Test for Starch in Leaves

Leaves from a plant kept in light and one kept in darkness are boiled briefly, decolorized in hot ethyl alcohol, and stained with iodine. A blue-black color indicates starch, showing that photosynthesis in light produced stored carbohydrate.

1. Place one healthy potted plant in a dark place for about 24 hours to remove stored starch; keep a second, similar plant in bright light.
2. After 24 hours, pick one leaf from each plant.
3. Set up a hot water bath by placing a beaker or jar with ethyl alcohol inside a saucepan of water; heat the pan gently until the alcohol is hot (near boiling). Turn off heat.
4. Using tweezers, dip each leaf in hot water for about 60 seconds to soften and kill the tissue.
5. Transfer the leaves into the hot alcohol until they turn pale or nearly white (chlorophyll removed).
6. Rinse the decolorized leaves briefly in cool water to soften them and lay them in a shallow dish.
7. Cover each leaf with iodine solution and observe the color change.
8. Record which leaf turns blue-black (starch present) and which remains yellow-brown (little or no starch).

Experiment: To test a leaf for starch - Science Projects:

Use iodine to test a leaf for starch - KClassScienceChannel:

📄 Test for Starch in Plants - Home Science Tools: https://learning-center.homesciencetools.com/article/test-for-starch-photosynthesis/

📄 Testing a leaf for starch - BBC Bitesize: https://www.bbc.co.uk/bitesize/guides/zpcvbk7/revision/3

• Cover part of a leaf with opaque foil while in light to show starch only forms in exposed regions.
• Compare different light intensities or colors during the 24-hour light period.
• Extend the dark period (e.g., 48 hours) and test whether starch disappears completely.
• Test leaves from different plant species or from sun versus shade leaves on the same plant.

• Adult supervision required when using hot water and heated alcohol.
• Heat ethyl alcohol only in a water bath; keep away from flames and sparks (alcohol is highly flammable).
• Use heat-resistant glassware and handle hot containers with tongs or gloves.
• Wear safety glasses, gloves, and a lab apron; iodine can irritate skin and stain clothing.
• Ensure good ventilation and keep lids on alcohol when not in use.
• Dispose of iodine and alcohol according to local guidelines; do not pour large amounts down the drain.

• Why decolorize the leaf before adding iodine? (Removing chlorophyll makes the iodine color change easy to see.)
• What does a blue-black iodine result indicate? (Starch is present, meaning photosynthesis produced and stored carbohydrates.)
• Why keep one plant in the dark first? (To use up stored starch so any new starch must come from photosynthesis during light exposure.)
• How does covering part of a leaf affect staining? (Covered areas receive no light, produce little or no starch, and stay yellow-brown.)