Examkin

Question

Difficulty: HardLogical Inferences

Under elevated carbon dioxide (CO2CO_2) levels, plants typically exhibit decreased leaf nitrogen concentrations. Some researchers attribute this decline to carbohydrate dilution, where increased photosynthesis produces excess starches that outpace nitrogen uptake. However, botanist Elena Rostova observed that nitrogen levels still drop under high CO2CO_2 even when carbohydrate accumulation is experimentally blocked. Pointing to the fact that nitrogen absorption depends on the transpiration stream—the water movement driven by evaporation—Rostova hypothesized that CO2CO_2-induced stomatal closure, which reduces transpiration, is the primary cause of the nitrogen deficit. If Rostova's hypothesis is correct, plants grown under elevated CO2CO_2 that are also exposed to wind speeds that artificially enhance transpiration should ______

Which choice most logically completes the text?

  1. exhibit leaf nitrogen concentrations that are closer to those of plants grown under ambient CO2CO_2 levels.Answer
  2. B
    accumulate higher levels of starches in their leaves than plants grown under elevated CO2CO_2 in calm conditions.
  3. C
    experience a more pronounced decrease in leaf nitrogen concentrations than they would in calm conditions.
  4. D
    respond by opening their stomata to match the transpiration rates of plants grown in ambient CO2CO_2 conditions.

Answer

exhibit leaf nitrogen concentrations that are closer to those of plants grown under ambient CO2CO_2 levels.
The correct option correctly infers that if the nitrogen deficit in plants grown under elevated CO2CO_2 is primarily caused by a reduction in transpiration due to stomatal closure, then artificially restoring transpiration via wind exposure should mitigate this deficit. As a result, these plants should maintain leaf nitrogen concentrations closer to those of plants grown under normal (ambient) CO2CO_2 levels.

Step-by-Step Solution

1
Identify Rostova's hypothesis regarding why elevated CO2CO_2 leads to reduced leaf nitrogen.
Rostova argues that CO2CO_2-induced stomatal closure reduces transpiration, which in turn limits nitrogen absorption.
This establishes the causal chain proposed by the researcher: elevated CO2CO_2 causes stomatal closure, which lowers transpiration, resulting in lower nitrogen uptake.
2
Analyze the experimental variable introduced at the end of the passage.
Plants under elevated CO2CO_2 are also exposed to wind speeds that artificially enhance transpiration.
This allows us to evaluate the impact of a physical factor (wind) that directly counteracts the reduced transpiration rate caused by stomatal closure.
3
Determine the logical outcome if the hypothesis is true.
If the nitrogen deficit is caused by reduced transpiration, artificially boosting transpiration with wind should counteract the deficit.
Because transpiration is restored physically by the wind despite the closed stomata, nitrogen levels should not drop as severely, meaning they will be closer to the levels seen in plants grown under ambient CO2CO_2 conditions.

Key Concept

Logical Inferences
Rate this question

Topics

Logical Inferences

More questions from this topic