Definition of Cell
From the previous discussion we know that every organism is made up of cells and cells are the structural and functional unit of the organism. Each cell is made of a jelly-like, slimy living substance called protoplasm. Surrounding the protoplasm is a semi-permeable (semi permeable) cover or screen, i.e. the cell membrane. Thus, the structural and functional unit of an organism surrounded by a semipermeable membrane and composed of protoplasm is called a cell. 2023.12.
The definitions of Kosh by various scientists are- (i) Kosh-Swanson & Webster (Swanson & Webster, 1978) are the basic unit of physical existence of life.
(ii) The basic structural and functional unit of the organism is the corpuscle Roberties (De Roberties, 1979).
Â
Size of cell
Just as the size and volume of living organisms are different, the volume of different cells is also different. The smallest organisms in the biosphere are Mycoplasma gallisepticum and M. laidlawii (bacteria-like organisms) – only 0.1 µm in diameter. The largest egg cell is the ostrich egg, 170 mm x 135 mm in diameter including the shell. The largest single-celled plant cell is an alga called Acetabularia, which is 5-10 cm long. Among the multicellular plants, a fiber (a cell) in the bark of Ramie (Boehmeria nivea) is about 55 cm long. The smallest cell in the human body is the white blood cell (7.5µ) called the lymphocyte and the longest cell is the neuron, ranging from about 90 cm to 1 m in length.
Number of Cell
Except for a few types of unicellular organisms, all multicellular organisms have numerous cells in their bodies. The number of cells in lower class multicellular organisms ranges from hundreds to several thousand, while the number of cells in higher class multicellular organisms can range from hundreds of thousands to hundreds of millions. An 80 kg adult male body has approximately 600,000 to 1000,000,000 cells (60 × 1015).
