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Type
science_lab
Pre Lab
Background: Have you ever wondered how scientists figure out what nutrients are inside a food without tasting it? Scientists use special chemical indicators that change color in the presence of specific molecules. One important group of molecules found in food is **protein**. Proteins are large, complex molecules made of smaller building blocks called amino acids. Your body uses proteins to build and repair muscles, make enzymes, and carry out thousands of other important jobs. Foods like meat, eggs, milk, and beans are all rich sources of protein.
To test for the presence of protein in a substance, scientists use a chemical reagent called **Biuret solution**. Biuret solution is normally blue in color because it contains copper sulfate dissolved in sodium hydroxide. When Biuret solution comes into contact with protein molecules, the copper ions in the solution bind to the peptide bonds that link amino acids together. This chemical interaction causes the solution to change from blue to a purple or violet color. The more protein present, the deeper and more intense the purple color will be. Scientists describe this change using the term **color intensity**, which refers to how dark or vivid the resulting color appears.
In any well-designed experiment, scientists include special samples called controls. A **positive control** is a sample that is known to contain the substance being tested — in this case, protein. It confirms that the Biuret solution is working correctly and shows what a true positive result looks like. A **negative control** is a sample that is known to NOT contain the substance being tested. It confirms that any color change seen in other samples is due to protein, not a contamination or error. By comparing your unknown samples to both controls, you can use your data as evidence to make a scientific **claim** about which substances contain protein. In this lab, you will act as protein detectives, testing mystery food substances and using Claim-Evidence-Reasoning (CER) to explain your findings.
Vocabulary
Term: Protein
Definition: A large molecule made of chains of amino acids that performs many important functions in living organisms, including building tissues and acting as enzymes.
Term: Biuret solution
Lab Type
Post Lab
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