Organisms require nutrients from food for energy, growth, repair, and health. There are six main types of nutrients: carbohydrates, proteins, lipids, vitamins, minerals, and water. Carbohydrates, proteins, and lipids provide energy and are made up of smaller units called monosaccharides, amino acids, and fatty acids, respectively. These macronutrients are broken down into their smaller subunits before the body can use them. In contrast, water and minerals can be absorbed directly.

1. Nutrients
Biology Notes
GCE Study Buddy

2. Nutrients
●Organisms require food for:
○Providing energy for the vital activities of the body
○Synthesize new protoplasm for growth and repair of worn-
out parts of the body and for reproduction
○Maintain health and fight against diseases
●Nutrients are the substances in food that provide for
cell development, growth and repair.

3. Types of nutrients
Carbohydrates Organic Nutrients
Fats
Proteins
Vitamins
Dietary fibre
Water Inorganic Nutrients
Mineral Salts
There are 6 kinds of nutrients that are available in
food

4. Organic and Inorganic
Nutrients
●Organic nutrients:
○Carbohydrates
○Proteins
○Lipids, and
○Vitamins
●Organic Nutrients are compounds of carbon
●Inorganic Nutrients:
○Minerals
○Water
●Inorganic Nutrients do not contain the element carbon and
care called

5. Nutrients
●Foods containing carbohydrates, fats, and proteins are
usually too complex to be absorbed right away by the
body.
○They are broken down into simpler molecules before the
body can utilize them.
●In contrast, minerals and water can be absorbed
directly into your bloodstream
○They do not require digestion or breakdown.

6. Macromolecules
●Biological molecules are very large and hence called
macromolecules.
●Most macromolecules are polymers.
●Polymers are large molecules of many similar "units"
linked together. These individual units are called
monomers
●Macromolecules are made by the process termed
condensation
●Macromolecules are broken down by a process termed
hydrolysis

7. Carbohydrates
●Carbohydrates are the main sources of energy for
organisms.
●Carbohydrates forms structural components such as
cell walls. E.g., cellulose
●Carbohydrates are used as energy reserves in plants
and animals. E.g., starch and glycogen
●Carbohydrates contain carbon, hydrogen, and oxygen
atoms.
●They have a general formula of Cx(H2O)y. E.g., glucose
is (CH2O)6 which can be re-written as C6H12O6.

8. Functions of Carbohydrates
●main source of energy
●cellulose:
○fibrous material of Plant Cell Wall
○dietary fibre: stimulates Peristalsis
●excess carbohydrates
○stored as glycogen in liver & muscle
○stored as fats under skin

9. Carbohydrate types
●There are 3 classes of carbohydrates

10. Monosaccharides
●Are the simplest sugars
●ratio of H : O = 2 : 1
●all are reducing sugars
●all are sweet and soluble in water
●Can be used for ‘fuel’
●Can be converted into other organic molecules
●Can be combined to form disaccharides and polysaccharides
●Can be produced by photosynthetic organism from CO2, H2O
and sunlight.
●Serves as raw material for other organic molecules
●Monosaccharides can be made up of
○3-carbon (triose)
○5-carbon (pentose)
○6-carbon sugars (hexose)

11. Monosaccharides
●Common hexose monosaccharides
include
○Glucose (found in all animals)
○Galactose (present in milk as milk
sugar)
○Fructose (common in plants)
●All three monosaccharides have
exactly the same chemical formula
C6H12O6.
○The atoms are arranged differently
within the molecules.
○Hence, they have different chemical
and biological properties

12. Disaccharides
●A double sugar that consists of two monosaccharides
joined together through condensation reaction.
○Eg. sucrose consists of a unit of glucose and fructose
Table sugar, most prevalent
disaccharide, transport form
in plants
Present in milk
Used in brewing beer

13. Test for reducing sugars
(Benedict's Test)
1. Is there any color change in
tubes A and B?
Ans: Only the mixture in tube A
has a color change
2. What is the sequence of
color change?
Ans: The blue solution changes
first to green, then to yellow, and
eventually a brick-red precipitate
is produced

