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Thursday, 23 February 2017

Cell Structure and Function I


Unicellular organisms are capable of independent existence and they can perform the essential functions of life. Anything less than a complete cell does not ensure independent living. Hence, a cell is the fundamental structural and functional unit of all living organisms
All organisms are composed of cells. They include unicellular organisms and multi-cellular organisms
Robert Hooke: Discovered cell
Anton Von Leeuwenhoek: First observed and described a live cell
The invention of the compound and electron microscopes revealed all the structural details of the cell

CELL THEORY
Malthias Schleiden (1838) observed that all plants are composed of different kinds of cells
Theodore Schwann (1839) reported that cells had a thin outer layer (now known as ‘plasma membrane’). He also found that cell wall is a unique character of plant cells. He proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells
Schleiden & Schwann formulated the cell theory
Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the cell theory

Cell theory states that:
All living organisms are composed of cells and products of cells
All cells arise from pre-existing cells.

AN OVERVIEW OF CELL

All cells contain a semi-fluid matrix called cytoplasm. It is the main arena of cellular activities and chemical reactions. This keeps the cell in ‘living state’
All cells contain non-membrane bound organelles called Ribosomes. These are found in the cytoplasm, chloroplasts (in plants), mitochondria and on rough ER

Cells differ in size, shape and activities
Smallest cells: Mycoplasmas (0.3 μm in length)
Largest isolated single cell: Egg of ostrich.
Longest cells: E.g. Nerve cell.
Size of bacteria: 3 to 5 μm.
Human RBCs are about 7.0 μm in diameter

Based on the functions, shape of cells may be disc-like, polygonal, columnar, cuboid, thread like, or irregular

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