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A2 Biology Discussion and Help

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1.

I'm asking this in reference to the measuring oxygen uptake experiment.

My teacher said that if the organisms are anaerobically respiring, they produce no gas, and if there's no soda lime (or KOH) then there'll be no pressure change and the liquid in the tube won't move.

But I read in my book that a waste product of anaerobic respiration is CO2, so I'm not sure.

This is Edexcel Biology A2 Unit 5.

Hey, does anyone know the difference between stretch receptors and sensory receptors? (In relation to maintaining breathing rates and heart rate). Thanks!
Original post by soraskeyblade

1.

I'm asking this in reference to the measuring oxygen uptake experiment.

My teacher said that if the organisms are anaerobically respiring, they produce no gas, and if there's no soda lime (or KOH) then there'll be no pressure change and the liquid in the tube won't move.

But I read in my book that a waste product of anaerobic respiration is CO2, so I'm not sure.

This is Edexcel Biology A2 Unit 5.



I think the experiment's about aerobic respiration. So when they respire they will take in oxygen and let out carbon dioxide, but because the soda lime takes in the carbon dioxide there will be less gas overall (because less oxygen due to respiration of the organisms as well as less carbon dioxide due to the soda lime). But if the soda lime wasn't there then there would be a conversion of oxygen to carbon dioxide through the respiration of the organisms so the pressure would not change as one's being converted into the other. Hope that makes sense!
Please help me with this question im desperate :frown:

"The refractory period of a neurones has two components, absolute and relative. Calculate the maximum number of impulses that can be generated in a neurones when the total refractory period is 5ms"
"Calculate the percentage increase in nerve impulses if the stimulus intensity is raised high enough to overcome the relative refractory period of 4ms?"
Original post by MarieSama
Please help me with this question im desperate :frown:

"The refractory period of a neurones has two components, absolute and relative. Calculate the maximum number of impulses that can be generated in a neurones when the total refractory period is 5ms"
"Calculate the percentage increase in nerve impulses if the stimulus intensity is raised high enough to overcome the relative refractory period of 4ms?"


This link might help, read till the end of the page where your question is answered. :smile:

http://www.physiologyweb.com/lecture_notes/neuronal_action_potential/neuronal_action_potential_frequency_coding_in_the_nervous_system.html
Hey, I know this is to do with A2, but since you did AS as well, just wanted to know what websites did you use to revise for AQA AS biology??


Original post by DavidYorkshireFTW
I couldn't already see an A2 Biology thread however I noticed there was an AS Biology thread so here it is ..:colondollar:

For those who want to either discuss A2 Biology, or even need help :smile:

Past Papers: (Specifications are also available using these links)
AQA : http://www.aqa.org.uk/subjects/science/a-level/biology-2410/past-papers-and-mark-schemes

OCR : http://www.ocr.org.uk/qualifications/as-a-level-gce-biology-h021-h421/

Edexcel : http://www.edexcel.com/quals/gce/gce08/biology/Pages/default.aspx

WJEC : http://www.wjec.co.uk/index.php?subject=12&level=21&list=paper





SYNOPTIC ESSAY PACK: https://www.dropbox.com/s/iprbtmo7vh0w903/Synoptic%20Essay%20Pack.pdf?dl=0


The following Youtube channel contains very good walkthroughs of fully explained Biological mechanism relevant in A2 Biology:
http://www.youtube.com/user/khanacademy/videos

I also have a PDF copy of a guide to writing the synoptic essay containing examples which have gained full marks, so PM me your email and I will be happy to send it :smile:

I also have 'exampro' but only for AQA, which I would also be happy to send to anyone who PM's me their email :smile:

I have done A-level AQA Biology already so if you need help with anything, just quote me :smile:
AQA BIOLOGY!!!

HELP! how do you structure the 25 mark essay?

how many points should you write? should there be an introduction and conclusion?

i understand it is 16 marks for scientific content, 3 relevance, 3 breadth and 3 quality of written communication.

my first essay given is on cycles in biology
Do we get any qs relating to AS topics in A2 biology for unit 4 edexcel
Because i just saw a qs on plant fibres structure of cellulose multiple times in the past papers????
:'(
I[QUOTE=Bloom

Yeah there are questions from AS
(edited 7 years ago)
Original post by Sara Elsaadany
I[QUOTE=Bloom

Yeah there are questions from AS

How many max.qs we will get from AS
And do we have to review all of AS Bio?
Original post by phaseshift
Great idea - as with the AS thread.

