This contains different chemicals of life that make up our bodies like water, carbohydrates, proteins, vitamins and DNA

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BY MR. NATHAN SSEKAMATTE
THE CHEMICALS OF LIFE
LEARNING OBJECTIVES
By the end of the chapter, I should be able to;
• To describe the role of water as a solvent in organisms.
• To list the chemical elements which make up carbohydrates,
fats and proteins.
• To know how large molecules come from smaller molecules.
• To explain that different sequences of amino acids give different shapes to
protein molecules.
• To relate the shape and structure of protein molecules to their function,
limited to the active site of enzymes.
• To describe the food test for carbohydrates, proteins, fats and oils, and
vitamins.
• Describe the structure of DNA
WATER
This compound is made of two elements namely Oxygen and
Hydrogen. In living things, water forms about 80% of weight.
Importance of water
✓ It’s a universal solvent in which absorbed foods, wastes and
hormones are transported around the body in blood.
✓ The plasma of blood is made up of water.
✓ It participates in many metabolic reactions or processes as a raw
material for example respiration, photosynthesis, gaseous
exchange, digestion, and removal of wastes.
✓ Plays a role in temperature regulation that is to say cooling the
body on hot days and plants through transpiration.
✓ Offers turgidity thus acts as a hydrostatic skeleton- hence
supporting organisms.
✓ It softens food.
✓ It is used in seed dispersal.
✓ It is a habitat for some organisms (home).

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BY MR. NATHAN SSEKAMATTE
✓ It acts as a Lubricant e.g. salvia lubricant the mouth, tears lubricate
eyes, synovial fluids lubricate the joints.
FOOD
Food is any substance which can be digested and absorbed by the
body to maintain the body’s life processes (Metabolic process).
Food is required by organisms for:
i. Growth so as to build new cells
ii. Respiration to produce energy
iii. Repair of worn out cells or tissues
iv. Protection of the body against diseases e.g.
vitamins, proteins.
CLASSES OF FOOD
There are three classes of food, namely: -
a) Energy giving foods (fats and oils).
b) Body building foods (growth foods) e.g. proteins.
c) Protective foods, these protect the body against infections and
diseases e.g. vitamins and minerals.
TYPES OF FOOD/NUTRIENT COMPOUNDS
There are six different nutrient compounds namely:-
1. Carbohydrates
2. Fats and oils (lipids)
3. Proteins
4. Vitamins
5. Mineral salts
6. Roughages and water

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BY MR. NATHAN SSEKAMATTE
CARBOHYDRATES
These are organic chemicals made up of elements: - carbon,
hydrogen and oxygen. The ratio of hydrogen atom to and oxygen atom
is 2:1. Therefore have a formula of CxH2xOX.
Carbohydrates are grouped into 3 categories which include
monosaccharides, disaccharides and polysaccharides depending on
number of sugar molecules they are composed of.
i) Monosaccharides
Monosaccharides (mono=one, saccharide= sugar) are substances
consisting of one molecule of sugar. They are also known as simple
sugars.
Structure of glucose molecule.
Properties of monosaccharides
➢ They have a sweet taste
➢ They are soluble in water
Examples of Monosaccharides include:
1. Glucose (present in grapes)
2. Fructose (present in many edible fruits)
3. Galactose (present in milk)
ii) Disaccharides
Disaccharides (di=two, saccharide= sugars) are carbohydrates
molecules made up two simple sugars joined together. When the
two monosaccharides combine, they form larger molecule
(disaccharides).
Glucose + Glucose = maltose + water

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BY MR. NATHAN SSEKAMATTE
Glucose + Galactose = lactose + water
Glucose + Fructose = sucrose + water
Properties of disaccharides:
i) They are sweeter than monosaccharides
ii) They can be crystallized
iii)They are soluble in water
Examples of disaccharides include:
1) Sucrose (present in sugar cane)
2) Maltose (present in germinating seeds)
3) Lactose (present in milk
iii) Polysaccharides
Polysaccharides (poly = many, saccharide = sugar) are complex
carbohydrates made up of many simple sugars joining together.
Properties of polysaccharides include:
✓ Are not sweet
✓ Do not dissolve in water
✓ Cannot be crystallized
✓
Examples of polysaccharides include:
1) Starch
2) Glycogen
3) Cellulose.
Functions of carbohydrates
i) They provide energy in the body when oxidized
during respiration.
ii) They are cheap sources of energy for living things
iii) They act as food reserves which are stored within organisms
e.g. many plants store food as starch and animals as
glycogen.

