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Difficulty: MediumInferences from the Text

In reconstructing ancient plant communities, paleoecologists have long relied on macrofossil and pollen analysis (palynology). However, wind-dispersed pollen can travel hundreds of kilometers, frequently overrepresenting anemophilous taxa—such as pines and birches—while underrepresenting entomophilous plants that rely on insect pollination. Recently, sedimentary ancient DNA (sedaDNA) retrieved directly from lake sediments has emerged as a complementary proxy. Unlike airborne pollen grains, extracellular plant DNA binds tightly to clay minerals and humic substances, significantly limiting lateral transport. Consequently, sedaDNA profiles reflect strictly local flora within the lake catchment basin. Nevertheless, sedaDNA degradation rates vary across taxonomic clades due to differences in cellular wall composition and secondary metabolite concentrations, meaning that relative DNA copy numbers cannot be translated directly into absolute vegetative abundance without empirical calibration models. Furthermore, extreme cold accelerates preservation while microbial activity in warm, oxygenated strata can completely hydrolyze short DNA fragments within a few millennia.

Based on the passage, which of the following statements regarding methods of paleoecological reconstruction are logically supported by the text? (Select all that apply.)

  1. Sedimentary ancient DNA provides a more geographically localized floristic record of a catchment basin than airborne pollen analysis does.Answer
  2. B
    Pollen analysis is entirely incapable of detecting the historical presence of insect-pollinated plant species in ancient environments.
  3. A greater relative quantity of recovered sedaDNA from one plant taxon compared to another in a sediment layer does not conclusively prove that the former was more numerous in the local environment.Answer
  4. D
    Sedimentary ancient DNA extracted from warm, oxygenated wetlands typically yields better-preserved genetic sequences than samples from subarctic permafrost.
  5. E
    Airborne pollen grains bind more tenaciously to lake-bottom clay minerals than extracellular plant DNA fragments do.

Answer

The statements indicating that sedimentary ancient DNA provides a more geographically localized floristic record than pollen analysis, and that greater relative sedaDNA quantities do not conclusively prove greater vegetative abundance, are both logically supported by the passage.
The passage explicitly supports two core deductions: first, that extracellular plant DNA binds to local lake catchment sediment and restricts lateral transport relative to airborne pollen (which disperses over hundreds of kilometers); second, that differing degradation rates among plant clades prevent researchers from assuming that higher DNA copy numbers directly correspond to higher plant populations without calibration.

Step-by-Step Solution

1
Evaluate the spatial distribution and transport claims for both proxies in the passage.
The text confirms that wind-blown pollen disperses over hundreds of kilometers, whereas sedaDNA binds tightly to minerals and limits lateral transport, providing a strictly local catchment record.
Establishing the spatial resolution directly validates the statement regarding the localized nature of sedaDNA.
2
Examine the quantitative relationship between recovered DNA copy numbers and actual vegetative abundance.
Varying degradation rates across taxonomic clades mean that raw DNA copy numbers do not directly reflect absolute plant counts without calibration.
This confirms that higher recovered DNA concentrations from one taxon do not inherently prove greater historical plant abundance.
3
Check the remaining statements against textual qualifiers and preservation facts.
Claims regarding absolute inability to detect insect-pollinated species, enhanced preservation in warm wetlands, and pollen mineral binding either overstate degrees or contradict explicit text facts.
Eliminating unsupported logical leaps isolates the two fully supported claims.

Key Concept

Drawing precise, scoped inferences from comparative scientific descriptions
Estimated Time:1m 30s
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Inferences from the Text

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