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The Origin Of Life
- There is no knowledge of life except on earth
- Man has tried to learn when, how and where life originated
- A number of theories have been proposed to account for the
origin of life
Theories of Origin of Life
1
...
Biogenesis
- process of reproduction or biogenesis explains that new life
comes only from a pre-existing life
- it affirms the genetic theory of the origin of life
3
...
Naturalistic or physico-chemical theory
- states that when the conditions of the early earth became
suitable to life, organic molecules like amino acids aggregated
- these organic molecules were derived from the atmosphere
- in the course of evolution protoplasmic particles developed
and gave rise to living organisms
- this concept on the origin of life gained support from the
recent studies on viruses
- several viruses crystallize like inorganic substances, but they
behave like living organisms by reproducing
5
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Organization
- a living organism, be it plant or animal is composed of one
or several cell
- the cell is defined as the fundamental unit of structure and
function of a living organism
- it is capable of independent existence and exhibits all the
characteristics of life
- in case of multicellular organisms, the cells combine
together and act in a coordinated manner to perform
processes essential to life

2
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Movement
- all living organisms have the ability to move
- this is made possible by the streaming of the protoplasmic
mass in cells called cyclosis
- movement of animals is more obvious than that of plants
- the animal body moves maybe as a result of muscular
contraction, of the beating of the cilia or flagella or of the
amoeboid motion of the cellular protoplasm
- movement characterized by change in position is locomotion
4
...
Reproduction
- each living organism is capable of duplicating itself in kind
- this is done by using materials within the body to insure
survival or perpetuation of the species
6
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Anabolism – which forms more complex substances from
simpler ones resulting in the storage of energy and
production of new cellular materials
2
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Adaptability
- ability of a living organism to adapt or adjust itself to its
environment in order to survive

Major Differences between Plants and Animals

PLANTS
ANIMALS
1
...
Extent of Growth
Indeterminate
Determinate
3
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Nervous System
Absent
Present in most
Mobility
Immobile
Mobile
Primary Food
Starch and Unsaturated Oil
Glycogen and Saturated Fats
Waste products
Oxygen from Photosynthesis
Carbon Dioxide and
and Carbon Dioxide from
Nitrogenous Waste
metabolism
PROTOPLASM
- living substance of the cell
- it possesses properties which include physical, chemical and
physiological properties
Properties of Protoplasm
A
...
Heterogeneous
2
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Translucent, colorless, slimy, viscous fluid
4
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Exhibits brownian movement
6
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Chemical properties
1
...
Elements may form compounds which may be classified as
inorganic or organic
Inorganic Compounds
Which are found in living and non-living bodies are more
numerous than the organic parts of the organisms
...
Water
2
...
Gases

WATER
Water makes up about 80-90% of the protoplasm
It consists of:
A
...
Bound water
- 4-5% of the cellular water, tied to polypeptide chains of
protein molecules by hydrogen bonds
Importance of Water: Physical Properties
1
...
capacity to absorb heat – due to its high specific heat it can
prevent drastic temperature changes efficiently
3
...
its function as an indispensable medium in chemical
reactions
5
...
its function as the agent in absorbing, dispensing and
transporting of substances
Physiological Properties of Water
1
...
furnishes medium for some vital processes
3
...
regulates body temperature
5
...
serves as lubricant for movable surfaces
7
...
considered as inorganic buffers
2
...
Calcium ions – found in circulating blood, in parts of the
cells, in bones and calcified cartilages, combined with
phosphates and carbonates
2
...
Chloride ions
- circulate in the blood and intercellular fluids as free ions;
found in small quantities in the cells and component of gastric
juices
...
Phosphorus ions
- present in high concentration within the cell protoplasm as
in muscle and red blood cells
- important in nerve conduction and muscle contraction
5
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Sulphur
- in the organic form found in amino acids like cysteine,
cystine, methionine where it is bound to carbon
- present in the amino acid linkages in protein
- essential constituents of many enzymes and co-enzymes
GASES
Is a state of matter where the molecules are widely dispersed
in a highly disordered fashion
Two gasses present in the protoplasm:
1
...
Carbon dioxide – waste product of oxidation
Organic Compounds
1
...
Lipids
3
...
Nucleic acid
CARBOHYDRATES
Organic compounds containing carbon, hydrogen and oxygen
The hydrogen and oxygen are present in approximately the
ratio of 2:1
It includes simple sugars, starches, gums, celluloses and resins
It is the main source of energy in the body

Classification of Carbohydrates
1
...
Glucose - blood sugar or dextrose
B
...
Galactose – milk sugar
2
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Lactose – milk sugar: glucose + galactose
B
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Sucrose: table sugar: glucose + fructose
3
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Starch energy storage in plants
B
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Cellulose – structural material in plants
LIPIDS
- Fat soluble compounds contain carbon, hydrogen and
oxygen
- Make up about 3% of the protoplasm
- Greasy texture or oily consistency
- Insoluble in water
- Soluble in organic acids such as ether, benzene or
chloroform
- Some are liquid or fluid at ordinary temperature but others
are solid
- Few are firm waxes
- It furnish fuel of high energy fuel

CLASSIFICATION OF LIPIDS
1
...
Complex lipids
- simple lipids plus other substances
Examples: phospholipids and cerebrosides
A
...
Glycolipids – with carbohydrates
C
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Steroids
- solid alcohols which are not chemically related to fat but
they are included among lipids because they exhibit-fat like
properties
Examples: sex hormones, adreno-cortical hormones, vit
...
Triglycerides
- fatty acids (3 hydrocarbon chains) when bounded through
their glycerol become neutral fats
- that provides insulation and energy reserves
2
...
Steroid – composed of four interlocking rings of carbon
atoms
PROTEINS
- 15% of the protoplasm
- Most abundant constituent of the protoplasm
- C,H,O,N with sulfur, phosphorus and iodine
- Colloidal in nature
- Components of amino acids
- Chief structural pattern of protoplasm form enzymes,
hormones, chromosomes and cell components
TYPES OF PROTEINS
1
...
Keratin – principal components of hair
b
...
Globular proteins – the polypeptides are so tightly folded
into spherical or globular shapes, such as hemoglobin, the
component of vertebrate blood used to transport oxygen

3
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Nucleoprotein – with nucleic acids e
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histones
b
...
g
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Lipoprotein – with fatty acids e
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serum ad brain tissue
d
...
g
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Enzymes as Proteins
- most of the proteins in the body cells are enzymes
- catalysts that control the rates of many chemical reactions
such as respiration, digestion, muscle contraction, nerve
conduction and other metabolic processes
SIX MAIN GENERAL GROUPS ACCORDING TO CHEMICAL
REACTIONS THEY PERFORM
1
...
Transferases – transfer of groups
3
...
Lyases – addition or removal of a group to and form double
bonds
5
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Ligases or synthetase – condense 2 molecules by splitting a
phosphate bond
Factors that Influenced or Inhibited the Enzymes
1
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Temperature
- increase rate of collision with substrate thus speed up
reaction
- optimum temperature is generally the body temperature
3
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relative concentration of the enzymes and substrate
Nucleic Acids
- In DNA, purines are adenine and guanine; pyrimidines are
cytosine and thymine
- In RNA, thymine is replaced by uracil



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