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08 CELL - THE UNIT OF LIFE
CELL: THE UNIT OF LIFE 9 SCAN CODE Cell: The Unit of Life Chapter 08 Cell: The Unit of Life Fig 8.1: The cell 1. Introduction to Cell  Both living and nonliving things are present around us.  Cells, the basic units of life, make an organism living. An inanimate thing does not have cells.  Cell is the basic and structural unit of life. All organisms are composed of cells like a wall is made of bricks!!!! Fig 8.2: Cell- the basic units of living organisms  Anything less than a complete structure of a cell does not ensure independent living. Hence, the cell is the fundamental structural and functional unit of all living organisms.
10 CELL: THE UNIT OF LIFE SCAN CODE Cell: The Unit of Life Fig 8.3: Development of complex organism from the simplest form  Humans also started their life with a single cell zygote and finally developed into complex organisms.  The term “Cell” was first used by Robert Hooke (an English Scientist) in 1665.  Robert Hooke observed thin slices of cork under his self designed simple microscope.  He noticed partitioned boxes or compartments separated by walls. The cells that he observed resembled a honeycomb.  The compartments reminded him of small rooms, and he gave them the name “cellulae” or cells. “cella” in Latin - ‘hollow spaces or compartments’.  The cells which Hooke observed were actually dead cells from the bark of the cork oak (Quercus suber) tree. His observations were published in his book ‘Micrographia’. Fig 8.4: Observations of Robert Hooke  In 1674, Antonie Van Leeuwenhoek, a Dutch scientist, with an improved microscope, observed free living cells (bacteria, protozoa, RBCs, etc.)  He observed bacteria, protozoa, spermatozoa and red blood cells etc. and could see tiny, very fast moving bodies.  He called them ‘Animalcules’ which means ‘Little animals’ in Latin.  Robert brown discovered the presence of nucleus in orchid root. The invention of the microscope and its improvement leading to the electron microscope revealed all the structural details of the cell.  Living semi-fluid substance of cells was discovered by Dujardin (1835), and named sarcode. Purkinje and Von Mohl renamed sarcode or the jelly like substance of the cells as protoplasm.
CELL: THE UNIT OF LIFE 11 SCAN CODE Cell: The Unit of Life 1.1 Cell Theory Fig 8.5: Cell theory  Schleiden and Schwann together formulated the cell theory.  In 1838, Matthias Schleiden examined many plants and observed that all plants are composed of different insides of cells which form the tissues of the plant.  Schwaann in 1839, studied different types of animal cells and reported that cells had a thin outer layer which is today known as plasma membrane.  He also concluded, based on his studies on plant tissues, that the presence of cell wall is a unique character of the plant cells.  He proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells.  In 1855, Rudolf Virchow first explained that cells divide, and new cells are formed from pre-existing cells (Omnis cellula-e cellulae). The findings of Rudolph gave cell theory its final shape. Fig 8.6: Formation of new cells from pre-existing cells  Louis Pasteur (1862) further proved that life originated from life.  Soon Haeckel (1866) established that nucleus stores and transmits hereditary traits.