Chapter: Cell: The Unit of Life
Unit: Cell Biology
Exam Focus: NEET (Concept Clarity + Quick Revision)
What is Cell Theory?
Cell Theory states that all living organisms are made up of cells, and the cell is the basic structural and functional unit of life.
It also states that new cells arise from pre-existing cells through cell division.
This theory forms the foundation of modern biology.
Scientists Involved in Cell Theory
| Scientist | Contribution |
|---|---|
| Robert Hooke (1665) | First observed cells in cork |
| M.J. Schleiden (1838) | All plants are composed of cells |
| T. Schwann (1839) | All animals are composed of cells |
| Rudolf Virchow (1855) | Proposed that cells arise from pre-existing cells |
➡️ Final cell theory = Schleiden + Schwann + Virchow
Postulates of Cell Theory
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All living organisms are composed of one or more cells.
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The cell is the basic structural and functional unit of life.
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New cells arise from pre-existing cells by cell division.
Modern Cell Theory (Important for NEET)
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Cells contain genetic material (DNA).
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Metabolic activities occur within cells.
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Cells have similar chemical composition.
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Energy flow takes place within cells.
Importance of Cell Theory
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Explains growth and development of organisms
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Explains repair and regeneration
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Forms the basis of genetics, molecular biology, and physiology
Exceptions to Cell Theory (NEET Traps)
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Viruses are acellular → cell theory does not apply
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Cell theory does not explain origin of the first cell
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Mammalian RBCs lack nucleus but are still cells
Quick Revision (NEET Last-Minute)
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Cell = basic unit of life
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Proposed by Schleiden & Schwann
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Modified by Virchow
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“Omnis cellula e cellula”
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Viruses are exceptions
NEET Practice MCQs
1. Who proposed that new cells arise from pre-existing cells?
A. Hooke
B. Schleiden
C. Schwann
D. Virchow
Answer: D
2. Cell theory does not apply to:
A. Bacteria
B. Amoeba
C. Virus
D. Plant cell
Answer: C
3. ‘Omnis cellula e cellula’ means:
A. Cells contain DNA
B. Cell is basic unit
C. Cells arise from pre-existing cells
D. Cells perform metabolism
Answer: C
