Levels of Structural Organisation: As evolution progressed and larger and larger organism appeared with enormous number of cells in the body, it became necessary that the bodies function are distributed among group of cells called tissues and even among group of tissues. Such higher and higher grouping of cells or tissue is known as levels of organization. These levels are cellular level, tissue level, organ level, organ system and organism.
Levels of Structural Organisation
Cellular level: The chemicals are grouped together to form the cellular level. Cells are the smallest unit of life. The cell has a very complex system of organelles and each organelle is concerned with a particular task. Thus there is a division of labour at the cellular level. E.g. nerve cell, muscle cell etc.
Tissue level: The cells that are similar in structure, origin and function are grouped together to form tissues. There are four main types of tissues: Epithelial, connective, muscular and neural tissue.
Organ level: Organ is a group of various tissues that performs a specific function. For example, stomach and intestine are organs to digest food. Similarly, lungs and trachea are organs meant for respiration. All these organs are collections of various tissues like connective, epithelial, muscular and nervous tissue.
Organ system level: Various organs group together to form even larger functional units called organ systems. Organ system is a combination of a set of organs all of which are usually devoted to one general function. For example, Respiratory system (consisting of lungs, trachea, bronchi, diaphragm etc) in man are example of organ system that works in a coordinated way.
Organism level: The complete individual comprised of different organ system is known as organism. For example, Man, Dog, Cat or a Mustard plant.
Thus, the different level of organization of the living body is:
Cells → Tissues → Organs → Organ Systems → Organism
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By Team Learning Mantras