Biology and Health Sciences

Key unit
competence
To be able to analyse the different food nutrients and their significance to the
human body.

Cross-cutting issue
Peace and values
education:

When you are working in pairs or as a group during an activity, work in unity and respect each
other’s point of view.

At the end of this unit, you should be able to:
• Explain the importance of the classes of foods
• List the main sources of food nutrients
• List the chemical elements that make up carbohydrates, fats and proteins
• Explain that large molecules consist of smaller molecules joined together
• State that a balanced diet is eating a variety of foods containing all the
nutrients and in the correct proportions
• Explain that people have different dietary needs, dependant on age, gender
and activity levels including pregnant and breastfeeding mothers
• Explain the effects of malnutrition
• Explain that obesity is the build-up of excess fat in the body due to excess
intake of calories
• Apply knowledge of deficiency symptoms to identify the different deficiency
diseases among individuals
• Test for carbohydrates, proteins and lipids in different food samples
• Demonstrate the different functions of water, mineral salts and vitamins in the
body
• Acknowledge the importance of having a balanced diet and its relation to age
and gender
• Appreciate the need for a specific diet for individuals who carry out strenuous
activities like sports and manual labour.
• Take care when using reagents to test for food types
• Appreciate the myths and values communities attach to certain foods
• Adopt and develop healthy eating habits by eating a balanced diet.

Figure 7.1 Healthy food means healthy people.

Oral activity
In groups, answer these questions.
1. Make a list of your favourite foods
or the foods you usually eat.
2. Can you think of the nutrients that
these foods contain?
3. Try to work out the functions of
each of these food nutrients.

Topic 2: Organisation and maintenance of life

Food nutrients
Nutrients are chemical substances that organisms need to live. In Unit 1 you
learnt that all living things need nutrition in order to live. Animals get their
nutrients from the food they eat. Plants get their nutrients from the air,
water and soil.
Food nutrients give organisms:
• energy for daily activities
• the building blocks for growth and cell repair
• substances that enable the organisms to function properly and stay
healthy.
There are six types, or classes, of food nutrients: carbohydrates, proteins,
lipids (fats and oils), vitamins, mineral salts and water. Food nutrients are
made up of elements such as carbon, hydrogen and oxygen, and sometimes
nitrogen, phosphorus and sulphur.
Sources of food nutrients
Table 7.1 shows sources of food nutrients for human beings.
Table 7.1 Sources of nutrients

Food nutrients	Foods
Carbohydrates (sugars and starches)	Bread, pasta, potatoes, cassava, maize, sorghum, rice, fruits, sweets, sugar
Lipids (fats and oils)	Nuts, fish oils, meat, milk, butter, cheese, cooking oil
Proteins	Meat, milk, chicken, fish, eggs, groundnuts, soya beans, seeds
Vitamins	Fruits, vegetables, meat, fish, milk, wholegrain cereals, nuts
Mineral salts	Salt, milk, meat, fruits, fish, eggs
Water	Drinking water, fruit and vegetable juices, food

Sources of nutrients.

Unit 7: Food nutrients and diet

Activity 7.1
Working in pairs, answer these questions.
1. Identify the nutrients present in the food sources A and B.

AB

Figure 7.2 Sources of food.

2. Keep a journal of the food that you eat over a week. Bring the list to
school, and discuss it with your partner.
a) Is your list of foods similar to your partner’s list? If it is not, how is
it different?
b) Did your list of foods change during the week? If it did, explain
why.
c) Were any of the food nutrients missing from your lists?

Carbohydrates
Carbohydrates are nutrients made up of the elements carbon (C),
hydrogen (H) and oxygen (O). Some carbohydrates, such as glucose, are
small, simple molecules. Other carbohydrates, such as starch and cellulose,
are large, complex molecules.
Simple sugars such as glucose are the basic units of all carbohydrates.
We call these units sugars, or monosaccharides (‘mono’ means ‘single’ and
‘saccharide’ means ‘sugar’). Examples of monosaccharides include glucose
and fructose. Monosaccharides can join together to form disaccharides; for
example, sucrose. Polysaccharides, such as starch, are made up of many
single units (‘poly’ means ‘many’).

Topic 2: Organisation and maintenance of life

Figure 7.3 shows how polysaccharides are formed.

Figure 7.3 Formation of large carbohydrates.

Starch is an important storage carbohydrate in plants. Glycogen is an
important storage carbohydrate in animals. It is stored in the muscles and
liver. Cellulose is another large carbohydrate. It is found in plant
cell walls.

Lipids
Lipids are fats and oils. Fats are lipids that are solids at room temperature.
They are used mainly to store energy in the bodies of living things. Like
carbohydrates, lipids are made of the elements carbon (C), hydrogen (H)
and oxygen (O). Lipid molecules consist of one molecule of glycerol joined
to three long fatty acid molecules.

