Biology - 3 Organisation and the Digestive System - Required Practical 4: Food Tests

Aims:

• to understand how to test for starch, proteins, sugars and lipids

Risk Assessment:

• chemicals used for food testing are potentially hazardous

• hot water can scald

Safety:

• wear safety goggles

• be cautious around hot water; carry carefully and keep away from edges of desks etc.

• keep chemicals away from mouth/face

Equipment:

• Pestle and mortar

• 2 spotting tiles

• 2 test tubes

• 4 beakers (or as many as foods as you are testing)

• stirring rods

• filter paper

• funnels

• pipettes

• iodine solution

• Biuret reagent

• ethanol

• distilled water

• Benedict’s reagent

• hot water (80 degrees)

Control variables:

n/a

Independent variable:

n/a

Dependent variable:

n/a

Method:

1. Grind food sample using pestle and mortar

2. Transfer to a beaker and add distilled water

3. Use stirring rod to break up food and release chemicals

4. Filter into a new beaker using a funnel and filter paper

Starch:

5. Transfer a small amount of food solution to the spotting tile using a pipette

6. Using another pipette, add a drop of iodine solution

7. The mixture should go from orange to blue/black

Protein:

5. Using a pipette, transfer 2cm³/a small amount of food solution into/onto a test tube/spotting tile

6. Using another pipette, add a few drops of Biuret reagent

7. The mixture should go from pale blue to purple

Lipid:

5. Using a pipette, transfer 2cm³ of food solution into a test tube

6. Using another pipette, add a few drops of ethanol

7. Using a pipette, add water

8. Shake the tube

9. A milky emulsion should form

Sugar:

5. Using a pipette, transfer 2cm³ of food solution into a test tube

6. Fill a beaker with hot water

7. Using another pipette, add a few drops of Benedict’s reagent

8. Place the test tube to stand in the water and wait 5 minutes

9. The mixture should go from blue to orange (low sugar concentration) or brick red (high sugar concentration)