Cell Biology: Definition of Cell, Types, Structure and Functions
At some point or the other, we’ve all marveled at how diverse the living world around us is. Detailed scientific studies of these organisms only emphasized their diversity even more. However, there also exists unity underlying this diversity — and the theory that emphasizes this unity is the cell theory.
The cell serves as the fundamental structural and functional unit of all living organisms. It is the cell that is a universally common feature in every living organism that ever existed, exists today, and will ever exist in the future. The cellular organization gives rise to a plethora of physiological, biochemical, and behavioral processes that lead to the genesis of life itself.
In order to study these processes in molecular terms, scientists have taken a physio-chemical approach and made use of cell-free systems. They further established this approach by analyzing the elements and compounds present in living tissues. Not only does this method explain the molecular basis of physiological processes, but it also helps us understand abnormal processes that take place during diseases.
The aforementioned method of using the concepts and techniques of physics and chemistry to understand biology is known as reductionist biology. It is a rapidly growing field that is helping scientists unravel the mysteries of the living world faster and clearer than ever. Let us now proceed to understand what exactly a cell in biology is, and what it holds a position of such great significance in the field.
To put it simply, the cell is what differentiates a living organism from a non-living object. An entity can be considered living if it possesses the basic unit of life — the cell. All living organisms you see around you (and even those you cannot see by the naked eye) are composed of cells. Some of them consist of a single cell and are known as unicellular organisms. Others are composed of numerous cells and are known as multicellular organisms.
However, it is worth mentioning that unicellular organisms are perfectly capable of both independent existences and performing all the essential functions of life. In other words, the capability to live independently does not exist for anything less than the complete structure of a cell.
The cell was first discovered in 1665 by Robert Hooke, an English scientist who first observed a slice of bottle cork under a primitive microscope. Although he only observed the dead cell walls, in this case, he laid down the foundations of cell biology. Rightfully, he is now known as the father of cytology.
In order to better understand the significance of a cell, let us now take a look at the famous cell theory.
In 1838, a German botanist named Matthias Schleiden closely studied a large number of plants and noticed that all of them had one thing in common — namely, all of them were composed of different types of cells, which were further organized to form tissues. About a year later, a British zoologist named Theodore Schwann (1939) studied various animal cells and discovered that cells possess a thin outer layer that is known today as the plasma membrane.
After conducting several meticulous studies on planet tissues, Schwann also concluded that the presence of cell wall is a unique feature of plant cells. Based on these observations, he proposed the cell hypothesis that states that the bodies of animals and plants are composed of cells and products of cells. Together, Schleiden and Schwann formulated the world-famous cell theory that revolutionized the field of biology.
However, the cell theory was unable to explain how new cells were formed. In 1855, Rudolf Virchow stepped in to rectify this flaw and first explained that new cells are formed from pre-existing cells ( “Omnis cellula-e cellula”) by the process of cell division. He proceeded to modify Schleiden and Schwann’s hypothesis to give a final shape to the cell theory.
Today, we understand the cell theory according to the following postulates:
- All living organisms are composed of cells and products of cells.
- All cells arise from pre-existing cells.
Originally published at https://gauravtiwari.org on December 18, 2021.