Question 153·Easy·Command of Evidence
Garden snails generally emerge after sunset to feed on vegetation. Zoologists Lina Chen and Rafael Ortiz observed that on nights with a bright full moon, noticeably fewer snails appeared. They hypothesized that strong moonlight increases the snails’ risk of predation, so the snails stay hidden when light levels are high.
To test this idea, the researchers placed equal numbers of snails in two identical outdoor pens for three successive nights of bright moonlight. One pen was left uncovered, while the other was fitted with translucent screens that blocked about 80% of the moonlight but allowed air to circulate. Each night, the scientists counted how many snails were visible on the soil surface in each pen.
Which result from the experiment, if observed, would most directly support Chen and Ortiz’s hypothesis?
For “which result best supports the hypothesis” questions, first restate the hypothesis in your own words, focusing on what variable is being changed (here, light level) and what behavior is predicted to change (snails surfacing more or less). Then look at the experimental setup to see which condition represents “more” of that variable and which represents “less.” Before looking closely at the choices, quickly predict what a supportive result would look like (e.g., more behavior in one condition than the other). Finally, eliminate any choices that show no difference between conditions, the opposite pattern from the prediction, or changes over time that don’t isolate the tested variable, and select the one that matches your predicted pattern most directly.
Hints
Identify what the scientists are trying to explain
Focus on the hypothesis: what do Chen and Ortiz think is causing fewer snails to appear on bright full-moon nights?
Connect the hypothesis to the experiment setup
Look at how the two pens differ. Which pen has more moonlight, and which pen has much less?
Predict what should happen if the hypothesis is right
If strong moonlight really makes snails stay hidden, which pen should have more visible snails, and why?
Eliminate choices that don’t test the light effect
Cross out any answer that either shows no difference between pens or talks only about changes over time, instead of differences in light level.
Step-by-step Explanation
Restate the hypothesis in simple terms
Chen and Ortiz observe that fewer snails appear on bright full-moon nights. They hypothesize that strong moonlight makes snails easier for predators to see, so snails stay hidden when light levels are high. In other words: more light → more danger → snails hide; less light → safer → snails come out.
Understand what the experiment is changing
The experiment uses two pens that are the same except for light level:
- Uncovered pen: gets full moonlight (bright).
- Covered pen: translucent screens block about 80% of the moonlight (much darker) but still let air in.
So the key difference is how much moonlight the snails experience, which directly tests the hypothesis about light and hiding behavior.
Translate the hypothesis into a predicted result
If bright moonlight makes snails hide, then on these bright nights we should see:
- Fewer snails coming out in the uncovered (bright) pen.
- More snails coming out in the covered (darker) pen.
So the result that best supports the hypothesis will say, in some form: more snails surface where moonlight is blocked than where it is not blocked, consistently over the three nights.
Match each answer choice to the prediction
Now compare the options to the prediction from Step 3:
- "Roughly the same number of snails surfaced in both pens" would mean light does not affect surfacing.
- "Significantly fewer snails surfaced in the covered pen" would mean snails come out more in bright light, the opposite of the hypothesis.
- "The number of snails surfacing declined in both pens over the three-night period" talks about change over time, not about light level.
- Only the option stating that significantly more snails surfaced in the covered pen than in the uncovered pen on each of the three nights shows snails coming out more when moonlight is reduced, so that is the correct answer.