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BY MR. NATHAN SSEKAMATTE
iv) They are important components of body structures e.g.
cellulose is a component cell walls, chitin forms exoskeleton
of arthropods.
Deficiency of carbohydrates results in a deficiency disease called
marasmus.
Symptoms of marasmus
i) High appetite.
ii) Dehydration of the body
iii)Growth retardation
iv) Wastage of muscles
FOOD TESTS ON CARBOHYDRATES
1. Test for reducing sugars
The reagent used is Benedict’s solution (blue). Boiling is required.
Procedure Observation Conclusion
To 1 cm3
of food solution,
add 1 cm3
of Benedict’s
solution and heat in a water
bath.
The solution turned to a
blue solution, then to a
green solution, to a yellow
precipitate, to orange
precipitate and to a brown
precipitate on boiling.
Little or
Moderate or
Much or
Too much; reducing sugars
present.
The solution turned to a
blue solution which
persists on boiling.
Reducing sugars absent.
2. Test for starch:
The reagent used is iodine which is a brown or yellow solution).
Procedure Observation Conclusion
To 1 cm3
of food solution,
add 3 drops of iodine
solution.
The solution turned to a
blue-black
starch present.
The solution turned to a
yellow or brown solution.
Starch absent.

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BY MR. NATHAN SSEKAMATTE
LIPIDS (FATS AND OILS)
Lipids also contain carbon, hydrogen and oxygen but with higher
proportions of hydrogen and less oxygen than carbohydrates.
Because of this, they are able to yield more energy than
carbohydrates or proteins. Fats differ from oils in that they are solids
at room temperature whereas oils are liquids at room temperature
(250
C).
Fats are mainly found in animal tissues while oils are obtained from
plant tissues.
Examples of fats include; kimbo, cow boy, tamu, margarine, etc.
Examples of oils include; fortune buto, sun seed cooking oil, ufuta
cooking oil, etc. Lipids are made up fatty acids and glycerol.
Food sources:
Ground nuts
Eggs
Sun flower
Palm oil
Castor oil, etc.
Properties of lipids
i) Fats and oils are distinguished from other nutrients in that they
make a permanent translucent mark or spot on papers. This
property also provides a simple test for fats and oils.
ii) They also don’t dissolve in water
Functions of lipids
i) Energy production during respiration
ii) Insulate the body to prevent excessive heat loss; this has been of
major adaptations in some small animals and those animals living
in cold regions where the sub- cutaneous fats are largely
deposited under the dermis of the skin.
iii) Prevent water loss and entry in cells and tissues
iv) They are also constituents of waxy cuticle of animals and plants
and the cell membrane.

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BY MR. NATHAN SSEKAMATTE
v) In some areas of animals, they act as shock absorbers
vi) They can be used as a source of water in desert animals such as
camels- when stored fat is broken down in the body, much water
is produced.
NOTE:
1. In animals, fats found in animal food is called saturated fats. The foods
also contain cholesterol. People who take in these fats are said to be
affected easily by heart diseases because fat deposits build up in their
arteries, making them stiffer and narrower. If this happens in the coronary
arteries supplying the heart muscle with blood, then little blood can pass
through. The heart muscles run short of oxygen and cannot work properly.
This is called coronary heart disease.
The deposits can also cause blood clot, which result in a heart attack.
Products with saturated fats include; milk, cream, butter, cheese, eggs,
red meat but fish and white meat like chicken contain less saturated fats.
2. People who take in more energy than they can use up get fat. Being
very fat is called obesity. Obese people are more likely to get heart
diseases, stroke, and diabetes.

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BY MR. NATHAN SSEKAMATTE
TESTS FOR LIPIDS
They are tested for using the emulsion test or the grease spot
(translucent spot) test.
a) The emulsion test:
The reagents used are ethanol and water.
Procedure Observation Deduction
To 1 cm3
of dry food
substance add 1 cm3
of
ethanol and shake.
Then poured into a test
tube of water.
The solution turns to a
cream emulsion
Lipids present.
The solution remains a
turbid or colourless
solution.
Lipids absent.
PROTEINS
These are food nutrients containing carbon, hydrogen, oxygen and
nitrogen and sometimes Sulphur or phosphorus. The smallest and
building unit of proteins are called Amino acids. The amino acid
molecule can condense to form dipeptide; further condensation
gives rise to polypeptide molecule (protein). There is a total of twenty
(20) amino acids present thus allowing the formation of a variety of
proteins.
The amino acids are of different shapes and sizes, thus when linked
together in a chain to form protein molecules, the proteins formed
will also be of different shapes.
This structural difference is very important when the protein is an
enzyme since the active site is of exactly the right shape to fit the
substrate molecule of the chemical reaction that it will catalyse.
Antibodies are also proteins in the blood with a binding site which
binds with the pathogen or antigen

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BY MR. NATHAN SSEKAMATTE
Structure of a protein
Sources of proteins:
Food substances rich in proteins are eggs, lean meat, beans, Soya,
milk and its products, fish and groundnuts.
The main functions of proteins
i) Body building which brings about growth thus involve in making of
new cells i.e. from structures like in cell membrane, fingernails and
hair which are made of keratin, etc.
ii) Repair and regenerate tissues that are damaged or worn out.
iii)They help in synthesis or formation of body chemicals like
enzymes, hormones, haemoglobin, antibodies.
iv) They are used to provide energy in times of starvation.
Note: Protein deficiency results in poor health especially in children
where it causes kwashiorkor.
Symptoms of kwashiorkor
• Loss of appetite
• Diarrhea
• The hair becomes soft and can easily be plucked out accompanied
by loss of its colour.
• Growth retardation
• swollen lower abdomen

