- A cell is the fundamental, structural and functional unit of (i) All living organisms are composed of cells and
all living organisms. products of cells.
- Robert Hooke: Discovered cell. (ii) All cells arise from pre-existing cells.
- Anton Von Leeuwenhoek: First observed and described a
AN OVERVIEW OF CELL
live cell.
- The invention of the compound & electron microscopes - All cells contain
revealed all the structural details of the cell. o Cytoplasm: A semi-fluid matrix where cellular
activities and chemical reactions occur. This keeps the
CELL THEORY cell in ‘living state’.
- Matthias Schleiden (1838) observed that all plants are o Ribosomes: Non-membrane bound organelles seen in
composed of different kinds of cells. cytoplasm, chloroplasts, mitochondria & on rough ER.
- Theodore Schwann (1839) found that cells have a thin - Cells differ in size, shape and activities.
outer layer (plasma membrane). He also found that plant o Smallest cells: Mycoplasmas (0.3 µm in length).
cells have cell wall. He proposed a hypothesis that animals o Largest isolated single cell: Egg of ostrich.
and plants are composed of cells and products of cells. o Longest cells: E.g. Nerve cell.
- Schleiden & Schwann formulated the cell theory. o Size of bacteria: 3 to 5 µm (Typical: 1 to 2 µm).
- Rudolf Virchow (1855) first explained that cells divide o Human RBCs are about 7.0 µm in diameter.
and new cells are formed from pre-existing cells (Omnis - Based on the functions, shape of cells may be disc-like,
cellula-e cellula). He modified the cell theory. polygonal, columnar, cuboid, thread like, or irregular.
- Cell theory states that: - Cells are 2 types: Prokaryotic cells & Eukaryotic cells.
PROKARYOTIC CELLS
- They have no membrane bound nucleus and organelles.
o In distribution of chromosomes to daughter cells.
- They include bacteria, blue-green algae, mycoplasma &
o In respiration and secretion processes.
PPLO (Pleuro Pneumonia Like Organisms). o To increase the surface area of the plasma membrane
- They are generally smaller and multiply more rapidly than and enzymatic content.
the eukaryotic cells. - Chromatophores are pigment-containing membranous
- They vary in shape & size. E.g. Bacteria have 4 basic infoldings in some prokaryotes (e.g. cyanobacteria).
shapes: Bacillus, Coccus, Vibrio and Spirillum.
1. Nucleoid
Cell organelles in prokaryotic cells - It is formed of non-membranous (naked) circular genomic
1. Cell Envelope DNA (single chromosome/ Genetic material) & protein.
- It is a chemically complex protective covering. - Many bacteria have small circular DNA (plasmid) outside
- It is made of 3 tightly bound layers. the genomic DNA. It gives some unique phenotypic
o Glycocalyx: Outer layer. Its composition and thickness characters (e.g. resistance to antibiotics) to bacteria.
vary in different bacteria. It may be a slime layer (loose 1. Flagella
sheath) or capsule (thick & tough). - These are thin filamentous extensions from the cell wall of
o Cell wall: Middle layer. Seen in all prokaryotes except motile bacteria. Their number and arrangement are varied
mycoplasma. It gives shape to the cell and provides a in different bacteria.
structural support to prevent the bacterium from bursting - Bacterial flagellum has 3 parts – filament, hook and basal
or collapsing. body. The filament is the longest portion and extends from
o Plasma membrane: Inner layer. It is semi-permeable in the cell surface to the outside.
nature and interacts with the outside. This is structurally
1. Pili and Fimbriae
similar to that of the eukaryotes.
- These are surface structures that have no role in motility.
- Based on the types of the cell envelopes and response to
- Pili (sing. Pilus) are elongated tubular structures made of a
Gram staining (developed by Gram), bacteria are 2 types:
special protein (pilin).
o Gram positive: They take up and retain the gram stain.
- Fimbriae are small bristle like fibres sprouting out of the
o Gram negative: They do not retain the gram stain.
cell. In some bacteria, they help to attach the bacteria to
1. Mesosomes & Chromatophores
rocks in streams and to the host tissues.
(Membranous structures)
- Mesosome is formed by the infoldings of plasma 1. Ribosomes
membrane. It includes vesicles, tubules & lamellae. - They are associated with plasma membrane of prokaryotes.
- Functions: Mesosomes help - They are about 15 nm by 20 nm in size.
o In cell wall formation. - They are made of 2 subunits - 50S & 30S (Svedberg’s
o In DNA (chromosome) replication. unit). They together form 70S prokaryotic ribosomes.
