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Thread: Photosynthesising plant advice

  1. #1 Photosynthesising plant advice 
    Forum Freshman
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    Nov 2008
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    I wonder if anyone could advise me?
    I am teaching myself biology (from scratch) using books and some materials and resources I have access to at home from an online foundation course. I recently carried out my own very basic lab investigation into the workings of plant photosynthesis (introductory experiment) by following some instructions that I found.

    In the investigation:

    I placed an aquatic plant in a boiling tube filled with a solution that provided a source of carbon dioxide (of concentration known and controlled).
    I placed this boiling tube in a beaker of unheated water in order to insulate it from any temperature fluctuations of the room.
    I directed a lamp over the apparatus (containing the plant in the solution) and then counted and recorded the number of oxygen bubbles produced during a set time.

    The boiling tube containing the plant in the carbon dioxide solution was not sealed with a stopper.

    I wonder how environmental gases affected my results (because the test tube was open).

    What I would like to know is:
    Does the fact that the boiling tube was not sealed with a stopper affect the results of my experiment because it exposes the plant in the solution to environmental gases?
    Would gas entering the test tube from the environment cause air bubbles in the solution that affect my results?
    If my boiling tube was filled completely to the top with the carbon dioxide solution, would that be sufficient to prevent air from entering the boiling tube and thereby forming air bubbles in the solution (if they can occur - see my previous question above) and affecting my results?
    Alternatively, would air only enter the boiling tube and affect my results if the carbon dioxide solution that the plant is immersed in only partially filled the test tube?

    I realize and appreciate that there are many variables in this experiment that were not controlled (e.g. the investigation did not take place in a dark room), and that these reduce its reliability anyway. However, I would initially like to understand specifically how my use of an open boiling tube has impacted my results.

    Unfortunately as a self-teaching biology student I have no one I can go to with my questions!

    I presently have a very limited understanding of this and would be grateful if anyone might be able to help me understand the basics.


    Last edited by emetzner; March 19th, 2013 at 03:56 PM.
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