Materials
- Fresh variegated leaf (variegated coleus or Variegated pothos) A variegated leaf is a leaf that has more than one color, usually green and white. The different colors appear because some parts of the leaf contain chlorophyll (the green pigment needed for photosynthesis), while other parts contain little or no chlorophyll.
- Hot plate
- Beaker
- Water
- Ethanol (alcohol)
- Water bath (a beaker of hot water to hold the ethanol container)
- Forceps or spoon
- Iodine solution
- Dropper
- Safety goggles
Instructions
- Carefully transfer the leaf into a container of ethanol, and place this container in a hot water bath. Do NOT heat ethanol directly.
- Leave the leaf in the hot ethanol for a few minutes until the green color fades. The chlorophyll dissolves, and the leaf becomes pale or white.
- Remove the leaf and rinse it in water to remove excess ethanol.
- Spread the leaf flat on a white plate.
- Add a few drops of iodine solution onto the leaf.
- Wait a few minutes. Observe the color change. Areas of the leaf that contain starch will turn blue-black, while areas without starch will remain unchanged.
What’s going on?
- During photosynthesis, plants use chlorophyll to absorb light energy. This energy allows plants to convert carbon dioxide and water into glucose.
- The glucose produced by photosynthesis can be used in respiration, converted into proteins and oils or stored as starch.
- Iodine is a chemical indicator that turns blue-black in the presence of starch.
- When iodine is added to the leaf, areas that contain starch turn blue-black, while areas without starch do not change color.
- In variegated leaves, only the green regions contain chlorophyll. These regions photosynthesize and produce glucose, which is stored as starch. As a result, only the green parts of the leaf turn blue-black with iodine. The white areas lack chlorophyll, do not photosynthesize, and do not produce starch.This shows that chlorophyll is essential for photosynthesis.
Safety
- Adult supervision required.
- Ethanol is flammable and must be heated only in a water bath. Wear safety goggles and follow adult supervision rules at all times.
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