FOOD PRODUCERS

PURPOSE : To demonstrate that starch, a food substance, is produced in leaves.

MATERIALS : Paper towels

                          Tincture of iodine

                          Leaf ( pale green )

                          Rubbing alcohol

                          Shallow dish

                          ( 500 ml ) jar with lid

                           Measuring cup ( 250 ml )

PROCEDURE : 

• Place the pale green leaf in the jar. The paler the leaf , the easier it will be to extract the green pigment, chlorophyll.
• Pour one cup of alcohol into the jar. Put the lid on the jar.
• Allow the jar to stand for one day.
• Remove the leaf and dry it by blotting with a paper towel.
• Lay the leaf in the shallow dish.
• Add enough iodine to cover the leaf.

RESULTS : Dark areas appear on the leaf.

WHY ? Photosynthesis is an energy producing reaction that occurs in the leaves of plants. Starch, a food substance is one of the product of this reaction. Soaking the leaf in alcohol removes the wax coating on the leaf plus it partially removes the green pigment chlorophyll. It is easier to see the result of the starch test without the presence of the green chlorophyll. Iodine combines with starch particles to form a dark purple to black color.