Figure 7.4 A lipid molecule consists of a glycerol molecule joined to three fatty
acid molecules.

Proteins
Proteins are nutrients made up of the elements carbon (C), hydrogen (H),
oxygen (O) and nitrogen (N). Some proteins also contain the element
sulphur (S). Proteins are large molecules that consist of chains of smaller
molecules called amino acids. There are over 20 different types of amino
acids. They can be joined in different combinations to make many different
proteins.

Unit 7: Food nutrients and diet

The importance of food nutrients
Table 7.2 shows the importance of the different food nutrient groups.
Table 7.2 Food nutrient groups and their importance

Food nutrients	Importance
Carbohydrates (sugars and starches	• Provide the body with energy
Lipids (fats and oils)	• Provide energy • Help with absorption of fat-soluble vitamins A, D, E and K • Form a layer beneath the skin that insulates the body and reduces heat loss • Form a layer around organs to provide protection from injury
Proteins	• Needed for growth • Needed for repair of damaged tissues • Needed for producing the enzymes required for chemical reactions in the body
Vitamins	Needed in small amounts for different functions in the body, for example: • Vitamin C is needed to fight infections and heal wounds, and for healthy bones, teeth, skin and gums • Vitamin D helps the body to absorb calcium from food, which is needed for healthy bones and teeth
Mineral salts	Needed in small amounts for many different functions in the body, for example: • Iron is needed to make haemoglobin, a substance in red blood cells that transports oxygen around the body • Calcium is needed for strong bones and teeth
Water	• Needed for chemical reactions in the cells • Keeps body temperature constant • Helps the movement of joints • Helps digestion of food • Helps to remove poisonous substances from the body

Food tests
We can test for the presence of food nutrients in different foods. In the next
activity, you will work in groups to find out whether food samples contain
carbohydrates, proteins or fats. You will use chemicals called reagents to do
this. Remember to work carefully while doing these experiments.

Topic 2: Organisation and maintenance of life

Experiment 7.1
Tests for carbohydrates, proteins and lipids.
You will need: some bread, maize porridge or other complex carbohydrate;
test tubes; a white tile; droppers; iodine solution; cooked chicken; meat or
egg; butter; water; nuts (crushed); sodium hydroxide solution; copper
sulphate solution; ethanol; test tube racks; permanent markers; test strips
for testing proteins, fats and glucose (if your school has these)
Procedure
Part A
1. Copy the table below. You will need this to record your results.

		Colour change
Food sample	Iodine	Biuret test	Ethanol
1. Bread
2. Maize porridge
3. Chicken
4. Meat
5. Egg
6. Butter

2. Set up your test tubes in a test tube rack. For each test, you need to
test all your food samples. Use the marker pen to label each test tube
with the number that matches the table.

Part B

Starch is a carbohydrate. We can easily test for its presence in a food
sample by using iodine.
1. Put a small piece of
each food sample
into a test tube or
onto a white tile.
2. Use a dropper and add
two drops of iodine to
each food sample.
3. Observe what happens,
and then record any
colour changes in
the table.

Figure 7.6 Test for carbohydrates

Unit 7: Food nutrients and diet

Part C
We test for proteins in a food sample by using the Biuret test. If proteins
are present in the food, it will turn purple when we add sodium
hydroxide solution (colourless) and copper sulphate solution (blue) to
the sample. If there are no proteins in the food, the sample will remain
blue.
1. Put a small piece of each food
sample into a test tube and add
some water.
2. Use a dropper to add about
20 drops of sodium hydroxide
solution to the test tube.
3. Use another dropper to add
about 2 drops of copper sulphate
solution to the test tube.
4. Gently shake each test tube.
5. Observe what happens, and then
record any colour changes in
the table.

Figure 7.7 Test for proteins.

Part D
We test for lipids by using organic
solvents such as ethanol. If lipids
are present, they will dissolve in
the ethanol. When water is added
to the ethanol, the water will
turn milky.
1. Put a small piece of each food
sample into a test tube and add
some ethanol. Shake the test tube
well and then allow the contents
to settle.
2. Add the same amount of water to
the test tube and shake it well.
3. Observe what happens, and then
record what you see.

Figure 7.8 Test for lipids.

Questions
1. Make a list of the foods that you tested that contained carbohydrates,
proteins and lipids. Some food samples may contain more than one
nutrient.
2. Did you take any precautions when you were doing these tests?
3. Is there anything that you would change if you did the tests again?

Topic 2: Organisation and maintenance of life

A balanced diet
A person’s diet consists of all the foods and liquids that he or she eats and
drinks. A balanced diet gives us all the nutrients we need in the right
amounts, as well as enough energy for our body to function well. The
amount of energy we need is measured in kilojoules (kJ).

Figure 7.9 A balanced diet includes foods from all five food groups.

