Natural Sciences, Gr. 9
Week 8 & 9: 5-16 April 2021
Main source:
De Beer, J.J.J. et al. (2013). Via Afrika natural sciences CAPS: Gr 9: Leaner book. Cape
Town: Via Afrika Publishers.
Strand 1: Life and living
Topic 5: Digestive system (pages 56-65)
1. Healthy diet
Food plays many important roles in the body:
⚫ Provides energy and heat
⚫ Provides nutrients that promotes growth
⚫ Heals and replaces damaged body tissues
⚫ Helps to fight illness and keeps the body strong
Diet = daily intake of food.
Different food types are sources of different nutrients. In a balanced diet, a variety of
food types is eaten in order to get all the necessary nutrients.
There are 4 main groups of nutrients:
1. Carbohydrates - starches and sugars
2. Proteins
3. Fats
4. Vitamins and minerals
 Water and fiber (=undigestible material) are also important for a balanced diet.
We can group nutrients according to the “work” they do:
• Energy producers = provide energy for the body
➢ Fats and oils, carbohydrates and sugars
• Body and muscle builders
➢ Proteins
• Protectors = immune system supporters
➢ Vitamins and minerals
A food pyramid shows how much of the different food types is needed to maintain a
healthy diet.
Portion = normal amount that is typically served
⚫ E.g., ‘n slice of bread, a glass of milk, a teaspoon of sugar, a bundle of grapes, etc.
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➢
Very little
➢
➢
➢
2 portions
2 portions
Fruits
➢ 2-4 portions
Vegetables
➢ 3-5 portions
6+ portions
Typical lunch/dinner portions:
In an unbalanced diet, the individual does not eat a large enough supply of foods,
and therefore does not get all the necessary nutrients. This leads to malnutrition.
Some people eat too little
⚫ It causes famine.
⚫ Tissues begin to break down, and the body systematically loses weight.
⚫ A lack of certain nutrients causes a variety of health issues
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Lack of
Symptoms:
Kwasjiorkor
Proteins
Fluid retention,
bloated stomach,
weak body
Rickets
Vitamine D
Soft bones that
bend out of normal
shape
Beriberi
Vitamine B
Weak, deformed
body
Some people eat too much
⚫ Body stores extra energy as fat
⚫ The body becomes overweight
⚫ It leads to obesity
⚫ Too much fat in the body causes a build up of fat in the inner wall of arteries (=
cholesterol), which can cause heart disease.
⚫ The chance of developing high blood pressure and diabetes increases.
2. Digestive process
Food that is eaten moves down the alimentary canal (gut) which runs from mouth to
anus. Each part of the alimentary canal is adapted to do a specific job to break down
food.
Digestion is the process whereby food is broken down from large, insoluble food
particles to small soluble molecules that the body can absorb. There are two main
types of digestion:
• Mechanical digestion
1. Teeth in the mouth chew large food particles.
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•
2. The stomach secreted digestive juices like hydrochloric acid, and
churns the food around (similar to how a washing machine moves
clothes around during cleaning cycles) to further break it down.
Chemical digestion
> Special chemicals named digestive enzymes break food down into
individual molecules.
> Takes place in the mouth, the stomach, and the small intestine.
When the food is properly digested, it forms soluble molecules that are taken up by
the blood. This is called absorption, and takes place mainly in the small intestine.
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