14. Polysaccharides
●Consist of polymers of a few
hundred or thousand of
monosaccharides.
●Have 2 important biological
functions:
○Energy storage
■starch and glycogen
■Cells can hydrolyse storage
polysaccharides into sugars
as needed.
○Structural support
■cellulose and chitin

15. Condensation reaction
A condensation reaction is a chemical reaction in which two
simple molecules are joined together to form a larger molecule
with the removal of one molecule of water.
H2O
water
+
+
C12H22O11
maltose (larger
molecule)
C6H12O6
glucose
(simple
molecule)
C6H12O6
glucose
(simple
molecule)

16. Hydrolysis reaction
Hydrolysis or a hydrolytic reaction is a reaction in which a water
molecule is needed to break up a complex molecule into smaller
molecules.
H2O
water
+
+
C12H22O11
maltose (double
sugar)
C6H12O6
glucose (single
sugar)
C6H12O6
glucose (single
sugar)
maltase
(enzyme)

17. Starch
●Glucose polymer that is a storage polysaccharides in
plants
○Stored as granules in plant cells.
○Amylose, the simplest from, is an unbranched polymer.
○Amylopectin is the branched polymer
○Most animals have digestive enzymes to hydrolyse starch.
○Major sources in the human diet are potato tubers and
grains (eg. wheat, corn, and rice)

18. Test for starch (Iodine Test)
1. What is the color change seen
in tube A?
Ans: The solution changes from
brown to blue-black
2. What is the purpose of setting
up tube B?
Ans: To act as a control

19. Hydrolysis of starch
part of a starch
molecule
maltose
molecules
glucose molecules
further bond-breaking by
maltase enzymes releases
glucose
maltas
e
maltas
e
maltas
e
maltas
e
amylas
e
amylas
e
amylas
e

20. Glycogen
●Glucose polymer that is a storage polysaccharide in
animals.
●Large glucose polymer that is more highly branched
than amylopectin.
●Stored in the muscle and liver of human and other
vertebrates.

21. Cellulose
●Linear unbranched polymer of glucose
●A major structural component of plant cell walls
●Differ from starch (also glucose polymer) in its
monomer linkages.
●Cellulose reinforce cell walls.
●Cellulose cannot be digested by most organisms,
including humans, because they lack an enzyme.
●Certain bacterial and fungi have the enzyme to digest
cellulose.

22. Cellulose

23. Proteins
●Polymers of amino acids are called polypeptides. A protein
consists of one or more polypeptides folded and coiled into
specific conformations.
●Very extensive in structure, each type has a unique 3D shape.
●Though vary in structure and functions, are commonly made of
only 20 amino acids monomers.
●cannot be stored
○excess proteins deaminated by liver
■to urea which will be excreted by the kidneys
■to carbohydrates (glycogen) which will be stored in the
liver

24. Functions of Proteins
Function Example
Structural support Silk of insects and spiders, collagen in
skin, keratin in hair and nails
Storage Albumin in egg white
Transport For making haemoglobin in blood
Signaling Chemical messenger
Movement Contractile proteins
Defence For making antibodies in blood
Catalyzing reactions To produce enzymes

25. Amino acids
●Amino acid is building block molecule of a protein.
●about 20 different types -
○essential and non-essential types
●Contains carbon, hydrogen, oxygen, and nitrogen
●Sulphur and phosphorus sometimes present
●Consists of
○Acidic group
○Amino group
○Side chain (variable R-group) specific to each amino acid.

26. Amino Acids

27. Polypeptide
●Polypeptide chains are polymers that are formed when
amino acid monomers are linked by peptide bonds.
○Peptide bonds are formed by a condensation reaction.
●Polypeptide chains range in length from a few
monomers to more than a thousand.

28. Protein structure and function
●Protein’s function depends on its specific 3-D shape.
●Protein shape is stabilized by many weak bonds.
●The specific 3-D shape of the protein is mainly held by
these weak bonds.
○Hydrogen bonds, which are easily broken by heat, acids
and alkalis
○The breaking of these cross-links causes the denaturation
of the protein
●The shape of the protein determines its function. For
example, haemoglobin.

29. Sickle-cell anaemia
●A single substitution of an amino acid is enough to
destabilize the protein structure that causes the sickle-cell
disease.
●The sickle-cells do not effectively transport oxygen because they
block circulation in small blood vessels.