You have learnt about the groups of food nutrients your body needs to stay
healthy. Your body needs different amounts of each food nutrient. The ‘pie
chart’ in Figure 7.9 shows the relative amounts of each food group that we
need for a balanced diet. Water is also an essential part of a balanced diet.

Unit 7: Food nutrients and diet

Table 7.3 describes the importance of each food group and gives the
proportion each group should make up in the diet.
Table 7.3 Food groups and their percentages in the diet

Food group	Importance	Examples	% of diet
Carbohydrates	Provide energy for growth and development. Wholegrain forms are best because they provide extra fibre.	Bread, maize and cassava	33%
Fruits and vegetables	These foods provide vitamins and minerals needed for a healthy immune system. They also provide fibre. You should aim to eat five portions of these foods per day.	Bananas, spinach and tomatoes	33%
Dairy foods	These foods provide fat for energy, protein for muscle and nerve development, calcium for bone development and vitamins for fighting infections.	Milk, yoghurt and sour milk	15%
Non-dairy proteins	These foods provide protein needed for muscle and nerve development, and for tissues to repair after infections.	Meat, eggs, beans	12%
Foods high in sugar or fat	These foods should be limited to prevent excessive weight gain or problems with blood sugar.	Cakes, biscuits, fried foods,chocolate and cooldrinks	7%

Activity 7.2
Work in pairs.
The amount of energy different people need is shown in the bar chart in
Figure 7.10. Look at the chart, and then answer the questions.

Figure 7.10 The amount of energy needed by different people

1. Which person needed:
a) the most energy b) the least energy?
2. Explain your answers to question 1.

Topic 2: Organisation and maintenance of life

Balanced diets for different people
In Activity 7.3 you saw that different people need different amounts
of nutrients and energy. A person’s needs depend on their age, gender,
level of activity and whether or not the person is ill. For example, males
need more energy per day than females of all ages, and people with very
active jobs need more energy than people who stay seated all day.
Young people
Children grow quickly and are very active, so they need a diet that provides
lots of food nutrients and energy. When they reach their teenage years,
they have times of rapid growth called growth spurts, when extra nutrients
and energy are needed. A balanced diet for a school child should contain
similar proportions of foods to those shown in Figure 7.9 (see page 75), but
in amounts that provide them with enough energy. The child should also
drink plenty of water.

Pregnant and breastfeeding women
Pregnant and breastfeeding women need more energy per day than the
average adult woman. A pregnant woman needs extra nutrients and energy
for the healthy growth and development of her baby.
A balanced diet for a pregnant woman should contain similar
proportions of foods to an average adult woman, but should include extra
fruits and vegetables, dairy foods, non-dairy proteins and water.
A breastfeeding woman needs extra energy and nutrients to make
breast milk. Her diet should contain similar proportions of foods to an
average adult woman, but with extra carbohydrates, dairy foods, non-dairy
proteins and water.
Sports players
People who play sport need extra energy for their sporting activities. They
also need extra nutrients to build and repair their muscles and to replace
the minerals lost in their sweat. A balanced diet for people who play sport
should contain similar proportions of foods to a healthy man or woman,
but should include extra carbohydrates and non-dairy proteins, as well as
extra water and other fluids.

Unit 7: Food nutrients and diet

Nutritional disorders
A nutritional disorder is also called malnutrition. It happens when a
person’s body has either too little or too much of a certain food nutrient.
As a result, their body does not grow or function properly. Examples of
nutritional disorders include deficiency diseases, starvation, obesity and
constipation.
There are many reasons for malnutrition. It can be caused by poverty,
where people are either too poor to buy enough food, or can only buy cheap
food that does not provide all the nutrients they need. Malnutrition can
also be caused by poor food choices and poor cooking methods.

Deficiency diseases
Deficiency diseases occur when a person has too little of a vitamin or
mineral. Examples of deficiency diseases include scurvy, rickets and
anaemia.

Figure 7.12 The gums and teeth of a person with scurvy

Table 7.4, on page 79, shows the causes, symptoms and prevention of some
deficiency diseases.

Topic 2: Organisation and maintenance of life

Starvation Starvation occurs when a person does not eat enough food. There are  two forms ofstarvation: marasmus and kwashiorkor.
Marasmus is caused by not eating enough of almost all nutrients, but especially energy-rich foods such
as carbohydrates, fats and proteins. Marasmus causes extreme loss of body fat and muscle. A sufferer
of marasmus is very thin. Other symptoms of marasmus include lack of energy, severe hunger and
swelling of the hands and feet. Kwashiorkor occurs when a person’s diet does not include enough proteins, vitamins and minerals. Mainly children are affected. Sufferers have a swollen stomach, while
the rest of their body is very thin and has little muscle. Other symptoms
of kwashiorkor include changes in hair colour, skin rashes, swollen hands and feet, and loss of appetite.

