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Difficulty: HardLogical Arguments and Causal Relationships

An agricultural research team investigated an outbreak of fungal root rot in crop fields following the application of a microbial bio-fertilizer. The team hypothesized a specific causal sequence: microbes in the fertilizer produce high concentrations of organic acids, these organic acids degrade root cell membranes, and the damaged membranes subsequently allow opportunistic fungal pathogens to infect the root system.

Which of the following findings, if true, would support the team's proposed causal sequence? Select all that apply.

  1. Root membrane degradation occurred consistently prior to fungal penetration, and synthetic exposure to organic acids alone produced identical membrane damage in pathogen-free environments.Answer
  2. Application of broad-spectrum fungicides successfully eliminated fungal spores but failed to reduce the severity of root membrane degradation in fields treated with the bio-fertilizer.Answer
  3. C
    Fungal pathogens, once established inside root tissues, secrete biochemical signals that stimulate soil microbes to increase organic acid production.
  4. D
    Plant roots undergoing fungal decay release nutrient exudates that accelerate the growth rate of bio-fertilizer microbes in the surrounding soil.
  5. E
    Crop fields utilizing conventional chemical nitrogen fertilizers achieved higher overall harvest yields than fields utilizing microbial bio-fertilizers.

Answer

The statements confirming that membrane degradation precedes fungal entry (and is inducible by organic acids alone) and that fungicide treatment fails to prevent membrane degradation both support the proposed causal sequence.
The hypothesis posits a sequential causal chain: bio-fertilizer microbes produce organic acid, organic acid damages root membranes, and damaged membranes permit fungal infection. The statement establishing that organic acid alone induces membrane degradation prior to fungal presence confirms the mechanism and sequence. The statement showing that eliminating fungi leaves membrane damage intact confirms that membrane damage is an independent precursor, not a symptom of fungal infection.

Step-by-Step Solution

1
Deconstruct the proposed causal chain in the stem
Microbial bio-fertilizer -> Organic acid production -> Root membrane degradation -> Fungal infection penetration.
To evaluate support for a causal hypothesis, each step in the chain must be tested for correct temporal order and independence.
2
Evaluate statements testing the cause-and-effect sequence
Demonstrating that organic acids cause membrane damage without fungi present confirms the intermediate mechanism. Showing that eliminating fungi does not prevent membrane damage proves membrane damage occurs upstream of fungal infection.
Both findings validate that organic acid damage is the cause, not the effect, of fungal invasion.
3
Identify and eliminate causal reversals and irrelevant scope options
Options claiming that fungal infection or decay causes microbial growth/acid production reverse the hypothesized causal order. General yield comparisons do not address the causal mechanism.
Reversing cause and effect invalidates the proposed direction of the mechanism.

Key Concept

Causal Order and Mechanism Validation in Logical Arguments
Estimated Time:2m 30s
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Topics

Logical Arguments and Causal Relationships

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