NEET Biology Revision Notes
Chapter: Cell - The Unit of Life (Class 11)
1. Introduction to Cell
Definition: Cell is the fundamental, structural, and functional unit of all living organisms.
Discovery: * Robert Hooke (1665): First observed dead cork cells.
o Anton Von Leeuwenhoek (1674): First saw and described a live cell (bacteria, protozoa).
o Robert Brown (1831): Discovered the Nucleus.
2. The Cell Theory
Formulated by Matthias Schleiden (1838) (German Botanist) and Theodore Schwann (1839)
(British Zoologist).
Schleiden concluded that all plants are composed of different kinds of cells.
Schwann studied animal cells and stated that cells have a thin outer layer (plasma membrane).
He also concluded that the presence of a cell wall is a unique character of plant cells.
Modfication by Rudolf Virchow (1855): He explained that cells divide and new cells are
formed from pre-existing cells ("Omnis cellula-e cellula").
3. Prokaryotic Cells vs Eukaryotic Cells
Feature Prokaryotic Cells Eukaryotic Cells
Poorly defined, no nuclear Well-defined with a double-layered
Nucleus
membrane (Nucleoid). nuclear membrane.
Membrane-bound Absent (No Mitochondria, ER, Present (Mitochondria, ER, Golgi,
Organelles Golgi, etc.). Lysosomes).
Ribosomes 70S type (50S + 30S subunits). 80S type (60S + 40S subunits).
Bacteria, Blue-green algae,
Examples Plants, Animals, Fungi, Protists.
Mycoplasma, PPLO.
4. Important Prokaryotic Structures (NEET Favorites)
Cell Envelope: Consists of a tightly bound three-layered structure:
1. Glycocalyx: Can be a loose sheath called slime layer or thick and tough called capsule.
, 2. Cell Wall: Determines shape, provides structural support.
3. Plasma Membrane: Selectively permeable, interacts with the outside world.
Mesosomes: Special membranous structures formed by the extensions of plasma membrane into
the cell. Functions: Cell wall formation, DNA replication, respiration, and secretion.
Mycoplasma: Smallest living cells known (0.3 $\mu m$ in length). They completely lack a
cell wall and can survive without oxygen.
5. Eukaryotic Cell Organelles
Endomembrane System: Includes those organelles whose functions are coordinated. Consists
of: ER, Golgi apparatus, Lysosomes, and Vacuoles. (Note: Mitochondria, Chloroplast, and
Peroxisomes are NOT part of the endomembrane system).
Mitochondria (Powerhouse of the Cell):
o Double-membrane bound. Inner membrane forms infoldings called cristae to increase surface
area.
o Contains its own circular DNA molecule, a few RNA molecules, and 70S ribosomes (Semi-
autonomous organelle).
o Site of aerobic respiration and ATP production.
Plastids (Chloroplast):
o Found in plant cells and euglenoids.
o Contains chlorophyll pigments for photosynthesis.
o Like mitochondria, chloroplasts also contain 70S ribosomes and small, circular, double-
stranded DNA.
Ribosomes (Protein Factories):
o First observed by George Palade (1953) as dense particles under electron microscope.
o Not bound by any membrane. Composed of ribonucleic acid (RNA) and proteins.
6. High-Yield Multiple Choice Questions (MCQs) for Practice
Q1. Which of the following statements is NOT correct regarding Mycoplasma?
A) They are the smallest living cells.
B) They lack a cell wall.
C) They cannot survive without oxygen.
D) They are pathogenic in animals and plants.
Answer: C (Explanation: Mycoplasma can easily survive without oxygen).
Q2. Which of the following organelles is NOT a part of the endomembrane system?
Chapter: Cell - The Unit of Life (Class 11)
1. Introduction to Cell
Definition: Cell is the fundamental, structural, and functional unit of all living organisms.
Discovery: * Robert Hooke (1665): First observed dead cork cells.
o Anton Von Leeuwenhoek (1674): First saw and described a live cell (bacteria, protozoa).
o Robert Brown (1831): Discovered the Nucleus.
2. The Cell Theory
Formulated by Matthias Schleiden (1838) (German Botanist) and Theodore Schwann (1839)
(British Zoologist).
Schleiden concluded that all plants are composed of different kinds of cells.
Schwann studied animal cells and stated that cells have a thin outer layer (plasma membrane).
He also concluded that the presence of a cell wall is a unique character of plant cells.
Modfication by Rudolf Virchow (1855): He explained that cells divide and new cells are
formed from pre-existing cells ("Omnis cellula-e cellula").
3. Prokaryotic Cells vs Eukaryotic Cells
Feature Prokaryotic Cells Eukaryotic Cells
Poorly defined, no nuclear Well-defined with a double-layered
Nucleus
membrane (Nucleoid). nuclear membrane.
Membrane-bound Absent (No Mitochondria, ER, Present (Mitochondria, ER, Golgi,
Organelles Golgi, etc.). Lysosomes).
Ribosomes 70S type (50S + 30S subunits). 80S type (60S + 40S subunits).
Bacteria, Blue-green algae,
Examples Plants, Animals, Fungi, Protists.
Mycoplasma, PPLO.
4. Important Prokaryotic Structures (NEET Favorites)
Cell Envelope: Consists of a tightly bound three-layered structure:
1. Glycocalyx: Can be a loose sheath called slime layer or thick and tough called capsule.
, 2. Cell Wall: Determines shape, provides structural support.
3. Plasma Membrane: Selectively permeable, interacts with the outside world.
Mesosomes: Special membranous structures formed by the extensions of plasma membrane into
the cell. Functions: Cell wall formation, DNA replication, respiration, and secretion.
Mycoplasma: Smallest living cells known (0.3 $\mu m$ in length). They completely lack a
cell wall and can survive without oxygen.
5. Eukaryotic Cell Organelles
Endomembrane System: Includes those organelles whose functions are coordinated. Consists
of: ER, Golgi apparatus, Lysosomes, and Vacuoles. (Note: Mitochondria, Chloroplast, and
Peroxisomes are NOT part of the endomembrane system).
Mitochondria (Powerhouse of the Cell):
o Double-membrane bound. Inner membrane forms infoldings called cristae to increase surface
area.
o Contains its own circular DNA molecule, a few RNA molecules, and 70S ribosomes (Semi-
autonomous organelle).
o Site of aerobic respiration and ATP production.
Plastids (Chloroplast):
o Found in plant cells and euglenoids.
o Contains chlorophyll pigments for photosynthesis.
o Like mitochondria, chloroplasts also contain 70S ribosomes and small, circular, double-
stranded DNA.
Ribosomes (Protein Factories):
o First observed by George Palade (1953) as dense particles under electron microscope.
o Not bound by any membrane. Composed of ribonucleic acid (RNA) and proteins.
6. High-Yield Multiple Choice Questions (MCQs) for Practice
Q1. Which of the following statements is NOT correct regarding Mycoplasma?
A) They are the smallest living cells.
B) They lack a cell wall.
C) They cannot survive without oxygen.
D) They are pathogenic in animals and plants.
Answer: C (Explanation: Mycoplasma can easily survive without oxygen).
Q2. Which of the following organelles is NOT a part of the endomembrane system?
