What is a Cell? - Definition and Discovery of Cells
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| Image by brgfx on Freepik |
Cells, the fundamental units of life are the building blocks of all living organisms. Whether as single-cell entities like Mycoplasmas or complex arrangements in humans, cells provide structure and convert nutrients into energy. These tiny architects exhibit diverse shapes and sizes, akin to the bricks in a Lego set, forming the basis of our intricate biological constructions. From bacteria to humans, cells represent the foundational level of organization in living entities. Within these microscopic marvels, cell organelles perform specialized functions, ensuring the smooth functioning of the cell and the overall organism. Acting as storytellers, cells carry the genetic material that connects the past, present, and future of life, making them integral to the enchanting narrative of existence. Most cells are microscopic and invisible to the naked eye. However, some exceptions can be observed. A bird's egg is made up of a single cell. Poultry eggs are visible to the naked eye. Ostrich egg is the largest cell (17 cm × 12.5 cm). A human neuron cell is about 1.37 meters long.
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| Image by brgfx on Freepik |
Definition of Cell
- According to Jean Brachet (1961) -
“Cell is the basic structural unit of an organism."
- According to Loewy and Siekevitz(1963) -
" Cell is a unit of biological activity surrounded by a semipermeable membrane and capable of self-reproduction without any other living medium."
- According to C. P. Hickman (1970) -
"The cell is the unit of biological structure and function and is the smallest biological unit capable of self-regulation and reproduction."
- According to De Roberties (1979) -
“Cells are the basic structural and functional units of organisms.”
Discovery of Cells
In 1665, Robert Hooke, the appointed Mechanical Keeper of the Royal Society of London, stumbled upon a fascinating discovery that would reshape our understanding of life at its most basic level. Contemplating the mysteries visible through a telescope, Hooke directed his attention to a wooden shell floating in the water, intrigued by the reasons behind its buoyancy. To unravel the secret, he crafted a thin section of the shell and examined it under a microscope. To his amazement, a myriad of tiny chambers resembling beehives came into focus. Drawing inspiration from the small rooms he recalled seeing in monastic ashrams, Hooke coined the term "Cell," derived from the Latin cellula, to describe these microscopic compartments. This groundbreaking revelation found its place in his book, "Micrographia."
The journey into the microscopic world continued to unfold as advancements in microscopy technology allowed Dutch scientist Antony van Leeuwenhoek, in 1674, to observe living cells with intact cellular materials, providing a more dynamic perspective. The quest for understanding cell structure progressed further when, in 1781, Felice Fontana proposed the existence of a nucleus within a cell. It wasn't until 1833 that Robert Brown made the pivotal discovery of a distinct spherical nucleus in a plant cell, marking a crucial milestone in cell biology. The exploration of cellular mysteries persisted, and in 1835, French cytologist Félix Dujardin identified the jelly-like substance inside cells as sarcode. Subsequent advancements in our comprehension of cell biology continued to unfold, with Parkins in 1840 coining the term "protoplasm" for the liquid living matter within cells. The culmination of these discoveries paved the way for a deeper understanding of cellular structures and functions. The transformative moment came in 1931 with the advent of the electron microscope, a groundbreaking invention by German scientists Max Knoll and Ernst Ruska. This technological marvel enabled scientists to delve even further into the microscopic realm, unraveling the intricate structures of cells and their organelles. As a result, the once-hidden world of cells became unveiled, opening new chapters in the story of life at its most fundamental level.