Different tests can be performed to find out if a food contains a biomolecule. For example, iodine – an orange- brown chemical – is used to test for the carbohydrate starch:
z If a drop of iodine is placed on a potato, the iodine will turn blue- black. This colour change is a positive result for starch in potatoes.
z If a drop of iodine is placed in milk, the iodine will not change colour. This is a negative result for starch in milk.
Fig. 2.1.2 Testing a potato for starch
The following table outlines the food tests that can be used to test for each biomolecule.
Name Proteins Fats Food test Carbohydrates Starch: iodine Glucose: Benedict’s reagent
Biuret reagent (sodium hydroxide and copper sulfate)
Brown paper Other Nutrients
In addition to biomolecules, organisms also need minerals and water in their diet.
The following table outlines the roles and sources of these other important nutrients. Name
Role Minerals
ƒ To build biomolecules and to assist chemical reactions within cells. For example, animals need iron to produce red blood cells and plants need magnesium to produce chlorophyll
Water
ƒ Acts as a solvent ƒ Helps transport materials in blood ƒ Removes waste ƒ Regulates temperature
Source
Lean meat, fresh fruit and vegetables, dairy products
Positive colour change
Orange-brown → blue-black Blue → brick red (needs heat)
