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Origin and Principles of Cell Theory

Renee Wunderlich, Lisa Roundy
  • Author
    Renee Wunderlich

    Renee Wunderlich has a B.S. in Marine Biology and minor in psychology from the University of North Carolina Wilmington. She also holds a teaching certificate for 6th-12th grade Biology in the state of Florida. She has taught middle school science for four years. Prior to the classroom, Renee conducted and implemented marine science education programs at a variety of summer camps and aquariums.

  • Instructor
    Lisa Roundy

    Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

What is cell theory? Learn the history of cell theory and the three main principles of cell theory with examples. See a modern interpretation of cell theory. Updated: 10/08/2021

What is Cell Theory?

In science, theories are widely accepted explanations of natural phenomena. These theories contain a great deal of evidence, but this evidence can change over time with new discoveries. The cell theory is a biological theory with many contributing scientists; as they have learned more, the overall understanding of cells has changed. Cell theory explains the role of cells in living things. A classical cell theory and a modern cell theory exist. The three principles, or parts, of classical cell theory are:

  • Cells are the basic unit of life.
  • All living things are made of cells.
  • Cells come from other cells.

History of Cell Theory

The invention of the microscope and contributions from a variety of scientists were critical in the development of cell theory. In the 1600s, Anton Van Leeuwenhoek, a scientist from the Netherlands, used his own version of a microscope to look at a variety of samples he found in his everyday life. His samples included scrapings from people's teeth and he called what he saw under the microscope animalcules (which were later discovered to be bacteria). The term cell, however, came from Leeuwenhoek's colleague in England-Robert Hooke. Hooke noticed chambers on a sample of cork, which reminded him of the rooms, or cells, used by monks at a monastery.

Hooke observed cells similar to those shown here. He thought the chambers looked like rooms at a monastery, so named them cells.

Plant cells under a microscope from a plant stem

It was not until the 1800s that the cell theory really started moving forward. Matthias Schleiden, a botanist from Germany, used a microscope to examine a wide variety of plants. He came to the conclusion that all plants were made of cells. Theodore Schwann, for whom the nerve cells in the peripheral nervous system are named, made a similar conclusion. He realized that all of the animal samples he studied were made of cells.

Although their belief that all living things were made up of cells aligned, Schleiden and Schwann disagreed on the topic of how cells were formed. Schleiden believed cells came from a process called free cell formation, or spontaneous generation. This idea stated that cells could arise from non-living matter. Schwann however, believed cells came from preexisting cells. Rudolf Virchow, an accomplished pathologist of the time, supported Schwann's idea that cells came from other cells. Virchow studied a variety of diseases and human tissues and was the first person to discover leukemia and the idea of embolisms. Virchow's expertise and credibility on the topic of cells allowed the idea of cells coming from other cells to be more widely accepted by scientists.

The Three Principles of Cell Theory

Just as buildings can be built from smaller materials, and words are built from the alphabet, living things are built from cells. This is why the first principle of cell theory states that cells are the basic unit of life or the building blocks of life. All matter contains atoms and molecules, but unless those atoms and molecules form a cell, something cannot be considered living. Natural features such as mountains, rocks, or soil are not considered living since they are not made up of cells. Each cell in a living organism carries out a function, and as cells combine to form tissues and organs, they contribute to the overall functioning of that organism. Without cells, there is no life.

All living things are made up of cells. This can include organisms that contain a single cell (unicellular) and more complicated organisms made of many cells (multicellular). Bacteria, such as the bacteria in your digestive system or on the surface of your workspace, are comprised of just one cell. You, your pet, and the grass in your backyard are all multicellular organisms. Any living organism - from plants to protists, fungi to animals - are all constructed from cells.

Cell Theory

Imagine what it must have felt like to be Robert Hooke when he first saw cork under a microscope. He noticed small compartmentalized areas that reminded him of the small rooms in a monastery. He named these areas 'cells'. We now know much more about these fundamental units of life because of the interest their discovery sparked. Further investigation led to the development of cell theory, or basic generalizations that are accepted by modern scientists about cells. Three main assumptions of cell theory were developed in the mid-1800s and remain a foundation of modern biology. These three assumptions are:

  1. All living things are made up of cells.
  2. Cells are the basic units of structure and function in living things.
  3. Living cells come only from other living cells.

Let's look at each of these statements in further detail.

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Bacteria are an example of unicellular organisms. Even though they are only made of one cell, they are considered living.

Labeled diagram of a bacteria cell

Living Things are Made of Cells

The first part of cell theory is the idea that all living things are made of cells. This means that in order for something to be alive, it must either be a cell or made up of many cells. All animals and plants, including trees, are made of cells. An amoeba is made up of just one cell, but it's still enough for it to be living. A rock, however, is'nt made up of cells, so it's not alive.

Cells are the Basic Units of Life

The second part of cell theory states that cells are the basic units of life. They are the fundamental units of a living organism's structure. They are also the basic units of function. This means that cells carry out all the processes necessary for an organism to survive. A cell is the smallest part of a living thing that can still be considered alive. One-celled organisms are alive, each individual plant cell is alive, and each individual animal cell is alive. A whole cell as a unit is alive, but any separate part of a cell is not alive by itself.

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Video Transcript

Cell Theory

Imagine what it must have felt like to be Robert Hooke when he first saw cork under a microscope. He noticed small compartmentalized areas that reminded him of the small rooms in a monastery. He named these areas 'cells'. We now know much more about these fundamental units of life because of the interest their discovery sparked. Further investigation led to the development of cell theory, or basic generalizations that are accepted by modern scientists about cells. Three main assumptions of cell theory were developed in the mid-1800s and remain a foundation of modern biology. These three assumptions are:

  1. All living things are made up of cells.
  2. Cells are the basic units of structure and function in living things.
  3. Living cells come only from other living cells.

Let's look at each of these statements in further detail.

Living Things are Made of Cells

The first part of cell theory is the idea that all living things are made of cells. This means that in order for something to be alive, it must either be a cell or made up of many cells. All animals and plants, including trees, are made of cells. An amoeba is made up of just one cell, but it's still enough for it to be living. A rock, however, is'nt made up of cells, so it's not alive.

Cells are the Basic Units of Life

The second part of cell theory states that cells are the basic units of life. They are the fundamental units of a living organism's structure. They are also the basic units of function. This means that cells carry out all the processes necessary for an organism to survive. A cell is the smallest part of a living thing that can still be considered alive. One-celled organisms are alive, each individual plant cell is alive, and each individual animal cell is alive. A whole cell as a unit is alive, but any separate part of a cell is not alive by itself.

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Frequently Asked Questions

What is cell theory and why is it important?

The cell theory is a widely accepted explanation of the role of cells in living things. It is important because it lays the foundation for scientists' understanding of cells and sets the distinction between living and non-living things.

What are the 3 principles of cell theory?

1. Cells are the basic unit (or building block) of life.

2. All living things are made of cells.

3. Cells come from other cells.

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