12th Class Biology blank Levels of Biological Organization

(1) Levels of Organization common in both living and non-living

(i) Atomic level : The lowest level of organization in both living and non-living is the atom. All living organisms are basically made up of four chemical elements carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) with only about 1% other elements. The non-living matter may possess other elements (such as silica, calcium, iron, etc.) in variable composition.

(ii) Molecular level : Atoms combine to form molecules, which undergo chemical reactions to form organelles.

Atoms \[\to \] Molecules \[\to \] Inorganic compounds \[\to \] Simple organic  compounds \[\to \] Complex organic compound \[\to \] Protoplasm \[\to \]  Cell.

(2) Levels of Organization found only in living organisms  

(i) Cellular level : All multicellular organisms are made up of cells. The cell is considered as basic unit of life and constitutes the smallest level of organisation of the living organisms.

(ii) Tissue level : In multicellular organisms similar or dissimilar cells, having a common origin and a common function, combine to form a tissue. Each tissue performs a specific role (e.g., xylem conducts water and minerals in plants).

(iii) Organ level : Different tissue are organised to form distinct organs. For example, xylem, phloem chlorenchyma, parenchyma get organised to form a leaf.

(iv) Organs System level : A group of organs that coordinates to performs a major function forms the organs system. For example, the brain works with the spinal cord and a network of nerves to form the nervous system.

(v) Individual or Organismic level : A multicellular individual, having many organ systems, forms an organismic level of organisation.

Cell \[\to \] Tissue \[\to \] Organ \[\to \] Organ system \[\to \] Individual.

(3) Levels of organization beyond the individual organism

(i) Population level : All the individuals of a species in a particular area, where they interact with each other, belong to a population. For example, there is a population of Oak trees in a temperate deciduous forest.

(ii) Community level : The populations of different species of plants and animals present in a particular area make up biotic community.

(iii) Ecosystem level : Populations of different plants and animals interact among themselves and with the non-living components of the area form as ecosystem.

(iv) Biosphere level : The different ecosystems (small or big) of all the geographical regions of the world form the biosphere or the entire livable part of the earth.