As the numbers of green algae in the river increase, the concentration of dissolved oxygen increases. Explain why the concentration of dissolved oxygen increases.

Green algae are photosynthetic organisms. They use light energy to convert carbon dioxide and water into glucose and oxygen. The chemical equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This process releases oxygen into the water, increasing the dissolved oxygen concentration. Although the algae also respire (using up some oxygen), during the day the rate of photosynthesis is much higher than the rate of respiration, so there is a net production of oxygen.