Discovery of Cells

Most cells are so tiny that they are not visible to the naked eye Most cells are so tiny that they are not visible to the naked eye. So how did we find out that cells are the basic unit of living things?

What would make someone think that a rabbit or a tree or a person is made up of tiny parts that cannot be seen?

There is a word that describes something that to small to see with the unaided eye. Who knows the name of the term?

Microscopic-extremely small; invisible without the use of a microscope

Actually, the first person to see cells was not even looking them.

In 1665, a British scientist named Robert Hooke was trying to find something interesting that he could show to other scientist at a meeting.

Robert Hooke- A British scientist who observed the first cells in 1665, by using a crude

microscope of his own invention to examine a variety of objects, including a thin piece of cork.

Earlier, he had built a crude microscope that allowed him to look at a very tiny objects. He decided to look at a thin piece of cork, a soft plant tissue found in the bark of trees.

To his amazement, the cork looked liked hundreds of tiny boxes To his amazement, the cork looked liked hundreds of tiny boxes. He named these tiny boxes cells. Which means “little rooms” in latin.

Compound Microscope invented by Robert Hooke

Later he look at slices of plants and saw living things that appeared to have “juice” in them. Those cells were plant cells.

He also looked at feathers, fish scales, and eyes of horse flies He also looked at feathers, fish scales, and eyes of horse flies. But he spent most of his time looking at plants and fungi.

Hooke thought that cells were found only in those types of organism and not in animals.

In 1672 a few years after Hooke made his observations, a dutch merchant named Anton van Leeuwenhoek used one of his own handmade microscopes to get a closer look.

Simple microscope

He was amazed to see tiny creature swimming around in pond scum He was amazed to see tiny creature swimming around in pond scum. He called the Animalcules, which means “little animals”. He also looked at blood from different animals.

He scraped tartar off their teeth and his own He scraped tartar off their teeth and his own. He was the first person to see bacteria. He discovered that in bread, the yeast used to make it were actually tiny organisms.

Anton van Leeuwenhoek- Dutch maker of microscopes, who first to discover protists he also observed red blood cells, capillary systems, and the life cycles of insects.

The Cell Theory After Hooke saw the first cork cells, almost two centuries passed before anyone realized that cells are present in all living things.

Things to ponder  Some Scientist began to put these ideas together and form a theory about cells and how they come into existence.

Theory- an idea of or belief about something arrived at through speculation or conjecture (means to guess)

Development of the cell theory The cell theory was created by different scientist who contributed different parts over a period of time. Let’s review each one and learn what they did to develop the cell theory.

Robert Brown 1833: was a Scottish botanist and palaeobotanist who made important contributions to botany. He discovered the nucleus in plant cells.

Matthias Schleiden, a German botanist, looked at many slides of plant tissues and in 1838 he concluded that all plant parts are made of cells.

Matthias Schleiden

The next year,1839, Theodore Schwann a German physiologist studied animals, stated that all animals tissue are made of cells. He used this to develop the Cell Theory.

Theodor Schwann

Albrecht von Roelliker In 1840, He was the first to observe that sperm and eggs are cells.

Carl Heinrich Braun 1845 he was the first to identify that cells were the basic unit of life.

In 1858, Rudolf Virchow, A German doctor saw that cells could not develop from anything except other cells. That applies to diseased tissue as well as to healthy tissue. He said that diseased cells come from healthy cells of normal tissue.

All cells come from existing cells. Virchow wrote the third part of the cell theory All cells come from existing cells.

Rudolf Virchow

The Cell Theory When Schleiden, Virchow and Schwann proposed the cell theory, cell biology research was forever changed. The cell theory states that: All life forms are made from one or more cells. Cells only arise from pre-existing cells. The cell is the smallest form of life.

The time line

Unicellular- Organisms that are composed of a single cell.

Multicellular- Organisms that are composed of two or more cells.