Q25

[alana.canfield]

The correct answer is (D). It says rubisco is isolated in the bundle sheath cells. Obviously rubisco is in these cells (lines 45-49). What threw me off was the word "isolated". There is no evidence that the cells contain ONLY rubisco (there is evidence to the contrary). There are other proteins and molecules in these cells so rubisco isn't isolated. Even if you read this to mean that rubisco is isolated from other parts of the plant, there still isn't any evidence that rubisco is isolated only in these cells. We know it is sequestered in tissues in the leaf. But maybe, in the tissue, rubisco is transported from one cell to another and therefore doesn't occur ONLY in these cells, but also can be found outside the cells. So to me isolation looks like an assumption. That's why I picked (C), even though (C) is obviously a stretch.

[giladedelman]

Thanks for your post!

"Isolated" doesn't mean rubisco is the only thing in the cells; it means the cells are the only place we will find rubisco. Since the passage says rubisco is "sequestered" in these sheath cells, and isolate and sequester are basically synonyms, (D) is very strongly supported.

Anyway, you make a good point about (C): it's a big stretch because all we know about rice is that it's very productive.

(A) is incorrect; gases are kept away from rubisco, not the water-splitting area.

(B) is unsupported in the passage.

(E) is likewise unsupported; we don't know which is more widely cultivated.

[alana.canfield]

Thanks for your post!

"Isolated" doesn't mean rubisco is the only thing in the cells; it means the cells are the only place we will find rubisco. Since the passage says rubisco is "sequestered" in these sheath cells, and isolate and sequester are basically synonyms, (D) is very strongly supported.

Anyway, you make a good point about (C): it's a big stretch because all we know about rice is that it's very productive.

(A) is incorrect; gases are kept away from rubisco, not the water-splitting area.

(B) is unsupported in the passage.

(E) is likewise unsupported; we don't know which is more widely cultivated.

Thanks! I think what threw my off here is that I come from a scientific background and usually when we say we "isolated" something in biology it means we were able to purify a mixture down into the 1 thing we wanted, so we only have that 1 thing. Thanks for the help.