Cell Theory Definition and Origin

  • In this cell theory definition and origin post we have briefly explained about cell theory, discovery of the cell, and timeline.

Cell Theory Definition and Origin

  • Cell theory states that living things are composed of one or more cells, that the cell is the basic unit of life, and that cells arise from existing cells.

Cell Theory

  • A cell is a fundamental and most structural component that all living creatures are made up of. The cell is also the least biochemical, structural, and functional unit of all living things and animals. Thus, cells are the “Building Blocks of Life or the “Basic units of Life.” Organisms comprised of just one cell are considered ‘unicellular’ while organisms comprised of many cells are called multicellular. Cells play various roles in living organisms, including digesting, respiration, and reproduction.
  • For instance, in our body, several cells create tissues. Tissue that makes an organ. Many organs make up an organ system, and many organ systems that work together comprise our body.

Discovery of the cell

  • Have you ever thought that over 300 years ago, there was no understanding of cells? They were too small to be seen by the naked eye. The invention of microscopes allowed us to see cells and analyse them in greater detail. 

  • While it was a scientist named Robert Hooke who coined the term “cell” following the observation of dead cells under his microscope, but it was Anton van Leeuwenhoek who first observed living cells! Later, Robert Brown discovered the “nucleus,” the engine that allows the cells to function.


  • The microscopes we have nowadays are more sophisticated than those used during the 16th century by Antony van Leeuwenhoek, a Dutch shopkeeper with exceptional ability in making lenses. Even with the limitations of old microscopes, van Leeuwenhoek observed the movement of Protista (a kind that is a single-celled animal) and Sperm, which he described as “animalcules”.
  • In a 1665 book titled Micrographia, a research scientist Robert Hooke coined the word “cell” to describe the box-like structures he observed when looking at cork tissue through lenses. It was in the year 1670 that van Leeuwenhoek discovered bacteria and protozoa. Further advances in microscopes, lenses, and staining techniques allowed others to view elements inside cells.
What Is Cell Theory

Structure of an Animal Cell: The cell is the basic unit of life and the study of the cell led to the development of the cell theory. Image Source: https://bio.libretexts.org/

  • In the 1830s, Botanist Matthias Schleiden and zoologist Theodor Schwann studied the tissues and came up with the concept of the unified cell. The unified cell theory affirms that everything living is made up of cells. Cells are the most fundamental unit in life, and new cells develop from existing cells. Rudolf Virchow later made significant contributions to the theory.
  • Schleiden and Schwann believed that spontaneous generation was the way to create cells. However, spontaneous generation (also known as Abiogenesis) was later proven false. Rudolf Virchow famously stated, “Omnis cellula e cellula” “All cells only arise from pre-existing cells”. The aspects in the hypothesis that didn’t relate to the origins of cells, nevertheless, have stood up to scrutiny by scientists and are widely accepted by scientists today.
  • Three important points of the modified cell theory are as follows:
  • The cell is the basic functional and structural unit of all living organisms.
  • All living organisms are made up of cells.
  • All cells arise from pre-existing cells.
  • The expanded version of the cell theory can also include:
  • Cells carry genetic material passed to daughter cells during cellular division
  • All cells are essentially the same in chemical composition
  • Energy flow (metabolism and biochemistry) occurs within cells

Further Readings