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Difficulty: MediumLogical Inferences

In plant biology, *Arabidopsis thaliana* accessions from northern latitudes typically produce higher baseline concentrations of aliphatic glucosinolates—compounds that deter generalist herbivores—than accessions from southern latitudes. Conversely, southern accessions exhibit a much higher degree of phenotypic plasticity, rapidly increasing their glucosinolate production only after initial tissue damage is detected. Researchers have noted that northern environments feature a constant, predictable presence of generalist pests throughout the growing season, whereas southern environments experience highly sporadic and unpredictable herbivore outbreaks. Because synthesizing glucosinolates is metabolically costly, maintaining high baseline levels in the absence of pests is disadvantageous. Which choice most logically completes the text?

  1. the phenotypic plasticity of southern accessions allows them to avoid unnecessary metabolic costs during periods when pests are not present.Answer
  2. B
    southern accessions are more effective at deterring a wider variety of generalist pests than northern accessions are.
  3. C
    northern accessions will eventually lose their ability to produce baseline glucosinolates if local pest populations become sporadic.
  4. D
    northern accessions rapidly increase their chemical defenses only after they sustain physical damage from herbivores.

Answer

the phenotypic plasticity of southern accessions allows them to avoid unnecessary metabolic costs during periods when pests are not present.
The correct option logically completes the passage by connecting the metabolic cost of glucosinolates with the sporadic nature of pest presence in southern environments. Because keeping defense levels high without pests is disadvantageous, southern accessions benefit from phenotypic plasticity, which ensures they only spend metabolic energy on glucosinolates when pests are active.

Step-by-Step Solution

1
Analyze the premises regarding the two accessions and their environments.
Northern accessions have high baseline defenses in environments with constant pests. Southern accessions have high plasticity (defenses rise only after damage) in environments with sporadic outbreaks.
To understand the relationship between the defense strategies and their respective ecological contexts.
2
Identify the constraint/cost associated with the defense mechanism.
Synthesizing defenses is metabolically costly, making high baseline levels disadvantageous when pests are absent.
To connect the metabolic cost of defense to the sporadic nature of southern pests.
3
Deduce the logical conclusion that completes the text.
Since southern pests are sporadic, southern accessions' plastic response allows them to conserve energy (avoiding metabolic costs) when pests are absent, while still defending themselves when outbreaks occur.
To find the conclusion that directly follows from the premises without introducing external assumptions.

Key Concept

Logical Inferences
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Topics

Logical Inferences

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