Chapter 8: Cell - The Unit of Life

The distinction between living and non-living things is defined by the presence of the basic unit of life, which is the cell.
All living organisms are composed of cells. They are classified into two categories based on cell count:
- Unicellular Organisms: Organisms composed of a single cell.
- Multicellular Organisms: Organisms composed of many cells, such as humans.

Unicellular organisms are defined by two primary capabilities:
- (i) Independent existence.
- (ii) Performing the essential functions of life.
Completeness of Structure: Anything less than a complete structure of a cell does not ensure independent living.
Fundamental Definition: The cell is the fundamental structural and functional unit of all living organisms.
Historical Milestones in Cell Biology:
- Antonie Von Leeuwenhoek: He was the first to see and describe a live cell.
- Robert Brown: He later discovered the nucleus.
- Impact of Technology: The invention of the microscope and its subsequent improvement leading to the electron microscope revealed all the structural details of the cell.

In $1838$ , Matthias Schleiden, a German botanist, conducted an extensive examination of a large number of plants.
Schleiden's Observations: He observed that all plants are composed of different kinds of cells which together form the tissues of the plant.
Around the same time, Theodore Schwann (a British Zoologist, though his full title and findings for this specific page are partially contained in the transcript ending) began his contributions to the theory.