Food and energy
Food supplies the body with energy
The energy in food can be measured by calorimetric methods in kJ or Calories
Cell respiration is the process of getting energy from food and is analogous to burning.
Nutrients in food
The main nutrients in food are fat, protein, carbohydrate, water, vitamins and minerals.
Different foods contain these nutrients in different proportions.
Chemical tests can detect the presence of different nutrients in food, for example the chemical test for starch uses iodine solution which changes from pale brown to deep purple.
Food labelling gives some information about the nutrient of food but can be misleading.
A balanced diet involves an intake of nutrients in an appropriate amount and proportions.
Different diets achieve a balanced intake of nutrients in different ways
Digestion
Food must be digested for it to be carried in the blood and used around the body.
Digestion is a physical and a chemical process.
Physical digestion involves breaking food into smaller pieces
Enzymes are necessary for chemical digestion and these break large food molecules into smaller molecules.
The Human digestive system
The organs involved in the digestive system are the mouth, tongue, oesophagus, stomach, small intestine (duodenem, ileum), large intestine (colon, rectum), anus, pancreas, liver.
Food takes around 2 days to pass through the alimentary canal, which is about 7m in length.
Saliva lubricates the passage of the food down the oesophagus.
Food passes through a tube from the mouth to the anus called the alimentary canal.
Digested food (sugar, amino acids, lipids, water, vitamins and minerals) is absorbed through the walls of the alimentary canal into the blood.
Undigested food passes through the amilmentary canal, is stored in the rectum and then excreted through the anus.
The stomach contains hydrochloric acid which breaks down food and kills pathogenic microorganisms.
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