Food Nutrients


  • Examples are sugars, starches (pasta, potatoes, flour) and cellulose (fibre)
  • Contain carbon, hydrogen and oxygen with the ratio of hydrogen atoms to oxygen atoms as 2H : 1O
  • An immediate source of energy for the body
  • In the process of respiration, glucose sugar and oxygen give energy and wastes of carbon dioxide and water
  • 3 forms of carbohydrates are:
  1. Monosaccharides (Simple Sugars e.g. glucose in honey, and fructose in fruit)
  2. Disaccharides (Double Sugars e.g. sucrose, lactose, maltose)
  3. Polysaccharides (e.g. starch, cellulose)
  • All carbohydrates are broken down to simple sugars (monosaccharides) by enzymes in the digestive tract


Lipids (Fats and Oils)


A (retinol) Carrots, tomatoes, leafy vegetables, egg yolk, milk, cheese Poor night vision, skin infections
B1 (thiamine) Wholemeal bread, eggs, milk, cheese Beriberi (loss of appetite, weakness)
B2 (riboflavin) Eggs, milk, cheese, yeast Pellagra (skin infections, mental illness)
C (ascorbic acid) Citrus fruit, green vegetables Scurvy (bleeding gums, loss of teeth)
D (calciferol) Eggs, cod liver oil, butter, milk Rickets (deformed bones)
E (tocoperol) Green vegetables, wheat-germ, milk Anaemia
K (phylloquinone) Green vegetables Impairs blood clotting

Mineral Ions

Calcium Milk, cheese, green vegetables Rickets (poor bones and teeth)
Iron Meat, eggs liver, vegetables Anaemia
Iodine Fish, water Goitre (poor growth and development)
Fluorine Drinking water Poor teeth
Phosphorus Dairy foods, eggs, meat, vegetables Poor bones, teeth and muscles
Potassium Meat, fruit, vegetables Affects nerves, muscles and blood
Zinc Green vegetables, onions, liver Part of the hormone called insulin

Tests for Chemical Components of Food

Protein Add a few drops of copper sulphate solution to the food sample, then a few drops of sodium hydroxide solution and mix well. Blue-purple
Starch Add a few drops of iodine solution to the food sample. Blue-black
Glucose Add an equal volume of Benedict's solution to the food sample and warm in a very hot water bath for a few minutes. Orange-red
Lipid (Fats and Oils) Rub a food sample onto brown paper and allow it to dry. Translucent spot

Human Digestive System

3 Processes in Digestion

  1. Ingestion - the mechanical taking in of food, chewing and swallowing
  2. Digestion - The breakdown of food into smaller particles by physical or chemical means
  3. Absorption - the absorption of these smaller food particles from the digestive tract into the blood

Did You Know That...? A "warm-blooded" or endothermic animal eats more than a "cold-blooded" or ectothermic animal because much of the energy from food is used to keep us warm.

2 Types of Food Breakdown

  1. Physical or Mechanical Breakdown - e.g. chewing, mixing with bile
  2. Chemical Breakdown - e.g. enzymes, hydrochloric acid

Parts and Functions of the Human Digestive System





Small Intestine

Large Intestine


Did You Know That...?
  • A person swallows the equivalent of half a bucket of saliva daily.
  • The Etruscans made the first false teeth with gold 3000 years ago.
  • Toilet paper was invented in 1899 by the Scott brothers in America.

The Role of the Liver in Digestion

Did You Know That...? Crohn's Disease is a type of inflammatory bowel disease that affects the digestive tract. More common to 15-30 year olds in industrialized nations, it may be an autoimmune disease triggered by environmental factors relating to diet.

Comparison between the Digestive Tracts of
Herbivores and Carnivores