Levels of Organization of Living Things

The study of different levels of organization of animate or living things helps us gain insights into complexities of their structure and functioning. Environmentalists find information and devise ways to preserve our fragile ecosystem through knowledge of these levels. Let us try to understand what are the levels of organization in living things.

Life on Earth
The life present on earth is complex and varied in its form. Living beings have evolved from their single-celled or unicellular forms into complex and giant multicellular bodies. In the process of development, their body systems and mechanisms have become specialized in nature. Thus, in the course of evolution, different levels were formed. Let us understand more about these levels of organization of living things. The article on classification of living things throws light on the subject and allows a better understanding.

Levels of Organization of Living Things
There are in all, five levels of organization of living things. These levels in sequence are the cells, tissues, organs, organ systems and organisms.

Cell: The cell is considered as basic unit of life. In other words, it is also known as the building block of life. A cell is bound by cell membrane and possesses a nucleus which acts as the brain of cell. Cytoplasm which surrounds the nucleus, contains cell organelles like mitochondria, ribosomes, vacuole, endoplasmic reticulum, chloroplasts, peroxisomes and ventricles. The average number of cells in a human body is 100 trillion. Cells are known to bring about conversion of nutrients into energy, reproduce (cell division) as the need arises and carry out specialized functions. Basically, cells are of 2 types, i.e. prokaryotic and eukaryotic. The prokaryotic cells with a smaller size and simpler form lack the nucleus and many other cell organelles found in eukaryotic cells. The eukaryotic cells are more specialized in structure than the prokaryotic cells. Moreover, they are greater in size (by almost 15 times) than the prokaryotic cells.

Tissue: The tissues are a collection of cells which perform specialized functions. Cells which form a tissue need not be identical however, should have the same origin. Different types of tissues which together form organs are the nervous, muscle, connective and epithelial tissues. Connective tissues are fibrous in nature and they are made up of cells separated by extracellular matrix. Muscle tissues, the active contractile tissues of our body are useful in producing force and motion. Skeletal, cardiac and smooth muscles are the three types of muscles. Nervous tissues form organs like brain, spinal cord, etc. Epithelial tissues cover the surface of body organs.

Organ: An organ is the next level in the organization of living things. It performs certain functions with the help of different tissues. The different organs of animals include lungs, brain, liver, etc. Roots, stem and leaves, etc. are different organs of plants. Organs can be classified on the basis of the functions they perform. For example, in case of animals, the tongue, ears, eyes, skin and nose are the sensory organs. Flowers and seeds are the reproductive organs in plants. Organs are formed of tissues which serve a common function. There are two types of tissues which form an organ: the main and sporadic tissues. For example, in the heart, myocardium is the main tissue while blood, nerves and connective tissues form the sporadic ones.

Organ System:: The organ systems are complex mechanisms which carry out important functions of the body; examples are the circulatory system in animals and vascular system in plants. Organ systems of an organism are interdependent, i.e. they take each others' help to carry out various functions of the body. For example, the digestive system which carries out the process of digestion is formed of salivary glands, stomach, esophagus, gallbladder, liver, intestines, pancreas, rectum and anus.

Organism: Amongst the different levels of organization of living things, this one is the highest. An organism could either be unicellular or multicellular. Organisms that are closely related can be grouped together under a single species.

These are the basic, 5 levels of organization of living beings. However, you can go ahead and add more levels like population, community, ecosystem, biome and biosphere. It is necessary to note that the higher we move, it becomes difficult to clearly define the levels of organizations; which means they are not as clearly defined as cells, tissues, organs, etc. For example, the ecosystem though is placed one level above community, the former is not a group of communities. Roughly defined, it is an environment where organisms of different populations live together and evolve. So, let us now delve into details of these levels.

Population: It is the term used in reference with a group of organisms which belong to the same species. Organisms which belong to the same population undergo interbreeding and share food and space.

Community: Two or more populations together constitute a community. A community is characterized by interactions taking place between its constituent populations. There are many different ways in which populations belonging to different species interact with each other. The different ways are competition, parasitism, predation, commensalism and mutualism.

Ecosystem: As we move up the ladder of levels of organizations of living things, the complications tend to increase. For instance, the term ecosystem is defined as an area or environment where a community thrives and flourishes. An ecosystem is however, not the same as community. In fact, it is a greater entity that provides space for a community.

Biome: A biome is an entity very much similar to ecosystem. Definition of biome is made in terms of condition (and not just space) suited to a group of communities (plants, animals, microbes, etc.). Classification of biomes of earth is carried out on the basis of condition/environment in which the constituent organisms live. Structure of plants is amongst the important criteria used for classifying biomes. Structural differences place the plants into groups like shrubs, trees, grasses, etc.

Biosphere: After all these complicated and bit confusing descriptions of terms like biome, ecosystem, community, etc. you would find the definition of biosphere quite easy to understand. Biosphere is simply the place, area, zone where life exists on earth. The hydrosphere, lithosphere and atmosphere together constitute the biosphere.

The levels of organization of living things mentioned in the above article present before us the systematic structure and functioning of various components of this organization. The biological or precisely the living entities of our planet constitute a far more complex and sophisticated systems to be understood through a single article. The information presented above should however, give a rough idea of the levels and components which constitute a rich biosphere called earth.