Why the body needs energy

Overview

Basal and other energy needs, kilocalories and kilojoules, energy values of the macronutrients and alcohol, bomb calorimetry and worked energy calculations.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Why does the body need a constant supply of energy even at complete rest?

   Model answer

   Energy is needed at rest to keep the heart beating, the lungs breathing and the nerves working. Energy also maintains body temperature and powers chemical reactions in every cell.

2. 2

   Name four uses of energy in the body beyond basal needs.

   Model answer

   Energy beyond basal needs fuels physical activity, growth, the digestion and processing of food, and milk production during lactation.

3. 3

   Why do children and teenagers need energy for growth?

   Model answer

   Growth requires energy to build new tissue such as bone, muscle and organs. Growing children also have a high BMR for their body size.

4. 4

   How is energy from food made available to the body's cells?

   Model answer

   Glucose, fatty acids and amino acids are oxidised in cell respiration. The energy released is captured as ATP, which cells use to power their work.

5. 5

   What units are used to measure the energy in food?

   Model answer

   Food energy is measured in kilocalories (kcal) or kilojoules (kJ). One kilocalorie equals 4.184 kilojoules.

6. 6

   State the energy provided by one gram each of protein, fat, carbohydrate and alcohol.

   Model answer

   Protein and carbohydrate each provide 4 kcal per gram. Fat provides 9 kcal per gram and alcohol provides 7 kcal per gram.

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The same content, four other ways.

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