Module 13 - Food & Digestion - Revision
Here are the key ideas from Module 13. Make
sure that you also look at your written notes and the sites on
the links page.
Food and Food groups
An ICT research exercise is available for this module. Students are expected to research questions on the food groups and their functions.
Nutrition Links Page (opens in a new window)
Question sheet (150k)
You require Adobe Acrobat Reader (get it here) to read this file.
Why do we need food?
We need to eat food for lots of different reasons:
For energy to live, move
To grow, and to repair
damaged cells and tissues in our body.
- To prevent diseases
Different foods contain different nutrients to
help us to achieve these things. Here are the main nutrients you
need to know about:
- CARBOHYDRATES (sugars and starch) for ENERGY
- PROTEINS for GROWTH and repairing
our cells and tissues
- FATS for energy and WARMTH
- VITAMINS and MINERALS to keep
us healthy and to PREVENT DISEASES.
Type of food
Why we need it
As starch in cereals (potatoes, bread,
pasta, rice). As sugars in sweet foods and
drinks (chocolate, soft drinks etc.)
For energy. Most of our carbohydrate should be in the form
of starch not as sugars.
Meat, fish, nuts, lentils
For growing and repairing our tissues. Children who receive
too little protein may grow too slowly or suffer from a condition
Meat, cakes, fried foods, fast food
For warmth and for energy. Too much fat in our diet leads
to severe health problems including heart attacks.
Vitamins and minerals
Lots of foods but especially fruit and vegetables
A lack of some vitamins may lead to particular illnesses;
e.g. a lack of Vitamin C (from oranges, limes
etc.) leads to a condition called scurvy.
Not having enough iron (a mineral) in the diet leads to anaemia.
You also need a lot of water - about 75% of your
body is made of water, remember. It is recommended that you drink
about 4 pints of water (or fruit juice / low sugar squash) every
Some foods contain lots of fibre. This cannot
be digested but it helps to keep our digestive system healthy.
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What is a 'balanced
A balanced diet contains the right amounts of different food groups
to keep us healthy. To illustrate a balanced diet, scientists sometimes
use a food pyramid:
The food pyramid shows how much of different types of foods you
should be eating:
- Breads and cereals should make up the major part of your diet
- You should eat lots of vegetables and fruit
- You should eat some (but not too much) meat (or veggie alternative)
and dairy products every day
- You should eat as few fats, oils and sweets as possible
HOW DOES YOUR DIET MATCH UP TO THESE STANDARDS?
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Testing for food groups
- For information on how to test for the different food groups
in food see the Learn.co.uk
Digestion and the Digestive System
does the digestive system do?
- The digestive system breaks down larger pieces of food into
smaller pieces of food. This can be done physically (e.g. the
teeth breaking down food in the mouth) or chemically (e.g.
chemicals called enzymes breaking down large molecules of food
into smaller molecules of food - e.g. breaking down starch
(a large carbohydrate) into sugars, which
are smaller carbohydrates)
- Once the food has been broken down, the molecules of food are
absorbed from the digestive system into the blood
in the small intestine. The nutrients can then
be carried round the body to where they are needed.
Are all types of food digested?
- Fibre cannot be digested at all. It gives your
food bulk so that your digestive system can push on it. Most of
faeces (poo) is made up of fibre.
- Vitamins and minerals are small molecules anyway,
so they don't have to be digested at all - they can pass into
the blood from the small intestine.
For information on the what the different parts of the digestive
system do, see the links on our links
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What are enzymes and how
do they work?
- Enzymes are special chemicals in the digestive system that break
down large food molecules into smaller food molecules. These small
molecules can then move from the small intestine into the blood.
- Starch is broken down into sugars by an enzyme
- Proteins are broken down into amino acids by enzymes
- Fats are broken down into fatty acids by enzymes
See the article and animation at Learn.co.uk
to see more on how food is broken down.
What conditions do enzymes work best in?
- Enzymes in the body work best at body temperature, which
is about 37 degrees Celsius. At very hot temperatures, enzymes
are destroyed (denatured) and stop working.
- Enzymes can also be damaged by changes to the pH (how acid or
alkali it is). Enzymes in the stomach, though, work at very low
pH (strong acid) because the stomach contains acid.
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Fascinating Digestive System Facts
(you don't need to know these, but they are interesting all the
- We each eat about 500kg (½ ton) of food per year.
- We each produce 1.7 litres (3 pints) of saliva every day.
- Muscles contract in waves to move the food down the oesophagus.
This means that food would get to a person's stomach, even if
they were standing on their head.
- An adult stomach can hold approximately 1.5 litres (2 ½
pints) of material.
- The digestive system of an adult human is about 8m long.
- Every day 11.5 litres (20 pints) of digested food, liquids and
digestive juices flow through the digestive system, but only 100mls
(one sixth of a pint) is lost in faeces (poo)