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NUTRITION
NUTRIENTS
chemicals in
food
biomolecules
WHAT’S IN
THE FOOD
YOU EAT?
CARBOHYDRATE
LIPIDS
COMPONENTS
OF FOOD
PROTEINS
VITAMINS
MINERALS
LABORATORY
EXPERIMENT
NUTRITION
• Nutrition, for living organisms, refers to the
processes of obtaining energy and matter in order
to survive.
• Energy and matter are found together in chemicals
called nutrients which are found in foods.
• Organisms are not able to grow, move, reproduce
or do anything without food.
• The energy and materials contained within food
are needed for metabolism and continuity.
THERE ARE TWO METHODS OF NUTRITION:
• Autotrophic nutrition:
where food is made from
inorganic nutrients and,
usually, sunlight energy. The
formation of organic
nutrients always requires an
energy input – generally
plant use light to make their
own food by
photosynthesis.
• Heterotrophic
nutrition, where existing
foods are broken down
to provide ready-made
nutrients. Animals
obtain their food by
eating existing matter;
foods that they find in
their habitat.
NUTRIENTS
Nutrients are grouped according to whether or not they
contain the element carbon (chemical symbol C);
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Organic nutrients
contain carbon and
originate from other
living organisms.
Examples include:
proteins,
fats and oils (lipids),
carbohydrates,
vitamins.
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Inorganic nutrients do not
contain carbon (except for
carbon dioxide). Examples
include:
dissolved salts (sodium
chloride, calcium
phosphate),
trace elements (iron, copper,
zinc),
carbon dioxide (CO2),
water (H2O).
THE CHEMICALS PRESENT IN FOOD
• Bio-molecules are the basic chemical structure
found within most organic chemicals. They are
found in food and in the bodies of living
organisms.
• Foods contain many different chemical elements:
some in large amounts, but many in tiny amounts,
i.e. traces.
• Originally all these elements are gathered by
plants and then passed along the food chains for
all other organisms.
• The six common bio-elements in food are:
carbon,
hydrogen,
nitrogen,
oxygen,
phosphorus and sulphur.
• Food also contains:
sodium, magnesium, chlorine, potassium and
calcium – all are present as salts dissolved in
water.
• There are also traces, tiny amounts of iron,
copper, zinc and other elements.
• All bio-molecules are constructed around carbon
atoms which form the “skeleton” of every organic
chemical.
• The carbon atoms can join to form chains, rings or
branched structures.
• Carbon is able to form up to four chemical bonds
at one time.
• The joining is called condensation, and breaking
the units apart is termed hydrolysis.
COMPONENTS OF FOOD
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Carbohydrates
Lipids
Proteins
Vitamins
Minerals
CARBOHYDRATES
• Carbohydrates include: glucose, sucrose, lactose,
ribose, starch, glycogen, cellulose and chitin.
• All carbohydrates contain the elements carbon,
hydrogen and oxygen. Hydrogen and oxygen are
always in a ratio of 2:1.
• The general formula can be written: Cx( H2O)y,
The chemical formula of glucose is:C6( H2O)6 and
of sucrose is C12( H2O)11
Carbohydrates are classified as monosaccharides,
disaccharides, and polysaccharides:
• Monosaccharides contain
single sugar molecules
with some carbon atoms:
(glucose, fructose, ribose).
• Disaccharides, are made
from pairs of single sugar
bio-molecules that are joined:
(sucrose, lactose, maltose).
• Polysaccharides are made from long chains of many sugar
bio-molecules joined together: (glycogen, cellulose, starch).
Where do you find
carbohydrates?
Why do you need
them?
Foods rich in carbohydrates
are:
grapes, honey (glucose);
sweet fruit (fructose);
cakes, biscuits (sucrose);
milk (lactose);
potatoes, flour, pasta, rice
(starch);
meat, liver (glycogen);
cereals, vegetables
(cellulose).
Carbohydrates function as:
• Fuel: they have a high energy
content and release their
energy quickly during
respiration. They are primary
sources of energy for cell
metabolism.
• Support: they can form the
cell walls in plants, or be the
supporting framework of a
DNA molecule.
LIPIDS
• Lipids include: fats, oils, waxes, phospholipids.
• They contain carbon, hydrogen and oxygen atoms
but with a different ratio of hydrogen : oxygen
atoms.
• Most lipids are constructed from glycerol
molecules and fatty acid molecules joined
together.
• The smallest fat is called a triglyceride.
• Fatty acids are a major component of lipids. They
contain long chains of carbon atoms and are
described as either saturated or unsaturated.
• Saturated fatty acids are found in animal fats,
and they are solid at room temperature (butter,
lard).
• Unsaturated fatty acids are found in plant fats
and they are liquid at room temperature (oils).
• All fats are insoluble in water, but they do
dissolve in organic solvents such as alcohol, ether,
or chloroform.