I've survived OCR AS and A2 Biology so if anyone has anything OCR specific, quote me!


how effecive were doing the past papers? like all of them since 2008?
Hi- not sure if im in the right place but can anyone explain what "heritable variation" means?
Reply 452
Avatar for Ali__X
Ali__X
3
Hey guys, I'm studying OCR A2 Biology (new spec from 2015).

Does anybody have any links to some really good biology notes which cover all the points on the specification? A girl I'm helping (studies the same spec as me) says she hates making notes and feels that she doesn't benefit much from them, and would much rather just learning straight off.

Thanks for any help, will be much appreciated!! :smile:
In Biology unit 6
Qs3 part d
They ask about recording and presenting data
In that do we have to draw our table and graph with empty boxes for data etc
Or do we just give a general idea of how our graph and table should look like
Original post by yl95
Can someone please help me with this question?
'The increase in productivity when manure was applied was lower than for other forms of nitrogen fertiliser. This is ecause the manure has to break down before its nitrogen is released and this process takes a few months. How might a farmer who spreads manrue on his/her crops, use this information in order to improve productivity?'


Let us take the problem by the neck and solve it! Firstly, what is the root cause of manure giving lower yield of crops? OK, the Q tells you that it breaks down too slowly - agreed? So the simple solution is to speed up this brekdown process.

How? Good Q! Assuming manure is cow's "s**t" (sorry not a nice thought haha :frown:), it will contain breakdown products remaining from the cow's digestive system (omentum??) after absorption, right?

These would be, as far as nitrogen goes, some proteins, uric acid, creatinine, ammoinium salts.

OK - now we are talking :smile: - we could add a mixture of some acidic material e.g. vinegar (acetic acid), which would react with the ammonium compounds plus some enzymes that could speed up the breakdown of the organic nitrogen material. (Just advise the farmer to stick some corks in his nostrils before doing this!!

I WOULD HAVE THOUGHT THIS WOULD GIVE YOU AT LEAST 2 MARKS! AHOY!
(edited 6 years ago)
Original post by Jessie15
Hey, does anyone know the difference between stretch receptors and sensory receptors? (In relation to maintaining breathing rates and heart rate). Thanks!


@Jessie15

Hi,

Firstly sorry for such a late response - did not look t this thread earlier - hope my answer still helps you!

Stretch receptors that conrol cardiovascular function would include the baroreceptors in the carotid sinus and in the aortic sinus - these respond to changes in blood pressure, obviously being "stretched" to a greater extent when the blood pressure rises. If the b.p. rises (and therefore stretches the baroreceptors more), this increases the rate of impulses fired from these receptors, whose neurones synapse in the cardiac centre in the medulla oblongata (in the brain stem); the result is an increase in the vagal outflow to the sinus node near the point of entry of the superior vena cava into the right atrium.

The naturally upward sloping (at rest) resting potential of the nodal myocytes reduces in gradient (rises slower), so that it reaches its threshold level later and action potential occurs later. Since the sinus node is normally the pacemaker of the heart (i.e. determines the intrinsic heart rate), this results in a slowing of the heart (relative bradycardia), tending to reduce b.p. to correct the original increase in b.p. (b.p. is directly related to cardiac output, and the latter is the product of the stroke volume and the heart rate). The opposite sequence of events occurs if the b.p. drops e.g. when the patient stands up from a sitting position.

Sensory receptors that you refer to are, I should think, the chemoreceptors in the carotid body, which detect the CO2 concentration in the blood passing through the carotid artery. These neurones also project to the medulla, in this case more so to the respiratory centre. An increase in CO2 concentration (more correctly the pCO2 (partial pressure of carbon dioxide in the blood)) causes an increase in the rate of ventilation (breathing) also called tachypnoea, therefore getting rid of CO2 from the lungs quicker, and tending to restore the pCO2 back to normal.

Thank you!

M (clinical pharmacologist)
(edited 6 years ago)
Original post by Bloom <3
Do we get any qs relating to AS topics in A2 biology for unit 4 edexcel
Because i just saw a qs on plant fibres structure of cellulose multiple times in the past papers????
:'(


@Bloom <3

Hi, the thing to take on board is that any A2 paper (including the so-called "synoptic" ones) will often require knowledge of AS material, in other words, although it is less likely that a whole Q in A2 will be an AS syllabus one, there will be several which will need to to understand, amalgamate and then present/display your appeciation of the concepts, both AS and A2, in some Qs.

e.g. there might be a Q on renal function, let us say, on the proximal tubule cell, and it might ask you to point out what features of that cell are adaptations to its function. Here, you will need to know that a proximal tubular cell has the primary function of re-absorption of substances needed by the body (and which, therefore, you do not want to throw away in the urine) e.g. glucose, amino acids, Na+, HCO3-, etc, and that some of these are re-absorbed by active transport so need ATP (A2 kidney syllabus - homeostasis), but you also need to know that ATP is ultimately generated by oxidative phosphorylation in the mitochondria, so this cell will have many large mitochondria (AS syllabus) AND also that surface area is crucial in life physiology (AS syllabus), so the microvilli of the luminal aspect of these cells (A2 syllabus) are also crucial for the efficiency of re-absorption.

