June 2006 LSAT Section 3 Question 23

Assuming that all other relevant factors remained the same, which one of the following, if it developed in a species ...

Veda on July 28, 2020

Why not C

I understand why B is correct, but why not C? Is it because if the plant does not use C-4 process then it doesn't matter if it has the impermeable vascular cells, and that the root of the problem is the excess oxygen interfering in the process?

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Shunhe on July 29, 2020

Hi @Veda-Bhadharla,

Thanks for the question! So we want to know which of the following would give a non C-4 plant the same advantages as C-4 plants if it developed in a non C-4 plant. (C) tells us that this is that the vascular structures of the leaf become impermeable to both carbon dioxide and oxygen gas. So the thought here is that if the cells that have rubisco are impermeable to CO2 and oxygen, then it’s the same as in the C-4 plants.

So now the question is: is rubisco in the vascular structures of the leaf? Let’s take a look at lines 45-50, where we’re told about the cells containing rubisco and also the vascular structures of the leaf. We’re told that the bundle sheath cells (that have the rubisco) surround the vascular structures of the leaf. But that means the rubisco isn’t in the vascular structures, it’s in the bundle sheath cells around the vascular structure. And if the vascular structures are impermeable, it doesn’t matter, since the rubisco isn’t there in the first place. And that’s why (C) is wrong.

Hope this helps! Feel free to ask any other questions that you might have.