Logical Reasoning

PT4 · S1 · Q10 Rhizobium bacteria living in the

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Rhizobium bacteria living in the roots of bean plants or other legumes produce fixed nitrogen, which is one of the essential plant nutrients and which for nonlegume crops, such as wheat, normally must be supplied by applications of nitrogen-based fertilizer.

Conclusion

If biotechnology succeeds in producing wheat strains whose roots will play host to Rhizobium bacteria, the need for artificial fertilizers will be reduced.

Evidence

(1) Rhizobium bacteria living in the roots of bean plants or other legumes produce fixed nitrogen, which is one of the essential plant nutrients. (2) For nonlegume crops like wheat, fixed nitrogen normally must be supplied by applications of nitrogen-based fertilizer.

Evaluate

The argument leaps from "Rhizobium in legume roots produces fixed nitrogen" to "Rhizobium in wheat roots would reduce fertilizer needs." That works only if Rhizobium would also produce fixed nitrogen when hosted in wheat roots. If the bacteria's nitrogen-fixing activity depends on something specific to legumes (root chemistry, host symbiosis details, etc.) and doesn't carry over to wheat, then having Rhizobium in wheat roots wouldn't actually deliver any fixed nitrogen — and there'd be no fertilizer reduction.

Goal

Find an answer that says Rhizobium in wheat roots would still produce fixed nitrogen. Negation test: if it wouldn't, the conclusion collapses.

10.

The argument above makes which one of the following assumptions?

  1. Biotechnology should be directed toward

    Bad Assumption

    The argument doesn't need to claim biotech should be directed toward fertilizer-free plants — only that if it succeeds in producing Rhizobium-hosting wheat, fertilizer needs will drop. The author is making a conditional claim, not a recommendation about biotech priorities. Negation test: even if biotech shouldn't be directed this way, the conditional claim still holds.

    2% picked this

  2. Fixed nitrogen is currently the

    Bad Assumption

    "Currently the only" is too strong. The argument needs Rhizobium-produced fixed nitrogen to reduce fertilizer needs — that doesn't require fixed nitrogen to be the only nutrient currently supplied artificially. Even if other nutrients also need fertilizer, replacing the nitrogen-based fertilizer with biological nitrogen fixation would still produce a reduction. Negation test: if other nutrients also require fertilizer, the conclusion (some fertilizer reduction) still goes through.

    15% picked this

  3. There are no naturally occurring

    Bad Assumption

    The argument doesn't need to claim no naturally occurring wheat strains host Rhizobium. It only claims that if biotech succeeds in producing such strains, fertilizer needs will drop. Whether nature already has such strains is irrelevant — the argument's conditional claim still holds either way. Negation test: even if some wheat naturally hosts Rhizobium, the biotech-conditional argument is unaffected.

    10% picked this

  4. Legumes are currently the only

    Bad Assumption

    The argument doesn't require legumes to be the only self-fertilizing crops. The conclusion is about wheat specifically — that wheat strains hosting Rhizobium would need less fertilizer. Whether other non-legume crops also produce their own fixed nitrogen has no bearing on this. Negation test: if some other crops also produce fixed nitrogen on their own, the argument's wheat-specific conclusion is unaffected.

    1% picked this

  5. Correct

    Rhizobium bacteria living in the

    Why this is right

    This is the assumption the argument needs. The author concludes that engineering wheat to host Rhizobium will reduce fertilizer use, but the only fact the author has cited is that Rhizobium produces fixed nitrogen in legume roots. The conclusion only follows if Rhizobium would also produce fixed nitrogen in wheat roots. Negation test: if Rhizobium in wheat roots would not produce fixed nitrogen, the bacteria contribute nothing, and there's no fertilizer reduction. The conclusion collapses — confirming this assumption is necessary.

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    72% picked this

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