1.3 Nutrition and Food Tests

Results for Benedict's reagent

turns from blue to brick-red when heated in presence of sugar

Biuret reagent

Turns from blue to lilac/purple in the presence of proteins

Iodine test

Turns from yellow-brown or orange to blue-black in the presence of starch

Ethanol and water

when shaken will turn from colourless to a milky-white emulsion in the presence of lipids

Balancing energy

energy content of food eaten must be equal to energy needs as excess energy will be stored as fat

Calorimeter

An instrument used to measure changes in thermal energy

Dependent variable

The variable that is measured

Independent variable

The variable that is changed

Control variables

Variables that are kept the same in an experiment

Burning food process

1. Add water - around 20cm³ - to a boiling tube clamped in stand.

2. Record the starting temperature of the water.

3. Place food sample on mounted needle.

4. Ignite the food sample using a Bunsen burner.

5. Hold the burning food sample under the boiling tube of water until completely burned

6. Record the final temperature of the water

7. Calculate the change in temperature

8. Calculate the energy released by this food type using equation

Energy released from food equation

Energy released (J) = mass of water (g) x rise in temperature (°C) x 4.2

One gram

The mass of one cm³ of water

Specific heat capacity

energy to raise mass of substance by 1 degree

e.g water = 4.2 Joules per gram per degree Celsius

Digestion

uses energy from respiration to break down large insoluble molecules into smaller soluble molecules

Carbohydrates

Provide energy for chemical reactions and can break down into sugars

made up of carbon, hydrogen and oxygen

Simple carbohydrate examples (energy)

Sugars, glucose and lactose

Complex carbohydrate examples (storage)

Cellulose, starch and glycogen

Proteins

building blocks of cells and tissues that can break down into amino acids

made up of carbon, hydrogen, oxygen and nitrogen

Lipids

fats and oils that can break down into glycerol and fatty acids