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Some aqa a2 questions

Q1. Explain why converting pyruvate to ethanol is important in allowing the continued production of ATP in anaerobic respiration (2marks)

investigating effect of temperature on rate of anaerobic respiration. Yeast suspension mixed with glucose solution and the volume of gas collected in 5 minutes was recorded. results for 30C
Result 1 =38.3
Result 2 = 27.6
Result 3 = 29.4

Q2: if aerobic respiration had been investigated rather than anerobic, how would you expect the volumes of gas collected at 30C to differ from these results? (3marks)

Q3: give two ways in which anaerobic respiration of glucose in yeast is different from anaerobic resp. of glucose in muscle cell.
For this one i said that 'lactate is produced in muscle cell whereas ethanol and co2 produced in yeast' what is the other one though???

Q4. (not linked to respiratiuon) : How many antigen determining alleles will be present in a white blood cell? why?

If anyone could help that would be great :biggrin:

Reply 1

nikk

Question One Answer

In the process of Glycolysis which produces a net gain of 2x ATP, two molecules of NAD⁺ are reduced to NADH. These molecules need to be re-oxidised to NAD⁺, otherwise Glycolysis would very quickly grind to a halt. In the absence of oxygen to act as the terminal electron acceptor, pyruvate is first decarboxylated and then reduced as the electrons and protons are transferred from NADH to Pyruvate to yield ethanol and NAD⁺ (catalysed by pyruvate decarboxylase) Hence NAD⁺ has been regenerated and Glycolysis is free to continue producing ATP from glucose by substrate-level phosphorylation.

Reply 2

moojoo

A1. The conversion is important as it regenerates NAD which is required for further ATP production (glycolysis)

A2. You'd expect the volumes of gas to be similar for aerobic respiration. This is because the gas is carbon dioxide and in both types of respiration it is given out via the link reaction. Thus there should be no difference between the two types, as both release carbon dioxide in the same way.

A3. Lactate in muscle and ethanol in yeast is correct. (I think) carbon dioxide given off in yeast but not in muscle cell, just lactate is produced.

A4. Each white blood cell (like B lymphocyte) is specific to one particular antigen, so therefore 2 alleles?

Hope that kinda helps lol

Reply 3

nikk

moojoo

A4. Each white blood cell (like B lymphocyte) is specific to one particular antigen, so therefore 2 alleles?

Yes I would assume that is the correct answer. But I think it's a bit of a dodgy question though because it doesn't state whether the antigen phenotype is controlled by one or more genes.

You beat me too it on the other questions! :p:

--------------

BTW - in alcoholic fermentation, does anyone know if both the decarboxylation of pyruvate and the reduction of acetylaldehyde to ethanol are both catalysed by pyruvate decarboxylase? Or is there another enzyme for the second step? I haven't got my notes with me and can't find anything on google ( :eek:

) hehe.

Reply 4

Muse

nikk

BTW - in alcoholic fermentation, does anyone know if both the decarboxylation of pyruvate and the reduction of acetylaldehyde to ethanol are both catalysed by pyruvate decarboxylase? Or is there another enzyme for the second step? I haven't got my notes with me and can't find anything on google ( :eek:

) hehe.

**** knows :p:

Reply 5

nikk

Miles

**** knows :p:

Sessh, don't they teach you medical students anything these days?! :wink:

:miles:

Reply 6

grapesugar

Thankyou so much for all the help on the questions!!!!! Ya all so clever! Thanks :wink:

Reply 7

grapesugar

Sorry, coming back to question 2 you said

A2. You'd expect the volumes of gas to be similar for aerobic respiration. This is because the gas is carbon dioxide and in both types of respiration it is given out via the link reaction. Thus there should be no difference between the two types, as both release carbon dioxide in the same way.

Would the volumes of gas not be more because in aerobic respiration, carbon dioxide is given off in the link reaction and in the krebs cycle. Anaerobic does not have the krebs and so less carbon dioxide?????????????

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