PrepTest 155, Section 4, Question 10
Many species of plants produce nectars known as(60 more words not shown)
Which one of the following,(8 more words not shown)
- AFor many species(14 more words not shown)
- BIn field experiments,(20 more words not shown)
- CSome species of(13 more words not shown)
- DExperiments with types(18 more words not shown)
- ERegions with large(12 more words not shown)
Reading the argument
The spiders like the nectar. Do they also protect the plant? We know the ants do. They are attracted to these plants and defend them against insects that eat the leaves. The greenhouse experiments show that jumping spiders also visit the nectar-producing plants much more often and eat the nectar. That's a shared attraction, but it doesn't yet establish a shared service.
Maybe the spiders eat the leaf-eating insects. Or maybe they interfere with the ants that already protect the plants. Simply arriving for food doesn't tell us whether their presence is helpful or harmful.
What we’re looking for
For a strengthener, I'd like evidence that the jumping spiders attack the harmful insects. That would connect their visits to the protection the author claims. Let's see whether the answers give us that evidence or another reason to think the spiders benefit these plants.
Working the answers
- A
Protection from leaf-eating insects can increase a plant's productivity. Fine, but are the jumping spiders providing that protection? A explains why protection would be useful without showing that these spiders supply it. We still need the connection between the spiders and the plants' defense.
- BCorrect
This isn't the direct evidence of spiders eating insects I predicted. Instead, it gives us evidence of a beneficial result: after jumping spiders were introduced, the population of these plants increased significantly. That fits the idea that the spiders are helping the plants survive.
The increase doesn't prove that protection from leaf-eating insects is the mechanism. There could be another explanation. But it gives the defense hypothesis more support than the original observation that spiders merely visit and drink nectar. A strengthener can add useful evidence without proving the whole story.
- C
Some of the plants need an outside defender. That doesn't establish that jumping spiders are among their defenders. The protection could come from ants or something else. A need for help doesn't identify which animal is providing it.
- D
These experiments concern other kinds of spiders. We need evidence about jumping spiders. Other spiders failing to defend the plants doesn't show that jumping spiders do defend them; different kinds could behave alike or differently in this respect.
- E
Large ant populations occurring with large populations of these plants concerns the relationship we already know has a protective side. It doesn't establish the corresponding relationship for jumping spiders. The question is whether we can extend the protection claim to this other animal.
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