Chapter – Cell: The Unit of Life
1. What is a Cell?
• Cell is the basic structural and functional unit of life.
• There are more than 200 different types of cells present in humans.
• All metabolic reactions occur inside the cell.
• A cell is the smallest thing that can survive independently. Anything less than a complete
structure of a cell cannot ensure independent living.
• Cellular organisation is a defining feature of all living organisms.
• Organisms: Unicellular (e.g., Monera & Protista) and Multicellular (e.g., Higher Plants &
Animals).
• Unicellular organisms are capable of independent existence and performing all essential
functions of life on their own.
2. Historical Landmarks (Scientists)
• Robert Hooke: Discovered cell for the first time (dead cork cell, termed 'cellular').
• Robert Brown (1831): Discovered the nucleus inside the cell.
• Anton von Leeuwenhoek: First saw and described a live cell.
• In 1950s (1950-1960): Due to advancement in electron microscopy, many structural details of
the cell were described.
3. Cell Theory
• 1838 - Schleiden (German Botanist): Examined a large number of plants and observed that all
plants are composed of different kinds of cells which form the tissues of the plant.
• 1839 - Schwann (British Zoologist): Studied different types of animal cells and reported that
cells had a thin outer layer, today known as the 'plasma membrane'. He also concluded, based on
studies on plant tissues, that the presence of a cell wall is a unique character of plant cells.
• Hypothesis: Schwann proposed the hypothesis that the bodies of animals and plants are
composed of cells and products of cells.
• The Cell Theory was together formulated by Schleiden and Schwann. However, their theory did
not explain how new cells were formed.
• Final Shape to Cell Theory - Rudolf Virchow (1855): He first explained that cells divided and
new cells are formed from pre-existing cells ('Omnis cellula-e cellula').
1. What is a Cell?
• Cell is the basic structural and functional unit of life.
• There are more than 200 different types of cells present in humans.
• All metabolic reactions occur inside the cell.
• A cell is the smallest thing that can survive independently. Anything less than a complete
structure of a cell cannot ensure independent living.
• Cellular organisation is a defining feature of all living organisms.
• Organisms: Unicellular (e.g., Monera & Protista) and Multicellular (e.g., Higher Plants &
Animals).
• Unicellular organisms are capable of independent existence and performing all essential
functions of life on their own.
2. Historical Landmarks (Scientists)
• Robert Hooke: Discovered cell for the first time (dead cork cell, termed 'cellular').
• Robert Brown (1831): Discovered the nucleus inside the cell.
• Anton von Leeuwenhoek: First saw and described a live cell.
• In 1950s (1950-1960): Due to advancement in electron microscopy, many structural details of
the cell were described.
3. Cell Theory
• 1838 - Schleiden (German Botanist): Examined a large number of plants and observed that all
plants are composed of different kinds of cells which form the tissues of the plant.
• 1839 - Schwann (British Zoologist): Studied different types of animal cells and reported that
cells had a thin outer layer, today known as the 'plasma membrane'. He also concluded, based on
studies on plant tissues, that the presence of a cell wall is a unique character of plant cells.
• Hypothesis: Schwann proposed the hypothesis that the bodies of animals and plants are
composed of cells and products of cells.
• The Cell Theory was together formulated by Schleiden and Schwann. However, their theory did
not explain how new cells were formed.
• Final Shape to Cell Theory - Rudolf Virchow (1855): He first explained that cells divided and
new cells are formed from pre-existing cells ('Omnis cellula-e cellula').
