1. Nutrient Testing
Year 10 Biology

2. Which chemical elements do food molecules contain?
Food molecules, like everything else, are made up of chemical elements.
Carbohydrates and fats are made of three types of element only: carbon, hydrogen and oxygen.
Protein molecules are made of the same three elements, but they also contain nitrogen.
Some proteins have other elements too, like sulphur.
We carry out chemical tests to help us identify nutrients.

3. What are carbohydrates?
Starchy foods contain carbohydrates which are made of long chains of identical small sugar molecules.
carbohydratemolecule
one sugar molecule
The long chains of carbohydrates are broken down into the smaller sugar molecules by the body.
The small molecules from carbohydrates are used by the body to release energy and make the body work.

4. What are proteins?
Proteins, like carbohydrates, are made of long chains of small molecules. In proteins, these small molecules are
not identical.
protein
molecule
one
amino acid
Proteins are made up of chains of small molecules called amino acids. There are over 20 different kinds of amino acid.
Proteins are used by the body for growth and repair.

5. What are fats?
Fats are made up of fat molecules which contain fatty acids and glycerol.
fat
molecule
fatty acids
glycerol
Fat molecules have to be broken down by the body so that they can be used for energy storage.
Fats are also used by the body to keep heat in and to make cell membranes.

6. Test for carbohydrates starch.
Orangey-brown iodine turns blue-black when it reacts with starch.
black = starch
drop iodine solution onto the food

7. Test for carbohydrates glucose (reducing sugar).
Blue Benedict’s solution turns orangey-red when it is boiled with glucose.
blue turns orange/red = glucose
chopped up food
hot water
heat

8. Test for Carbohydrate (glucose)
Glucose is a small, soluble molecule. It is a carbohydrate
It is type of reducing sugar.
To test food for reducing sugar we chop a sample and dissolve in H2O, to a height of about 2 cm in a test tube
Add an equal volume of Benedict’s solution (a blue coloured liquid)
Place the test tube in a hot water bath (60ºC) for 5 minutes.
A predictable sequence of colour changes will take place if reducing sugar is present.

9. Reducing Sugar Test: Colour Changes
The more reducing sugar (glucose) present, the greater the colour change. Lots of reducing sugar in food gives orange/red colour.

10. In the Biuret test the solution turns purple.
8A What’s in food?
Test for Protien
In the Biuret test the solution turns purple.
purple = protein
potassium hydroxide
copper sulphate
shake
chopped up food

11. The Biuret Test (for Protein)
Proteins are large molecules
To test for presence of protein in a food sample we add a chemical called biuret solution.
Like the reducing sugar test, chop up the food and dissolve in water to a height of 2cm.
Now add an equal volume of buiret solution
If protein is present (a positive result) the solution turn purple/violet in colour.

12. The Emulsion test (for fats)
Fats (lipids) are large molecules.
The presence of lipids can be detected by the emulsion test.
First collect a sample of the food and add a few drops of ethanol.
Cover the test tube with your thumb, shake for a few seconds.
Now add a few drops of water.
Cover, shake for a few seconds.
If lipids are present (positive result) the solution will turn white/cloudy.

13. Fats go cloudy white when they are mixed with ethanol and water.
8A What’s in food?
Fats go cloudy white when they are mixed with ethanol and water.
add water
filter
grind food with ethanol
cloudy = fat
Now see if you can use these tests to identify the food chemicals on the next slides.

14. http://www. slideshare