30. Protein denaturation
●If a protein’s environment is
altered it may become
denatured and loses its
structure.
●Denaturation is a process
that alters a protein structure
and biological activity.
●Proteins can be denatured by:
○Excessive heat
○Chemical agents that disrupts
the chemical bonds
○Acids and bases
○Agitation

31. Digestion of proteins
●Proteins must be broken down
in animals before absorption.
○Protein molecules are too large
to pass through the plasma
membranes.
●Proteins are broken down to
amino acids in the human body
by the process known as
hydrolysis.
●The process of protein digestion
involves enzymes.
Hydrolysis of protein

32. Protein deficiency
●In human beings, the average adult needs 50 to 100g
of proteins a day
●The deficiency of proteins in the diet of children may
lead to a disease called kwashiorkor
○Swollen abdomens, skin cracks and becomes scaly

33. Test for proteins (Biuret Test)
1. What color changes seen in
tubes A and B?
Ans: Mixture in tube A changes
from blue to purple while mixture
in tube B remains blue without
any change

34. Lipids
●Oils, Fats, and Waxes Are Lipids Containing Only Carbon,
Hydrogen, and Oxygen
●A diverse group of substances that are insoluble in water.
●Important groups are fats, phospholipids and steroids
●Fats are macromolecules constructed from:
1.Glycerol
2.Fatty acid
●During formation of a fat, enzyme catalysed condensation
reactions
○Each glycerol is bonded to three fatty acids
○The resultant product is called a triglyceride.

35. Hydrolysis of fats
Fats can be broken down into simpler compounds by hydrolysis. This
involves the addition of water molecules (hydrolysis) and occurs readily
with an enzyme or a catalyst.
catalyst
glycerol three fatty acid
molecules
three water
molecules
fat molecule
+
+
H O
H - C - O - C - R
=
_
=
=
_
_
O
H - C - O - C -
R
H
O
H - C - O - C - R
_
H2O
H2O
H2O
H
H - C - OH
_
_
_
H - C - OH
H
H - C - OH
_
O
HO - C - R
=
=
=
O
HO - C - R
O
HO - C - R

36. Characteristics of fat
●Fats are insoluble in water.
●Fatty acids in a fat may all be the same or some (or all) may
differ.
●Fatty acids may vary in length.
●Fats may be saturated or unsaturated
●Saturated
○Usually a solid at room temperature
○Most animal fats: Bacon grease, lard and butter
○Fatty acid chains are straight
●Unsaturated
○Vegetable fats
○Do not cause heart diseases
○Have kinks in the fatty acid chains

37. Functions of fat
●As an efficient source and storage of energy
○1 g of fat stores twice as much energy as a g of polysaccharide.
●More compact fuel reservoir than carbohydrate. Animals
store more energy with less weight than plants which use
starch, a bulky form of energy storage.
●Cushions vital organs in mammals
●Insulates against heat loss
●Reduce water loss – glands in skin secrete oily substances
●As a solvent for fat-soluble vitamins and many other vital
hormones
●As constituent of protoplasm, especially in the protoplasmic
membranes

38. Phospholipids
●Are major constituents of cell membranes.
●At the cell surface, phospholipids form a bilayer held
together by hydrophobic interaction.
●Phospholipids in water will spontaneously form such a
bilayer.

39. Steroids
●Steroids include substances such as cholesterol and
hormones.
●Despites its ‘bad’ reputation cholesterol provides the
starting point for other necessary lipids such as
vitamine D and the hormones such as oestrogen and
testosterone.
●Cholesterol is a common component of animal cell
membrane.

40. Ethanol emulsion test for fats
1. In which test tube is an emulsion formed?
Ans: test tube A
2. What happens to the other tube?
Ans: The mixture separates into two layers because fats do
not dissolve in water.

41. Water
●Why is water is important to life?
○Water interacts with many other molecules.
○Water is an essential component of the protoplasm.
○Water makes up about 70% of the body mass.
○Every cell in the human body needs water.
■Many body’s processes, including chemical reactions take
place in water.
○Water makes up a large part of our blood and tissue fluid.
○Water is a component in digestive juices.

