1.13B **Higher and Biology Only** - Core Practical: Investigating Macronutrients Flashcards
(13 cards)
What is the aim of the core practical?
To identify the presence of starch, reducing sugars, protein, and lipids in food samples using chemical reagents.
What macronutrients are tested in the practical?
Starch, reducing sugars, protein, and lipids.
What test is used for Starch?
Iodine Solution
Add iodine solution to the food sample. Positive result is a colour change from orange → blue-black.
What test is used for Reducing Sugars?
Benedict’s Solution
1. Add 2 cm³ of food sample and 2 cm³ of Benedict’s solution. 2. Heat in boiling water bath for 5 mins. Positive result is a colour change from blue → green, yellow, orange or brick-red depending on amount of sugar.
What test is used for Protein?
Biuret Solution
Add Biuret solution to the food sample and mix gently. Positive result is a colour change from blue → lilac/purple.
What test is used for Lipids (Fats)?
Sudan III or Ethanol Test
1. Mix food sample with ethanol, shake. 2. Pour into water. Positive result is a cloudy white emulsion appears (fat present).
What should be controlled in practical work?
Use the same volume of food sample and reagents each time.
What safety precautions should be taken during experiments?
Wear goggles; Benedict’s and Biuret are corrosive; ethanol is flammable.
How should Benedict’s test be heated?
Use a water bath to avoid direct flame.
What type of results do the tests provide?
Qualitative results only – tests do not measure amount, just presence/absence.
What should we use in each experiment to improve results?
We should use a control in each experiment to ensure we know what a positive and negative result looks like.
What is a positive control for the Biuret test?
A positive control for the Biuret test would be anything containing protein (e.g egg white).
What is a negative control for the Biuret test?
A negative control would be a solution that does not contain protein (e.g distilled water).
