After 24 hrs, the amount of gas that accumulated at the top of the inverted test tube is measured. the students conclude that the light source is causing the water to evaporate, causing water vapor to fill the top of the tube. the best alternative explanation of the differences between the setups is that the - a. light caused the elodea plants to photosynthesize, releasing o2 gas b. gravity increases the downward flow of the trapped water c. metabolism of the elodea plants absorbed co2 from the water d. heat from the light source caused the escape of the dissolved gas