The following passage is adapted from an essay on deep-sea piezobiology and organismal ada… — ACT

The following passage is adapted from an essay on deep-sea piezobiology and organismal adaptations.

In 2009, a deep-sea research expedition to the Mariana Trench's Challenger Deep retrieved specimens of the supergiant amphipod *Hirondellea gigas* from depths exceeding $10,000\text{ meters}$ . Researchers analyzed the organism's exoskeletal armor and digestive physiology to understand how it survives under hydrostatic pressures exceeding $100\text{ megapascals}$ .

Unlike shallower crustaceans whose exoskeletons rely predominantly on calcium carbonate—a compound that readily dissolves under extreme pressure and low temperature—*H. gigas* utilizes an extraordinary biomineralization strategy. Chemical analysis revealed that the amphipod's carapace contains an outer layer composed of amorphous aluminum hydroxide. The amphipods synthesize this protective coating by processing sediment-derived metal ions through an acidic gut environment, where ingested sediment containing aluminum debris reacts with endogenous organic acids before being secreted onto the epicuticle as a stabilizing gel.

Furthermore, enzymatic assays performed on the midgut secretions of *H. gigas* uncovered remarkable digestive versatility. To process detrital matter falling from the photic zone, the amphipod secretes high concentrations of cellobiase, amylase, and a specialized pressure-tolerant cellulase enzyme designated as Hg-Cel1. Crucially, laboratory assays demonstrated that Hg-Cel1 exhibits its maximum catalytic rate under a hydrostatic pressure of $80\text{ megapascals}$ at a baseline temperature of $2^\circ\text{C}$ , making it one of the few known obligate piezophilic cellulases.

Osmolytes within the muscle tissue of *H. gigas* also showed distinct structural adaptations. While shallow marine invertebrates maintain intracellular osmotic balance using glycine and betaine, *H. gigas* exhibits elevated cellular concentrations of trimethylamine N-oxide (TMAO) alongside a secondary piezolyte, scyllo-inositol. Cellular assays indicated that scyllo-inositol acts synergistically with TMAO to stabilize lactate dehydrogenase against pressure-induced denaturation, preserving metabolic flux during rapid vertical locomotion along trench slopes.

Based on the passage, the specialized cellulase enzyme Hg-Cel1 achieves its maximum catalytic rate under which of the following specific conditions?

A hydrostatic pressure of $80\text{ megapascals}$ at a temperature of $2^\circ\text{C}$ Answer
B
Atmospheric pressure at a baseline temperature of $2^\circ\text{C}$
C
A hydrostatic pressure exceeding $100\text{ megapascals}$ within an acidic gut environment
D
Elevated cellular concentrations of trimethylamine N-oxide and scyllo-inositol

Answer

The specialized cellulase enzyme Hg-Cel1 achieves its maximum catalytic rate under a hydrostatic pressure of

80\text{ megapascals}

at a temperature of

2^\circ\text{C}

The passage explicitly specifies in the third paragraph that Hg-Cel1 achieves its maximum catalytic rate under a hydrostatic pressure of

80\text{ megapascals}

at a baseline temperature of

2^\circ\text{C}

Step-by-Step Solution

Locate the paragraph in the passage that discusses the enzyme Hg-Cel1.

Paragraph 3 discusses midgut digestive enzymes, explicitly naming Hg-Cel1.

Scanning for precise technical terms mentioned in the question stem directs focus to the relevant text section.

Identify the exact stated conditions corresponding to the maximum catalytic rate of Hg-Cel1.

The text explicitly states that laboratory assays demonstrated Hg-Cel1 exhibits its maximum catalytic rate under a hydrostatic pressure of

80\text{ megapascals}

at a baseline temperature of

2^\circ\text{C}

Literal comprehension requires verifying stated numerical and environmental parameters directly without inference.

Key Concept

Identifying Explicit Details

Estimated Time:1m 30s

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