21. Which of the food samples contained starch? ...... 2.2. Which of the food samples can be used as a source of protein? 2.3. Explain how you will test for the presence of lipids in each of the food sain

Below is one way to answer these parts by describing what to look for and the procedures used in testing. ––––––––––––––––––––––––––––––––––––––––––––––––– 1. Testing for Starch Typically, starch is detected by adding iodine solution. Iodine reacts with starch to form a blue-black complex, so if a food sample turns deep blue or purple when iodine is applied, you can conclude that starch is present. In many classroom experiments, common starchy foods (such as potatoes, bread, rice, or pasta) give a positive reaction. (For example, if you add iodine to a slice of potato and you see the blue-black color, then that food sample contains starch.) ––––––––––––––––––––––––––––––––––––––––––––––––– 2. Testing for Protein A common test for proteins is the Biuret test. In this test, when you add a few drops of Biuret reagent (which contains copper sulfate in an alkaline solution) to a food sample (or its extract), the presence of peptide bonds causes the solution to turn a violet or purple color. Food samples such as meat, eggs, beans, or dairy products that have enough protein will show this color change. Thus, any food sample that turns purple upon adding Biuret reagent can be considered a good source of protein. ––––––––––––––––––––––––––––––––––––––––––––––––– 3. Testing for Lipids Lipids (fats and oils) can be tested using a lipid stain such as Sudan III and/or using the grease spot test: • Sudan III Test:   – Place a small amount of your food sample in a test tube or on a watch glass.   – Add a few drops of Sudan III solution, which is a fat-soluble dye.   – If lipids are present, they will dissolve in the solution and appear as red, orange, or pink globules.   – The more intense the red coloration, the higher the lipid content. • Grease Spot Test (Alternative Method):   – Take a small amount of the food sample and rub it onto a piece of unglazed filter paper or a brown paper bag.   – Let it stand for a few minutes. If a translucent oily spot remains on the paper (that does not evaporate as water normally would), it indicates the presence of lipids. By carrying out one (or both) of these tests, you can determine whether each food sample contains lipids. ––––––––––––––––––––––––––––––––––––––––––––––––– In summary: • For starch: Use iodine solution and look for the blue-black complex; the sample(s) that show this color change contain starch. • For protein: Use the Biuret test; samples that turn purple are protein sources. • For lipids: Use the Sudan III test (or grease spot test) to look for red-stained droplets or oily spots, respectively, indicating the presence of lipids. Using these qualitative tests, you can classify the food samples based on their starch, protein, and lipid content.