Table 1. Benedict's Test Results Test tube Color positive or negative? 1 2 3 4 5 6 e. Please answer the following questions: What was the purpose of test tube #1? Did you expect starch to give you a positive or negative result? Why? How are glucose and sucrose different from one another? 2. The Iodine Test for Starches The iodine test is a carbohydrate test that identifies the presence of starch. Starch molecules are actually polymers of glucose commonly found in plants. In the presence of starch, iodine solution (IKI) changes from yellow to blue-black. If the solution stays yellow, the test is negative for starch. a. Obtain a reaction well from the trolley. b. Add 2 drops of each of the following solutions to the reaction plate: water, glucose, sucrose, and starch. (Make sure you know which well contains which solution). c. In two other wells, cut a small thin slice of onion and potato and place into the wells. d. Add one drop of I2KI solution to each of the wells and record your result in the table below. Table 2. Iodine Test Results Spot Color positive or negative? water glucose sucrose starch onion slice potato slice e. Please answer the following questions about your results: 1. Did you expect water to turn blue-black in the presence of IKI? Why did we test it? 2. What general statement can you make about the differences between carbohydrate storage in onions compared to potatoes? 3. Why didn’t glucose give a positive result? B) Proteins Proteins are made up of chains of amino acids. Each protein folds into a characteristic three dimensional shape that is essential to its function. They perform a variety of functions in cells and are probably the most diverse macromolecule in living systems. The Biuret test detects the presence of proteins and short peptides (short chains of amino acids). Biuret reagent contains a strong solution of sodium hydroxide (NaOH) and a very small amount of dilute copper sulfate solution. The reagent changes color in the presence of a protein because
Table 1. Benedict's Test Results Test tube Color positive or negative? 1 2 3 4 5 6 e. Please answer the following questions: What was the purpose of test tube #1? Did you expect starch to give you a positive or negative result? Why? How are glucose and sucrose different from one another? 2. The Iodine Test for Starches The iodine test is a carbohydrate test that identifies the presence of starch. Starch molecules are actually polymers of glucose commonly found in plants. In the presence of starch, iodine solution (IKI) changes from yellow to blue-black. If the solution stays yellow, the test is negative for starch. a. Obtain a reaction well from the trolley. b. Add 2 drops of each of the following solutions to the reaction plate: water, glucose, sucrose, and starch. (Make sure you know which well contains which solution). c. In two other wells, cut a small thin slice of onion and potato and place into the wells. d. Add one drop of I2KI solution to each of the wells and record your result in the table below. Table 2. Iodine Test Results Spot Color positive or negative? water glucose sucrose starch onion slice potato slice e. Please answer the following questions about your results: 1. Did you expect water to turn blue-black in the presence of IKI? Why did we test it? 2. What general statement can you make about the differences between carbohydrate storage in onions compared to potatoes? 3. Why didn’t glucose give a positive result? B) Proteins Proteins are made up of chains of amino acids. Each protein folds into a characteristic three dimensional shape that is essential to its function. They perform a variety of functions in cells and are probably the most diverse macromolecule in living systems. The Biuret test detects the presence of proteins and short peptides (short chains of amino acids). Biuret reagent contains a strong solution of sodium hydroxide (NaOH) and a very small amount of dilute copper sulfate solution. The reagent changes color in the presence of a protein because
3.1_chemical_composition_of_cell.docx