Cell Theory

Cell theory is a way that we can describe the living things around us in a biological way.

Since cells are a basic life unit, we consider them to be alive and they can also be part of bigger living things. Other cells, such as bacteria, are smaller and can exist as a single unit.

The Three Principles of Cell Theory

To make things easier to explain and understand, scientists have divided cell theory into three principles:

  • All living things are made of cells.
  • The cell is the smallest living thing that can perform all the functions of life.
  • All cells come from other cells.

Breaking things down to these three principles is important so that scientists can study cells, what they are made of, and how they reproduce.

The study of cells also helps us understand us and the other animals and plants that are around us.

Cell History

The old idea of Spontaneous Generation

Science is always learning and changing and before scientists developed cell theory, they had another idea that they called spontaneous generation.

In that idea they thought that life could be created from non-living things. An example of this really old idea is that they thought fleas could be made from dust.

It may sound silly because we know fleas only come from fleas.

Aristotle was a Greek philosopher and while very respected, he was the one that came up with the idea of spontaneous generation.

Because Aristotle was so smart, no one disputed it until the mid-1800’s when they changed the idea to living things can only come from other living things.


Scientists were trying to get more information about cells for many years. The problem was that they didn’t have very powerful microscopes and they had to do the best that they could with what they had.

Robert Hooke made use of a compound microscope that had two lenses so that he could view the inside of a cork, and some insects and leaves. In 1665, he was the first scientist to develop the idea of a cell.

There were a lot of other scientists and naturalists that made use of this new miracle instrument and the ongoing investigation was accomplished by Nehemiah Grew (1641-1712), and Marcello Malpighi (1628-1694).

Grew had his work published in 1682 as The anatomy of plants. However, it isn’t very clear who was the first to see animal cells, Malpighi, Jan Swammerdam (1637-1680) or Antonie van Leeuwenhoek (1632-1723).

It was Leeuwenhoek that made discoveries and drawings of what he called “little animalules,” and this opened up a whole new world of research.

By the 1800’s, the competition for discovery was getting fierce. Theodore Schwann and Matthias Schleiden (1804-1881) are given the credit for their cell theory, even though some of their information wasn’t completely correct.

Working together they made the assumption that all living things are made up of cells and they stated that the basic units of life were cells.

Scientists were very excited about the new theories and one that came up with a phrase of “omne vive ex ovo” (every living thing comes from other things) was Rudolph Virchow. He added to the basic idea of cell theory with his quote.

Today’s Modern Cell Theory

The cell theory of modern times has taken the original idea and added new principles as part of modern cell theory:

  • During division, cells pass their DNA information to new cells
  • Cells have energy flowing inside of them.
  • All cells are made out of the same materials/chemicals.

Facts about Cell Theory

  • Eukaryotic cells have a nucleus and prokaryotic cells don’t have a nucleus. This makes eukaryotic cells 10 times larger than prokaryotic cells.
  • Animal cells don’t have chloroplasts because animal cells don’t create chlorophyll.
  • Every cell has a different type of job to do in an organism.
  • Human cells have 46 chromosomes, however, if there is a mutation that allows the cell to have 47 chromosomes, it can cause Down’s Syndrome.
  • Cells provide structure to hold all of the various parts that participate in the functions that keep the cell alive.

The first rule of Cell Theory is all living organisms are composed of one or more cells. This has been disputed as there are non-cellular entities such as viruses that are sometimes given the title of a life form.

Interesting Facts about Biology

  • Some scientists believe that there are more bacteria in the human mouth than are in the world.
  • The human body contains 650 skeletal muscles.
  • Your tongue has 8 muscles in it.
  • Slow twitch muscles have proteins in them that give them a red color. This muscle is responsible for carrying more oxygen in an efficient manner and uses proteins, fats, and carbs as energy.
  • Fast twitch muscles have a whiter color because they have less of the myoglobin protein that carries oxygen.
  • Fast twitch muscle fibers contract powerfully and fast, but they are also become tired quickly.

Cell Theory Quiz

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