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5.2: Formative/Summative Questions

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    Formative Questions

    1. What causes Benedict's reagent to turn from blue to orange after boiling?

    Answer: Terminal aldehyde or internal ketone (double-bonded oxygen) portion of a monosaccharide react with the Cu2+ portion of Benedicts solution to produce Cu+. Heat is required to break the bond within the monosaccharide.

    1. What are the contents of Lugol's reagent?

    Answer: Key ingredients of Lugol's solution is potassium iodide.

    1. Create a hypothesis for an experiment testing for the presence of starch. What are the dependent and independent variables?

    Answer: Hypotheses can vary. Something like, "If starch is present, then the iodine in the Lugol's reagent will react, and show a blue/black color."
                 Independent variable: type of carbohydrate.
                Dependent variable: color change of Lugol's reagent (blue-black indicates polysaccharide.)

    1. Why might potatoes test positive for reducing sugars?

    Answer: potato contains both starch and a reducing sugar (glucose.)

    Summative Questions

    1. Name the reagent used to detect each of the following: 1. reducing sugars, 2. starch, 3. lipids, 4. proteins, and 5. amino acids.

    Answer:
    1 Benedict's reagent.
    2 Lugol's reagent.
    3 Sudan IV reagent.
    4 Biuret's reagent.
    5 Ninhydrin reagent.

    1. For the reagents above, describe their appearance if the test is negative, and if the test is positive.

    Answer:
    1 Blue (- for reducing sugars,) orange/red (+ for reducing sugars).
    2 Yellow/tan (- for starch,) Brown (some starch,) Black (+ for starch.)
    3 Red globs/lipid layer (+ for lipids,) uniform red (- for lipids.)
    4 Dark purple (+ for many peptide bonds,) light purple (+ for some peptide bonds,) blue (- for peptide bonds.)
    5 Purple violet (+ for amino acid,) yellow (+ for proline,) clear (- for amino acid.)

    1. Name 2-3 common household foods/items that contain each of the following: carbohydrates, lipids, proteins, amino acids.

    Answer: This is a long list. Feel free to come up with any you prefer.

    This page titled 5.2: Formative/Summative Questions was last modified on Tue, 27 Aug 2024 07:44:37 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Darcy Ernst, May Chen, Katie Foltz, and Bridget Greuel (Open Educational Resource Initiative at Evergreen Valley College) .