| 1. |
Eating food to stay alive is
called nutrition. To be healthy,
we need to eat a balanced diet. |
| 2. |
A balanced diet must have the following
seven important and different
foods.
- Carbohydrates
in bread, potatoes and rice for energy.
- Fats
in milk, cheese, butter and red meats for energy
and as insulators to keep
us warm.
- Proteins
in fish, meat, eggs, peas and beans to provide the chemicals
for the growth and repair of tissues. Proteins are
sometimes called body-building
foods.
- Vitamins
in fruit and vegetables to keep
us healthy. Vitamins are only needed in very small
amounts for vital processes.
- Minerals
such as
 ions
for blood, and  and
 ions
in all cells.
- Water
to keep the concentration
of substances in our cells at a steady
level.
- Fibre
as roughage to help the
movement of food through the gut.
|
| 3. |
Digestion
is the process in which large insoluble food molecules are
broken down into smaller, soluble molecules. These smaller
molecules can pass through the walls of the gut and into the
bloodstream to be carried to other parts of the body. |
| 4. |
Digestion in mammals takes place in the gut
or alimentary canal. Digestion involves both physical and chemical
processes. |
| 5. |
The physical processes involved in digestion
are:
- Chewing and cutting with teeth.
- Churning and mixing by muscles in the
wall of the stomach.
- Breaking up fats into an emulsion
of tiny droplets by the action of bile.
|
| 6. |
The chemical processes in digestion involve
enzymes. Enzymes catalyse
the breakdown of large food molecules into smaller molecules,
so that they can pass through the walls of the small intestine
into the bloodstream.
- Carbohydrate
enzymes catalyse the breakdown of carbohydrates,
e.g. amylase in saliva breaks down starch into maltose.
- Protease enzymes
catalyse the breakdown of proteins, e.g. pepsin in gastric
(stomach) juices breaks down proteins to peptides; peptidases
in the small intestine break down peptides to single amino
acids.
- Lipase
enzymes catalyse the breakdown of fats (lipids) into fatty
acids and glycerol in the small intestine.
|
 |
| 7. |
Most of the chemical processes in digestion
occur in the small intestine. The small intestine is a very
long, thin tube wound round and round.
|
| 8. |
Finger-like villi
on the walls of the small intestine have blood capillaries close
to
their surface. Small molecules like glucose and amino acids
seep out of the small
intestine and into the bloodstream for transport to all parts
of the body. |
| 9. |
Digestion is complete by the time food
reaches the large intestine. Here, water is absorbed by blood
capillaries, while semi-solid, indigestible material collects
in the rectum. At regular intervals, this is excreted through
the anus. |
