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Class 9 Science

Chapter: Cell – The Fundamental Unit of Life

What is Cell

A cell is the basic structural and functional unit of life. All living organisms are made up of cells. All important life processes such as respiration, growth, excretion and reproduction take place inside the cell.

Some organisms are made up of only one cell and are called unicellular organisms, while others are made up of many cells and are called multicellular organisms.

Discovery of Dead Cell

The dead cell was first discovered by Robert Hooke in 1665. He observed a thin slice of cork under a microscope and saw many small box-like structures. He called these structures cells because they looked like small rooms. These cells were dead because cork tissue consists of dead plant cells.

Discoveries Related to Cells and Scientists

The first discovery of cells was made by Robert Hooke, who observed dead cells in cork.

Later Antonie van Leeuwenhoek observed living cells and microorganisms with a powerful microscope.

The nucleus was discovered by Robert Brown in 1831.

Matthias Schleiden stated that all plants are made up of cells.

Theodor Schwann stated that all animals are made up of cells.

Later Rudolf Virchow proposed that new cells arise from pre-existing cells.

Prokaryotic Cell Discovery

The term prokaryotic cell was introduced by Édouard Chatton in 1925. He distinguished organisms that do not have a true nucleus (prokaryotes) from those that have a true nucleus (eukaryotes).

Cell Theory

The cell theory explains the importance of cells in living organisms.

It states that all living organisms are made up of cells. The cell is the basic structural and functional unit of life. New cells are formed from pre-existing cells.

The cell theory was mainly proposed by Matthias Schleiden and Theodor Schwann, and later improved by Rudolf Virchow.

Chain of Cells

Cells join together to form tissues. Tissues form organs, organs form organ systems, and organ systems together form a complete organism.

Example:

Cell → Tissue → Organ → Organ System → Organism

Difference Between Unicellular and Multicellular Organisms

Unicellular Organisms

Made up of a single cell

One cell performs all life processes

Usually microscopic

Example: Amoeba, bacteria

Multicellular Organisms

Made up of many cells

Different cells perform different functions

Usually larger and visible

Example: Humans, plants, animals

Difference Between Prokaryotic Cell and Eukaryotic Cell

Prokaryotic Cell

No true nucleus

Simple structure

Smaller in size

No membrane-bound organelles

Example: Bacteria

Eukaryotic Cell

True nucleus present

Complex structure

Larger in size

Membrane-bound organelles present

Example: Plant cells and animal cells

✅ If you want, I can also make 2 more exam-important pages:

Plant cell and animal cell explanation + diagram

Cell organelles (nucleus, mitochondria, ribosome, etc.)

These are very important for Class 9 exams.