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BY MR. NATHAN SSEKAMATTE
TEST FOR PROTEINS
We use the biuret test to test for proteins.
The Biuret test:
Procedure Observation Conclusion
To 1 cm3
of food solution,
add 1 cm3
of dilute sodium
hydroxide solution, then
add 3 drops of Copper II
sulphate solution and
shake.
The solution then to a v
purple solution.
Proteins present.
The solution turned to a
blue solution.
Proteins absent.
VITAMINS
These are organic compounds required in small amounts in the diet
for the normal functioning of the body. They are designated with
alphabetical letters and are classified into two:
i)Water
soluble
vitamins
ii) Fat soluble
vitamins
Water soluble vitamins are those which dissolve in water. They
include vitamins B and C.
Fat soluble vitamins dissolve in fats but not in water. They include
vitamins A, D, E, and K.
A table showing vitamins and their deficiency diseases
Vitamin Common food
source
Functions Symptom of deficiency
C (Ascorbic
acid)
Fresh citrus fruits
(oranges, limes)
and raw
vegetables
Keeps the tissues in
good repair.
Also used to make
collagen found in
the skin.
Scurvy- Sore gums,
poor healing of sores in
the gum

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BY MR. NATHAN SSEKAMATTE
D(calciferol) liver, butter, fish,
egg yolk, formed
beneath skin of
man in sunlight
Helps calcium to be
absorbed, for
making bones and
teeth.
Weak bones and teeth,
rickets in children in
which bones become
soft and deformed and
dental caries
TEST FOR VITAMIN C:
The reagent used is DCPIP (Dichloro Phenol Indole Phenol). It is a deep blue
solution. The sources of vitamin C are fresh fruits e.g. oranges, mangoes,
lemon, etc.
Procedure Observation Conclusion
To 2 cm3
of DCPIP
solution in the test tube,
add the food solution drop
wise.
The blue DCPIP solution
is decolourised or turned
to a colourless solution.
Vitamin C present
The blue DCPIP solution
remained blue.
Vitamin C absent
MINERAL ELEMENTS AND SALTS
These are inorganic food constituents required in small amounts
but whose deficiency affects the normal functioning of the body
leading to deficiency diseases.
A table showing some elements and their deficiency diseases
MINERAL
ELEMENTS
SOURCE IMPORTANCE DEFFICIENCY
Fe
Iron
- Beef, liver,
kidney, G. nuts,
beans, egg
yolk, green
vegetables.
-for making of
Haemoglobin the
pigment in blood
which carries
oxygen.
Anaemia
- Reduced red blood cell
account.
- Reduction in
oxygen transportation
rate.

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BY MR. NATHAN SSEKAMATTE
Ca
Calcium
Vegetables,
milk, bread.
- In blood
clotting
- hardening of
bones and teeth.
Rickets in children
- Delay in blood clotting
- Soft bone, poor skeletal
growth.
ROUGHAGES / DIETARY FIBRE
They are indigestible materials in food and consist mostly of cellulose,
pectin, and lignin.
The major sources of roughages include: vegetables, such as
cabbages, dodo, fruits, etc.
Functions of roughages
✓ They stimulate muscular movements called peristalsis which move
food through the alimentary canal.
✓ Some delay food in the intestines whereas others enable food pass
through the intestines very fast.
✓ The deficiency or lack of roughages causes constipation.
Balanced Diet:
A balanced diet is a diet containing all food nutrients in their right
amount and proportions. If a person depends on a poor diet
(unbalanced diet) i.e. containing inappropriate quantities of nutrients,
then the person suffers from Mal nutrition.
Mal-Nutrition:
This refers to an unhealthy state of the body resulting from a long-
term deficiency or excess of one or more of the essential nutrients. It
is caused by not eating a balanced diet
Malnutrition is normally detected by the onset of some deficiency
diseases like;
1. kwashiorkor due to lack of proteins mostly between ages of nine
months and two years after they have stopped being fed on breast
milk.
2. Marasmus due to shortage of energy in the diet which results in a
child’s low body weight.

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BY MR. NATHAN SSEKAMATTE
RESEARCH QUESTION
Explain how age, gender and activity affect the dietary needs of humans including during
pregnancy and whilst breast-feeding.
DNA (Deoxyribonucleic acid)
This is a chemical that makes up our genes and chromosomes. It is the
material that we inherit from our parents thus gives us many of our
characteristics.
DNA is made up of two long strands which coil together to form a double
helix. Each strand has a series of bases arranged along it. These bases
are held together by bonds forming cross links.
There are four kinds of bases, noted by letters A, C, G and T
T and A always link up with each other and also C and G. These bases
pair up in this way.
The sequence of the bases in our DNA provides a code that is used to
determine the kind of proteins that are made in our cells, thus in turn
determine s how our cells, tissues and organs develop.

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BY MR. NATHAN SSEKAMATTE