About this Video

• Video Title: GCSE Biology Revision "Required Practical 4: Food Tests"
• Channel: Freesciencelessons
• Speakers: The transcript does not name the speaker.
• Duration: 00:03:42

Introduction

This video provides a comprehensive guide to performing GCSE Biology's required practical 4: food tests. It details the procedures and expected results for identifying carbohydrates (starch and sugars), proteins, and lipids in food samples. Emphasis is placed on the chemicals used and the safety precautions necessary.

Key Takeaways

• Food Sample Preparation: Food samples are ground with distilled water, then filtered to remove solid particles before testing.
• Carbohydrate Tests: Iodine solution tests for starch (blue-black positive result); Benedict's solution tests for reducing sugars (color change from blue to green, yellow, or brick red indicating increasing sugar concentration).
• Protein Test: Biuret solution tests for proteins (color change from blue to purple/lilac).
• Lipid Test: Ethanol and distilled water are used to test for lipids (a white, cloudy emulsion indicates a positive result). Crucially, the solution is not filtered for this test.
• Safety: Safety goggles are mandatory due to the hazardous nature of the chemicals used. Ethanol's flammability necessitates the absence of open flames.

To test for starch, 2 cm³ of the food solution is placed in a test tube. A few drops of iodine solution (orange) are added. A blue-black color indicates the presence of starch; if no starch is present, the solution remains orange.

To test for glucose (a sugar), 2 cm³ of food solution is mixed with 10 drops of Benedict's solution (blue) in a test tube. The test tube is placed in a beaker of hot water for about 5 minutes. A color change in the Benedict's solution indicates the presence of reducing sugars: green indicates a small amount, yellow more, and brick red a large amount. The test does not work for all sugars (only reducing sugars).