Class 9 Biology Notes
Chapter: The Fundamental Unit of Life
Introduction
All living organisms are made up of cells. The cell is the basic structural and functional unit of life.
Cells were discovered by Robert Hooke in 1665.
Cell Theory
• • All living organisms are composed of one or more cells.
• • The cell is the basic unit of life.
• • All cells arise from pre-existing cells.
Types of Cells
1. Unicellular organisms: Made of a single cell (e.g., Amoeba).
2. Multicellular organisms: Made of many cells (e.g., Humans).
Cell Structure
1. Plasma Membrane
It is the outermost covering of the cell. It allows some substances to pass through while
preventing others (selectively permeable).
2. Cell Wall (in plants)
A rigid outer layer made of cellulose. It provides shape, protection, and rigidity to plant cells.
3. Nucleus
Controls all activities of the cell and contains genetic material (DNA). It is surrounded by a
nuclear membrane.
4. Cytoplasm
A jelly-like substance present between the nucleus and plasma membrane where all cell
organelles are found.
Cell Organelles
• • Mitochondria: Powerhouse of the cell; site of respiration.
• • Endoplasmic Reticulum: Helps in transport of materials.
• • Ribosomes: Site of protein synthesis.
• • Golgi Apparatus: Modifies, packages and transports proteins.
• • Lysosomes: Known as suicidal bags; help in digestion.
• • Vacuole: Storage sac; large in plant cells.
Difference Between Plant Cell and Animal Cell
Chapter: The Fundamental Unit of Life
Introduction
All living organisms are made up of cells. The cell is the basic structural and functional unit of life.
Cells were discovered by Robert Hooke in 1665.
Cell Theory
• • All living organisms are composed of one or more cells.
• • The cell is the basic unit of life.
• • All cells arise from pre-existing cells.
Types of Cells
1. Unicellular organisms: Made of a single cell (e.g., Amoeba).
2. Multicellular organisms: Made of many cells (e.g., Humans).
Cell Structure
1. Plasma Membrane
It is the outermost covering of the cell. It allows some substances to pass through while
preventing others (selectively permeable).
2. Cell Wall (in plants)
A rigid outer layer made of cellulose. It provides shape, protection, and rigidity to plant cells.
3. Nucleus
Controls all activities of the cell and contains genetic material (DNA). It is surrounded by a
nuclear membrane.
4. Cytoplasm
A jelly-like substance present between the nucleus and plasma membrane where all cell
organelles are found.
Cell Organelles
• • Mitochondria: Powerhouse of the cell; site of respiration.
• • Endoplasmic Reticulum: Helps in transport of materials.
• • Ribosomes: Site of protein synthesis.
• • Golgi Apparatus: Modifies, packages and transports proteins.
• • Lysosomes: Known as suicidal bags; help in digestion.
• • Vacuole: Storage sac; large in plant cells.
Difference Between Plant Cell and Animal Cell