Unit 7: Food nutrients and diet

Figure 7.15 Obesity can lead
to serious health problems.

Obesity
Obesity is caused by eating a diet that contains
too many energy-rich carbohydrates and fats.
These foods are usually called junk foods and
contain very few nutrients. The body stores the
extra energy as body fat. Obesity can lead to
serious health problems such as heart disease,
stroke and diabetes.

Impact of deficiency diseases
Deficiency diseases can affect a person negatively if they are left untreated.
Some of the effects are: stunted growth, increased likelihood of getting
infections, blindness (in the case of untreated vitamin A deficiency), being
unable to take part in everyday activities, deformity, and death.
When children get sick, parents or guardians and other family
members have to care for them. So, there is less time to do other activities
that are necessary for the family’s well-being. This can have negative effects
on the family.
At a community and national level, caring for sick people takes
up valuable resources that could be used for the development of the
community and nation. In this way deficiency diseases, which are easily
preventable, can slow down the development of the community and nation.

Case study
Work in pairs. Read the case study and then discuss how soya milk can
improve children’s health.
Life-saving soyamilk
Soyamilk contains all the proteins necessary to replace meat and milk.
In a village in eastern Rwanda, women have learnt how to extract soya
milk from soya beans. Soyamilk contains more proteins than cow’s milk
and many adults and children prefer it. Malnutrition amongst children
in this area has decreased in the last few years since the women’s soya
milk production has started. There has also been a decrease in the
number of childhood illnesses in this area.
Constipation
Constipation occurs when a person does not eat enough fruits and vegetables.
Their stools become hard and difficult to pass. We can prevent constipation
by eating food rich in fibre and by drinking plenty of water.

Topic 2: Organisation and maintenance of life

Unit 7: Food nutrients and diet 81

Activity 7.3
Work in pairs.
1. a) Discuss with your partner some of the nutritional disorders that
occur in your local community.
b) What impact do these disorders have on:
i) an individual
ii) a family
iii) a community
iv) the nation?
2. Kalisa recorded the number of children at his local clinic that suffered
from nutritional disorders over three months. His results are shown in
this table.

a) How many children in total had kwashiorkor?
b) In which month were there the most children with anaemia?
c) Which foods should children with anaemia eat?
d) Which vitamin and mineral should children with rickets eat more
of in their diet?

Homework
Draw a table with three columns: Disease, Cause, Prevention. Complete
the table using the information about nutritional disorders that you learnt
in the section above (see pages 78 to 80).

Exercise 7.1
1. Name six food nutrients.
2. Give an example of a food that contains:
a) carbohydrates b) proteins c) vitamins.
3. Name the elements that are found in each of the following:
a) carbohydrates b) proteins c) fats.
4. Give the basic units of each of the following:
a) carbohydrates b) proteins c) fats and oils.
5. What is a balanced diet?
6. Name three deficiency diseases.

Unit 7: Food nutrients and diet

Checklist of learning
In this unit, I have learned that:
All living things need food nutrients to provide energy, build and repair cells and
keep them functioning properly.
The main food groups are carbohydrates (sugars and starches), proteins, lipids (fats and oils),
vitamins, mineral salts and water.
Different foods contain different nutrients.
Simple carbohydrates are made up of single sugars, such as glucose; complex carbohydrates, such as
starch and glycogen, consist of many single sugar units joined together.
Lipid molecules are made up of a molecule of glycerol and three fatty acids.
Protein molecules are large molecules that are made up of amino acids.
Foods can be tested using reagents to find out which nutrients they contain.
A balanced diet contains all the food nutrients that a person needs in the right quantities.
Different people need different diets depending on their age, gender, level of activity and whether or
not they are ill.
A nutritional disorder occurs when a person does not have enough food or when their diet is lacking
certain vitamins or minerals.
Scurvy, rickets, anaemia, starvation and obesity are examples of nutritional disorders.

Topic 2: Organisation and maintenance of life

Self-assessment
1. Match the word in Column A with the correct statement in Column B.

2. Name the reagents that are used to test for the presence of the following in a food sample:
a) proteins
b) starch.
3. A family has four members: an 80-year-old grandfather, a 35-year-old father, and 28-year-old
pregnant mother, and a 2-year-old boy.
a) Between the boy and the grandfather, who should be given more milk?
b) Why?
4. Miss Umutoni visited a doctor as her gums were bleeding and she complained that she was always
tired. The doctor told her to eat two oranges, spinach and plenty of red meat every day for one
month. After two weeks, Miss Umutoni felt better and went
to thank the doctor.
Discuss the causes of Miss Umutoni’s symptoms, and explain why her treatment
was successful.
5. Describe any two nutritional disorders. Include the causes, prevention and treatment of each
disorder.

Unit 7: Food nutrients and diet