The Cell Theory

THE CELL THEORY

Cell theory refers to the idea that cells are the basic unit of structure in every living thing.

The study of cells started about 350 years ago.

#  Before that time cells escaped notice because of the cells is impossible to be view by using naked eyes.

#  With the invention of the microscope and its subsequent improvement, cells became “visible” and many new discoveries were made about them.

Schleiden’s and Schwann’s Classical Cell Theory

Matthias Jakob Schleiden (A) and Theodor Schwann (B), who are usually given credit for elucidating the cell theory, made their marks in 1838 and 1839.

Statement	✓ / ✗
The cell is the unit of structure, physiology, and organization in living things.	✓
The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.	✓
Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).	✗

Statement

✓ / ✗

The cell is the unit of structure, physiology, and organization in living things.

✓

The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.

✓

Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).

✗

✓ = statements of cell theory is still valid until today
✗ = statements of cell theory is not valid until today 

Rudolf Virchow

In 1855, Rudolf Virchow added the third tenet to cell theory.

#  In Latin, this tenet states Omnis cellula e cellula.

#  This translated to: All cells arise only from pre-existing cells.

#  Once this tenet was added, the classical cell theory was complete.

Contributions of Scientists in Microscopy

The formulation of the Classical Cell Theory during the 1850s, based on work that began with the development of the microscope in the 1600s.

Hans and Zacharias Janssen

Hans and Zacharias Janssen

Credit for the first compound (more than one lens) microscope is usually given to Hans and Zacharias Jansse.

One lens was at the eyepiece of the microscope (ocular), and the second lens was near the sample to be studied (objective).

Compound microscope developed by Hans and Zacharias Janssen 

Robert Hooke

Robert Hooke

Robert Hooke is an English scientist, who discovered cells in a piece of cork, which he examined under his primitive microscope.

The cork cells (right), which Robert Hooke examined under his primitive microscope (left)

He drew the structures that he saw and called these structures ‘cells’. The word cell is derived from the Latin word 'cellula' which means small compartment.

Anton van Leeuwenhoek

Anton van Leeuwenhoek

Anton van Leeuwenhoek used his own (single lens) monocular microscopes to make pioneering discoveries concerning protozoa and blood cells.

Anton van Leeuwenhoek's monocular microscopes

His skill at grinding lenses, together with his naturally acute eyesight and great care in adjusting the lighting where he worked, enabled him to build microscopes that magnified over 200 times, with clearer and brighter images.

The Modern Cell Theory

The generally accepted parts of modern cell theory, include

1.  The cell is the fundamental unit of structure and function in living organisms.

2.  All known living things are made up of one or more cells.

3.  All cells arise from pre-existing cells by division.

4.  Energy flow (metabolism and biochemistry) occurs within cells.

5.  Cells contain hereditary information (DNA) which is passed from cell to cell during cell division.

6.  All cells are basically the same in chemical composition in organisms of similar species.

7.  The activity of an organism depends on the total activity of independent cells.

Short Quiz

Ultrastructure of an Eukaryotic Cell

Viruses

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