Energy Sources

ninja icon


•  Determination of the energy content of food by combustion

Determining Energy Content

The energy content of food can be estimated by burning a sample of known mass and measuring the energy released via calorimetry

  • Combustion of the food source causes the stored energy to be released as heat, which raises the temperature of water
  • The amount of energy required to raise 1 g of water by 1ºC is 4.18 J – this is the specific heat capacity of water

The equation for calculating the energy content of a food source via calorimetry is as follows:

  • Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature increase (ºC)

The biggest source of error in calorimetry is usually caused by the unwanted loss of heat to the surrounding environment

  • The food sources should be burnt at a constant distance from the water to ensure reliability of results
  • The initial temperature and volume of water should also be kept constant (1 g of water = 1 cm3 or 1 ml)

Measuring Energy Content of Food via Calorimetry

My Image 1 My Image 2

Comparing Energy Content

The three types of nutrients that are commonly used as energy sources are carbohydrates, lipids (fats) and proteins

  • Carbohydrates are preferentially used as an energy source because they are easier to digest and transport
  • Lipids can store more energy per gram but are harder to digest and transport (hence are used for long-term storage)
  • Protein metabolism produces nitrogenous waste products which must be removed from cells

The relative energy content of carbohydrates, proteins and fats are as follows:

  • Carbohydrates – 1,760 kJ per 100 grams
  • Proteins – 1,720 kJ per 100 grams
  • Fats – 4,000 kJ per 100 grams

Role of Organic Molecules in Energy Production

energy sources