Testing Leaves for Starch
Biology: Edexcel IGCSE, topic 2.3.6
Testing Leaves for Starch
Some of the glucose made by photosynthesis in the leaves is stored as starch. It is possible to test for starch stored in leaves.
Boil
- Boil a leaf to denature the enzymes and halt photosynthesis.
Ethanol
- Soak the leaf in ethanol to remove the green chlorophyll from the leaf, turning it white.
Iodine
- Add droplets of iodine onto the leaf.
- The iodine will turn dark blue in the parts of the leaf where starch is present.
Altering starch content
- The starch content of leaves can be changed.
- For example, keeping plants in the dark would decrease the rate of photosynthesis. This would force leaves to use up their starch stores, so if these leaves were tested, not as much of the leaves would turn dark blue with iodine.
- Plants could also be kept in low carbon dioxide (using sodium hydroxide to absorb CO2) to reduce photosynthesis.
Test yourself on Testing Leaves for Starch
When testing for stored starch in leaves, why are they first soaked in ethanol?
Testing Leaves for Starch
What can be used to test for the presence of starch in leaves?