Updated: Oct 24, 2019
The Cell Theory
The scientist Robert Hooke is seen as the main founder of the cell theory, however many other scientists contributed to theory.
The Cell Theory states that:
1. All Organisms are composed of cells. They may be Unicellular or Pluricellular.
2. The cell is the basic unit of life.
3. Cells arise from preexisting cells.
There are two primary types of cells:
● Prokaryotic cells (Do not contain a nucleus or any other membrane-bounded organelles,
their Ribosomes are also smaller than the Ribosomes in the Eukaryotic cells).
● Eukaryotic cells (Contain a nucleus, membrane-bounded organelles and larger
Example: Animal, plants and fungi cells.
Organelles are tiny cellular structures that carry out specific function necessary for
normal cellular operation. Those are:
● Nucleus - DNA storage and “control center” of the cell.
● Plasma membrane - Separates the cell from its external environment and is selectively
permeable. Inside the same is the Cytoplasm, a liquid where the organelles lie.
● Smooth Endoplasmatic Reticulum (SER) - Lipid production and detoxification.
● Rough Endoplasmatic Reticulum (RER) - Contain Ribosomes in contrast with the
SER. It is responsible for protein production and export of protein out of the cell.
● Ribosomes - Production of proteins. The cell “factory”.
● Golgi apparatus - Stores and export proteins, combine molecules to more complex
● Lysosome - Digest enzymes, molecules and even other cells such as bacteria. It is the
“Stomach” of the cell.
● Mitochondria - Produces energy in form of ATP ( Adenosine Triphosphate) through
cellular respiration. The “powerhouse” of the cell.
● Vacuoles - Storage of food, water, and minerals
Some Organelles are only found in specific kinds of cells. The following organelles can only be found in plant cells:
● Cell Wall - A Rigid organelle composed of cellulose. Protection for the cell from the
● Chloroplasts - Absorbs sunlight and converts it into energy.
● Central Vacuole - Large fluid-filled vacuole. Mainly for storage of liquids and nutrients.
Now the following can only be found in animal cells or Prokaryotic cells
● Flagellum - Locomotion
● Pili - Locomotion, and assists the cell to Attach to another cell
There are also organelles that can only be found in prokaryotic cells:
● Capsule - A third protective covering made up of polysaccharides
● Cell envelop - Protection of the cell. There are two types gram-negative and
● Nucleoid - Where the DNA is located in a Prokaryotic cell.
1. http://www.edu.pe.ca/gray/class_pages/rcfleming/cells/notes.htm - 10/04
2. https://www.thoughtco.com/cell-theory-373300 - 10/04
3. https://en.wikipedia.org/wiki/Cell_theory - 10/04
4. http://study.com/academy/lesson/eukaryotic-and-prokaryotic-cells-similarities-and-differences.html - 10/04
5. http://www.diffen.com/difference/Eukaryotic_Cell_vs_Prokaryotic_Cell - 10/04
6. https://www.khanacademy.org/test-prep/mcat/cells/eukaryotic-cells/a/organelles-article - 10/04
7. http://www.sparknotes.com/biology/cellstructure/celldifferences/section1.rhtml - 10/04