When the rate of photosynthesis increases, H2CO3 turns purple why?

Question

pond weed is placed in a test tube of hydrogen carbonate indicator solution (red) when placed in dark the solution turns yellow, more carbon dioxide released (respiration). Want to know why the solution turns purple when left in bright light.

Answer 1

While I am not familiar with your experiment, if you have H2CO3, and you cause it to lose CO2, then you will be left with H2O, which is less acidic than H2CO3. The indicator changes colour accordingly.