will increase.

- However, DURING and towards the END of exercise, baroreceptors in carotid arteries etc send impulses to the CVC which stimulates the parasympathetic nerve to slow down the heart rate and dilates blood vessels to lower blood pressure (Negative feedback)

That's what I think - let me know if there are any mistakes etc. but hope it helps :biggrin:

As for the baroreceptors and chemoreceptors, I usually use baroreceptors when referring to heart rate and chemoreceptors with breathing rate. Of course, chemoreceptors affect heart rate too but apparently it's not a direct effect but related to their effect on the stretch receptors that detect changes in ventilation rate which in turn increases heart rate so ultimately, it's the baroreceptors that are controlling the heart rate in both cases.
Reply 1845
Original post by tkoki1993
I just started on topic 8 this morning. But i have an exam on tuesday so I'll probably finish on thursday


Sorry to pester you, but by any chance have you finished your topic 8 notes? If you have, would you mind uploading them? Thank you :smile: The topic 7 ones, were/are so useful!
Original post by InItToWinItGetIt?
I was reading in the green edexcel book, and it says the reverse actually happens during exercise. Adrenaline released during exercise actually dilates the blood vessels and this causes the blood pressure to drop a little. This reduces the stretch of the baroreceptors and causes the sympathetic nerve to get activated.

Heart rate increases during exercise. Explain the mechanisms involved in controlling this increase in heart rate.

Do we talk about baroreceptorrs (as there is apparently drop in BP during exercise) or chemoreceptors (due to drop in pH during exercise).

Because like say in the MS above, it talked about baroreceptors but in another one it talks only about chemoreceptors. :confused:


Ok i see the answer to your problem :smile:

The book is a bit crap in bits of DETAIL, this should help you understand it better, it is all a bit complicated, but i dont think you should over complicate it and dont learn it for the exam:


Spoiler

Original post by sparkle*92
Hey, this confused me too but after reading the book more carefully, it makes more sense now :smile:
Basically, the difference is that the responses take place BEFORE, DURING and towards the END of exercise.

- At the start of exercise, adrenaline is released which dilates vessels and blood pressure falls. Baroreceptors detect a fall in pressure and stimulates the CVC which sends impulses down the sympathetic nerve to increase heart rate and blood pressure (Negative feedback). This is good before exercise as it INCREASES CARDIAC OUTPUT.

- At the beginning of exercise, more blood returns to the heart from the veins due to sudden increase in movement so more blood flows to the atria and more receptors are stretched which send impulses to the CVC that stimulates the sympathetic nerve to increase heart rate. Also, like 'chemdweeb' said, stroke volume also increases...it's not affected by the CVC however- the cardiac muscle contracts harder due to increased stretching so stroke volume increases and overall cardiac output will increase.

- However, DURING and towards the END of exercise, baroreceptors in carotid arteries etc send impulses to the CVC which stimulates the parasympathetic nerve to slow down the heart rate and dilates blood vessels to lower blood pressure (Negative feedback)

That's what I think - let me know if there are any mistakes etc. but hope it helps :biggrin:

As for the baroreceptors and chemoreceptors, I usually use baroreceptors when referring to heart rate and chemoreceptors with breathing rate. Of course, chemoreceptors affect heart rate too but apparently it's not a direct effect but related to their effect on the stretch receptors that detect changes in ventilation rate which in turn increases heart rate so ultimately, it's the baroreceptors that are controlling the heart rate in both cases.


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.


Original post by chemdweeb1234
Ok i see the answer to your problem :smile:

The book is a bit crap in bits of DETAIL, this should help you understand it better, it is all a bit complicated, but i dont think you should over complicate it and dont learn it for the exam:


Spoiler



But when you are doing exercise your blood pressure doesn't decrease? :s-smilie: - I am probably being really idiotic, but I don't get it at all :frown: - Thanks for going to all this trouble mate, I really appreciate it :smile: Dunno what's wrong with me lol
(edited 12 years ago)
Original post by sparkle*92



As for the baroreceptors and chemoreceptors, I usually use baroreceptors when referring to heart rate and chemoreceptors with breathing rate. Of course, chemoreceptors affect heart rate too but apparently it's not a direct effect but related to their effect on the stretch receptors that detect changes in ventilation rate which in turn increases heart rate so ultimately, it's the baroreceptors that are controlling the heart rate in both cases.


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
http://www.mediafire.com/?mhuznkz3njt

The question was from the heart document from this link ^ Question 8 if anyone wants a closer look at it. There are other topic questions as well, it's generally very good.
Original post by InItToWinItGetIt?
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.




But when you are doing exercise your blood pressure doesn't decrease? :s-smilie: - I am probably being really idiotic, but I don't get it at all :frown: - Thanks for going to all this trouble mate, I really appreciate it :smile: Dunno what's wrong with me lol


Agreed

Blood pressure does not decrease during exercise...

but what would happen if the pressure kept increasing?


also as sparkle mentioned... the adrenaline is good... the small decrease in blood pressure at the start of exercise consequentially leads to the increase in blood pressure as the baroreceptors of the blood vessels are not stimulated.... this increases the cardiac output which allows the needs of the organism's increased respiration to be met
(edited 12 years ago)
ive created a facebook page in protest against unit 4 exam! join :smile:
it wont let me post it :frown:
Original post by chemdweeb1234
Agreed

Blood pressure does not decrease during exercise...

but what would happen if the pressure kept increasing?


also as sparkle mentioned... the adrenaline is good... the small decrease in blood pressure at the start of exercise consequentially leads to the increase in blood pressure as the baroreceptors of the blood vessels are not stimulated.... this increases the cardiac output which allows the needs of the organism's increased respiration to be met


I think I get it a bit better now. I looked up Bainbridge on wiki.. it's not on our spec is it? Because it's not in the books or anything.
ive created a facebook page in protest against unit 4 exam! join wont let me post so search
Protest agains Edexcel biology unit 4 exam - 13/06/11
xx
Reply 1856
Original post by claire4095
ive created a facebook page in protest against unit 4 exam! join wont let me post so search
Protest agains Edexcel biology unit 4 exam - 13/06/11
xx


yeah!

Here's the link! http://www.facebook.com/pages/Protest-against-Edexcel-Biology-Unit-4-Exam-130611/130890383657523

'LIKE' every1n! :biggrin:
Reply 1857
Does anyone have any advice on how to revise for the pre-release, for the rest of the paper i just learn from the spec and feel a bit lost on this part!
Original post by medtobe

Original post by medtobe
Just dnt know what to say abt the paper.
its the type where you could have owned it or could have messed it big time.

to many long marks Qs which meant wehave to write a lot and miss on points.
edexcel is :angry:

6 mrks on wavelenght lost :mad:

and 6 mrks fr why the scientist didnt agree.

i too couldn't answer those seaweed and wavelength related question(2+4) due to shortage of tym......but i attempted the rest...still nt that much satisfied with my exam..but i could well organize the answer for fossil fuel ques....Best of Luck
AND PEOPLE PLEASE LETS DISCUSS ABOUT ARTICLE FROM NOW ON TILL THE EXAM DAY.LETS JUST NOT LEAVE A SINGLE WORD OF ARTICLE UNKNOWN.
Original post by L2R1C
Sorry to pester you, but by any chance have you finished your topic 8 notes? If you have, would you mind uploading them? Thank you :smile: The topic 7 ones, were/are so useful!


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

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