42. Functions of water
●Solvent: water dissolves many biological molecules
and substances
Functions Mode of action
Transport Main part of blood and body fluid
Medium for transport of nutrients
Reactions Solvent for chemical reaction
Needed for digestion
Lubrication Part of the fluid in muscular joint
Part of mucus in the alimentary canal
Homeostasis Evaporation of water, cools down the body
Prevents overheating

43. Vitamins
●Organic compounds nor built in a definite pattern like
carbohydrates, proteins, and fats
●no energy value
●Required in small quantities for normal health and
development
●Excessive of some vitamins may be harmful
●2 types
○Fat-soluble vitamins: can be stored in the fats of the body
(A, D, E, K_
○Water-soluble vitamins: cannot be stored in the body, and
have to be supplied in the daily diet (B, C)

44. Vitamin D
Vitamins Sources Functions Deficiency
D
(fat-soluble)
●Fish liver oils (eg.
cod and halibut)
●UV rays in sunlight
can convert a
natural substance
(ergosterol) in the
skin to vitamin D
●Promotes
absorption of
calcium and
phosphorus
compounds from
the intestines
●Enables the body to
use these
compounds in the
formation of teeth
and bone
●May result in
demineralization of
the bones with
multiple fractures
and widespread
calcification of
many soft tissues,
including the lungs
and kidneys
●formed in the skin from UV light
●helps to regulate calcium and phosphorus metabolism

45. Vitamin C
Vitamins Sources Functions Deficiency
C
Ascorbic acid
Note: easily
destroyed y
heat eg
cooking and
canning
Excess is
excreted by
body
●Richest sources are
fresh citrus fruits
(oranges, lemons),
other fruits (eg
papaya, guava,
tomatoes, bananas)
●Fresh green
vegetables
●Fruit juices such as
blackcurrant juice
and rose hip syrup
●Needed for the
formation of
intercellular
substances. Such
substances are
found in between
the cells and they
hold the cells
together
●Necessary for
maintaining healthy
epithelial cells
●Scurvy,
characterized by
swollen bleeding
gums and
loosening of the
teeth
●Haemorrhages or
internal bleeding in
the musces and
skin, poor healing
of wounds and
painful swollen
joints
●destroyed after prolonged cooking
●necessary for healing wounds

46. Detection of Vitamin C in lemon juice
using DCPIP
1. What color change has occurred?
Ans: the blue DCPIP decolourizes
2. What can you conclude?
Ans: Lemon juice contains vitamin C
which decolourizes blue DCPIP

47. Other vitamins
●Vitamin A
○Needed for
■formation of a light-sensitive pigment (visual purple) in
the retina to maintain dim light vision
■maintaining healthy epithelial tissues
○Rich sources include dairy products, fish liver oils, and
green leafy vegetables
○destroyed at high temperature
●Vitamin B complex
○Several are important coenzymes in cellular respiration
○Deficiency diseases: beri-beri, pellagra, pernicious
anaemia
○Sources: yeast, liver and bran

48. Vitamin deficiencies
Vitamin Sources Deficiency
A egg yolk, cheese,
milk, carrot, green
vegetables
night blindness
C fresh fruits and
green vegetables
scurvy
D cod liver oil, egg
yolk
rickets

49. Minerals
●Inorganic salts which do not provide energy but are
indispensable to bodily functions
●needed in small amounts
●include Ca, S, K, Na, Mg, Fe, I
●functions
○necessary for construction of certain tissues
○essential for healthy growth
○regulate body metabolism
●We obtain minerals from other animals or from plants
●Mineral elements required in large amounts include
calcium, phosphorus, sodium, potassium, and iron

50. Calcium
Mineral Sources Requirements Functions
Calcium
Severe
deficiency
results in
crickets
●Milk, cheese,
eggs
●Small fish
eaten with their
bones
●Cereals, soya
beans, dark
green
vegetables
such as
spinach and
watercress
●About 1g a day in
growing children
●Adults need
slightly less –
more is required
during pregnancy
and lactation
●Required for the
building of bones
and teeth
●Needed for the
normal functioning
of the muscles
●Necessary for the
clotting of blood to
prevent excessive
loss of blood

