So this question pops up on my test tonight:
“In glycolysis, ATP is synthesized by the process of substrate level phosphorylation. Which of the following statements about substrate level phosphorylation is INCORRECT?”
there were two answers I was fighting with that both seemed incorrect. After coming back and checking the book, they still both seem incorrect. Needless to say I picked the wrong one, and it follows:
“In the absence of O[sub]2[/sub], ATP from substrate phosphorylation is the only ATP made in the oxidation of glucose.”
So my question would be, why is this “correct”. The book and lecture made a major point of bringing up fermentation which obviously functions in the absence of O[sub]2[/sub]. In a cell capable of fermentation, there is no O[sub]2[/sub], and ATP is synthesized by the same oxidation that occurs in respirative glycolysis, only difference being that the NAD+ that was reduced during glycolysis is regenerated by the oxidation of the products of glycolysis to either ethanol or lactate. So given all that, why is it CORRECT to say that in the absence of oxygen, substrate level phosphorylation is the only way to make ATP?
There’s an exam comment session tomorrow where I plan on presenting this argument, so if anybody can point out a flaw I would appreciate it.
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Ok well I don’t want to start up a second thread for this… so here’s the second one I’m having trouble with:
“Which of the following statements comparing a red blood cell of an animal and the mesophyll cell of a plant leaf is CORRECT? Assume that both cells are in equilibrium with the solution surrounding them as far as both water and solute movement are concerned and that the cells are normal with regard to their water status (eg: the red blood cell is not about to burst and the plant cell is turgid).”
The two I fought with, and I think it might be a mix-up of language:
“b) the solute potential is higher inside the plant cell than outside the cell, but the same inside and outside the red blood cell.”
“c) the magnitude (absolute value) of the solute potential exceeds the pressure potential in both types of cells”
Notice (b) says the potential is “higher”. At first I thought they meant to say “the concentration is higher” or “the potential is more negative”, but in © they very clearly specified, so “higher” should mean MORE positive, LESS negative, and thus “lower” solute concentration right? If this is the case, I really can’t figure out why their answer (b), was right and © was wrong.
It seems like the only way for there to be a lower solute concentration in the plant cell than the surrounding solution would be if somehow there was a negative pressure potential on the plant cell by the cell wall, which I don’t think the cell wall is capable of providing.