Q27

[LSAT-Chang]

Could someone help me understand answer choice (A)? I found that lines 43-45 mentions about "rubisco is sequestered within airtight tissues in the center of the leaf" but is this what (A) is getting at? "sequestered = not isolated"? But what about "some" in the passage and "many" in the answer choice? Since some = many, is that something that we just have to be OKAY with?

[timmydoeslsat]

I think a brief rundown of this passage is in order to understand this question.

We start off with the idea that maize (corn) is an extremely productive crop. The author states that we now know why that is.

The author talks about what happens in plants during photosynthesis.

Plants split water into hydrogen and oxygen.

The hydrogen is used for energy and the oxygen is released into the atmosphere.

An enzyme in these plants, rubisco, helps in the sugar forming chemical reaction. This entire process we are talking about is the process of producing carbohydrates.

Rubisco is declared as important in photosynthesis, but that does not stop the idea of there being hindrances.

The hindrance is that when oxygen reaches a certain point in relation to its counterpart of carbon dioxide, bad things happen for rubisco. The oxygen starts to then bind to rubisco! (Talk about shooting yourself in the foot!)

The author then tells us of an evolutionary adaptation that some plants have produced. It is a mechanism in photosynthesis where the pesky oxygen will not both rubisco anymore.

How is this accomplished?

These evolved plants separate the two actions.

The splitting of water happens over here ----->

And the sugar forming stuff with rubisco happens over here <-----

The author is very specific in the fact that ALL plants split the water in the same place, in specialized chlorophyll-containing
structures in the green leaf cells.

However, in these evolved plants, the rubisco is isolated (sequestered) in airtight tissues in the center of the leaf.

THIS IS THE INFERENCE FOR #27

The water splitting action takes place in the same place for all plants, but the rubisco isolation is what is different!

[LSAT-Chang]

Timmy, thanks so much for the GREAT explanation! Your run through of the passage made me double check whether I had actually understood the passage like you did. I misunderstood answer choice (A) in that, I thought "many plants" = "evolved plants", but now I see that the question meant "many plants" = "normal plants that are not evolved". I was looking at the exact line reference you provided when I was solving this question, but thought that (A) had it the other way around, but I definitely misunderstood the "many plants".

Quick question: Are the stuff written in your passage run through what you actually read for? I've noticed a lot of detail, but wasn't sure if it was useful to do that for these dense science passages.. I seem to get so lost in the terminologies, but you seem to understand what C4 is, and how it works, and all the detail about how water splits and blah blah blah. Do you normally do that? Or do you just happen to have good memory that by the time you are done reading the passage you have an understanding of how processes work, etc.

[giladedelman]

That's a wonderful breakdown of the passage, and I think you strike a nice balance between getting TOO detailed, on the one hand, and not detailed enough, on the other. You could probably afford to get through this passage without a clear understanding of what C-4 is, for example, but you do need to understand

1) what rubisco is/does
2) what the problem is in most plants
3) how plants like maize solve this problem (sequestration)

Great post!

[erho]

Thanks for the great run through of the passage.
But I still don't understand why C would be incorrect.

I understand that B is unsupported, for D it's not rubisco itself, but the process and structure in which rubisco functions and is positioned in the C-4 process, and for E, this information is unsupported as well.

I ruled out A b/c we are not sure whether there are many non-C-4 plants or not. I understand that C-4 plants are specially evolved plants, but no where in the passage does it say that therefore, non-C-4 plants are more prevalent compared to C-4 plants...

I know this reasoning seems like hair-splitting...and I did have a hunch that there certainly "could" be more non-C-4 than C-4 plants, but I had to find a reason why A would be incorrect since C seemed right.

FYI, I chose C b/c Rubisco "assists in the sugar (a nongas molecule) forming reaction" when CO2 enters the plant.

[wguwguwgu]

Thanks for the great run through of the passage.
But I still don't understand why C would be incorrect.

FYI, I chose C b/c Rubisco "assists in the sugar (a nongas molecule) forming reaction" when CO2 enters the plant.

I would like to know this too. A is obviously right, but why is C wrong? Is this because LSAC doesn't expect us to KNOW that sugar is not gas and thus qualify it as unwarranted additional assumption???

[jimmy902o]

Thanks for the great run through of the passage.
But I still don't understand why C would be incorrect.

FYI, I chose C b/c Rubisco "assists in the sugar (a nongas molecule) forming reaction" when CO2 enters the plant.

I would like to know this too. A is obviously right, but why is C wrong? Is this because LSAC doesn't expect us to KNOW that sugar is not gas and thus qualify it as unwarranted additional assumption???

In my opinion, C is tricky because it could be true, but not supported by the passage (kind of similar to "which one of the following cannot be true" types in logical reasoning). All we know from the passage is that "carbon dioxide, which cannot enter these cells as a gas, first undergoes a series of reactions to form an intermediary, nongas molecule..." (lines 50-55). Do we know carbon dioxide undergoes a conversion? Yes. However, the test makers strategically leave out ANY discussion about other related factors. Sure, rubisco is mentioned earlier in the paragraph, but it is impossible to know its role one way or the other because its not discussed within the context of those lines. Hope that helps

[timmydoeslsat]

I would say that we can use the text to disprove (C).

Lines 45-48 tell us that rubisco is separated from the gases. And we know that CO2 must be converted into a non-gas molecule to do the C-4 stuff. So we have rubisco and CO2 completely separated in the plant.

[sojisong]

Can you explain why (D) is wrong?
I thought that rubisco helps oxygen building up and it prevents oxygen from impairing photosynthesis. = protect against detrimental effects of oxygen.
I considered (A) right too but (D) seemed more like a very direct inference related to the main idea so i chose D.
Thanks in advance.

[emilynotini]

I think the main evidence for C being wrong can be found in lines 24-28, where it says that during photosynthesis CO2 is used to build sugars in the plant and rubisco ASSISTS in the sugar forming chemical reaction. Key word here being ASSISTS. Just because Rubisco is sufficient does not mean it is necessary to the forming of sugars from carbon dioxide. And again in the third paragraph, lines 39-41 state that certain plants separate the place where they split water atoms into hydrogen and oxygen from the places where they build sugar from CO2. Rubisco greatly helps with this process because it is important to photosynthesis, but we cannot infer from the info given in the passage that photosynthesis couldn't happen without it.

Answer choice D is wrong because it states that rubisco is the element that helps to protect against the effects of oxygen buildup in leaves. This is wrong because rubisco is defenseless against oxygen, which is why certain plants have evolved to separate the places where they split hydrogen/oxygen from where they build sugars. Without this evolved mechanism for photosynthesis, rubisco would likely be defenseless to the effects of oxygen.

[Dtodaizzle]

I thought (A) was wrong as well, but a quick use of "common sense" logic made me realize why it is right. From the passage, we know that all plants go through photosynthesis; there are plants that are impaired by oxygen binding to the enzyme, and those that are not impaired by this process. The keyword is that only "some" are not impaired.

As a result, we have the following options.

Option A.

1.Most are impaired

2. Some are not impaired.

Option B.

1. Some are impaired

2. Some are not impaired

3. Some are not impaired but use a different process that is not mentioned in the passage.

Choice 3 of Option B would force us to make a logical leap that is beyond the scope of this passage. Hence, Option A is the most logical sound option.