Describe the levels of organization in living system and some of the methods of classification. Describe the levels of organization in living system and some of the methods of classification. Solution Answer: The levels of organization in living system are: (1) Organelle and cellular level All living organisms have cellular level of organization, be it unicellular or multicellular. The cell is the unit of life which carries out the necessay functions for survival. The functions are in turn divided among different organelles present inside the cell. The prokaryotes have small set of organelles while eukaryotes have richer collection of organelles which are more complex. (2) Tissue level Tissues are composed of similar type of cells which are same in origin and function. For example, nerve cells have the same origin and function and forms the nervous tissue. These are found in multicellular organisms. (3) Organ level Different tissues having similar functions together form the organ system in multicellular organisms. Stomach is a digestive organ which are composed of muscular tissue for contraction and secretory epithelium for gastric juice secretion. (4) Organ system When a number of organs group together to perform one or more functions, it forms an organ system. Examples-Respiratory system, endocrine sytem and circulatory system, etc. (5) Organism An entire living being which can carry out all the necessary functions for basic processes is called organism. An organism is usually made up of organ systems, but may be unicellular as in case of bacteria. Some methods of biological classification have been discussed as under: (1) Natural system of classification: In this system of classification, anatomy, physiology, pathology, biochemistry, reproduction & cytology are taken into account to compare relationships among organisms. It is considered advantageous over the artificial system of classification. This sytem was proposed by Bentham and Hooker. (2) Artificial sytem: In this sytem of classification, external features such as form and shape are used for comparing relationships among organisms. Since it does not take into account the internal properties such as anatomy, pathology and biochemistry among others, it is difficult to to study evolution. Linnaeus system of classification is considered as artificial. (3) Phylogenetic classification: It is classified on the basis of evolutionary relationships among organisms and is based upon Darwin\'s theory of natural selection. (4) Phenetic classification: For classification, it takes relies upon similarities and disimilarities among organisms, but do not take into account the evolutionary relationships. (5) Cytotaxonomy: It is classified based upon cytological features such as number of chromosomes..