Which of the following factors is crucial for living organisms in water?

The pH level is crucial for living organisms in water because it directly affects the availability of essential nutrients and the overall health of aquatic ecosystems. Most aquatic organisms, including fish and invertebrates, are adapted to specific pH ranges. A pH that is too low (acidic) or too high (basic) can harm these organisms by influencing metabolic processes, reproduction, and the solubility of harmful substances.

For instance, at extreme pH levels, biochemical reactions required for survival can be disrupted, leading to physiological stress or even death. Moreover, many aquatic plants rely on a certain pH range for optimal nutrient uptake, affecting the food web and overall ecosystem health. Maintaining a balanced pH is therefore essential for sustaining diverse aquatic life and ensuring the stability of aquatic environments.

Other factors like water temperature, water depth, and the presence of nutrients are also important, but their impact is often mediated by the pH level, highlighting the foundational role pH plays in aquatic ecosystems.