PrepTest 138, Section 4, Question 24
Mammals cannot digest cellulose and therefore cannot directly(75 more words not shown)
Which one of the following(8 more words not shown)
- AMammals obtain no(6 more words not shown)
- BIf extracts from(26 more words not shown)
- CThe greater the(16 more words not shown)
- DImmune-cell activity in(10 more words not shown)
- EAny organism capable(11 more words not shown)
Reading the argument
The mushrooms can do something mammals can't: use cellulose from wood to produce beta-glucans. The passage then gives us an effect of the extracts in mammals—slowing, reversing or preventing tumor growth—and tells us how that effect occurs.
Keep the mechanism straight. The extracts don't directly kill cancer cells. They increase immune-cell activity. We're also told that more branching goes with greater antitumor activity. Those are the connections we can use; we don't need to understand the chemistry beyond what the passage supplies.
What we’re looking for
My broad first impression is that these mushroom extracts can help oppose tumor growth in the described circumstances. But the most-supported answer may connect the details more precisely. Follow the relationships the passage gives us.
Working the answers
- A
Inability to digest cellulose and obtain glucose from it doesn't establish that eating it has no health benefit whatsoever. It could conceivably help some other process, such as digestion, without supplying glucose. The passage rules out a particular route to glucose, not every possible benefit.
- B
This assumes any mushroom extract with an antitumor effect works through beta-glucans made from cellulose. We are told about that route, but not that it is the only possible route. Another type of extract might act through a different compound. Its antitumor effect alone wouldn't establish how the mushroom uses cellulose.
- CCorrect
More branching is associated with greater antitumor activity, and the stated way these extracts oppose tumor growth is by increasing immune-cell activity. Connecting those facts supports the conclusion that greater branching triggers greater immune-cell activity. C ties together the degree of branching, the stronger effect and the mechanism the passage provides.
- D
Watch what doesn't kill cancer cells directly: the extracts. That doesn't tell us how the immune cells perform their work. The extracts could stimulate immune cells that then kill cancer cells, or the immune response could work another way. The passage doesn't establish D's denial about immune-cell activity itself.
- E
We are told that some mushrooms use cellulose to make beta-glucans. That doesn't establish the ability in every organism that can obtain glucose from wood. Obtaining glucose and making these particular compounds are different capacities; the passage links them for some mushrooms without extending that link to all organisms.
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