Biochemists investigated whether adding proline, an amino acid, protects the marine microalga *Nannochloropsis oculata* from high-salinity stress. They prepared 4 culture flasks under identical light and temperature conditions for 72 hours:
• Flask 1: Standard nutrient medium () + *N. oculata*
• Flask 2: Elevated salinity medium () + *N. oculata*
• Flask 3: Elevated salinity medium () + proline + *N. oculata*
• Flask 4: Elevated salinity medium () without *N. oculata* (cell-free)
Match each experimental flask setup to its primary methodological purpose in the experimental design.
- Flask 1 ( + *N. oculata*)Establishes a baseline level of microalgal growth under standard, non-stressed salinity conditions.
- Flask 2 ( + *N. oculata*)Serves as the unsupplemented high-salinity control to measure the effect of salt stress alone.
- Flask 3 ( + proline + *N. oculata*)Acts as the experimental treatment group to evaluate the protective effect of proline under salt stress.
- Flask 4 ( without *N. oculata*)Serves as an abiotic control to ensure that measured changes in the medium are due to biological activity.
Answer
Flask 1 matches the standard baseline growth condition; Flask 2 matches the unsupplemented high-salinity control group; Flask 3 matches the experimental treatment group evaluating proline; Flask 4 matches the abiotic control group.
Each setup plays a specific methodological role: Flask 1 establishes baseline performance under standard growth conditions (); Flask 2 serves as the negative control for proline addition by isolating the impact of elevated salinity alone (); Flask 3 is the experimental treatment testing the hypothesis that proline mitigates salinity stress; and Flask 4 is an abiotic control ensuring that any observed changes in the medium depend on living microalgal cells rather than non-biological chemical processes.
Step-by-Step Solution
Key Concept
Determining Control Groups and Baseline Conditions