Pearson Edexcel GCSE Biology Core Practical - testing for starch, reducing sugars, protein and fats

Summary

In this Core Practical video, Mr. Osman, a science teacher at Claremont High School, guides students through an experiment to identify starch, reducing sugars, proteins, and lipids in various food samples using common chemical reagents. The process includes iodine for starch, Biuret for proteins, ethanol for lipids, and Benedict's solution for reducing sugars. Detailed instructions are provided for each test, emphasizing proper technique, equipment use, and safety precautions. This experiment helps students build practical skills in chemical testing while enhancing their understanding of basic biological components in food.

Takeaways

• 😀 Always wear eye protection when conducting chemical experiments.
• 😀 Use a 10ml measuring cylinder, spatula, and other essential lab equipment for the experiment.
• 😀 Clean the spatula and stirrer with a paper towel between tests to avoid cross-contamination.
• 😀 To test for starch, apply iodine solution to a powdered food sample and observe any color changes.
• 😀 To test for proteins, add biuret solution (or potassium hydroxide and copper sulfate) to a food sample in a test tube and observe any color change.
• 😀 For lipids, mix ethanol with the powdered food and shake it vigorously, then pour it into a water-filled boiling tube to observe if the water turns cloudy.
• 😀 To test for reducing sugars, mix Benedict solution with a food sample in a boiling tube and heat it in a water bath at 70°C, then observe the color change.
• 😀 The experiment involves using iodine solution, Benedict solution, biuret solution, ethanol, and a water bath to identify starch, reducing sugars, proteins, and lipids in food samples.
• 😀 Record the results in a table, noting the food tested and the color or appearance after each test.
• 😀 You may be provided with unknown substances to test, helping you build confidence in the techniques used in the practical.

Q & A

What is the purpose of this Core Practical video?

The purpose of the video is to demonstrate how to investigate the use of chemical reagents in identifying the presence of starch, reducing sugars, proteins, and lipids in food samples.

What equipment is needed for this experiment?

The experiment requires eye protection, water, a 10ml measuring cylinder, spatula, powdered food or suitable food samples, paper towels, test tubes, boiling tubes, racks and bungs, a stirrer, iodine solution, dropper bottle, Benedict solution, biuret solution, ethanol, a dimple spotting tile, and a water bath set to 70°C.

Why is it important to wipe the spatula and stirrer in between tests?

It is important to wipe the spatula and stirrer between tests to prevent cross-contamination between different food samples and reagents, which could lead to inaccurate results.

How can you test for the presence of starch in a food sample?

To test for starch, place a small amount of powdered food on a dish or spotting tile and add a few drops of iodine solution. A color change, typically to blue-black, indicates the presence of starch.

What should you do to test for proteins in a food sample?

To test for proteins, place a spatula of powdered food into a test tube, add water, stir to mix, then add biuret solution. If using potassium hydroxide and copper sulfate solutions instead of biuret, add potassium hydroxide first, then copper sulfate. A color change to purple indicates the presence of protein.

How do you test for the presence of lipids in a food sample?

To test for lipids, place a spatula of powdered food into a test tube, add ethanol, and shake the tube vigorously. After the contents settle, pour the liquid into a boiling tube half-filled with water. If lipids are present, the water will become cloudy.

What is the procedure for testing reducing sugars using Benedict’s solution?

To test for reducing sugars, place powdered food into a boiling tube, add water, and then add Benedict’s solution. Mix well and heat the tube in a water bath at 70°C for a few minutes. A color change to green, yellow, or red indicates the presence of reducing sugars.

What is the role of the water bath set to 70°C in this experiment?

The water bath set to 70°C is used to heat the Benedict’s solution in the test for reducing sugars. The heat causes the solution to change color, indicating the presence of reducing sugars.

What color change indicates the presence of protein when using biuret solution?

A color change to purple indicates the presence of protein when using biuret solution or a combination of potassium hydroxide and copper sulfate.

How can you identify the type of food tested based on the results of these chemical tests?

By observing the color changes in the test solutions, you can identify the presence of starch (blue-black with iodine), protein (purple with biuret), lipids (cloudy water with ethanol), and reducing sugars (green, yellow, or red with Benedict’s solution). These results can help you match the food to the correct category from a list of known substances.