Question 62·Medium·Command of Evidence
Agronomist Alicia Chen suspects that a soil–dwelling bacterium enables tomato plants to thrive in salty conditions by enhancing their root development. To investigate, she grows two sets of tomato seedlings in identical salt-contaminated soil: one set is inoculated with the bacterium, and the other set receives no inoculation.
Which outcome, if observed, would most directly support Chen’s hypothesis?
For questions asking which result would “most directly support” a hypothesis, start by translating the hypothesis into a simple cause-and-effect statement: identify the cause (here, inoculation with the bacterium), the condition (salty soil), the specific mechanism or trait (root development), and the predicted effect (thriving, such as higher survival). Then quickly scan the choices and eliminate any that (1) use the wrong condition (e.g., non-salty soil), (2) ignore the key trait or mechanism mentioned, or (3) show no advantage or even a disadvantage for the experimental group. Choose the option where the experimental group vs. control difference in the correct condition matches the prediction as closely and specifically as possible.
Hints
Focus on the exact prediction
First, restate Chen’s hypothesis: what does she think the bacterium changes in the plants, and under what conditions (what kind of soil)?
Identify what counts as strong support
To most directly support her hypothesis, what kind of difference should we see between inoculated and uninoculated plants in salty soil, and in which specific plant feature?
Check each option against the hypothesis
As you read each choice, ask: (1) Is this about salty soil? (2) Does it compare inoculated vs. uninoculated plants? (3) Does it say anything about root development and how well the plants are doing overall?
Watch out for off-topic measurements
Be careful with answers that talk about traits Chen didn’t mention (like fruit or leaf color) or conditions she wasn’t testing (like soil without salt). Those won’t directly support her idea.
Step-by-step Explanation
Restate the hypothesis in your own words
Chen thinks that:
- A soil bacterium causes tomato plants to do well ("thrive") in salty soil, and
- It does this by enhancing their root development (making roots longer/more branched).
So we are looking for an outcome where:
- Plants with the bacterium are compared to plants without it.
- They are in salty soil.
- The plants with the bacterium have better roots and do better overall (for example, higher survival).
Understand what “most directly support” means
“Most directly support” means the result should match the hypothesis as closely as possible:
- It should involve salt-contaminated soil, since that’s the condition in the hypothesis.
- It should measure root development, because that’s the proposed mechanism.
- It should show a difference in how well plants thrive (such as survival or health) that lines up with the hypothesis.
Any choice that focuses on non-salty soil, ignores root development, or shows no advantage for inoculated plants will not directly support the hypothesis.
Eliminate choices that don’t test the right condition or trait
Go through the options and check what each actually measures:
- Choice A: Talks about growth in soil without added salt, not salty soil.
- Choice B: Says root systems are similar between groups, but fruit production differs.
- Choice C: Says no difference in survival in salty soil, but a difference in leaf color.
None of these show that, in salty soil, the bacterium both improves roots and helps plants thrive. So they do not directly support Chen’s full hypothesis.
Match the remaining choice to the hypothesis
The remaining outcome is the one where, in salty soil, the plants that received the bacterium develop noticeably longer, more highly branched roots and also survive at a higher rate than plants without the bacterium. This directly supports Chen’s idea that the bacterium enhances root development and enables tomato plants to thrive in salty conditions.
Therefore, the correct answer is: D) The bacterium-inoculated plants form noticeably longer, more highly branched roots than the uninoculated plants and also survive at a higher rate in the salty soil.