51. Iron
Mineral Sources Requirements Functions
Iron
Deficiency
results in
lowering of the
haemoglobin
level in the
blood -
anaemia
●Liver, red
meat, egg
yolk
●Bread, flour,
dark green
vegetables
●Very little is
required –
about 0.02g a
day
●Pregnant
women
required more
●Iron is a structural
component of the following
and so is essential for their
formation
●Haemoglobin: the red
coloured pigment that
transports oxygen in the
body
●Myoglobin: a protein in
muscle cells which stores
oxygen for use in muscular
contraction
●Certain enzymes involved in
cellular respiration

52. Trace elements and
Dietary Fibre
●Trace elements
○Minerals needed in minute quantities
○Eg iodine, zinc, manganese
●Dietary fibre
○Indigestible fibrous materials eg cellulose
○Prevents constipation
○Good sources are fresh fruits and vegetables, bran, cereals,
and wholemeal bread
○Important because it provides bulk to the intestinal contents and
helps peristalsis
○Peristalsis is a series of wavelike, muscular movements of the
walls of the digestive tract
■Such movements enable food to be mixed with the digestive
juices
■Also cause food to move along the digestive canal

53. Balanced diet
●A balanced diet contains the right amount of
carbohydrates, fats, proteins, vitamins, minerals, water,
and fibre to meet the daily requirements of the body
●The amount of energy needed to carry on vital life
processes of the body when it is in complete rest is
known as basal metabolism
○Affected by climate, body size, age, sex, health,
occupation of an individual

54. Energy value of food
●Different organic food substances have different energy
values.
●Energy value of
○carbohydrates is 16kJ/g
○proteins is 17kJ/g
○fats is 38kJ/g

55. Measure the energy value of food
1. Explain why the energy
value of the peanut is lower
than those from standard
tables
Ans: Because there is a number
of inaccuracies associated with
this method due to incomplete
combustion and heat loss

56. Basal Metabolic Rate (BMR)
●minimum amount of energy needed by an individual lying
awake in bed to maintain breathing, body temperature and
heartbeat
●varies from person to person
●daily energy requirement > basal metabolic rate

57. Summary
Carbohydrates
may be
Functions of water In
animals, water: • is a
medium for chemical
reactions to occur; •
transports digested
food products,
excretory products,
and hormones from
one part of the body to
another; • is an
essential part of
protoplasm, lubricants,
digestive juices and
blood; • is essential for
hydrolysis; and • helps
to control body
temperature.
Monosaccharides
(single sugars), e.g.
glucose, fructose
and galactose
In plants, water: • is essential for photosy
is needed to keep plant cells turgid; • tran
mineral salts from the roots to the leaves
transports food substances from the leav
other parts of the plants.
Water
Fats
Organic compounds
made up of carbon,
hydrogen and
oxygen but they
contain much less
oxygen in proportion
to hydrogen.
Organic compounds made up of carbon,
hydrogen and oxygen in a ratio of 1 : 2 : 1.
Organic compounds made up
of carbon, hydrogen, oxygen
and nitrogen. Sulphur may
also be present.
Inorganic nutrient. Water
does not contain carbon.
Protein
s
Disaccharides
(double sugars), e.g.
maltose, lactose and
sucrose
Polysaccharides
(complex
carbohydrates)
made up of many
monosaccharides
e.g.
Starch
Glycogen
Cellulose • forms the cell walls in plants; and • cannot be digested by
mammals, but is used as fibre in their diet.
Identification
Test for
reducing
sugars: A
reducing sugar
gives a brick-red
precipitate when
boiled with
Benedict’s
solution.
Sucrose is a
non-reducing
sugar.
• serves as the main form of storage for carbohydrates in
green plants; and • gives a blue-black colour with iodine
(test for starch).
• serves as the main form of storage for carbohydrates in
animals and fungi.
Basic units Fats
are hydrolysed to
form fatty acids
and glycerol.
Identification Test
for fats: A cloudy
white emulsion is
formed in the
ethanol emulsion
test.
Basic units Proteins
consist of amino acids
linked together by peptide
bonds.
Identification Test for
proteins: Proteins give a
violet colouration with
Biuret reagent.
amino acids
polypeptide
s
proteins