Characteristics of Living Organisms
In order to survive, all living organisms, whether simple like bacteria or
complex like humans, must carry out certain essential life processes. These
characteristics distinguish living organisms from non-living things
1. Order and organization
2. Metabolism – Anabolic + catabolic
3. Growth and development
4. Irritability and coordination
5. Adaptation – Structural, physiological, behavioral
6. Reproduction
7. Heredity and evolution.
1. Order and Organization
•
•
•
All living organisms show a highly organized structure, from the
molecular level up to the biosphere.
Each level is built upon simpler units organized in a specific pattern.
Example: Structure of the human eye or a plant leaf — specialized design
ensures efficiency in function.
Human Eye
•
•
•
The eye is made of many small parts: lens, cornea, retina, etc.
Each part has a special shape and job.
Together, they help us see clearly and respond to light.
1
2. Metabolism
•
•
•
Metabolism is the sum of all chemical reactions in a living organism.
It includes:
o Anabolism – building up molecules (e.g., protein synthesis)
o Catabolism – breaking down molecules (e.g., digestion)
These reactions release or use energy, allowing life processes to occur.
3. Growth and Development
•
•
All organisms start life as a single cell.
Growth: Irreversible increase in dry mass or size.
2
It is called "irreversible" because it cannot be reversed - once something
grows, it doesn't shrink back to its original small size (unless it dies or is damaged).
"Dry mass" means the weight of the organism without water (only the solid
parts like cells, tissues, etc.).
So, growth is not just about getting heavier because of water. It’s about adding
more living material (like proteins, cells, etc.).
•
•
Development: All the changes (structural, functional, behavioral) that occur
during an organism's life.
Example: A seed growing into a plant, a baby growing into an adult.
4. Irritability and Coordination
•
•
•
Irritability: Ability to sense and respond to stimuli (changes) in the internal
or external environment.
Coordination: Organisms work together using systems (like nervous,
muscular, and hormonal systems) to respond efficiently.
Example: Moving your hand away from a hot surface.
5. Adaptation
•
•
•
Adaptation is a special feature in structure, behavior, or physiology that
increases an organism’s chance of survival.
These features are evolutionarily developed.
Examples:
o Sunken stomata in xerophytes to reduce water loss.
o Viviparity (live birth) in mangroves for survival in salty soil. (Seeds
germinate while still attached to the parent plant)
3
o
Splayed feet in camels for walking on sand.
6. Reproduction
•
•
•
The process of producing new individuals (offspring).
Ensures the continuation of the species.
Can be:
o Asexual (e.g., binary fission)
o Sexual (involving gametes)
7. Heredity and Evolution
•
•
Living organisms pass on genetic information (genes) to their offspring.
Genes determine physical, physiological, and behavioral traits.
Physical trait – A gene decides eye color.
Physiological trait – A gene controls insulin production to regulate blood
sugar.
4
Behavioral trait – A gene can affect food-searching behavior in animals.
•
•
Over time, genetic changes (mutations, natural selection) lead to evolution
— the development of new species.
Example: Evolution of antibiotic resistance in bacteria.
Important Note:
•
•
Some non-living things (e.g., crystals grow, waves move) may show one or
two of these features.
But only living organisms show all these characteristics at once or during
some point in their life.
1. Which of the following best describes order and organization in living
organisms?
A. Random arrangement of cells
B. Highly organized structure from molecules to the biosphere
C. Only organs are organized, not cells
D. Organization happens only in humans
E. Structure is not important for function
2. Metabolism includes:
A. Only breaking down molecules
B. Only building up molecules
C. Both anabolism (building) and catabolism (breaking)
D. Only chemical reactions outside the cell
E. Only energy release without chemical reactions
3. Growth in organisms is considered irreversible because:
5
A. Organisms can shrink back to original size
B. It includes increase in water only
C. Dry mass and living material increase permanently
D. Growth is always temporary
E. Only cells increase in water content
4. Development in living organisms refers to:
A. Increase in size only
B. All structural, functional, and behavioral changes during life
C. Only behavioral changes
D. Only reproduction
E. Only increase in dry mass
5. Irritability is defined as:
A. Ability to grow rapidly
B. Ability to reproduce sexually
C. Ability to sense and respond to stimuli
D. Ability to evolve
E. Ability to digest food
6. Coordination in living organisms involves:
A. Random movement of body parts
B. Working together of systems like nervous, muscular, and hormonal
C. Only chemical reactions in cells
D. Only structural changes
E. Only adaptation
7. Which of the following is an example of adaptation?
6
A. A baby growing into an adult
B. Sunken stomata in xerophytes to reduce water loss
C. Formation of crystals
D. Movement of waves
E. Increase in dry mass
8. Reproduction is important because it:
A. Helps organisms grow bigger
B. Ensures continuation of the species
C. Allows cells to move
D. Changes behavior of animals
E. Maintains surface tension in water
9. Heredity involves:
A. Passing genetic information to offspring
B. Growth of crystals
C. Adaptation of plants to sunlight
D. Formation of water molecules
E. Only behavioral traits
10. Evolution occurs because:
A. Non-living things grow
B. Living organisms can change traits over generations through genetic changes
C. Cells shrink and die
D. Water evaporates from the body
E. Organisms move randomly
7
Hierarchical Levels of Organization of Living Things
1. Molecules – Smallest chemical components of life (e.g., DNA, proteins).
2. Organelles – Structures inside cells made of molecules (e.g., mitochondria,
nucleus).
3. Cells – Basic unit of life; some organisms are unicellular (e.g., Amoeba),
others multicellular (e.g., humans).
4. Tissues – Group of similar cells performing a function (e.g., muscle tissue,
xylem).
5. Organs – Structures made of different tissues working together (e.g., heart,
leaf).
6. Organ Systems – Groups of organs performing major functions (e.g.,
digestive system, circulatory system).
7. Organisms – An individual living thing (e.g., human, dog, tree).
8. Populations – Group of the same species living in an area (e.g., a herd of
elephants).
9. Communities – Different populations living together (e.g., plants, animals,
and microbes in a forest).
10.Ecosystems – Community plus non-living environment (e.g., forest
ecosystem, pond ecosystem).
11.Biosphere – All ecosystems together; the part of Earth that supports life.
3URKI[RKY
5XMGTKRRKY
8