#24 - Mammals cannot digest cellulose and therefore cannot

[Administrator]

Complete Question Explanation

Must Be True. The correct answer choice is (C)

The stimulus in this Must Be True question contains a large number of facts concerning mushrooms’ ability to make beta-glucans. Pay careful attention to the language, as there are many rules involving conditional reasoning as well as rules involving Formal Logic. The first sentence states that mammals cannot digest cellulose and therefore cannot obtain glucose from wood. Mushrooms, on the other hand, can obtain glucose from wood and therefore can digest cellulose. Some mushrooms use this cellulose to make beta-glucans and some beta-glucan extracts from mushrooms cause antitumor activity in mammals by increasing immune cell activity. This antitumor activity caused by beta-glucans increases as the degree of polymer branching increases.

Answer Choice (A): This answer choice is too exaggerated to follow from the stimulus. While mammals may not be able to digest cellulose, they still might obtain beneficial health effects from cellulose.

Answer Choice (B): The stimulus provides enough information to determine that some extracts from mushrooms capable of using cellulose to make beta-glucans slow, reverse, or prevent the growth of cancerous tumors. As with any Formal Logical statement using “some,” this statement is reversible. That means we also know that some extracts that have these antitumor effects are from mushrooms that can use cellulose to make beta-glucans. However, the answer choice states that all extracts that have these antitumor effects must be from mushrooms with the ability to use cellulose to make beta-glucans. This answer choice exaggerates the logic in the stimulus and cannot be proven from the facts.

Answer Choice (C): This is the correct answer choice. We know from the last sentence that the antitumor activity of beta-glucans causes an increase in immune-cell activity. We also know this antitumor activity increases as the degree of branching increases. This allows us to conclude that the greater the degree of branching, the greater the degree of immune-cell activity triggered in mammals.

Answer Choice (D): The stimulus does not explain how immune-cells prevent tumor growth. The stimulus only explains how the beta-glucan extracts prevent tumor growth. While beta-glucan extracts increase immune cell activity instead of killing cancer cells directly, the immune cells could then directly target cancer cells and kill them.

Answer Choice (E): This answer choice is far too broad to be supported by the stimulus. While all mushrooms can obtain glucose from wood, only some mushrooms have the ability to make beta-glucans. There is not enough information here to conclude that all other organisms that can obtain glucose from wood share this ability to make beta-glucans.

[ds72]

Hi!

I was wondering what is the best way to attack a stimulus as long as (large number of facts) this question for MBT question types? I feel like I tend to spend a lot more time that I need to on these questions types because I dont know what would be the most effective way to make sense of the facts being said. I attack these questions better when conditional reasoning is present or if its a shorter stimulus with formal logic.

Thank you in advance for you help!

[Adam Tyson]

There's no shortcut to avoid all the reading, DS! Strategically speaking, you may at times want to simply skip a longish stimulus, guess on the answer and move on to another question that appears like it will take less time, saving the longer ones or harder ones (not always the same thing!) until the end. After all, the questions are not individually weighted - you don't get more points for answering a harder question correctly than an easier one - so you may as well spend your time on the easiest questions before getting bogged down in a harder or longer one.

Once that choice is out of the way, though, and assuming you have the time to answer every question (or nearly every question), the only thing to do is get on in there and read it all. Take note of key words and phrases, be aware of possible gaps in the argument, new ideas being brought up in the conclusion, etc. If you see a particular type of reasoning, such as formal logic or causal reasoning, use the tools you know how to use to attack that, but if not, then just do your best. Paraphrase the argument if it helps to make it simpler and more easily digestible. Prephrase an answer that accomplishes what the stem asks you to accomplish. Quickly sort losers and contenders - no time wasted thinking about any one answer choice until you have completed the sorting process - and then, once you have it down to two or more contenders, start comparing them to one another, and to your prephrase, and to the goal you are supposed to be accomplishing, and pick the best one.

I wish I had a magic wand to help with these! Instead, you just have to go at them with a bulldozer and knock them down the hard way.

[mariahenain]

What is the best way to prephrase such a long stimulus as this one? More importantly, is it even possible to prephrase MBT questions? If so, how?

[AthenaDalton]

Hi Maria,

Yes, you can prephrase on Must Be True questions! The exact nature of your prephrase will differ depending on what question type you're tackling, but you should be able to use this technique on all Logical Reasoning questions. More detail on this is available on the PowerScore blog:

https://www.powerscore.com/lsat/help/lr_prephrasing.cfm

As far as prephrasing this one, there are so many conditional statements at play that you won't be able to come up with a perfect prephrase. You can, however, benefit from a generalized prephrase. The one I came up with was, "animals can benefit from the anti-tumor properties of beta glucans if they eat mushrooms." This links the key ideas in the passage together, even if it doesn't explicitly discuss every single element in the conditional logic chains.

The actual answer did link anti-tumor properties and mammals' diets. The link between branching and beta-glucans was a simple add-on, as it is basically a re-statement of the last phrase in the second sentence. In sum, a general pre-phrase can be helpful even in complex questions like this one.

Good luck studying!

[jpincus]

Hello,

I picked answer choice B for this question. I now see why C is correct, however, I'm not exactly seeing why B is wrong. The stimulus states that some mushrooms and in the explanation, it states "However, the answer choice states that all extracts that have these antitumor effects must be from mushrooms with the ability to use cellulose to make beta-glucans. " Answer choice B says "a type" so I'm not seeing where the all is coming from.

Thanks!

[James Finch]

Hi jpincus,

The issue with (B) is that it logically excludes the possibility parts of a mushroom other than beta glucans could slow,reverse, or prevent cancerous tumors in mammals. Since we don't know that the only things that slow, reverse or prevent cancerous tumors in mammals are beta glucans, or even that the only mushroom extracts that do so are beta glucans, we can't say with any certainty that just because mushroom extracts slow, reverse, or prevent the growth of cancerous tumors in mammals, that we know that those extracts are beta glucans.

Hope this clears things up!