Different Forms of Carbohydrates and Differences Between Simple and Complex Sugars (page 2)

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Author: Janice VanCleave

Try New Approaches

  1. Test other food products by repeating the experiment. Science Fair Hint: Prepare a bar graph to compare the monosaccharide content of each food sample tested.
  2. Fruits and vegetables change chemically as they continue to ripen. Taken straight from the garden, they may test negative for the presence of simple sugars. Once they are picked, their carbohydrates (in the form of starches and disaccharides) begin to break down into simple sugars. Demonstrate this change by repeating the experiment using fresh fruits and/or vegetables. A cluster of grapes provides a sample that can be tested daily to observe any changes in the monosaccharide level of the ripening fruit.
  3. Milk contains lactose, which is a polysaccharide (large molecules containing many simple sugars bonded together). Does heat break this polysaccharide into monosaccharides? Repeat the original experiment using milk as the food source. Observe the color after three minutes of heating; then continue to heat the milk for five additional minutes and observe again.

Design Your Own Experiment

  1. Starch and cellulose are polysaccharides. Use drops of tincture of iodine to distinguish between starch and cellulose. CAUfION: Keep the iodine out of reach of small children. It is poisonous and is for external use only. Starch turns blue-violet to black when iodine touches it, but cellulose does not alter the reddish brown color of iodine. Demonstrate this by putting several drops of iodine on a slice of apple and on a slice of white potato (see Figure 10.2).
    1. During the human digestive process, macromolecules of starch are chemically changed into glucose. Much of this change occurs in your mouth. Demonstrate this by cutting two small, equal-size pieces from a slice of bread. Place one piece in your mouth and chew it 30 times. It will become very mushy. Make an effort to mix as much saliva as possible with the bread. Spit the mushy bread and saliva mixture onto a piece of wax paper. Place the dry piece of bread on a separate piece of wax paper. Test for the presence of starch by adding four drops of iodine to each sample.
    2. Test for the presence of monosaccharides in the bread before and after it is chewed. Repeat the experiment two times, first using a dry piece of bread, and then chewing the bread 30 times and testing the mushy bread and saliva mixture.

Carbohydrates: Mono-, Di-, and Polysaccharides

Get the Facts

  1. Sucrose is a double sugar called a disaccharide. It is represented by the formula C12H22O11. Glucose is known as blood sugar because it is the sugar transported by the blood to cells where it is used as a fuel to make energy. Fructose is found in fruits and honey and is much sweeter than sucrose or glucose. Glucose and fructose are simple sugars, and both are represented by the formula C6H12O6, but the arrangement of the atoms within these sugars is different Find out more about the physical structure of these sugars and how it affects their chemical behavior. Which sugar is an aldo-hexose? Which is a keto-hexose? What products are produced by the hydrolysis of sucrose, maltose, and lactose (examples of complex sugars)?
  2. Starch serves as a nutrient and is found in plant products such as grains, fruits, and vegetables. Cellulose, like starch, is a carbohydrate. Although it is not easily digested by humans, it is important as the dietary fiber commonly called roughage. Use a chemistry text to find out more about the physical properties of these two chemicals. What is the difference between their molecular structures? How do the tastes of starch, cellulose, and sugars compare?
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