the experiment test for oxygen realease in aquatic plants

sodiem hydrocarbonate is uesd to provide carbon dioxide.
as the pant use carbon dioxide as raw material to carry our photosynthesis with the present of light. during photosynthesis, oxygen is released as by-product.
though there are carbon dioxide dissolved in the water but it is lettle, to in crease the rate of photosynthesis, you can provide more carbon dioxide.