Materials
- Small pieces of green (unripe) banana and yellow (ripe) banana
- Iodine solution
- Microscope
- Glass slides and coverslips
- Dropper or pipette
- Tweezers or toothpick
- Distilled water
Instructions
- Scrape a tiny amount of banana pulp from each sample (one green, one ripe) using a toothpick or tweezers. You only need a small smear for each.
- On the left side of the slide, place one drop of distilled water.Add the ripe banana smear into the water and spread it thinly.
- On the right side of the slide, place another drop of distilled water.Add the green banana smear and spread it thinly.
- Add one drop of iodine onto each smear. The iodine will react immediately with any starch.
- Lower the coverslip slowly at a 45° angle so it covers both smears without trapping bubbles.
- Observe under the microscope. Left side (ripe banana):Few or no starch granules.Iodine stays light brown/yellow. Right side (green banana):Many blue or purple starch granules due to the iodine–starch reaction.
- Draw or photograph your slide. Left: Ripe banana = little or no starch Right: Green banana = blue starch granules
What’s Going On?
- Green bananas contain a high amount of starch, which is a complex carbohydrate. As the banana ripens, natural enzymes begin breaking this starch down into simpler sugars. This process is called starch hydrolysis.
- The conversion of starch into sugars is what makes a ripe banana taste sweeter and feel softer.
- In the green banana, iodine reacts with starch and turns blue or purple. In the ripe banana, most of the starch has already been converted into sugar, so the iodine stays light brown or yellow. This experiment visually shows how bananas shift from starch to sugar during ripening.
Safety
- Iodine stains! Handle carefully.
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