There are 6 Themes 
      that this book and the study of Biology will continually refer back to.  
      These themes give guidelines in which to define "LIFE."   These 
      are:1.  Cell structure and function - All cells are composed of 
      cells.  Some are unicellular and self contained while some are 
      multicellular  with each cell type performing a generalized life 
      function.  All cells have membranes that surround them and all 
      contain a nucleus that contain DNA that controls its activities
      2.  Stability and Homeostasis - Homeostasis is maintaining a 
      constant internal condition.  All cells must control its' internal 
      environment and act to change it if it is to survive.  A cell must 
      also be able to "sense" any change in its' environment and react 
      accordingly
      3.  Heredity - Heredity is the transmission of "developmental 
      instructions from parents to offspring.  If damage (mutation) occurs 
      it must correct the change or pass it down to its offspring.  
      Mutation is what allows evolution to take place.
      4.  Evolution - Inherited change in a populations characteristics 
      over time.  
      5.  Interdependence - All things rely on each other either 
      directly or indirectly
      6.  Matter energy and organization - All organisms are composed of 
      atoms, which assemble into molecules.  cells are made of molecules.  
      All life requires energy and life is organized into many levels.