Class 9 Biology – The Fundamental Unit of Life
1. Cell – The Basic Unit of Life
A cell is the basic structural and functional unit of life.
All living organisms are made up of one or more cells. Cells perform all the essential functions
required for life.
Examples:
Amoeba consists of a single cell.
Human beings consist of billions of cells.
2. Discovery of Cell
In 1665, Robert Hooke observed cork under a microscope and discovered cells.
In 1674, Antonie van Leeuwenhoek observed living cells for the first time.
3. Cell Theory
Cell theory was proposed by Matthias Schleiden and Theodor Schwann.
Main Points:
All living organisms are made up of cells.
The cell is the basic unit of life.
New cells arise from pre-existing cells.
4. Types of Organisms
(a) Unicellular Organisms
Organisms made up of only one cell.
Examples:
, Amoeba
Paramecium
Bacteria
(b) Multicellular Organisms
Organisms made up of many cells.
Examples:
Human beings
Plants
Animals
5. Shape and Size of Cells
Cells vary in shape and size according to their functions.
Examples:
Nerve cell – long and branched
Red blood cell – disc-shaped
Muscle cell – elongated
6. Cell Structure
The main parts of a cell are:
(a) Cell Membrane
The cell membrane is the outer covering of the cell.
Functions:
Protects the cell
Controls the movement of substances in and out of the cell
(b) Cell Wall
1. Cell – The Basic Unit of Life
A cell is the basic structural and functional unit of life.
All living organisms are made up of one or more cells. Cells perform all the essential functions
required for life.
Examples:
Amoeba consists of a single cell.
Human beings consist of billions of cells.
2. Discovery of Cell
In 1665, Robert Hooke observed cork under a microscope and discovered cells.
In 1674, Antonie van Leeuwenhoek observed living cells for the first time.
3. Cell Theory
Cell theory was proposed by Matthias Schleiden and Theodor Schwann.
Main Points:
All living organisms are made up of cells.
The cell is the basic unit of life.
New cells arise from pre-existing cells.
4. Types of Organisms
(a) Unicellular Organisms
Organisms made up of only one cell.
Examples:
, Amoeba
Paramecium
Bacteria
(b) Multicellular Organisms
Organisms made up of many cells.
Examples:
Human beings
Plants
Animals
5. Shape and Size of Cells
Cells vary in shape and size according to their functions.
Examples:
Nerve cell – long and branched
Red blood cell – disc-shaped
Muscle cell – elongated
6. Cell Structure
The main parts of a cell are:
(a) Cell Membrane
The cell membrane is the outer covering of the cell.
Functions:
Protects the cell
Controls the movement of substances in and out of the cell
(b) Cell Wall
