Final answer:
The increase in pH in water with healthy elodea and duckweed is a result of photosynthesis, which removes carbon dioxide and releases oxygen. This process leads to an increase in pH and makes the water more basic.
Step-by-step explanation:
The increase in pH in water with healthy elodea and duckweed can be attributed to the process of photosynthesis.
Elodea and duckweed are aquatic plants that perform photosynthesis, which involves the absorption of carbon dioxide (CO₂) from the water and the release of oxygen (O₂).
During photosynthesis, CO₂ reacts with water to form carbonic acid (H₂CO₃), which then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO₃-). The release of oxygen and the removal of carbon dioxide lead to an increase in pH, making the water more basic.