Cell Theory – Discovery of cell

Key Concepts

• Cell
• Microscope
• Cell theory

Introduction: 

We know that cell is the building block of living organisms. All living things like plants and animals are made up of cells. Majority of the cells are less than 100 µm (100 × 10^-3 m) in diameter, which is smaller than the full stop at the end of the sentence. How do we see such a small cell?  

Microscope 

To observe very tiny things, you cannot use a magnifying glass. We need a microscope. If you are trying to see the cells in a leaf, then you need a microscope.  

A microscope is a tool used to see very tiny things which cannot be seen with the human eyes. 

Early microscope 

Till the development of the microscope, scientists were not even aware of the presence of cells. The first microscope was made by a Dutch person in the late 1500, who was the maker of reading glasses. He kept two magnifying glasses together in one tube and got an image which was larger than the image made by single lens. 

Antonie van Leeuwenhoek made simple microscope with a small glass for a lens. He observed living organisms in pond water, milk, etc. The work of Leeuwenhoek and other scientists helped others to discover many new things. 

Compound Light microscope: It has a high magnification. It comprises of more than one lens. It is also called the bright microscope because the image is observed against the bright background. This microscope is generally used in the laboratory to observe cells.  

Modern microscope: 

Scientists use various microscopes to observe various parts of cells that are very tiny to observe with the human eye. Simple microscope contains only one lens. Compound microscope contains two sets of lenses, i.e., eye piece and objective lense. 

Electron Microscopes: 

There are certain things that are too small to be seen with other microscopes can be viewed with an electron microscope. In electron microscope, direct beam of electrons(light) is used to magnify the image. The resolution power of electron microscope is higher than light microscope. 

Cell Theory 

Discovery of cell was impossible until the discovery of improved version of microscope. In 1665, Robert Hooke, took the thin slice of cork and observed it under his microscope. He saw empty boxes and named it cells. 

In the 1670s, Antonie van Leeuwenhoek discovered bacteria and protozoa. Later developments in lenses and microscope construction helped other scientists to observe various structures present in the cell.  

In 1838, Matthias Schleiden a German scientist studied plant tissues and concluded that all plants are composed of one or more cells. In 1839, another German Scientist Theodor Schwann came up with his observations that animal tissues also consist of cells. In 1855, German scientist Rudolf Virchow, while studying cells under the microscope, saw that cells are dividing and forming new cells. He understood that living cells divide from other living cells. 

The ideas or observations of all these three scientists – Schleiden, Schwann and Virchow led to the formation of cell theory. 

Cell theory states that – 

• All living things are made up of cells. 
• Cell is the basic unit of life. 
• Cell comes from pre-existing cells. 

Discovery of cell and development in cell theory was possible due to the improvements made in microscopes. Advancements in microscope helped the scientists to study cells in more detail than early scientists.

Summary

• Cell is the life of living things.
• Microscope is an instrument used to see very tiny things which cannot be seen with the human eyes.
• There are various types of microscopes – light microscope, compound microscope, electron microscope, etc.
• Robert Hooke coined the term ‘Cell’.
• Cell theory was suggested by Shleidon, Schwann and Virchow.