Organisation of Living Organisms: 3 Types | Biology

The following points highlight the three main types of organisation of living organisms. The types are: 1. Molecular or Protoplasmic Level of Organisation 2. Individual Level of Organisation 3. Higher Level of Organisation.  

Type # 1. Molecular or Protoplasmic Level of Organisation:

All the living organisms have cellular nature and may be unicellular or multicellular. A cell is a mass of protoplasm bounded by a cell membrane/cell wall. Protoplasm is formed of a number of complex organic macro biomolecules like proteins, polysaccharides, fats, etc.

These polymers are formed of simple organic compounds like amino acids, monosugars, fatty acids, etc. interlinked by specific bonds e.g. peptide bonds between the amino acids. Each simple organic compound is formed of inorganic compounds e.g. CO₂ and H₂O react during photosynthesis to form glucose in the chloroplasts of the plants. Each inorganic compound is formed of specific elements.

So molecular level of organisation has following categories:

Atoms →Molecules → Inorganic compounds → Simple organic compound → Complex organic compound → Protoplasm → Cell

Molecular organisation is found in one-celled protozoans e.g. Amoeba, Paramecium, etc., which show the division of labour at the level of cell-organelles.

Type # 2. Individual Level of Organisation (Biological Hierarchy):

In multicellular organisms, division of labour is at the level of tissue or organ level. In such organisms though each cell type is specialized for a specific function but no cell can show independent existence and the cells show interdependence. In coelenterates (e.g., Hydra, Obelia etc.), similar cells coordinate to perform a specific function and form the tissue. In them, there are four types of tissues and division of labour is at the tissue level. This is called tissue organisation.

But from flatworms (e.g., Tapeworms) to mammals (e.g., human beings), different tissues coordinate to perform specific function to form organs like stomach (for storage and initiation of digestion of food), heart (for pumping the blood), lungs (for respiration), kidneys (for excretion), etc.

So in them, division of labour is at the organ level. But the organs do not show independent existence but coordinate to form systems. Each system is specialized for a specific function. These systems coordinate to form an organism. This is called organ- system organisation.

So a multicellular organism with organ-system organisation with following categories:

Cells → Tissues → Organs → Organ → systems → Organism

Type # 3. Higher Level of Organisation (Ecological Hierarchy):

Ecological hierarchy includes a graded series of ecological categories.

Categories of ecological hierarchy (Fig. 13.2):

Ecological hierarchy involves the following catego­ries:

(a) Organism.

(b) Population.

(c) Species.

(d) Biotic community.

(e) Ecosystem.

(f) Biome.

(g) Biosphere.

(a) Organism:

1. It is the smallest level of ecological hierarchy.

2. It is most distinct and easily observable unit.

3. It performs all the life processes independently of those going on in other living organisms.

4. It always has cellular nature and may be acellular or multicellular.

5. It is a quantitative unit and can be counted or measured.

6. The parts of the organism cannot exist independently of one another.

7. Organisms cannot live in isolation of one an-‘ other. It shows interdependence with other biotic factors and abiotic factors of the environment. It derives matter and energy from the environment and expels wastes out of it for its survival.

8. An organism has the ability to grow, repair and regenerate, self-regulate, self-perpetuate and auto­nomous movements.

9. New organisms are produced from the pre-existing organisms by the process of reproduction which may be vegetative, asexual or sexual. This ensures the ‘continuity of life’.

10. Organisms resemble their parents in a number of characters. It is so because they can transmit their characters to their offsprings.

11. An organism is fully adapted to its environment.

12. An organism has a definite life span which involves definite series of stages like birth/hatching, growth, maturity, ageing and death.

(b) Population:

Population is defined as the total number of individuals of a species in a specific geographical area, while similar populations of a species occupying different geographical areas are called sister-populations of a species e.g. all the frogs (Rana tigrina) and water hyacinth (Eichhornia—an aquatic weed) plants found in a pond form the populations of frog and water hyacinth respectively of that pond. The frogs (Rana tigrina) found in different ponds form the local populations and are sister – populations of one another.

In a geographical area, the population is further divisible into sub-groups called demes. The individuals of a population are capable of interbreeding among themselves. The chances of this sexual communication are more between the members of same deme than between the members of different demes of that population which are further reduced between the members of sister-populations. Due to this mating ability, there is free flow of genes in a species.

Various characteristics of a population are:

Population density, natality (birth) rate, mortality (death) rate, age distribution, biotic potential, dispersion and growth form.

(c) Species:

The sum of all the populations of same kind of organisms all over the world is called species. It is basic unit of classification and the population is subordinate to species. Only the species has a real existence, other units of classification (e.g. Genus, Family, Order, Class, Phylum and Kingdom) are man-made artificial groups.

(d) Biotic Community:

The assemblage of all the populations of different species that function as an integrative unit through co-evolved metabolic transformations in a specific area is called biotic community e.g. a forest. So a biotic community is a higher ecological category than population.

It is formed of 3 types of communities:

1. Animal Community:

It is formed of all the animal populations of that area.

2. Plant Community:

It is formed of all the plant populations (herbs, shrubs, trees, climbers, etc.) of that area.

3. Microbial Community:

It is formed of all the populations of microbes (bacteria and fungi) of that area.

In a biotic community, the different populations show interactions and interdependence. It is now called biocoenosis.

(e) Ecosystem:

The sum of the biotic (living) and abiotic (non­living) components of a particular geographical area, collectively called ecosystem. It is so as the living organisms are not independent units but depend upon one another and also draw matter and energy from their non-living environment. It is now called biogeocoenosis.

It is a stable and self-regulating system e.g. pond ecosystem, desert ecosystem etc. Abiotic substances of an ecosystem include basic inorganic and organic compounds, and climatic factors of that area, while biotic organisms of an ecosystem include the producers (e.g. plants), macro-consumers (e.g. animals) and micro- consumers or saprotrophs (e.g. bacteria and fungi). In an ecosystem, two types of components show interactions and interdependence. These ecosystems may be natural (pond, lake, forest, etc.) or artificial (a flower pot, an aquarium, space ship, etc.)

A landscape is a unit of land with a natural boundary having a mosaic of patches. These patches usually represent different ecosystems.

(f) Biome:

It is a large regional or sub-continental biosystem characterized by a major vegetation type or other distinct landscape characters e.g. tropical deciduous forest, tundra biome etc.

On global scale, all the earth’s terrestrial biomes and aquatic systems constitute the biosphere.

(g) Biosphere:

Biosphere, also called ecosphere or giant ecosystem, is the largest and nearly self-sufficient biological system.

It is formed of all the ecosystems of the world. It is also called “life-supporting zone” of the earth because in the biosphere, living organisms interact with one another and also with the physical environment to maintain a steady-state (self-adjusting equilibrium) system. It is divisible into three components—hydrosphere, atmosphere and lithosphere.