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# A2 Biology OCR June 2015 Revision Thread Watch

1. (Original post by brooklyniona)
Past question that I don't understand to do with respiration...

"The equation below shows aerobic respiration of compound A.
C55H100O6 + 77O2 → 55CO2 + 50H2Ocompound A
The respiratory quotient (RQ) is defined as: volume of CO2 releasedvolume of O2 absorbed|
(ii) Calculate the RQ for this reaction. Show your working."

I got 0.71 which was correct. But the next question was...
"Compound A is a fat. Suggest what the RQ of a carbohydrate such as glucose might be" The answer is 1.0 but I have no idea why! Anyone know why it's 1.0?? thanks
It's a value you should be aware of! so the RQ of carbs is 1.0, proteins is 0.8 - 0.9 and RQ of lipids is 0.7
2. (Original post by corey7695)
perfect

it is decarboxylated to form ethanal, which is hydrogenated by red nad to form nad, and ethanol is formed (my book doesn't reference the enzymes, is it lactate dehydrogenase and decarboxylase?)

explain the process that occurs when the body is dehydrated
I think it's pyruvate decarboxylase and also ethanol dehyrogenase. You'll get marks for mentioning the enzymes used. The ones you mentioned are for lactate fermentation (i.e. anaerobic respiration in mammals).
3. (Original post by tewas)
i think it's something that you need to know eg. carbohydrate = 1.0, fats = 0.7 and proteins = 0/9
Are we expected to know how to work out RQ values?
4. (Original post by coolerthanbeans)
Polygenic - caused by BOTH environment and genes, i.e. continuous variation.

Monogenic - caused by genes ONLY, i.e. discontinuous variation.

For example...
Height = continuous variation. Influenced by your genes (how tall your parents are) but also influenced by environment (type of food you eat, how much exercise you do etc)

Eye colour = discontinuous variation. Influenced by genes only. Eye colour is never changed by environmental variations ... (unless you can get some plastic surgery to change your eye colour? )

Hope that helped!
I think you're slightly off with your definition of polygenic there, please correct me if I'm actually off though!

My understanding is that polygenic is simply poly(many) genes, as in, a characteristic that is influenced by many genes, in such a way that the characteristic is continuous because there are many alleles affecting it. It may well be that for a given characteristic, the environment influences it, such as height, but that is not part of the term polygenic and a polygenic characteristic could be entirely genetically determined.
5. (Original post by Beni24)
What does a low and a high Respiratory substrate indicate?
Low: volume of oxygen consumed is much larger than volume of carbon dioxide produced. Lipids are most likely being respired.

High: volume of oxygen consumed is much smaller than volume of carbon dioxide produced. Carbohydrates most likely being respired, unlikely to be protein's being respired.

How was that?
6. (Original post by corey7695)
perfect

it is decarboxylated to form ethanal, which is hydrogenated by red nad to form nad, and ethanol is formed (my book doesn't reference the enzymes, is it lactate dehydrogenase and decarboxylase?)

explain the process that occurs when the body is dehydrated
Yes bang on , just slap in lactate dehydrogenase and lactate decarboxylase as there are always marks for it in AVP

Low W.P in blood detected by osmoreceptors in the hypothalamus
ADH flows down axon of neuroscretory cells to the posterior pituitary gland

ADH released into the blood and binds to specific receptors on walls of collecting duct where aquaporins move in and form water channels

water is reabsorbed form the collecting duct and water potential returns back to normal via negative feedback

why does anaerobic respiration makes less ATP than aerobic respiration ?
7. (Original post by corey7695)
perfect

it is decarboxylated to form ethanal, which is hydrogenated by red nad to form nad, and ethanol is formed (my book doesn't reference the enzymes, is it lactate dehydrogenase and decarboxylase?)

explain the process that occurs when the body is dehydrated
No pyruvate decarboxylase catalyses the decarboxylation of pyruvate to ethanal and ethanol dehydrogenase catalyses the hydrogenation of ethanal to ethanol.
8. (Original post by Star Light)
I think you're slightly off with your definition of polygenic there, please correct me if I'm actually off though!

My understanding is that polygenic is simply poly(many) genes, as in, a characteristic that is influenced by many genes, in such a way that the characteristic is continuous because there are many alleles affecting it. It may well be that for a given characteristic, the environment influences it, such as height, but that is not part of the term polygenic and a polygenic characteristic could be entirely genetically determined.
No, I think you're right! You're more likely to be correct anyway because I haven't looked at F215 in a few weeks as I've been focussed on F214 :P

Your answer makes a lot more sense to me
9. (Original post by bbadonde2)
No pyruvate decarboxylase catalyses the decarboxylation of pyruvate to ethanal and ethanol dehydrogenase catalyses the hydrogenation of ethanal to ethanol.
gotcha, thanks
10. (Original post by tewas)
i think it's something that you need to know eg. carbohydrate = 1.0, fats = 0.7 and proteins = 0/9
ah, i couldn't find it in the book. thank you
11. (Original post by coolerthanbeans)
Polygenic - caused by BOTH environment and genes, i.e. continuous variation.

