Photosynthesis Experiments


Testing for Starch with IODINE:

End product of photosynthesis is STARCH.  Therefore, experiments can be performed to find out what affects starch production in a leaf and hence photosynthesis.  Obviously, the answer is Light and carbon dioxide!

Before the experiments are carried out, the leaves of a plant must be 'de-starched'.  This is done by placing the plant in darkness for 24 hours.

Once the leaves are de-starched, the plant can be left in light for 24 hours with some leaves deprived of  CO2, some of light and others left alone.  They are then tested for starch using IODINE.


Iodine can stain starch.  If the leaf being tested for starch turns blue/black with iodine, then starch is present.  This show that photosynthesis had taken place.  If the iodine stays yellow/brown then there is no starch, which indicates that the leaf could not perform photosynthesis because it did not have either CO2 or light.


Testing WATER UPTAKE or Transpiration:

Up take of water by the plant can be investigated by using a POTOMETER.  It allows you to test the rate of water uptake by a plant in different atmospheric conditions.  The apparatus is setup as below.  As soon as the water evaporates from the leaves, it is drawn up the xylem tubes and the air bubble moves along the glass tube.  The further along the bubble moves in a given time, the faster the rate of TRANSPIRATION or WATER UPTAKE.  A Plant can be exposed to different conditions, such as wind/heat/humidity etc., to find out how it affects the rate of TRANSPIRATION.

Relationship between Photosynthesis and Respiration


Tags:Photosynthesis, Water uptake, Transpiration, Starch, Iodine




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