Digestion

During digestion, foods are broken down into their constituent molecules: carbohydrates, fats (lipids), and proteins. However, different foods are made up of different molecules. For example, meat contains considerable protein but few carbohydrates. In this lab, you will perform a series of tests that allow you to identify what kinds of nutrients are contained in various types of foods.

Carbohydrates typically occur as monosaccharides (e.g., glucose), dissacharides (such as sucrose) or polysaccharides (e.g., starch). In Part 1, you will test for the presence of monosaccharides (or, more accurately, a reducing sugar) in a variety of substances using Benedict's test. Starch is a large polysaccharide. Even though it is a carbohydrate, because of its large size, it does not react with Benedict's solution. In Part 2, to test for the presence of starch, you will use Lugol's test. In Part 3, the presence of lipids will be determined using the Sudan IV test and in Part 4, the presence of proteins will be determined using the Biuret test. Finally, in Part 5, you will determine the complete nutrient composition of an "unknown" substance by testing it for the presence of monosaccharides, starch, fats, and proteins. Full descriptions of the protocols involved in each part of this lab are available from the links below.

Part 1: Testing for Sugar

Part 2: Testing for Starch

Part 3: Testing for Fat

Part 4: Testing for Protein

Part 5: Testing the Nutrient Composition of an Unknown Substance

Digestion Lab Worksheet