OverviewSucrose is a two-molecule chain of simple sugars. A starch molecule is made of long chains of simple sugar molecules. Plants make starch molecules as a way of storing sugar because it can be easily converted back to sugar when needed. If you have any doubt that starch is made of sugar, an experiment using a chemical made by your own body can give you the answer. Do the following experiment and see for yourself.
Materials & Equipment- Plain unsalted crackers (those typically used for soup)
Procedure1. Provide each student with two crackers.
2. Have students eat the first cracker.
3. Once they have eaten the first cracker, have them slowly chew the second cracker and hold it in their mouths, without swallowing, for 3 to 5 minutes.
ExplanationDigestion of starch normally begins in the mouth of humans where an enzyme, salivary amylase, is secreted. This enzyme catalyzes the breakdown of the starch. Starch is a polymer, made from thousands of glucose molecules joined chemically into one giant chain-like molecule. Starch, a complex carbohydrate polymer, can be found in grains like wheat, corn and oats. When starch is broken down into glucose monomers – a sweet-tasting carbohydrate molecule – we notice a change in taste. Starches are typically flavourless due to their large size – their large size prevents them from stimulating our taste buds. Although the reaction catalyze by amylase begins to work almost instantly, it usually takes time for the effect to take place because our taste buds have a particular threshold for detection of taste that differs among chemicals. In fact, no taste is elicited by a single molecule of anything.
Why is this a worthwhile Lesson Hook Activity?This hook provides an effective way of initiating a discussion on the properties of starches and simple sugars. Many students have the misconception that all carbohydrates are sugars or that all carbohydrates are sweet tasting. This lesson hook is an excellent way to demonstrate this fact, especially if you are starting a unit or lesson on biochemistry. Moreover, this hook can also open discussion on enzymes. Many students have the common misconception that proteins are only found in muscles; they have a hard time understanding the roles of the various types of proteins in living systems. This hook demonstrates how important enzymes are in the body;
what would happen to the digestion process if we did not produce amylase? Why are enzymes important in the body? Where else might you find proteins in the digestion system? Are carbohydrates the only substrate that fit into enzymes? Questions like these will build on pre-existing ideas from former units they have learned.
Course: SBI3U
Unit: Biochemistry
Expectations: B3.2 -Describe the structure of important biochemical compounds, including carbohydrates, proteins, lipids, and nucleic acids, and explain their function within cells.
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