Question 198·200 Super-Hard SAT Reading Questions·Information and Ideas
Mean Root-to-Shoot Biomass Ratio
| Grass species | Standard conditions | Low nitrogen | Low water |
|---|---|---|---|
| Prairie dropseed | 0.84 | 1.29 | 0.88 |
| Sideoats grama | 0.79 | 0.83 | 1.24 |
Plants can respond to limited resources by changing how they divide biomass between roots and shoots. A higher root-to-shoot biomass ratio indicates greater root biomass relative to shoot biomass, but it does not indicate whether absolute root biomass has increased. Researchers grew two perennial grasses under standard conditions, low-nitrogen conditions with normal watering, or low-water conditions with normal nitrogen. They regarded a difference of at least 0.10 between a treatment mean and the mean for the same species under standard conditions as a reliable response. The researchers concluded that ______
Which choice most effectively uses data from the table to complete the statement?
For table-based command-of-evidence questions, identify the precise comparison and any threshold defined in the passage before evaluating the options. Compare values within the correct groups, and avoid conclusions that change what the table measures—for example, interpreting a ratio as an absolute amount.
Hints
Use within-species comparisons
For each grass, compare the two treatment values with that grass's own standard-condition value.
Check reliability
Calculate each difference and determine whether it reaches the stated threshold of 0.10.
Interpret the measurement carefully
Distinguish between an increase in a root-to-shoot ratio and an increase in the absolute amount of root biomass.
Step-by-step Explanation
Identify the required comparisons
Compare each treatment value with the standard-condition value for the same species. A change must be at least 0.10 to count as reliable.
Calculate the changes
For prairie dropseed, the low-nitrogen change is , while the low-water change is . For sideoats grama, the low-nitrogen change is , while the low-water change is .
Apply the reliability threshold
The two changes of 0.45 are reliable, but the two changes of 0.04 are not. Because the table reports ratios, these changes concern relative allocation rather than absolute root biomass.
Select the supported conclusion
The correct answer is low nitrogen reliably shifted prairie dropseed, but not sideoats grama, toward greater relative belowground allocation, whereas low water reliably shifted sideoats grama, but not prairie dropseed, in that direction.