IGCSE Biology – 2c: Biological Molecules
Biological Molecules
Elements
o Carbohydrates, lipids and proteins are all made of carbon, oxygen and hydrogen.
o Proteins also contain nitrogen.
Carbohydrates
o Complex (large) carbohydrates such as starch and glycogen store energy.
o Simple carbohydrates are made of chains of smaller subunits for rapid energy
release.
o The subunit of starch is glucose.
Proteins
o Proteins are made from chains of amino acids.
o This is very important as enzymes are protein and proteins also have structural roles
in cells.
Lipids
o Lipids are made from fatty acids and glycerol.
o Fat is solid at room temperature.
o Oil is liquid at room temperature.
Food Tests
Starch
o Sample the food into the well of a spotting tile.
o Add iodine indicator solution.
o If the solution turns blue or black, then it contains starch.
o A negative result will stay orange.
Glucose
o Add food into a boiling tube.
o Add excess Benedict’s solution.
o Heat the boiling tube in a water bath.
o The solution will go from blue to green to orange and finally to brick red depending
on the concentration of glucose.
Protein
o Add Biuret’s Reagent to a sample of food.
o If protein is present, the solution will turn purple.
o A negative result will stay blue.
Biological Molecules
Elements
o Carbohydrates, lipids and proteins are all made of carbon, oxygen and hydrogen.
o Proteins also contain nitrogen.
Carbohydrates
o Complex (large) carbohydrates such as starch and glycogen store energy.
o Simple carbohydrates are made of chains of smaller subunits for rapid energy
release.
o The subunit of starch is glucose.
Proteins
o Proteins are made from chains of amino acids.
o This is very important as enzymes are protein and proteins also have structural roles
in cells.
Lipids
o Lipids are made from fatty acids and glycerol.
o Fat is solid at room temperature.
o Oil is liquid at room temperature.
Food Tests
Starch
o Sample the food into the well of a spotting tile.
o Add iodine indicator solution.
o If the solution turns blue or black, then it contains starch.
o A negative result will stay orange.
Glucose
o Add food into a boiling tube.
o Add excess Benedict’s solution.
o Heat the boiling tube in a water bath.
o The solution will go from blue to green to orange and finally to brick red depending
on the concentration of glucose.
Protein
o Add Biuret’s Reagent to a sample of food.
o If protein is present, the solution will turn purple.
o A negative result will stay blue.
