The group of different tissues performing same function is called organs. Different tissues are organized into the organs except simplest animals (sponges and cnidarians). Some organs have their tissue layers. For example, the stomach has four major layers.

  • The lumen is lined by a thick epithelium. This epithelium secretes mucus and digestive juices.
  • Outside this layer is a zone of connective tissue
  • It is followed by a thick layer of smooth muscle.
  • The entire stomach is encapsulated by another layer of connective tissue A laminated organization is also present in the dermis. It is the outer skin of the body.Man of the organs of vertebrates are suspended by mesenteries. Mesenteries are heets of connective tissue present in the body cavities. Mammals have an upp r thoracic cavity separated from a lower abdominal cavity by a sheet of must le called the diaphragm.

    0 an system

    The group of different organs performing same functions is called organ sys m. Organ system is a level of organization higher than organs. The organs car out major functions of vertebrates and members of most invertebrate phyla. Org n system consists of several organs. Examples are the digestive, arc latory. respiratory, and excretory system. Each system has specific func ions. But the efforts of all systems must be coordinated for the survival of ani als. For instance, nutrients are absorbed from the digestive tract. They are distr buted throughout the body by the circulatory system. But the heart itself dep nds on nutrients absorbed by the digestive tract. The respiratory system abs rbs oxygen from the air. This oxygen is transported by blood.



        I                             DEFINITIONS
      Homoeostasis The     maintenance      of a     constant    internal    environment

    despite fluctuations in the external environment is called homoeostasis.

    Simple diffusion The movement of molecules from the area of higher concentration to the area of lower concentration is called simple diffusion.
    Fac diffusion

    litated ., ,

    The      movement     of    molecules      through     the      protein

    molecules from      higher to lower concentratiOn          is called
    facilitated diffusion.

      OsmoSis The diffusion       of water across a selectively permeable



    membrane from an area of higher concentration to an area of lower concentration is called osmosis.

    Tonicity   The relative concentration of solutes in the water inside and outside the cell is called tonicity
      Filtiation Filtration is a process that forces small molecules across

    selectively     permeable      membranes     with     the     help    of
    hydrostatic pressure.

    Act ye transport The movement of molecules form the area of lower

    concentration to the area          higher concentration       by the
    expenditure of energy is called active-transport.

    Enc ocytosis The movement of substance inside the cell by infolding of



      the     membrane    and     formation     of   vacuole     is    called

    endosytosis. The nonspecific uptake of all droplets of extracellular fluid is called pinocytosis.

    Phagocytosis The   uptake    of solid    particles     by  invagination     is  called
    Phagolysosome Lysosome combines with the food vacuole to form a phagolysosome.
    Exocytosis The removal of cell secretions from the cells by out folding is called exocytosis.
    Lysosome Lysosome     is a     membrane-enclosed     bag    of hydrolytic

    enzymes that the cell uses to digest macromolecules..

    Tissues The sheets of tightly packed           cells are called       epithelial
    Connective tissues The tissue, with loose arrangement of cells and the cells

    are    scattered      in   an    extracellular      matrix    are   called
    connective tissue.


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