7.1.
1 Diet & Deficiencies
Balanced Diet
• A balanced diet consists of all of the food groups in the correct proportions
• The necessary food groups are:
o Carbohydrates
o Proteins
o Lipids
o Vitamins
o Minerals
o Dietary Fibre
o Water
Food Groups Table-
Vitamin and Mineral Requirements Table
7.2- The Human Digestive System
Functions of the Digestive Organs (Table)
Physical Digestion
• Physical digestion (sometimes referred to as mechanical digestion) is the breakdown of food
into smaller pieces without chemical change to the food molecules.
• The processes that take place during physical digestion help to increase the surface
area of food for the action of enzymes during chemical digestion.
• It is mainly carried out by the chewing action of the teeth, the churning action of
the stomach and the emulsification of fats by bile in the duodenum.
Types of Human Teeth
• Mechanical digestion is the breakdown of food into smaller pieces without chemical
change to the food molecules
• It is mainly carried out by the chewing action of the teeth, the churning action of
the stomach and the emulsification of fats by bile in the duodenum
• Teeth are held firmly in the bone of the jaw
o They are used for chewing to increase the surface area of the food so that it can
be exposed to saliva and other digestive juices and broken down more quickly
• The differing shapes and sizes of teeth enable them to perform slightly different functions:
o Incisors - chisel-shaped for biting and cutting
o Canines - pointed for tearing, holding and biting
o Premolars and molars - larger, flat surfaces with ridges at the edges for chewing
and grinding up food
Structure of tooth-
The Stomach
• The stomach is one of a number of organs that make up the digestive system
• The role of the digestive system is to break down large insoluble molecules into smaller,
soluble food molecules to provide the body with nutrients
• The stomach lining contains muscles which contract to physically squeeze and mix the
food with the strong digestive juices that are present
o Also known as "stomach churning"
• The stomach produces several fluids which together are known as gastric juice
• One of the fluids produced is hydrochloric acid
• This kills bacteria in food and gives an acid pH for enzymes to work in the stomach
How is a low pH helpful in the stomach?
• The low pH kills bacteria in food that we have ingested as it denatures the enzymes in
their cells, meaning they cannot carry out any cell reactions to maintain life
• Pepsin, produced in the stomach, is an example of an enzyme which has a very low
optimum pH - around pH 2
• The hydrochloric acid produced in the stomach ensures that conditions in the stomach
remain within the optimum range for pepsin to work at its fastest rate.
• Food is digested within the stomach for several hours
Emulsification of Fats & Oils
• Cells in the liver produce bile which is then stored in the gallbladder
Bile production and secretion
Bile has two main roles:
• It is alkaline to neutralise the hydrochloric acid which comes from the stomach
• The enzymes in the small intestine have a higher (more alkaline) optimum pH than
those in the stomach
• It breaks down large drops of fat into smaller ones. This is known
as emulsification. The larger surface area allows lipase to chemically break down
the lipid into glycerol and fatty acids faster
Assimilation-
• Assimilation occurs when movement of digested food molecules is observed into the cells of
the body where they are used.
• Assimilation of glucose: Glucose is oxidized to carbon dioxide and water. This process
provides energy (ATP) to drive many chemical process
• Assimilation of fats: Source of an energy, part of cell membrane and other cell structure.
• Assimilation of amino acids: Part of cell membrane, built up into proteins, enzymes
formation. Amino acids not needed for making proteins are converted by liver into glycogen.
