PrepTest 102, Section 4, Question 13
Unlike other primroses, self-pollinating primroses do not need(69 more words not shown)
Which one of the following,(13 more words not shown)
- AInsects that collect(12 more words not shown)
- BWhen insect pollinators(19 more words not shown)
- CSelf-pollinating primroses that(23 more words not shown)
- DMany primroses are(17 more words not shown)
- ESelf-pollinating primroses can(17 more words not shown)
Reading the argument
What is the tradeoff for not needing insect pollinators?
At first, I wonder whether the ordinary primroses make up for their disadvantage in years when insects are plentiful. Maybe self-pollination helps in a bad insect year but loses out in a good one. Then the passage closes that route: in the other years, seed production is approximately equal. The self-pollinating plants produce more seeds in some years without producing fewer in the rest.
That makes their rarity puzzling. The passage says they are otherwise indistinguishable, yet the apparent reproductive advantage hasn't made them common.
There must be something about the outcome that the seed count isn't capturing. My broad prediction is another disadvantage that offsets the apparent advantage. Could the trait fail to spread reliably from one generation to the next? That is a possibility to investigate, not a fact about how these plants inherit traits.
What we’re looking for
We're asked to explain the apparent discrepancy. Keep both observations: the self-pollinating plants produce more seeds on average, and they remain rare. An answer should help us understand how those can coexist, rather than simply repeat why making seeds without insects is useful.
Working the answers
- A
Insects treating both kinds alike doesn't explain why one remains rare despite its seed-production advantage. We need a relevant difference in what happens to the two kinds. Equal treatment supplies no offsetting disadvantage.
- BCorrect
The non-self-pollinating plants make fewer seeds when insects are scarce, but their seeds are larger and more likely to germinate—to begin growing. More seeds isn't necessarily more successful new plants.
For example, a plant producing ten seeds of which eight sprout could outperform a plant producing twenty seeds of which only two sprout. Those numbers are just an illustration of the distinction. B gives the ordinary primroses an advantage in successful germination that the earlier seed counts leave out. That helps explain why the self-pollinating kind doesn't take over despite producing more seeds on average.
- C
Self-pollinating plants producing no fewer seeds in low-insect areas fits their independence from insect pollination. It doesn't supply a reason for their rarity. It reinforces the feature that made the outcome puzzling instead of explaining what could offset it.
- D
Poor soil could keep many seeds from germinating. But which kind of primrose is especially affected? D doesn't distinguish the self-pollinating plants from the other plants. A difficulty shared across primroses doesn't by itself explain why the self-pollinating kind is rare among them.
- E
Being able to use insect assistance without needing it still sounds like an advantage. It doesn't identify a cost or limitation that would explain rarity. The question isn't asking us to restate how self-pollination works; it asks why that apparently useful feature hasn't made these plants common.
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