Plants produce glucose during photosynthesis. Some of the sugar is converted into starch which can be stored in the roots and leaves of the plant. This practical involves taking a leaf from a plant and testing it for the presence of starch.
Equipment required (per set):
The student should use hot water from a kettle to half fill a beaker and add the leaf to this beaker whilst the water is still hot. Leave the leaf in there for a few seconds. This will stop any further chemical reactions taking place in the leaf.
- Medium beaker
- Heatproof mat
- Petri dish
- Iodine solution
- A large leaf
Half fill a test tube with ethanol (ensure you do this away from any naked flames or heat sources). Remove the leaf from the water using tongs and put it into the ethanol in the test tube. Stand the test tube in the hot water until the ethanol turns green. This removes the chlorophyll in the leaf which makes the later staining clearer to see.
Remove the leaf with tongs (remembering the water is still very hot) and dip back into the hot water to remove any ethanol and to soften the leaf.
Place the leaf into the petri dish and flatten out. Add some of the iodine solution to the surface of the leaf. If there is starch present, the leaf will turn blue/black in colour.
This test for starch can form part of the practical investigation into whether plants need carbon dioxide and sunlight for photosynthesis. A link to these practicals can be found below.