1
, (S= sedimentation coefficient; a measure of density & size). - These are non-membranous, stored reserve material seen
- Function: Ribosomes are the site of translation (protein freely in the cytoplasm of prokaryotic cells.
synthesis). Several ribosomes may attach to a single - E.g. phosphate granules, cyanophycean granules and
mRNA to form a chain called polyribosomes (polysome). glycogen granules, gas vacuoles etc.
Ribosomes translate the mRNA into proteins. - Gas vacuoles are found in blue green and purple and green
1. Inclusion Bodies photosynthetic bacteria.
EUKARYOTIC CELLS
- They have well organized membrane bound nucleus and o Peripheral proteins: Lie on the surface of membrane.
organelles. - Fluid mosaic model of cell membrane: Proposed by
- Presence of membranes gives clear compartmentalization Singer & Nicolson (1972). According to this, the quasi-
of cytoplasm. fluid nature of lipid enables lateral movement of proteins
- Their genetic material is organized into chromosomes. within the overall bilayer. This ability to move within the
- They have complex locomotory & cytoskeletal structures. membrane is measured as its fluidity.
Plant cell and Animal cell
Functions:
o Transport of the molecules. The membrane is selectively
permeable to some molecules present on either side of it.
o Due to the fluid nature, the plasma membrane can help in
cell growth, formation of intercellular junctions, secretion,
endocytosis, cell division etc.
Types of Transport
1. Passive transport: It is the movement of molecules across
the membrane along the concentration gradient (i.e., from
higher concentration to the lower) without the expenditure
of energy. It is 2 types:
a. Simple diffusion: It is the movement of neutral solutes
across the membrane.
b. Osmosis: It is the movement of water by diffusion
across the membrane.
Polar molecules cannot pass through the non-polar lipid
bilayer. So they require membrane carrier protein for
Cell organelles in eukaryotic cells transport.
2. Active transport: It is the movement of molecules across
1. Cell Membrane
the membrane against the concentration gradient (i.e. from
- Chemical studies on human RBCs show that cell membrane
lower to the higher concentration) with the expenditure of
is composed of a lipid bilayer, protein & carbohydrate.
energy (ATP is utilized). E.g. Na+/K+ pump.
- Lipids (mainly phosphoglycerides) have outer polar head
and the inner hydrophobic tails. So the non-polar tail of 2. Cell Wall
saturated hydrocarbons is protected from the aqueous - It is a non-living rigid structure found outer to the plasma
environment. membrane of fungi and plants.
- Ratio of protein and lipid varies in different cells. E.g. In - Cell wall of Algae is made of cellulose, galactans, mannans
human RBC, membrane has 52% protein and 40% lipids. and minerals like CaCO3. In other plants, it consists of
- Based on the ease of extraction, membrane proteins are 2 cellulose, hemicellulose, pectins and proteins.
types: - Cell wall of a young plant cell (primary wall) is capable
o Integral proteins: Partially or totally buried in membrane. of growth. It gradually diminishes as the cell matures and
2
all living organisms. products of cells.
- Robert Hooke: Discovered cell. (ii) All cells arise from pre-existing cells.
- Anton Von Leeuwenhoek: First observed and described a
AN OVERVIEW OF CELL
live cell.
- The invention of the compound & electron microscopes - All cells contain
revealed all the structural details of the cell. o Cytoplasm: A semi-fluid matrix where cellular
activities and chemical reactions occur. This keeps the
CELL THEORY cell in ‘living state’.
- Matthias Schleiden (1838) observed that all plants are o Ribosomes: Non-membrane bound organelles seen in
composed of different kinds of cells. cytoplasm, chloroplasts, mitochondria & on rough ER.
- Theodore Schwann (1839) found that cells have a thin - Cells differ in size, shape and activities.
outer layer (plasma membrane). He also found that plant o Smallest cells: Mycoplasmas (0.3 µm in length).
cells have cell wall. He proposed a hypothesis that animals o Largest isolated single cell: Egg of ostrich.
and plants are composed of cells and products of cells. o Longest cells: E.g. Nerve cell.
- Schleiden & Schwann formulated the cell theory. o Size of bacteria: 3 to 5 µm (Typical: 1 to 2 µm).
- Rudolf Virchow (1855) first explained that cells divide o Human RBCs are about 7.0 µm in diameter.
and new cells are formed from pre-existing cells (Omnis - Based on the functions, shape of cells may be disc-like,
cellula-e cellula). He modified the cell theory. polygonal, columnar, cuboid, thread like, or irregular.
- Cell theory states that: - Cells are 2 types: Prokaryotic cells & Eukaryotic cells.
PROKARYOTIC CELLS
- They have no membrane bound nucleus and organelles.
o In distribution of chromosomes to daughter cells.
