Dissolved oxygen in water is most influenced by temperature; as temperature rises, DO tends to

• A. Increase
• B. Decrease
• C. Remain the same
• D. Vary unpredictably

Answer: (B)

Dissolved oxygen in water is governed by how much oxygen can physically dissolve, which depends on temperature. As water warms, the solubility of oxygen decreases, so less oxygen can remain dissolved. That’s why DO tends to fall when temperature rises. Cooler water can hold more oxygen, supporting aquatic life, while warming reduces this capacity. While temperature can also influence how fast organisms use oxygen, the key point here is the inverse relationship between temperature and oxygen solubility, so the DO decreases with higher temperature. The other options don’t fit because oxygen solubility does not increase with temperature, remain unchanged, or vary unpredictably.