The Cell – Summary Notes
Cells are the basic structural and functional units of life. Every living organism is made up of cells. Some organisms
contain only one cell, while others contain millions of cells working together. Cells carry out important functions such
as respiration, nutrition, growth, reproduction, and excretion.
1. Discovery of the Cell
Robert Hooke discovered cells in 1665 while observing a thin slice of cork under a microscope. He saw tiny box-like
structures and named them “cells.” Later, Anton van Leeuwenhoek observed living cells. The invention of the
microscope helped scientists study cells in detail.
2. Cell Theory
The Cell Theory states:
• All living organisms are made up of cells.
• The cell is the basic unit of life.
• All cells arise from pre-existing cells. Scientists Matthias Schleiden, Theodor Schwann, and Rudolf Virchow
contributed to this theory.
3. Types of Organisms Based on Cells
Organisms can be unicellular or multicellular.
Unicellular organisms consist of a single cell, such as Amoeba and Paramecium.
Multicellular organisms contain many cells, such as humans, plants, and animals. In multicellular organisms, cells
are specialized for different functions.
4. Shape and Size of Cells
Cells differ in shape and size depending on their functions.
• Nerve cells are long for transmitting messages.
• Muscle cells are spindle-shaped.
• Red blood cells are circular and flat.
• Plant cells are usually rectangular. The ostrich egg is one of the largest cells, while bacteria are among the smallest.
5. Structure of a Cell
A typical cell contains three main parts:
Cell membrane: Controls movement of substances in and out of the cell.
Cytoplasm: Jelly-like substance where cell activities occur.
Nucleus: Controls all cell activities and contains genetic material. The nucleus is often called the “brain of the cell.”
6. Cell Organelles
Cell organelles are specialized structures inside the cell.
• Mitochondria: Produce energy and are called the powerhouse of the cell.
• Ribosomes: Help in protein synthesis.
Cells are the basic structural and functional units of life. Every living organism is made up of cells. Some organisms
contain only one cell, while others contain millions of cells working together. Cells carry out important functions such
as respiration, nutrition, growth, reproduction, and excretion.
1. Discovery of the Cell
Robert Hooke discovered cells in 1665 while observing a thin slice of cork under a microscope. He saw tiny box-like
structures and named them “cells.” Later, Anton van Leeuwenhoek observed living cells. The invention of the
microscope helped scientists study cells in detail.
2. Cell Theory
The Cell Theory states:
• All living organisms are made up of cells.
• The cell is the basic unit of life.
• All cells arise from pre-existing cells. Scientists Matthias Schleiden, Theodor Schwann, and Rudolf Virchow
contributed to this theory.
3. Types of Organisms Based on Cells
Organisms can be unicellular or multicellular.
Unicellular organisms consist of a single cell, such as Amoeba and Paramecium.
Multicellular organisms contain many cells, such as humans, plants, and animals. In multicellular organisms, cells
are specialized for different functions.
4. Shape and Size of Cells
Cells differ in shape and size depending on their functions.
• Nerve cells are long for transmitting messages.
• Muscle cells are spindle-shaped.
• Red blood cells are circular and flat.
• Plant cells are usually rectangular. The ostrich egg is one of the largest cells, while bacteria are among the smallest.
5. Structure of a Cell
A typical cell contains three main parts:
Cell membrane: Controls movement of substances in and out of the cell.
Cytoplasm: Jelly-like substance where cell activities occur.
Nucleus: Controls all cell activities and contains genetic material. The nucleus is often called the “brain of the cell.”
6. Cell Organelles
Cell organelles are specialized structures inside the cell.
• Mitochondria: Produce energy and are called the powerhouse of the cell.
• Ribosomes: Help in protein synthesis.
