In the experiment, maintaining the water level above the stem of the funnel is crucial for several reasons such as preventing air bubbles, keeping presure balance, prevent contaminations, etc
Why must the water level be above the funnel stem?
Preventing Air Bubbles: If the water level dips below the funnel's stem, air bubbles can enter the test tube where the hydrilla plant is submerged. These air bubbles would interfere with the collection of oxygen bubbles produced during photosynthesis, potentially leading to inaccurate results.
Maintaining Pressure Balance: The water level above the funnel acts as a hydrostatic pressure head, providing a constant upward force against the oxygen bubbles accumulating in the test tube. This hydrostatic pressure prevents the bubbles from escaping prematurely and allows them to collect efficiently.