Why do you need them?
Where can you find lipids?
• Foods rich in animal fats:
butter (margarine), milk,
cheese, egg yolk…
• Food rich in plant oils:
sunflower oil, maize oil,
nuts, olives …
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The functions consist of:
Fuel: they have twice the
energy of carbohydrates, they
are primary sources of energy.
Protection: fats protect
human and animals from falls
and bruising
Insulation: fat stored adipose
tissue is a heat insulator
Structural: phospholipids are
used to form all cell
membranes.
PROTEINS
• Examples of proteins are:
collagen in skin, ligaments and bone; keratin in
hair and nails; myosin in muscle; albumin in egg
white, all enzymes and antibodies.
• Proteins are constructed from amino acids of
which there are about 20 different kinds occurring
in nature. The amino acids are joined in chains to
form proteins.
• Proteins have a complicated overall structure, with
chains linked, folded or branched. This means that
there are unlimited variations.
• This huge variation is necessary because an
organisms requires thousands of different enzymes
(which are proteins) in order to maintain itself.
• The correct structure in enzymes is extremely
important. For example, the enormous amount of
information contained in a DNA molecule is
concerned with the instructions for joining amino
acids in the correct order to produce enzymes.
Where do you find proteins?
• Plants can synthesise their own amino acids from simple chemicals;
animals assemble the proteins and enzymes they need from the amino
acids in their diet.
• There are nine essential amino acids, that are not easily made by
animals and must be included in their diet. They are found in first class
proteins which come from animal sources (meat, fish, eggs)…
• There are also non-essential amino acids: they can be synthesised from
any protein including plant proteins. These are second class proteins.
• No single plant protein contains all of the essential amino acids, but a
mixture of plant proteins does.
Why do you need them?
Proteins function as:
• Metabolic regulators: almost all enzymes are proteins, every
chemical process in biology is directed and regulated by a
specific enzyme.
• Fuel: they are secondary sources of energy for cell
metabolism. They give up their energy only in case of
extreme starvation.
• Structural: they give strength and support, for example
collagen in skin, hair, nails, tendons.
• Movement: actin and myosin produce movement in muscles.
• Communication: many hormones are formed from proteins.
• Growth and repair: amino acids are needed for growth and
to maintain almost all tissues.
VITAMINS
• Vitamins are needed only in tiny amounts, but
they are essential for all living organisms.
• They are synthesised by all plants and are required
in the diet of all animals.
• They are named with letters and numbers.
• Vitamins A, D, E and K are fat-soluble, while the
B group vitamins and vitamin C are watersoluble.
Vitamin C
Vitamin D
• is found in citrus
fruits and green
vegetables.
• is found in fish, liver oil,
milk, eggs and diary
products.
• is needed for the
formation of
connective tissue.
• is needed for absorbing
calcium and phosphorus
from food, for hardening
bones, and for aiding
blood clotting.
MINERALS
• are found in:
soil, water and in almost all
foods material.
• are inorganic nutrients
obtained from mineral salts.
• are common metalcontaining compounds often
dissolved in water.
• tend to have two-part names
such as calcium phosphate.
their functions are:
• to form parts of
rigid structures
(e.g. calcium in
bones, and teeth)
• to form soft tissues
• to function in
cellular and body
fluids
LABORATORY EXPERIMENT:
QUALITATIVE TESTS FOR COMMON NUTRIENTS
• Various food samples can be tested in the
science laboratory in order to test for
substances (chemicals) in food, such as:
starch, fats, reducing sugars or proteins.
• You will do a test to identify whether there
is glucose or fructose in fruit.
• Objective: test for reducing sugar.
• Materials: samples of fruit, reducing sugar
solution, Benedict’s solution or Fehling’s solution I
and II, water, (DCPIP solution dichlorophenolindophenol -for the optional test).
• Resources: test tubes, heat source, microscope,
slide holders, dropping pipettes.
• Introduction: prepare a chart to show the
results and carry out a control experiment with
water rather than food to check and compare the
results.
Procedure:
• Place about 2 cm of food sample in a test tube and
add an equal amount of Benedict’s reagent or
Fehling’s solution I and II.
• Warm the test tube gently – do not boil.
• A brown or brick-red precipitate indicates
reducing sugar.
• A green colour indicates relatively little sugar.
• As a control experiment repeat with water and
compare.
Results and conclusion:
• Look for changes in colour and check the results.
• A brick red colour is positive for glucose or other
reducing sugars.
• Make notes of your results on a chart.
AN OPTIONAL TEST
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You can also test for the presence of vitamin C in
your food sample:
Add 2 cm. of DCPIP solution to a test tube.
Drip the food solution into the tube and observe.
Watch for a change from blue to pink and then to
colourless.
Repeat with water and compare as a control
experiment.