Cell definition
A cell is the basic unit of life that can perform all the essential functions of living organisms. Structurally, cell can be defined as follows:
A cell is a tiny mass of protoplasm (the living substance) enclosed by a delicate cell membrane and containing a nucleus.
Cell Theory
Cell theory is one of the fundamental principles of biology that states that:
- All living organisms are composed of one or more cells.
- Cells are the basic units of structure and function in living organisms.
- Cells arise from pre-existing cells by cell division.
- Cells carry genetic information in the form of DNA, which is passed from parent to daughter cell or from parents to offspring.
The theory was first proposed by German scientists Matthias Jakob Schleiden (a German Botanist) and Theodor Schwann (a German Zoologist) in 1838 and later expanded by Rudolf Virchow. It marked a significant advance in biological sciences by emphasizing the role of cells in the composition of plants and animals and in the continuity of life.
The third principle was put forward by the German scientist Rudolf Carl Virchow in the year 1855. He stated “omnis cellula e cellula", which translates to "each cell comes from another cell".
The fourth principle of cell theory was proposed by James Watson and Francis Crick in 1953, after they discovered the structure of DNA and its role in encoding hereditary information.
Cell theory is important because it explains:
- the diversity and unity of life.
- The relationship between structure and function and
- The mechanism of inheritance and evolution.