Class 11 Biology Structural Organisation In Animals Introduction


  • In unicellular organisms, all functions like digestion, respiration and reproduction are performed by a single cell. In multicellular animals, a group of similar cells along with intercellular substances perform a specific function; such an organization is called tissue.
  • Tissues are organized in specific proportion and pattern to form an organ. Examples- stomach, lung, heart and kidney.
  • When two or more organs perform a common function by their physical and/or chemical interaction, they together form organ system. Examples- digestive system, respiratory system, etc.
  • Cells, tissues, organs and organ systems exhibit division of labor for the survival of the whole body.


Fig. digestive system of human

  • Animal tissues are broadly classified into four types
  • Epithelial
  • Connective
  • Muscular

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