Question 19·200 Super-Hard SAT Reading Questions·Information and Ideas
During dry seasons, juvenile mangroves growing beneath mature trees often retain more water than juveniles in nearby open areas. Ecologist Mara Venn proposes that this difference results from hydraulic redistribution: at night, mature roots draw water from deep, moist layers and release some into drier surface soil, where shallow-rooted juveniles absorb it. Critics note that canopy shade alone could reduce water loss from juveniles, producing the same observed pattern without any underground transfer. Therefore, differences in juvenile hydration or survival by themselves would not establish that hydraulic redistribution is responsible.
Which finding, if true, would most directly support Venn’s explanation for the juveniles’ greater water retention?
For a command-of-evidence question about a causal explanation, separate the explanation into its required links and identify any competing explanation named in the passage. Then choose the finding that tests the full causal chain while ruling out the alternative; evidence showing only correlation, biological possibility, or one stage of the mechanism is less direct.
Hints
Break the claim into parts
Identify where the water is said to originate, how it is said to reach the surface, and which plants are said to absorb it.
Consider the alternative
Look for evidence that distinguishes underground water movement from the reduced water loss that cooler, darker conditions could cause.
Prefer causal evidence
A direct test of the water’s source and route is stronger than a correlation between proximity to mature trees and juvenile hydration.
Step-by-step Explanation
Identify the proposed mechanism
Venn claims that mature trees move deep water into surface soil at night and that shallow-rooted juveniles then absorb this water.
Account for the competing explanation
Because shade could independently reduce juvenile water loss, the strongest evidence must control light and temperature rather than merely show that juveniles near mature trees contain more water.
Select the most direct evidence
Choice A establishes the water’s deep source, prevents juveniles from accessing that source directly, traces the water into surface soil and juvenile leaves, and controls canopy conditions. It therefore supports the complete proposed mechanism rather than only one part of it.