Final answer:
Water temperature is the factor that influences where an organism lives in an aquatic ecosystem, as it affects dissolved oxygen levels, enzyme activity, and overall metabolic processes in aquatic organisms.
Step-by-step explanation:
The correct option is A:
Which factor influences where an organism lives in an aquatic ecosystem is a) Water temperature. This is because water temperature affects the concentration of dissolved oxygen in the water, which is crucial for the survival of aquatic organisms.
Water temperature is an abiotic factor that plays a significant role in determining the distribution of organisms within aquatic ecosystems. Aquatic organisms are greatly influenced by the temperature of the water because it affects the levels of dissolved oxygen and nutrients, as well as the metabolic rates of the organisms. For instance, cold water holds more dissolved oxygen than warm water, thus supporting aquatic life that requires high oxygen levels. Additionally, certain enzymes within organisms function optimally at specific temperatures, further influencing where certain species can live. Salinity and sunlight are also critical abiotic factors as they affect the survival of organisms that cannot tolerate high salt levels and those that rely on photosynthesis, respectively. The interplay between these abiotic factors shapes the dynamic ecosystem that aquatic organisms inhabit.