Initially, scientists thought that life formed spontaneously on the earth from non-living substances, but experiments and the invention of the microscope shed clarity on this hypothesis, and scientists understood that life and cells originate from preexisting life and cells, respectively.
The proposed ‘Principle of Cell Theory’ is the basic principle applied in biology to study cellular events. Many scientists contributed to the formulation of cell theory which, include Theodore Schwann, Rudolf Virchow, and many more (detailed discussion on the contribution of scientists later in the article).
The original cell theory formulated postulates that state:
- All living organisms are composed of one (unicellular) or more cells (multicellular).
- A cell is the basic unit of life of the structural organization of an organism.
- Cells arise from pre-existing cells. (Hence not derived from spontaneous generation)
Cells are the basic functional unit of life, and ‘cell theory; is a universally accepted principle that helps in unifying biological theories, hypotheses, and principles. With technological advancement in the microscope, development happened, and scientists began to dig deeper and understand the nature of functional cells and their biological processes. There is always an update as new information emerges.
This modern or updated version of cell theory includes ideas like:
- Energy flows within the cells.
- Hereditary information (DNA and nucleic acids) is passed on from parents to daughter cells or between cells without replication or division.
- The basic biochemical composition of all cells is the same.
Cells- Basic Unit of Life
The term cell is derived from the Latin word ‘cellula’, which refers to a small room. And cells are the functional and structural unit of life that houses many biomolecules such as carbohydrates, proteins, nucleic acids, lipids, and metabolites in a fluid matrix called cytoplasm enclosed within a plasma membrane.
It is of two types:
- Prokaryotic– This includes organisms like bacteria, archaea, and blue-green algae (cyanobacteria). They contain a nucleoid region but lack a fixed nucleus with a nuclear membrane.
- Eukaryotic– This includes all organisms which are not prokaryotes, which contain a specialized region called a nucleus enclosed in a nuclear membrane that preserves and protects complex genetic information.
A cell contains many subcellular components such as cell membranes, cytoskeleton, organelles, and genetic information that carry out the necessary cellular processes for survival.
Continuous upgradation of microscopic equipment led to the discovery of cells and their internal environment. Let’s look at some of the scientists who contributed to the formation of cell theory.
Timeline of Cell Theory Development Events
- 1590 – Invention of the first microscope.
- 1665 – Robert Hooke discovered ‘cells’ in a cork slice which he described as rectangular and resembled ‘little rooms’ as seen in monasteries.
- 1675 – Antoine Lee Vanhawk sees tiny objects in the pond water.
- 1838 – Mathias Schleiden came to the conclusion that all plants are made from cells.
- 1839 – Theodore Schwann proposes that all animals are made of cells, hence all living organisms are made of cells.
- 1855 – Rudolf Virchow includes that all cell/life is formed from pre-existing cells/life.
Cell theory came into existence when Robert Hooke, an English scientist discovered cells while looking at a thin slice of cork in his primitive compound microscope in 1665. He analyzed and made several observations that he documented in his book ‘Micrographia’, which also includes all the illustrative descriptions of organisms he had studied under his microscope. The cork cells which resembled box shapes reminded hooke of rooms in the monasteries, and he coined the term ‘Cells’, derived from the Latin word ‘cellula’. Hooke had no idea if cells were alive or not.
Antonie Van Leeuwenhoek
Antonie van Leeuwenhoek, a Dutch scientist used to make simple microscopes with only single lenses but with high resolution to study plant tissues and microscopic organisms. He is often known as the ‘father of microbiology,’ and coined the term ‘animalcules’ for freshwater protozoans. He descriptively wrote about bacteria from his own teeth. And he observed for the first time, the sperm cells found in humans and animals.
Matthias Schleiden and Theodore Schwann
They are referred to as the ‘Founders of the Cell Theory’. Matthias Schleiden, a German botanist studied plant tissues under the microscope. He stated “All plants are composed of cells and products of cells” in his literature in 1838. He studied the nucleus and its importance for plant cell division. And noted that the old cell nucleus is involved in the production of new cells.
Theodore Schwann, a German physiologist used to study animal tissues, and was a good friend of Matthias Schleiden. He proposed that all animal tissues are made of cells that have a nucleus and gave three conclusive statements:
- A cell is a unit of structure, function, and organization in living entities.
- A cell is both a distinct entity and a building unit in the construction of organisms.
- Living cells form in the same way as crystals are formed (this statement is disapproved).
Rudolf Virchow, a German pathologist is credited for the postulate that ‘all cells arise from pre-existing cells’ from the Principle of Cell Theory. French scientist, François-Vincent Raspail coined ‘Omnis cellula e cellula’, which means ‘all cells come from cells’ was popularized by Rudolf Virchow. He is a German scientist who specializes in the study of diseases and epidemiology. He believed that imbalances and abnormal activities within a cell contribute to the diseased condition.
The credit for the proposal of the ‘Principle of Cell Theory’ is given to the two scientists, Matthias Schleiden and Theodore Schwann, in the 1830s. This theory has since been updated and modified as new theories and discoveries regarding the cell happen. The postulates of the cell theory include that all living organisms are composed of cells, which are the basic structural and functional unit of life and cells come from pre-existing cells. This suggests that every function of living organisms from respiration to digestion occurs within a cell. For the growth and development of living organisms, cells reproduce to give rise to new cells by the division of existing cells.
- Cell Theory: A Core Principle of Biology – https://www.thoughtco.com/cell-theory-373300
- Lesson Explainer: Cell Theory – https://www.nagwa.com/en/explainers/754176579570/
- Cell Theory – https://education.nationalgeographic.org/resource/cell-theory/
- Cell theory – https://en.wikipedia.org/wiki/Cell_theory
- Cell (biology) – https://en.wikipedia.org/wiki/Cell_(biology)