Question

A student is considering adding Egeria densa, an aquatic plant, to her freshwater tank. She is concerned about the effects of pH levels on her fish, because increasing carbon dioxide (CO2) concentrations result in a decrease in pH. She decides to test the effects of Egeria on water pH levels. She removes her fish from the tank and then adds the water plant. Construct an argument to explain her observations of how the plant affected the pH levels in her tank during the day and at night over a 24-hour period

Answer 1

Egeria densa is an aquatic plant which has developed different means of carrying out photosynthesis under conditions of low carbon dioxide. During the process, the plant generate low pH at the leaf surface during high light intensity and this acidification shift the process equilibrium towards carbon dioxide which will then diffuse into the cell through passive diffusion.
Thus, if the student place the plant inside her fresh water tank, the plant will increase the carbon dioxide content of the water, which will lead to an increase in pH and the increase in pH will negatively affect the fish.