Examkin

Question

Difficulty: MediumInferences from the Text

In contrast to magmatically driven black-smoker hydrothermal vents, which rely on intense volcanic heat to circulate highly acidic, mineral-rich fluids, alkaline hydrothermal vents—such as those found at the Lost City field—are powered by serpentinization. This exothermic geochemical reaction occurs when seawater percolates into mantle peridotite rock, oxidizing iron and hydrating olivine minerals into serpentine. Because serpentinization produces vast quantities of molecular hydrogen (H2H_2) and methane in a strongly alkaline environment (pHpH 9–11) at moderate temperatures (40°C–90°C), it establishes steep electrochemical and proton gradients across porous, carbonate-mineral chimneys when the effluent meets cooler, slightly acidic ambient ocean water. Consequently, several geochemists hypothesize that such alkaline vent networks served as natural inorganic incubators for prebiotic metabolic pathways prior to the evolution of cellular membranes, since the microporous inorganic cavities could have concentrated catalytic iron-nickel sulfides while sustaining a continuous flow of chemical energy without requiring sunlight or volcanic activity.

Which of the following inferences regarding alkaline hydrothermal vents is most strongly supported by the passage?

  1. A
    Magmatically driven black-smoker vents produce steeper electrochemical gradients across their structures than alkaline vent systems do.
  2. B
    Serpentinization reactions require ongoing thermal energy from active volcanic magma chambers to sustain geochemical activity.
  3. The generation of proton gradients across the vent chimneys depends on a difference in acidity between the hydrothermal fluid and the surrounding seawater.Answer
  4. D
    Submarine hydrothermal vents are the only geological settings on early Earth where prebiotic metabolic reactions could have emerged.
  5. E
    The microporous cavities within the carbonate chimneys were formed through the metabolic processes of early cellular life.

Answer

The generation of proton gradients across the vent chimneys depends on a difference in acidity between the hydrothermal fluid and the surrounding seawater.
The correct answer accurately synthesizes the passage's explanation of gradient formation: the passage explicitly specifies that steep proton gradients are established across porous carbonate chimneys when the strongly alkaline effluent (pHpH 9–11) interacts with slightly acidic ambient seawater, directly confirming that the gradient relies on this pHpH differential.

Step-by-Step Solution

1
Locate the textual basis for proton gradient formation in the passage
Identified the sentence stating that gradients are established when strongly alkaline vent effluent (pHpH 9–11) meets cooler, slightly acidic ambient ocean water across carbonate chimneys.
LSAT reading comprehension inference questions require finding explicit premises that logically entail the correct conclusion.
2
Synthesize the relationship between pHpH conditions and gradient establishment
Recognized that 'alkaline' and 'acidic' describe differing degrees of acidity (pHpH), meaning the gradient arises from this chemical differential across the porous boundary.
An inference must directly restate or synthesize stated passage mechanics without introducing unsupported assumptions.
3
Evaluate and eliminate unsupported or contradictory distractors
Discarded choices that make unsupported comparative claims, contradict stated geochemical independence from volcanism, introduce unmentioned exclusivity claims, or misattribute inorganic structures to biological origins.
Ensures that only the single logically airtight inference is selected.

Key Concept

Direct Textual Synthesis and Inferences from Mechanism
Estimated Time:1m 30s
Rate this question

Topics

Inferences from the Text

More questions from this topic