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Zorluk: ZorLogical Inferences

To defend against herbivorous insects, certain tobacco plants produce nicotine, a potent neurotoxin. However, synthesizing nicotine is metabolically costly, requiring nitrogen that would otherwise support leaf growth. Researchers observed that when tobacco plants are exposed to volatile organic compounds (VOCs) released by neighboring plants already under attack, they do not immediately increase nicotine production. Instead, their roots initiate transcription of genes associated with nicotine synthesis, leaving the actual production pathway inactive until direct herbivore damage occurs. Which choice most logically completes the text?

  1. tobacco plants that detect VOCs from neighboring plants but do not experience direct herbivory will not incur the metabolic costs associated with active nicotine synthesis.Cevap
  2. B
    tobacco plants exposed to VOCs will ultimately produce a larger quantity of nicotine once attacked than plants that did not receive any warning signals.
  3. C
    nicotine is the most metabolically demanding chemical defense mechanism available to tobacco plants when responding to herbivore threats.
  4. D
    tobacco plants immediately initiate active nicotine production in their leaves upon detecting VOCs to deter potential herbivores before they arrive.

Cevap

tobacco plants that detect VOCs from neighboring plants but do not experience direct herbivory will not incur the metabolic costs associated with active nicotine synthesis.
The correct answer is supported by the text's explanation of the relationship between nicotine production and its metabolic costs. Nicotine synthesis is costly, but when plants detect VOCs, they only transcribe the necessary genes without activating the synthesis pathway. Because active production is delayed until direct herbivore damage occurs, a plant that only detects VOCs but is not attacked will not activate the pathway and thus will not incur the metabolic costs of synthesis.

Adım Adım Çözüm

1
Identify the key premises regarding nicotine synthesis in tobacco plants.
Nicotine synthesis is metabolically costly (requires nitrogen), but plants do not immediately produce it when exposed to VOCs; they only transcribe genes (preparatory phase) while keeping the synthesis pathway inactive until direct damage occurs.
This establishes the boundary conditions for when costs are incurred versus when preparation occurs.
2
Evaluate the logical implication of keeping the pathway inactive during the preparatory phase.
If the pathway remains inactive until direct herbivore damage occurs, then VOC exposure alone does not trigger actual synthesis.
This allows us to infer the metabolic state of a plant that is exposed only to VOCs.
3
Select the option that logically extends these premises without introducing external assumptions.
The option stating that plants detecting VOCs without direct herbivory will avoid the metabolic costs of active synthesis is the only conclusion directly supported by the text.
It matches the premise that synthesis is costly and is kept inactive until direct damage occurs.

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