(2) The two indicator gases for measuring photosynthetic rate are CO2 consumption and O2 release. If we want to observe the effect of breathing on the rise and fall of the "Spirogyra", we must put the device in a dark environment.
(3) If this device is used to detect the effects of different polluted water bodies on the photosynthesis of Spirogyra, the independent variable of the experiment is different polluted water bodies, and the dependent variable is the floating speed of the "Spirogyra parachute". Because some pollutants may make the water eutrophication and make Spirogyra grow more actively, the stronger the photosynthesis, the less the water pollution.
So the answer is:
(1) dead weight of the device, amount of spirogyra, amount of pigment in spirogyra and amount of enzyme.
(2)CO2 consumption and O2 release? dark
(3) The floating speed of Spirogyra in different polluted water bodies.