Monogenic - caused by genes ONLY, i.e. discontinuous variation.

For example...
Height = continuous variation. Influenced by your genes (how tall your parents are) but also influenced by environment (type of food you eat, how much exercise you do etc)

Eye colour = discontinuous variation. Influenced by genes only. Eye colour is never changed by environmental variations ... (unless you can get some plastic surgery to change your eye colour? )

Hope that helped!

monogenic: characteristic coded for by one gene -> discontinues
polygenic: characteristic coded for by many genes -> continues
12. (Original post by TheLegalDealer)
Yes bang on , just slap in lactate dehydrogenase and lactate decarboxylase as there are always marks for it in AVP

Low W.P in blood detected by osmoreceptors in the hypothalamus
ADH flows down axon of neuroscretory cells to the posterior pituitary gland

ADH released into the blood and binds to specific receptors on walls of collecting duct where aquaporins move in and form water channels

water is reabsorbed form the collecting duct and water potential returns back to normal via negative feedback

why does anaerobic respiration makes less ATP than aerobic respiration ?
In anaerobic respiration glycolysis takes place which generates small amounts of ATP for protein synthesis/muscle contraction etc since there is no oxygen for the final hydrogen/electron acceptor so links, krebs and ox phos don't take place, however in aerobic respiration not only does glycolysis take place but also oxidative phosphorylation and Kreb's cycle generate ATP through chemiosmosis etc
13. Tips to getting high ums tomorrow?
14. (Original post by bbadonde2)
No pyruvate decarboxylase catalyses the decarboxylation of pyruvate to ethanal and ethanol dehydrogenase catalyses the hydrogenation of ethanal to ethanol.
so lactate dehydrogenase is for pyruvate to lactate, is there another enzyme for lactate fermentation?
15. Can someone go through selective reabsorption can't get my head around it
16. (Original post by corey7695)
so lactate dehydrogenase is for pyruvate to lactate, is there another enzyme for lactate fermentation?
Yes lactate dehydrogenase is pyruvate to lactate. There are no other enzymes involved in lactate fermentation.
17. (Original post by Star Light)
I think you're slightly off with your definition of polygenic there, please correct me if I'm actually off though!<br />
<br />
My understanding is that polygenic is simply poly(many) genes, as in, a characteristic that is influenced by many genes, in such a way that the characteristic is continuous because there are many alleles affecting it. It may well be that for a given characteristic, the environment influences it, such as height, but that is not part of the term polygenic and a polygenic characteristic could be entirely genetically determined.
Yes, you are correct, such as epistasis being polygenic whereas sex is monogenic

Some discontinuous phenotypes can also be polygenic, such as petal colour
18. I've got some hard questions on f214 and i need someones help in answering these question in detail.
19. (Original post by kad7422)
Can someone go through selective reabsorption can't get my head around it
Selective Reabsorption occurs in the proximal convoluted tubule
1. H+ ion are pumped out of the the cells into the tissue fluid. This uses active transport and so ATP
2. As a result there's a higher concentration of Na+ outside of the cells lining the PCT compared to inside so a diffusion gradient is set up
3. Na attaches/associates itself with glucose/amino acids and this complex moves back into the cell by facilitated diffusion (if you remember mass flow from F211 it is a similar concept)
4. The glucose concentration inside the cells rises (because it has moved into the cell by facilitated diffusion)
5. The rise in glucose conc means glucose diffuses to the other side of the cell and into tissue fluid where there's a lower concentration
(remember tissue fluid bathes cells and they (cells) use the glucose etc for respiration)
6. the increase in solute concentration in the tissue fluid decreases the water potential so water moves in by osmosis

Hope this makes sense and helps!
20. (Original post by kad7422)
Can someone go through selective reabsorption can't get my head around it
1) There's a sodium-potassium pump in membrane of the cells lining the PCT, next to the tissue fluid. This actively transports 3 Na+ ions out of/ 2 K+ ions into cell.

2) There's a low concentration of Na+ ions in the cell as a result.

3) Na+ ions are transported by facilitated diffusion into the cell, bringing with them glucose or amino acids, through a co-transporter protein embedded in the cell membrane (cell membrane between cells lining PCT and tubule fluid)

4) Concentration of amino acids/glucose increase in cell, so they diffuse out of cell, into tissue fluid (down concentration gradient). They then diffuse from tissue fluid into the blood capillaries to be taken away by blood.

5) All the entry of salts, glucose and amino acids previously into the cell caused it to have a lower water potential than the tubule fluid outside it, so water diffuses by osmosis, down it's water potential gradient into the cell from the tubule fluid.

I hope that wasn't too waffly?

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