Levels of Organization of Living Things

The study of different levels of organization of animate or living things helps us gain insights into the complexities of their structure and functioning. 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. The living beings have evolved from their single celled or unicellular forms to complex and giant multicellular bodies. In the process of development, their body systems and mechanisms became specialized in nature. Thus, in the course of evolution, different levels were formed. Let us understand these levels of organization of living things.

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

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

Tissue: The tissues are a collection of cells which perform specialized functions. The cells which form a tissue need not be identical but have the same origin. The different types of tissues which form organs are the nervous, muscle, connective and epithelial tissues. The connective tissues are fibrous in nature and are made up of cells separated by the extracellular matrix. Muscle tissues, which are the active contractile tissues of the body, are useful in producing force and motion. Skeletal, cardiac and smooth muscles are the three types of muscles. The nervous tissues form organs, like, brain, spinal cord, etc. The 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 various organs of animals include the lungs, brain, liver, etc. Roots, stem and leaves, etc. are different organs of the plants. The organs could be classified on the basis of the functions they perform. For example, in case of animals, tongue, ears, eyes, skin and nose form the sensory organs. Flowers and seeds are the reproductive organs in plants. The organs are formed of tissues which serve a common function. There are two types of tissues that form an organ: the main and sporadic tissues. For example, in the heart, myocardium is the main tissue while blood, nerves and connective tissues are the sporadic ones.

Organ System: The organ systems are complex mechanisms which carry out important functions of the body. For example, the circulatory system in animals and vascular system in plants. The 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 the anus.

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

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.

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