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Experimental Techniques

Biological tests, colorimetry, chromatography and osmosis

  • 3 things to know
  • AS 1

Overview

Tests for starch, reducing sugars, protein and lipids, colorimeters, blanks and calibration curves, amino acid chromatography with ninhydrin and Rf values, and osmosis in potato cylinders.

What you need to know

Answer each one before you reveal it.

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Key term

What is a calibration curve, and how is one produced for glucose using a colorimeter?

Key term

How is starch identified in a food sample?

Key term

How are reducing sugars identified?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How is starch identified in a food sample?

    Model answer

    Iodine solution is added to the sample. A colour change from orange-brown to blue-black shows starch is present.

  2. 2

    How are reducing sugars identified?

    Model answer

    Benedict's reagent is added and the mixture heated in a water bath. A colour change from blue through green and yellow to brick-red shows reducing sugar.

  3. 3

    How is protein identified?

    Model answer

    Biuret reagent is added to the sample. A colour change from blue to lilac or purple shows protein is present.

  4. 4

    How are lipids identified?

    Model answer

    The sample is shaken with ethanol and then poured into water. A cloudy white emulsion shows lipids are present.

  5. 5

    What is a colorimeter?

    Model answer

    A colorimeter measures how much light of a chosen colour passes through a coloured solution. The reading is given as absorbance or transmission.

  6. 6

    What is a calibration curve?

    Model answer

    A calibration curve plots colorimeter readings for solutions of known concentration. The concentration of an unknown sample is read from the curve.

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