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Difficulty: HardExplicit Details

In vascular plants, the phloem transports photoassimilates through sieve tube elements, which are connected by perforated sieve plates. When a plant experiences mechanical wounding or pathogen attack, it rapidly deposits callose—a β\beta-1,3-glucan polymer—around these perforations. Researchers led by Dr. Evelyn Vance studied *Arabidopsis thaliana* mutants lacking the callose synthase gene *CalS7*. The team observed that while wild-type plants completely sealed their sieve plates within twenty minutes of a puncture wound, the *cals7* mutants showed no callose deposition at the wound site even after two hours. Surprisingly, however, the rate of photoassimilate translocation in the wounded *cals7* mutants decreased by only 15%15\% compared to pre-wound levels, indicating that callose deposition is not the sole mechanism restricting transport after injury.

Based on the text, what is true of the *cals7* mutants studied by Vance's team?

  1. A
    They completely sealed their sieve plates via callose deposition two hours after receiving a wound.
  2. B
    They suffered a total cessation of photoassimilate transport because they lacked the *CalS7* gene.
  3. They experienced a 15%15\% decrease in their rate of photoassimilate translocation following injury.Answer
  4. D
    They exhibited no callose deposition at the wound site until two hours had passed.

Answer

They experienced a 15%15\% decrease in their rate of photoassimilate translocation following injury.
The passage explicitly states that the rate of photoassimilate translocation in the wounded *cals7* mutants decreased by only 15%15\% compared to pre-wound levels. This directly supports the claim that the mutants experienced a 15%15\% decrease in their rate of photoassimilate translocation following injury.

Step-by-Step Solution

1
Analyze the passage to locate the specific details reported about the *cals7* mutants.
The passage details that the *cals7* mutants lacked the callose synthase gene, showed no callose deposition at the wound site even after two hours, and experienced a 15%15\% decrease in translocation compared to pre-wound levels.
To identify the explicit facts directly associated with the mutants in the passage.
2
Compare these findings with the four answer choices.
The statement describing a 15%15\% decrease in translocation directly matches the explicit detail in the text. The other options contradict the passage by asserting that the mutants sealed their plates, suffered total cessation of transport, or began deposition after two hours.
To select the option that accurately reflects the passage's explicit claims without extrapolation.

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Explicit Details
Estimated Time:1m 30s
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