Question 59·Medium·Inferences
By installing fine-mesh barriers to sever mycorrhizal fungal connections between paired fir saplings while still allowing water and dissolved nutrients to pass through the soil, botanists Sara Nunez and Paulo Rios tested whether drought stress information can travel between plants. In each pair, one sapling was subjected to mild drought while its partner was kept well watered. Partners linked by intact fungal networks closed their stomata hours earlier and lost less water than partners in trenched pairs. In a follow-up trial, the droughted saplings were enclosed in airtight bags to block airborne chemical signals, and connected partners still responded early. The researchers therefore hypothesize that _____
Which choice most logically completes the text?
For “Which choice most logically completes the text?” questions, first identify what the final sentence must do: usually summarize a conclusion or hypothesis based only on the information given. Track the experiment’s design (what changed, what stayed the same) and the key results, then ask: What explanation fits all these facts and nothing else? Eliminate choices that contradict any detail (like controls or follow-up trials) or that introduce new, unsupported ideas. Finally, select the option that restates the conclusion the researchers would naturally draw from their evidence.
Hints
Focus on what was controlled
Notice that the mesh barriers blocked only fungal connections, but still allowed water and dissolved nutrients to move. What does that tell you about what the experiment is testing?
Compare the behavior of connected vs. unconnected partners
Look at how the well-watered partners behaved when they were connected by fungal networks versus when they weren’t. How did their stomatal closing and water loss differ?
Use the follow-up trial to eliminate options
In the second trial, the droughted saplings were sealed in airtight bags. How does this detail affect any explanation that relies on airborne chemicals? Which answer choices conflict with that result?
Think about what “therefore hypothesize” must summarize
The last sentence needs to state a conclusion that directly follows from both the initial results and the follow-up trial. Which option best fits all the evidence without contradicting any part of the experiment?
Step-by-step Explanation
Understand what the researchers changed
The botanists used fine-mesh barriers that blocked fungal connections but still allowed water and dissolved nutrients to move between the soil around the two saplings. This means the only major difference between the paired saplings was whether they were connected by mycorrhizal fungi or not. One sapling in each pair was put under mild drought; the other was kept well watered.
Connect the first experiment to a possible signal pathway
In the first trial, partners with intact fungal networks closed their stomata earlier and lost less water than partners in trenched pairs (where fungal connections were severed). Since water and nutrients still moved equally in both setups, this suggests that something traveling through the fungal network—not just soil water changes—is affecting the partner’s stomatal behavior.
Use the follow-up trial to rule out airborne signals
In the follow-up, the droughted saplings were put in airtight bags so that airborne chemical signals could not reach the partners. The partners that were still connected by fungal networks still responded early by closing their stomata. This shows that airborne chemicals are not required for the partner to receive drought information; another pathway must be responsible.
State the logical hypothesis and match it to a choice
Putting both experiments together, the most logical hypothesis is that shared mycorrhizal networks carry drought-related signals from the stressed sapling to its partner, causing the partner to close its stomata early and conserve water before it becomes drought-stressed itself. This is exactly what choice A) shared mycorrhizal networks can transmit drought-related signals that trigger preemptive water-conserving responses in neighboring plants. says, so A is the correct answer.