Question 102·200 Super-Hard SAT Reading Questions·Information and Ideas
Mean Growth Rate of Algae Populations by Salinity History and Test Condition
| Salinity history | Salinity unchanged | Abrupt salinity increase | Abrupt salinity decrease |
|---|---|---|---|
| Constant | 2.8 | 1.5 | 1.7 |
| Fluctuating | 2.4 | 2.2 | 2.1 |
Researchers randomly assigned genetically similar populations of freshwater algae to environments with either constant or fluctuating salinity. After 30 generations, the researchers divided each population among three test conditions: salinity unchanged from its recent level, an abrupt salinity increase, or an abrupt salinity decrease. The table shows each group's mean growth rate in cell divisions per day during the test. The researchers claimed that adaptation to fluctuating salinity produced broad resilience to later salinity shifts but that this resilience came with a cost when salinity remained predictable.
Which choice best describes data from the table that support the researchers' claim?
For a table-based command-of-evidence question, break the claim into all of its required components and make the same comparison in every relevant condition. Prefer the choice that directly compares the experimental groups and supports the claim's full scope; reject choices that use accurate but incomplete within-group comparisons.
Hints
Separate the claim
Look for evidence of both a disadvantage under predictable conditions and an advantage under changing conditions.
Use consistent comparisons
For each test condition, compare the fluctuating-history rate directly with the constant-history rate.
Interpret the differences
Consider what a negative or positive fluctuating-minus-constant difference would indicate in each condition.
Step-by-step Explanation
Identify the required comparisons
The claim has two components: fluctuating-history populations should perform worse when salinity remains predictable but better than constant-history populations after either kind of abrupt shift.
Calculate the between-history differences
Subtract the constant-history rate from the fluctuating-history rate in each condition. The differences are under unchanged salinity, after an increase, and after a decrease.
Interpret the signs
The negative first difference represents lower growth under predictable conditions, while both positive shift-condition differences represent higher growth after abrupt changes. Therefore, the correct answer is The fluctuating-history rate minus the constant-history rate was under unchanged salinity, after an increase, and after a decrease.