Examkin

Soru

Zorluk: ZorExplicit Causal Relationships

Read the following passage carefully.

While the phenomenon of plant-to-plant communication via airborne volatile organic compounds (VOCs) has been well documented, recent ecological research emphasizes the pivotal role of common mycorrhizal networks (CMNs) in mediating subterranean biochemical signaling. When a 'donor' plant is subjected to aphid herbivory, the mechanical tissue damage and the introduction of salivary elicitors initiate a localized synthesis of jasmonic acid. This accumulation cascades into the upregulation of defense-gene transcription, producing specific signaling molecules that travel through the fungal hyphae connecting the donor to uninfested 'receiver' plants.

Crucially, the reception of these mycelial signals does not immediately trigger the costly production of defensive toxins in the receiver plant. Instead, the signals precipitate a 'priming' state. Researchers have demonstrated that the arrival of these network-transmitted signals causes the rapid demethylation of specific promoter regions associated with defense genes in the receiver's genome. This epigenetic modification alters the chromatin structure, thereby facilitating a significantly faster and more robust transcription of defensive enzymes, but only if the receiver plant itself is subsequently subjected to herbivore attack.

According to the passage, the arrival of network-transmitted signals at an uninfested receiver plant directly causes which of the following?

  1. A
    The localized synthesis of jasmonic acid, which cascades into the immediate upregulation of defense-gene transcription.
  2. B
    A rapid and robust transcription of defensive enzymes that proactively shields the uninfested plant from impending herbivory.
  3. An alteration in the physical structure of chromatin that enables a faster transcription of defensive enzymes should a subsequent attack occur.Cevap
  4. D
    The permanent suppression of costly defensive toxin production in favor of utilizing more metabolically efficient epigenetic mechanisms.
  5. E
    The preemptive emission of airborne volatile organic compounds designed to repel aphids before mechanical tissue damage can be inflicted.

Cevap

An alteration in the physical structure of chromatin that enables a faster transcription of defensive enzymes should a subsequent attack occur.
The correct answer accurately synthesizes the passage's explicit causal chain regarding the receiver plant. The text states that the signals cause demethylation, which alters chromatin structure. This alteration facilitates faster enzyme transcription, but strictly contingent on a future attack. The correct option captures both the structural change and the conditional nature of the defense response.

Adım Adım Çözüm

1
Analyze the question stem to determine the specific causal relationship being asked for.
The question asks for the direct causal consequence of network-transmitted signals arriving at an uninfested 'receiver' plant.
Accurately targeting the correct entity (receiver plant vs. donor plant) is critical in complex causal passages.
2
Locate the explicit textual evidence describing the effect of these signals on the receiver plant.
The second paragraph states: 'the arrival of these network-transmitted signals causes the rapid demethylation of specific promoter regions... This epigenetic modification alters the chromatin structure...'
This directly answers the prompt's request for the explicit causal mechanism.
3
Identify any constraints or qualifiers attached to this causal mechanism.
The text adds a strict qualifier: the altered chromatin facilitates faster transcription 'only if the receiver plant itself is subsequently subjected to herbivore attack.'
Failing to account for qualifiers often leads to selecting a distractor that overstates the passage's claims.

Anahtar Kavram

Explicit Causal Relationships
Bu soruyu puanla

Konular

Explicit Causal Relationships

Bu konudan daha fazla soru