Help with experiment?

Question

I am doing a biology experiment that involves taking a water plant and putting the stem in a straw. Then sucking water into the straw and clamping it shut. Next putting it next to a heat source. Supposedly water bubbles are supposed to come out of the stem...why? Also what's supposed to happen if you put sodium carbonate(baking soda) in the water? do more or less bubbles form? Please help!?!?

Answer 1

it sounds like you have not done the experiment your self yet. and are asking for someone that has done it before.   i tried to find a homework site that held this experiment listed but could not find it sorry

Answer 2

There could be several factors involved with the failure of the plant to evolve bubbles.  I assume you are using what is commonly called "Elodea" which is actually Anarcharis!  The stem with leaves should be healthy with no dying or decayed leaves.  Make sure you make a fresh cut on the end of the stem with a sharp razor blade so you don't crush the stem.  Be sure to have a strong light source with a bottle of water in the light path to act as a heat absorber.  If the plant is healthy, it will photosynthesize releasing oxygen gas bubbles from the cut end of the stem.  By counting the number of bubbles being released from the cut end of the stem for a given time period, you can determine the rate of photosynthesis.  By adding sodium bicarbonate ions to the water, you are increasing the availability of carbon dioxide for photosynthesis so the number of bubbles should increase significantly.  You can demonstrate you exhale carbon dioxide by blowing through a soda straw into the water in which the stem is immersed.  It should also increase the rate of photosynthesis.

Fresh Elodea stems, good strong light source, maintain a moderate temperature and you should get good results.  If you buy the Elodea from a pet shop try to get the freshest bunch available!