White clover (*Trifolium repens*) produces hydrogen cyanide (HCN) to deter herbivores, but winter freezing can damage cell membranes, releasing HCN and causing self-poisoning. Consequently, clover populations in colder environments typically exhibit lower rates of HCN production. Although urban areas are generally warmer than rural ones due to the urban heat island effect, researchers in a northern city observed that clover in urban parks where snow was regularly cleared had lower rates of HCN production than clover in undisturbed, snow-covered rural fields nearby. Since snow cover provides thermal insulation that buffers soil from freezing air, which choice most logically completes the text?
- Aherbivores in urban parks are more active during the winter than those in rural fields, driving the selection for self-poisoning traits.
- Bthe urban heat island effect causes soil temperatures in urban parks to remain higher than rural soil temperatures throughout the winter.
- the removal of snow from urban parks exposed the clover to colder winter soil temperatures than those experienced by the insulated rural clover.Answer
- Dclover populations in northern climates produce higher levels of HCN when they are exposed to direct winter sunlight in cleared parks.
Answer
the removal of snow from urban parks exposed the clover to colder winter soil temperatures than those experienced by the insulated rural clover.
The correct answer logically bridges the premises. Colder temperatures lead to lower HCN production to avoid autotoxicity. While cities are generally warmer, clearing snow removes the thermal insulation that normally protects the soil. Therefore, removing snow from urban parks left the clover exposed to colder soil temperatures than the insulated rural clover, prompting selection for lower HCN production.
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