The 3 Pillars of Cell Theory and Their History

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Our guide to the principles of cell theory and how it was discovered
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Our simple cell theory primer will get you up to speed with easy explanations on the 3 main points of classic cell theory, the 3 main points of modern cell theory, and the history of how scientists discovered all of it. Want to learn more? Let's dive in!

Things You Should Know

  • The 3 parts of modern cell theory are:
    • 1. Cells pass DNA to new cells
    • 2. Cells of the same species are made of the same stuff
    • 3. Energy flow happens inside cells
  • The 3 parts of classic cell theory are:
    • 1. Cells are the most basic building blocks of all living things
    • 2. Every living thing is made up of cells
    • 3. Cells come from other cells
Section 1 of 4:

3 Pillars of Modern Cell Theory

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  1. When cells create other cells, they also pass all their genetic info to the new cells. [1] This genetic info tells the cell, and the organism the cell makes up, how to develop, survive, and reproduce. [2]
  2. The cells that make up you and I are virtually identical in their structure. Likewise, the cells that make up 2 fern plants are identical. Cells of like species will be the same from specimen to specimen. [3]
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  3. Though cells are the most basic building block of living organisms, there’s still plenty of things happening inside each cell, like metabolic functions that break down sugars into energy that the cell can use. [4]
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Section 2 of 4:

The 3 Pillars of Cell Theory

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  1. This means that cells are the most basic unit of every living thing. [5] An organism might have many different parts, but if you use a microscope to zoom in close enough, all those parts are made up of individual cells.
  2. If you put any organism under a microscope, you’d find it’s made up of cells, the same way a house might be made up of bricks. An organism can be just a single cell, or it can be made up of many different cells, but cell theory suggests that a living organism cannot be less than a single cell. [6]
  3. This means that new cells are created by other preexisting cells, which give the new cells everything they need to become fully functioning cells. [7] At the time, some biologists thought that new cells might spontaneously come into existence, but cell theory eventually argued against this, saying instead that cells come from other cells. [8]
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Section 3 of 4:

History of Cell Theory

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  1. Thanks to the invention of the microscope, biologists could now take a closer look at living things. Hooke looked at bits of corks and other plants and found that they appeared to be made up of little compartments. He called these compartments “cells” because they looked like the little rooms or cells that monks in a monastery live inside. [9]
  2. Even though microscopes still weren’t powerful enough to take a clear look at cells, the Dutch microscopist Leeuwenhoek used the technology of the day to discover that animal blood also contains cells. This led to a rush of research in the scientific world—scientists found out that many living things were made of cells, but they couldn’t quite figure out exactly what cells were or how they worked. [10]
  3. 200 years after Hooke, the Scottish botanist Robert Brown looked through a more advanced microscope and found that every plant cell he looked at contained a nucleus, which suggested that cells themselves were made up of smaller parts. [11] This began a flood of information about what cells actually looked like and how they worked.
  4. Schleiden stated that some living things are made up of only one single cell, while larger, more complex living things are made up of many cells. [12]
  5. Schwann declared that animals also had cells the same way plants had cells. Then, Schwann and Schleiden got together and, using everything they had learned and discovered about cells, created the first 2 pillars of cell theory: cells are the most basic building blocks of living things, and all living things are made of cells.
  6. While studying how diseases spread, Virchow proposed that diseases come from changes happening to normal cells. He used this theory to develop another theory: that all cells come from other cells. [13] The third pillar of cell theory was established.
  7. Better microscopes and an expanded understanding of how cells work led many later scientists to add some points to classic cell theory in order to better describe what cells are and how they work. There are a number of important ideas in modern cell theory, but the main 3 are: cells pass DNA to new cells, cells of the same species are made of the same stuff, and energy flow happens inside cells. [14]
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Section 4 of 4:

Exceptions to Cell Theory

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  1. Cell theory has a few complications, and the first is the existence of viruses. After all, viruses don’t seem to adhere to cell theory. Viruses, however, are not considered living organisms, and they don’t reproduce the same way cells do. For this reason, viruses also aren’t considered cells. [15]
  2. It’s like the problem of the chicken and the egg: which came first? The first cell had to come from somewhere, but it couldn’t have come from another cell—it was the first, after all! Biologists are still figuring this one out. [16]
  3. Both of them have their own genetic material distinct from the cells they occupy, but they aren’t considered cells themselves, and they reproduce on their own, independent from the cell. [17]
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      References

      1. ↑ https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/04%3A_Cell_Structure/4.03%3A_Studying_Cells_-_Cell_Theory
      2. ↑ https://www.genome.gov/about-genomics/fact-sheets/Deoxyribonucleic-Acid-Fact-Sheet
      3. ↑ https://resources.saylor.org/wwwresources/archived/site/wp-content/uploads/2010/11/Wiki-Cell-Theory.pdf
      4. ↑ https://www.nature.com/scitable/topicpage/cell-metabolism-14026182/
      5. ↑ https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/04%3A_Cell_Structure/4.03%3A_Studying_Cells_-_Cell_Theory
      6. ↑ https://www.britannica.com/science/cell-theory
      7. ↑ https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/04%3A_Cell_Structure/4.03%3A_Studying_Cells_-_Cell_Theory
      8. ↑ https://resources.saylor.org/wwwresources/archived/site/wp-content/uploads/2010/11/Wiki-Cell-Theory.pdf
      9. ↑ https://www.britannica.com/science/cell-theory
      1. ↑ https://www.britannica.com/science/cell-theory
      2. ↑ https://www.britannica.com/science/cell-theory
      3. ↑ https://www.britannica.com/science/cell-theory
      4. ↑ https://embryo.asu.edu/pages/rudolf-carl-virchow-1821-1902
      5. ↑ https://openstax.org/books/microbiology/pages/3-2-foundations-of-modern-cell-theory
      6. ↑ https://socratic.org/questions/how-do-viruses-violate-the-cell-theory
      7. ↑ https://resources.saylor.org/wwwresources/archived/site/wp-content/uploads/2010/11/Wiki-Cell-Theory.pdf
      8. ↑ https://resources.saylor.org/wwwresources/archived/site/wp-content/uploads/2010/11/Wiki-Cell-Theory.pdf

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