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Difficulty: MediumCommand of Evidence: Textual

Many plant species adapt to urban fragmentation, where pockets of soil are surrounded by inhospitable concrete. Ecologist Dr. Sarah Jenkins and her team investigated the common dandelion (*Taraxacum officinale*) across urban and rural zones in Chicago. The team hypothesized that urban dandelion populations have adapted to soil fragmentation by producing seeds with lower wind-dispersal capacity—specifically, shorter pappus hairs relative to seed mass���thereby increasing the probability that seeds will settle in the immediate, hospitable soil of the parent plant rather than drifting onto concrete surfaces.

Which choice, if true, would most directly support the team's hypothesis?

  1. A
    Urban dandelion populations in areas with high concrete coverage were found to have a much higher density of plants per square meter than populations in areas with more open soil.
  2. In controlled wind-tunnel tests, seeds collected from urban dandelion populations fell closer to their source and had a significantly lower ratio of pappus length to seed mass than seeds collected from rural populations.Answer
  3. C
    Seeds collected from rural dandelion populations exhibited a lower ratio of pappus length to seed mass, allowing them to travel farther in wind-tunnel tests than seeds from urban populations.
  4. D
    Urban dandelions will likely face eventual extinction due to a lack of genetic diversity resulting from limited seed dispersal across concrete barriers.

Answer

In controlled wind-tunnel tests, seeds collected from urban dandelion populations fell closer to their source and had a significantly lower ratio of pappus length to seed mass than seeds collected from rural populations.
The correct option directly supports the hypothesis by showing that urban dandelion seeds have a lower ratio of pappus length to seed mass and fall closer to their source under controlled wind-tunnel conditions, confirming both the structural adaptation and its functional effect on dispersal distance.

Step-by-Step Solution

1
Identify the researchers' hypothesis in the passage.
The hypothesis is that urban dandelion populations adapt to fragmented soils by producing seeds with lower wind-dispersal capacity (shorter pappus hairs relative to seed mass) so they land near the parent plant rather than on concrete.
Understanding the specific hypothesis is necessary to determine what kind of evidence would support it.
2
Evaluate the choices to find which one offers empirical support for this exact mechanism.
The option describing wind-tunnel tests shows that urban seeds fell closer to the source and had a lower ratio of pappus length to seed mass.
This directly confirms the physical adaptation and the resulting decrease in dispersal capacity hypothesized by the researchers.

Key Concept

Command of Evidence: Textual
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Command of Evidence: Textual

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