Cell Theory

Cell theory is a biological hypothesis that says that all beings are fundamentally made up of cells, these cells are the basic structural and organizational unit of all living organisms, and all cells originate from pre-existing cells. It was first proposed in the middle of the nineteenth century. Cells are the fundamental building blocks of all the living creatures, as well as they are the basic unit of reproduction. There are major three postulates of cell theory, which are as follows: 

1. One or more cells make up every living entity. 

2. In organisms, the cell is the fundamental unit of structure and organisation. 

3. Pre-existing cells give rise to new cells.

Why the Cell Theory? The History of Cell Theory

The technology used for magnification purposes improved to the point where cells might be discovered as a result of continuous advancements to the microscopes over time. Robert Hooke is widely credited with this discovery, which brought in the scientific study of cells, known as cell biology. When he looked through the scope at a piece of cork, he noticed pores. This was surprising at the time because no one else was thought to have seen them. Matthias Schleiden and Theodor Schwann both examined animal and plant cells to support their theories. What they noticed was that the two types of cells had considerable distinctions. This established the notion that cells were not only important to plants but also to mammals.

Although the hypothesis was originally widely accepted, some scientists today regard non-cellular things like viruses to be living beings, contradicting the first premise. "Expert opinion remains divided around a third each between yes, no, and don't know," according to 2021. There will be more debate since there is no globally agreed concept of life.

The Theory of The Cell: Cell Theory Timeline

Two scientists are widely known as the people who discovered cell theory or who formulated the cell theory – Theodor Schwann and Matthias Jakob Schleiden. Schleiden proposed in 1839 that every structural component of a plant is made up of cells or is the product of cells. He also proposed that cells were formed by a crystallisation process that occurred either within other cells or outside of them. Schleiden, on the other hand, did not come up with the notion. Although Barthelemy Dumortier had proposed this hypothesis years before him, he claimed it as his own. Modern cell theory no longer accepts this crystallisation process. Animals, like plants, are formed of cells or the products of cells in their structures, according to Theodor Schwann in 1839. This was a significant breakthrough in biology since, in comparison to plants, little was understood about animal anatomy at the time. Two of the three tenets that explained cell theory were proposed based on these discoveries concerning plants and animals. 

1. Every live entity contains one or more cells. 

2. The cell is life’s most fundamental unit.

Robert Remak, Rudolf Virchow and Albert Kolliker rejected Schleiden’s idea of free cell creation by crystallisation in the 1850s. The third postulate of cell theory was added by Rudolf Virchow in 1855. This tenet is written in Latin as Omnis cellula e cellula. This is what it means: 

3. Only pre-existing cells give rise to new cells.

The theory that all cells arise from pre-existing cells, on the other hand, was offered by Robert Remak; it has been alleged that Virchow copied Remak and failed to acknowledge him. Remak presented cell division findings in 1852, saying Schleiden and Schawnn were wrong regarding generation methods. Instead, he claimed that binary fission, which was initially proposed by Dumortier, was how new animal cells were reproduced. The classical cell theory was complete after this tenet was included.

The Modern View of Cell Theory

The following are some of the most widely acknowledged aspects of current cell theory: 

• All known living organisms are made up of one or more cells. 

• By the process of division, all live cells develop from pre-existing cells. 

• In all of the living species, the cell is the basic structural and functional unit. 

• The cumulative activity of separate cells determines an organism's activity. 

• Within cells, energy flow (metabolism and biochemistry) happens. 

• DNA is present particularly in the chromosome, whereas RNA is found in the nucleus and cytoplasm of cells. 

• In creatures of comparable species, all cells have a chemical makeup that is almost identical.

Energy flow happens within cells, according to the contemporary version of the cell hypothesis. DNA (genetic information) is handed down from generation to generation. The chemical makeup of all cells is the same.

The Different Types of Cells

The following subcategories can be found inside cells: 

Prokaryotes: Prokaryotes are tiny cells that are enclosed by the plasma membrane and have a distinct cell wall that varies in composition depending on the organism. Prokaryotes lack a nucleus and other membrane-bound organelles (though they do have circular or linear DNA) (though they do contain ribosomes). The chromosomal region, which appears as fibrous deposits under the microscope, and the cytoplasm are both found in the protoplasm of a prokaryote. Prokaryotes are divided into two groups: bacteria and archaea.

Eukaryotes: Eukaryotes are the first complex cells, previously referred to as proto-eukaryotes. These cells grew a mitochondrial symbiont over time and eventually produced a nucleus. This, along with other developments, has created a considerable distinction between the two. 

In a multicellular organism, animals have developed a wider diversity of cell types (100–150), compared to 10–20 in plants, fungi and protoctista. 

Is There Anything Else Apart from Cell Theory?

Robert Hooke used a microscope to find the cell for the first time in 1665. Theodor Schwann and Matthias Jakob Schleiden's work in the 1830s is credited with developing the first cell hypothesis. The interior components of cells were referred to as protoplasm in this hypothesis and were characterised as a jelly-like material, often referred to as living jelly. Around the same time, colloidal chemistry was gaining traction, and the notion of bound water began to emerge. Brownian motion is sufficient to avoid sedimentation in a colloid, which lies somewhere between a solution and a suspension.

Around the same time, the concept of a semipermeable membrane, a barrier that is permeable to solvent but impermeable to solute molecules, was invented. The word osmosis was coined in 1827, and its significance in physiological phenomena was recognised in 1877, when botanist Pfeffer presented the membrane hypothesis of cell physiology. The cell was seen to be encompassed by a thin surface, the plasma membrane and cell water, and solutes like the potassium ion were in a physical state similar to that of a dilute solution in this perspective.

Hamburger employed erythrocyte hemolysis to test the permeability of different solutes in 1889. The pace at which solutes entered the cells could be measured by monitoring the time it took for the cells to inflate over their elastic limit and the resulting change in cell volume. He also discovered that red blood cells have an apparent nonsolvent volume of roughly 50%, which he later proved that this consists of water of hydration as well as protein and other nonsolvent components of the cells.