Characteristics of Life
Learning Outcomes
At the end of this sub section students should be able to:
1.
Present an outline of the diversity of living things
2.
Describe the requirements in a search for a definition of Life
3.
List the common features & behaviours identified as living.
4.
Define the term: metabolism.
5.
Define the expression: continuity of life.
6.
Define the term: life.
7.
Define and identify of the "characteristics of life", through fundamental
principles and interactions of organisation, nutrition, excretion, response and
reproduction.
1.2.1 A search for a definition of Life

All organisms have many features or characteristics in common.
Variety of life
All living things are divided into two main groups
Plants
Animals
The Diversity of Animals
•
There are more than a million different species of animals on earth
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•
Scientists have organised all these animals according to how they are related
•
The animal kingdom is divided into groups called classes for example
Reptiles Birds Mammals

These all have similar features which distinguish them from animals in other
classes
The Diversity of Animals
1. Vertebrates
Fish
Reptiles
Birds
2. Invertebrates
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Worms
Insects
Arachnids
The Diversity of Plants
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Algae
Ferns
Moss
Conifers
Flowering Plants
Common Characteristics of Living things:
•
are highly organised
•
are composed of tiny units called cells
•
grow
•
excrete
•
move
•
react to their surroundings
•
feed
•
reproduce
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Metabolism

Metabolism is the chemical reactions that occur in the cells of living organisms
These reactions are responsible for the process of:
•
Growth
•
Repair
•
Responsiveness
•
Reproduction
All living things metabolise.
There are 2 types of Metabolic Reactions.
Anabolic Reactions
These reactions use energy to join small molecules together to form larger molecules
Example: Photosynthesis
Catabolic Reactions
These reactions use energy to break down large molecules into smaller ones
Example: Respiration
Continuity of Life




Continuity of life is the ability of an organism to exist from generation to the next
You need reproduction and heredity to achieve continuity.
Genes are hereditary factors that are passed on from one generation to the next
during reproduction.
All living things reproduce.
1.2.2 Definition of Life



Is something that all living things have.
It is very difficult to quantify.
It involves the interaction of the characteristics of life.
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1.2.3 Characteristics of Life
How do we know something is alive?
•
It has organization – cells, tissues, organs, etc.
•
It uses energy
•
Grows and develops
•
Excretes
•
Reproduces
•
Responds to the environment
•
Adapts to the environment
“Characteristics of life”: (OGNERR) organisation,
growth, nutrition, excretion, response, reproduction
1. Organisation
 Unicellular or multicellular
 Specialized structures
 Cell is the basic unit of
structure and function
 If cell structure is damaged
its function is also affected.
Level of organisation
• Cell
• Tissue
• Organ
• Organ system
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• Organism
• Population
• Community
• Ecosystem
• Biosphere
Energy
• All energy for living things can be traced back to the sun (primary source of
energy)
• Organisms use light energy to see (vision), to make food (photosynthesis), for
warmth (respiration)
• Plants use sunlight to make food (producers)
• Other organisms eat the plants to get energy (consumers)
2. Growth
 Growth – increase in size
 Development – change in form or shape
 Amount of growth varies in different organisms
 Nutrition maintains the organisation and growth of living organisms 7
3. Nutrition
 This is the process involved in the making and receiving or the absorption
and utilisation of food (energy and materials) from the environment.
Sources of nutrition:
In Animals: feed on other organisms
In Plants: make food by photosynthesis and absorbing chemicals from the
environment
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Energy flow: Sun  Plants Animals
4. Excretion
 Excretion - is the elimination of the waste products of metabolism from a cell,
tissue or organ
 All living things must get rid of waste material – if it was allowed to
accumulate it would become toxic to the organism
 A balance must be maintained between their internal and external
environments
Methods of excretion
 Various organised structures involved
 In Animals: the urinary system, skin, lungs
 In Plants: the stomata
5. Response & Adaption
 The ability to detect and react to stimuli
Methods of response
• In Animals: organised structures respond to light, sound, touch, etc.
• In Plants: growth towards or away from a stimulus e.g. light, water, fertilisers, etc.
6. Reproduction
• Life comes from life.
• Reproduction is the ability of an organism to produce new individuals of its own
kind and pass on genetic information to the next generation.
• Necessary for the survival of the species
• Offspring can be the same as or different from parent(s)
Methods of reproduction
• Asexual: e.g. in bacteria and protista – binary fission (simple division in two) –
mitosis
• Sexual: e.g. in plants and animals – involves two parents and the production of
male and female gametes
Summary:
• One characteristic is not enough to qualify something as being alive.
• Life involves an interaction between metabolism and continuity
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• Metabolism requires an interaction of organisation, nutrition, excretion and
behaviour
• Continuity requires organisation, nutrition, behaviour and reproduction
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