e.g. a Q on genetics, perhaps testing your knowledge of the mutation in specific disease (which may be outside the syllabus, but which they will tell you the basic principles of e.g. they might give a brief description of Hartnup disease in which there is a defect in the absorption of histidine from the intestine - DON'T PANIC - there is no way they will expect you to know Hartnup disease beforehand!! :smile: - A2 syllabus (digestion, nutrition, etc) and ask you to work out something that needs AS knowledge in this e.g. they might divert to the structure of amino acids, telling you that histidine is a basic a.a. and therefore has an extra amino (-NH2) group, and perhaps ask you something about the amphoteric (Greek ampho = BOTH so both acidic and alkaline [so a.a.'s are good buffers] e.g. amphibian can live in BOTH land and water) nature of a.a.-s and how DNA structure and the triplet code (AS syllabus) might have been altered (mutated) to cause this disease.

If you think about it, AS is taught before A2 for a reason!

BEST OF LUCK in two weeks!
(edited 6 years ago)
Original post by macpatelgh
Let us take the problem by the neck and solve it! Firstly, what is the root cause of manure giving lower yield of crops? OK, the Q tells you that it breaks down too slowly - agreed? So the simple solution is to speed up this brekdown process.

How? Good Q! Assuming manure is cow's "s**t" (sorry not a nice thought haha :frown:), it will contain breakdown products remaining from the cow's digestive system (omentum??) after absorption, right?

These would be, as far as nitrogen goes, some proteins, uric acid, creatinine, ammoinium salts.

OK - now we are talking :smile: - we could add a mixture of some acidic material e.g. vinegar (acetic acid), which would react with the ammonium compounds plus some enzymes that could speed up the breakdown of the organic nitrogen material. (Just advise the farmer to stick some corks in his nostrils before doing this!!

I WOULD HAVE THOUGHT THIS WOULD GIVE YOU AT LEAST 2 MARKS! AHOY!


Hi, thanks for the reply but I posted that three years ago and I'm about to graduate from university, haha.
Reply 458
Avatar for f999
f999
10
When writing the null hypothesis how do u know whether to write "no significant difference" or "no significant correlation" between the variables?
@f999

Hi,

It is a slightly involved concept to grasp. Let me walk you through it step by step (before you run! :smile:).

The very fact that the null hypothesis is called "null" (meaning almost like "none" or "zero":wink: is intentional and is therefore a hypothesis you set out at the beginning of your analysis that would mean a "null" or "zero" significance of your potential results. THEN, YOUR EXPERIMENTS ATTEMPTS TO PROVE THAT THE NULL HYPOTHESIS is not true or is invalid. If the results show this intended end-product, i.e. that the null hypothesis does not apply (i.e. is not true), then you have proven, within the constraints of the significance value of your statistical analysis, THAT WHAT YOU SET OUT TO PROVE OR ESTABLISH, YOU HAVE ACTUALLY ACHIEVED!

So, your first possibility (no signifiant difference) would be a phrase in your null hypothesis if what you are trying to establish is that THERE IS A DIFFERENCE BETWEEN YOUR TWO SUBSETS OF DATA. e.g. if doing a double-blind placebo-conrolled crossover trial to confirm that a particular drug has an expected effect, e.g. to show that carvedilol (a beta-receptor blocking agent) has efficacy in controlling angina pectoris, you want to show that patients treated with carvedilol have reduced anginal pain (of course, everything else being kept steady as far as possible) compared to patients receiving an identical-looking placebo tablet i.e. that there IS A SIGNIFICANT difference between the two sets of data (opposite of your null hypothesis) and if you do this i.e. if you show that you have disproved the null hypothesis, then you have shown that carvedilol is of use in angina.

It is the opposite in your 2nd option (no significant correlation); here, you are trying to prove that two variables are related (possibly causally), so if you prove beyond reasonable doubt that the null hypothesis is not applicable, then there is a correlation between the two sets of data, i.e. your results are significant - in other words, you have proved what you set out to show. Otherwise not.

It seems to be the wrong way round to do things, the logic being that it is easier to prove beyond doubt that something exists than to prove that it does not!

Sorry about the nerdy length of this explanation, but hope it helps.
BEST OF LUCK IN CURRENT EXAMS!!

M (former medical student)
(edited 6 years ago)

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