Biology is the science of life forms and living processes. The living world comprises a wide diversity of organisms. The observation of the diverse forms of life on earth was made initially through the naked eyes and later by using instruments such as magnifying lenses and microscopes. The organisms were described on the basis of observed structural features, both external and internal. The detailed description of life forms on the basis of appearance external and internal features brought out their concept of diversity. It is the cell theory that emphasised the unity underlying this diversity of forms, i.e., the cellular organisation of all life forms. Cell theory also created a sense of mystery around living phenomena, i.e., physiological and behavioural processes. This mystery was the requirement of integrity of cellular organisation for living phenomena to be demonstrated or observed.The course will deal with “Diversity in the Living world”, “Structural Organization in Plants and Animals” and “Cell Structure and Function” from class XI Biology.