Overview
This lecture explains how to test for starch in plant leaves using an experiment and describes the role of photosynthesis in starch production.
Photosynthesis and Starch Formation
- Leaves produce glucose through photosynthesis when exposed to sunlight.
- Excess glucose in leaves is converted into starch, which serves as stored food in plants.
Starch Test Experiment
- Collect a leaf that has received sunlight for several hours.
- Boil the leaf in water to kill it and soften cell structures for better chemical access.
- Submerge the leaf in alcohol and heat in boiling water to remove chlorophyll; alcohol turns green.
- Bleach the leaf so iodine-induced color change will be visible.
- Place the bleached leaf in a petri dish and add iodine solution.
- A color change to dark green (violet complex) indicates the presence of starch in the leaf.
Experiment Variation: Light Exposure
- Cover a leaf with black paper for a few days to block sunlight, then repeat the starch test.
- Check if starch is still present in leaves deprived of light.
Key Terms & Definitions
- Photosynthesis — the process by which plants use sunlight to convert carbon dioxide and water into glucose.
- Starch — a carbohydrate stored in plant cells, formed from excess glucose.
- Chlorophyll — the green pigment in leaves needed for photosynthesis.
- Iodine Solution — a chemical that reacts with starch to produce a dark green or violet color.
Action Items / Next Steps
- Perform the starch test on both sunlit and covered leaves.
- Observe and compare changes in color to confirm the role of light in starch formation.