Purpose
To demonstrate the existence of starch in plants by separating the compound from potatoes.
Additional information
Starch is a white powdery substance that is often colorless and tasteless and exists in all plant seeds and tubers. Examples of every day starches include potato starch, cornstarch, and tapioca. People use starch for a multitude of purposes, especially in cooking. Starch is used in its basic form to thicken food such as sauces. It's also used in the manufacturing of textiles and paper, laundry purposes, and as a mold for jelly beans and wine gums.
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Required materials
- 5 Large potatoes
- Peeler
- Grater
- 2 Bowl
- Water
- Sieve
Estimated Experiment Time
About 15 minutes to set-up, up to several hours to conduct.
Step-By-Step Procedure
- 1. Peel the potatoes to remove the skin.
- 2. Grate the potatoes into your bowl.
- 3. Fill the bowl with water until the grated potatoes are completely submerged.
- 4. Reach in and squeeze the potatoes with your fingers for several minutes.
- 5. Leave for about 30 minutes. When you return, repeat step 4.
- 6. Place your second (empty) bowl on a table. Take the potato out of the bowl by slowly pouring the mixture through the sieve, catching the cloudy water in the empty bowl beneath it.
- 7. Place the bowl of cloudy water in a sunny place and leave until it dries up. What happens?
Note
Make sure you squeeze the potatoes with force and do it for several minutes. You'll need to apply a lot of pressure to get the best results from this experiment.
If you don't have a peeling tool handy, you can peel the potatoes using a conventional kitchen knife or even a butter knife. As always, be careful with sharp objects and ask for help from an adult if you need one!
Observation
What do you think is the purpose of squeezing the potatoes? Why do you suppose it's best to let the potatoes soak for 30 minutes before squeezing them again? Can you think of any other plant or vegetable where you can apply a similar process to extract the starch?
Result
A compound is a substance made up of two or more elements. After your cloudy water dries up, you should be left with a white powder in the bowl. This white powder is called "starch". Starch is present in many plants because it's a way they store energy. When you eat potatoes, your body changes the starch into sugar for energy. The process starts when the chemicals in your saliva break down the starch.
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