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Difficulty: MediumDirect Factual Retrieval

Phytoremediation—the deployment of vegetation to decontaminate polluted soil and water—has emerged as a vital biological strategy in environmental engineering. Among hyperaccumulating flora, the ladder brake fern (*Pteris vittata*) exhibits a remarkable capacity to extract arsenic from contaminated substrates and concentrate it within its harvestable fronds. For most terrestrial vascular plants, arsenic exposure triggers immediate cellular toxicity and severe oxidative damage. In contrast, *Pteris vittata* utilizes a specialized internal detoxification pathway. Upon uptake by root transport proteins, toxic arsenate (AsO43−\text{AsO}_4^{3-}) is swiftly reduced to arsenite (AsO33−\text{AsO}_3^{3-}) inside root cells through the catalytic action of phosphate-induced arsenate reductase. Following this enzymatic reduction, arsenite is translocated via xylem vessels to the fern's fronds, where it is pumped across tonoplast membranes into intracellular vacuoles.

Within these vacuolar lumens, arsenite forms stable complexes with thiol-rich peptides, effectively sequestering the heavy metal away from metabolic machinery in the cytoplasm. Biochemical investigations demonstrate that phosphorus enrichment in the growth medium significantly accelerates the rate of root-to-frond arsenic translocation by upregulating phosphate-transporter gene expression. Conversely, while nitrogen supplementation increases total plant biomass, it leaves the intrinsic root-to-frond arsenic concentration ratio unchanged.

According to the passage, which of the following processes occurs within root cells of *Pteris vittata* before arsenic is translocated to the fronds?

  1. Arsenate is enzymatically reduced to arsenite by phosphate-induced arsenate reductase.Answer
  2. B
    Arsenite is converted into arsenate by tonoplast-bound transport proteins.
  3. C
    Arsenic forms complexed bonds with thiol-rich peptides inside xylem vessels.
  4. D
    Nitrogen supplementation directly reduces toxic arsenate into vacuolar lumens.
  5. E
    Phosphate-transporter genes sequester heavy metals within root cell cytoplasm.

Answer

Arsenate is enzymatically reduced to arsenite by phosphate-induced arsenate reductase.
The passage explicitly notes that inside root cells, toxic arsenate is reduced to arsenite by the enzyme phosphate-induced arsenate reductase prior to translocation through xylem tissue to the fronds.

Step-by-Step Solution

1
Locate the targeted detail in the passage regarding physiological processes occurring in root cells prior to translocation.
Identified the sentence: 'Upon uptake by root transport proteins, toxic arsenate (AsO43−\text{AsO}_4^{3-}) is swiftly reduced to arsenite (AsO33−\text{AsO}_3^{3-}) inside root cells through the catalytic action of phosphate-induced arsenate reductase.'
Direct factual retrieval requires pinpointing the specific sentence describing root cell chemical processes.
2
Match the explicit statement from the text to the semantically equivalent option.
The statement directly matches the answer describing the reduction of arsenate to arsenite by phosphate-induced arsenate reductase.
Ensures the selected answer is grounded strictly in explicit passage evidence.

Key Concept

Direct Factual Retrieval from Reading Comprehension Passages
Estimated Time:1m 30s
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Direct Factual Retrieval

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