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How do you prove in an experiment that digestion occurs and how?
Answer 1:

Scientists don’t usually do experiments to prove that things happen. They usually do experiments to try to support their explanations of why they happen. These may sound like the same thing at first, so let’s think about that some more.

Let’s say you notice that gum loses its flavor after you chew it for a while. You may want to do some research about how long it takes, and whether it takes the same amount of time for all people, or all flavors, or all brands. You’re not really trying to prove that it does lose its flavor, you’re just trying to get more information about flavor loss in gum.

Now for the more interesting question, why does gum lose its flavor when we chew it? We may have a few different guesses or hypotheses. Maybe being crushed by teeth breaks down the flavor. Maybe the water in our saliva (spit) breaks down the flavor. Maybe the water in our saliva washes away the flavor and we swallow it. Maybe enzymes (digestive chemicals) in our saliva break down the flavor.

We can test these hypotheses with experiments. For example, if being crushed by teeth breaks down flavor, I can just crush gum and test whether its flavor is gone. I can use my earlier tests to see how long I should crush it. If gum lost its flavor after 5 minutes of chewing, five minutes of crushing with a hammer should do the same thing. At least, it should if my crushing idea is right. If the gum still has flavor after five minutes of crushing, I know that crushing is not the answer. It may still be part of an answer, but I would need to do more testing to find out. I never really prove I was right, I can just say that my hypothesis is a good explanation for all the facts I know so far.

Let’s get back to your question. You already know that food looks a lot different coming out of our bodies than it does going in. So you know that digestion occurs. Testing how is not easy. Only people with a lot of training can do experiments on actual people because experiments can be dangerous. They have to go through a strict process to show that their experiments are safe and important.

You can experiment on the first step of digestion by having it happen outside your body. Starch is the stuff in flour, potatoes, and foods like that. Starch is actually long chains of sugars. Enzymes are chemicals that speed up reactions. One of the enzymes (amylase) speeds up the breakdown of starch into sugar. This starts to happen right in your mouth. You can test how this happens by using your own spit. Remember, all of the testing happens OUTSIDE your body. You are NOT putting anything IN your mouth.

Go to this site:
click here and print off the first 2 pages. You will need the help of your biology or chemistry teacher to get a solution to test for starch and to make sure that you do things safely. Think about different questions you could ask. Will water by itself break the starch down into sugar? Is the smashing part of chewing enough to break down the starch into sugar? Does smashing help? What else could you ask? When you design an experiment, make sure that it’s a fair one. For example, you wouldn’t test water that was cold against spit that was warm because then two things are different between your samples (temperature and enzymes). You only want one thing to be different.


Write back if you have any questions.
Thanks for asking,

Answer 2:

You do an experiment every day, showing that digestion occurs. You eat food that looks one way, and you poop out the leftovers, and they look different! I suppose you could do some more experiments, to make sure that the chewed food doesn't look like the pooped out food. You could chew bites of food at each meal and spit them out, to see whether they look the same as the poop.

Keep asking questions!


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