- They include bacteria, blue-green algae, mycoplasma &
o In respiration and secretion processes.
PPLO (Pleuro Pneumonia Like Organisms). o To increase the surface area of the plasma membrane
- They are generally smaller and multiply more rapidly than and enzymatic content.
the eukaryotic cells. - Chromatophores are pigment-containing membranous
- They vary in shape & size. E.g. Bacteria have 4 basic infoldings in some prokaryotes (e.g. cyanobacteria).
shapes: Bacillus, Coccus, Vibrio and Spirillum.
1. Nucleoid
Cell organelles in prokaryotic cells - It is formed of non-membranous (naked) circular genomic
1. Cell Envelope DNA (single chromosome/ Genetic material) & protein.
- It is a chemically complex protective covering. - Many bacteria have small circular DNA (plasmid) outside
- It is made of 3 tightly bound layers. the genomic DNA. It gives some unique phenotypic
o Glycocalyx: Outer layer. Its composition and thickness characters (e.g. resistance to antibiotics) to bacteria.
vary in different bacteria. It may be a slime layer (loose 1. Flagella
sheath) or capsule (thick & tough). - These are thin filamentous extensions from the cell wall of
o Cell wall: Middle layer. Seen in all prokaryotes except motile bacteria. Their number and arrangement are varied
mycoplasma. It gives shape to the cell and provides a in different bacteria.
structural support to prevent the bacterium from bursting - Bacterial flagellum has 3 parts – filament, hook and basal
or collapsing. body. The filament is the longest portion and extends from
o Plasma membrane: Inner layer. It is semi-permeable in the cell surface to the outside.
nature and interacts with the outside. This is structurally
1. Pili and Fimbriae
similar to that of the eukaryotes.
- These are surface structures that have no role in motility.
- Based on the types of the cell envelopes and response to
- Pili (sing. Pilus) are elongated tubular structures made of a
Gram staining (developed by Gram), bacteria are 2 types:
special protein (pilin).
o Gram positive: They take up and retain the gram stain.
- Fimbriae are small bristle like fibres sprouting out of the
o Gram negative: They do not retain the gram stain.
cell. In some bacteria, they help to attach the bacteria to
1. Mesosomes & Chromatophores
rocks in streams and to the host tissues.
(Membranous structures)
- Mesosome is formed by the infoldings of plasma 1. Ribosomes
membrane. It includes vesicles, tubules & lamellae. - They are associated with plasma membrane of prokaryotes.
- Functions: Mesosomes help - They are about 15 nm by 20 nm in size.
o In cell wall formation. - They are made of 2 subunits - 50S & 30S (Svedberg’s
o In DNA (chromosome) replication. unit). They together form 70S prokaryotic ribosomes.
1
, (S= sedimentation coefficient; a measure of density & size). - These are non-membranous, stored reserve material seen
- Function: Ribosomes are the site of translation (protein freely in the cytoplasm of prokaryotic cells.
synthesis). Several ribosomes may attach to a single - E.g. phosphate granules, cyanophycean granules and
mRNA to form a chain called polyribosomes (polysome). glycogen granules, gas vacuoles etc.
Ribosomes translate the mRNA into proteins. - Gas vacuoles are found in blue green and purple and green
1. Inclusion Bodies photosynthetic bacteria.
EUKARYOTIC CELLS
- They have well organized membrane bound nucleus and o Peripheral proteins: Lie on the surface of membrane.
organelles. - Fluid mosaic model of cell membrane: Proposed by
- Presence of membranes gives clear compartmentalization Singer & Nicolson (1972). According to this, the quasi-
of cytoplasm. fluid nature of lipid enables lateral movement of proteins
- Their genetic material is organized into chromosomes. within the overall bilayer. This ability to move within the
- They have complex locomotory & cytoskeletal structures. membrane is measured as its fluidity.
Plant cell and Animal cell
Functions:
o Transport of the molecules. The membrane is selectively
permeable to some molecules present on either side of it.
o Due to the fluid nature, the plasma membrane can help in
cell growth, formation of intercellular junctions, secretion,
endocytosis, cell division etc.
Types of Transport
1. Passive transport: It is the movement of molecules across
the membrane along the concentration gradient (i.e., from
higher concentration to the lower) without the expenditure
of energy. It is 2 types:
a. Simple diffusion: It is the movement of neutral solutes
across the membrane.
b. Osmosis: It is the movement of water by diffusion
across the membrane.
Polar molecules cannot pass through the non-polar lipid
bilayer. So they require membrane carrier protein for
Cell organelles in eukaryotic cells transport.
2. Active transport: It is the movement of molecules across
1. Cell Membrane
the membrane against the concentration gradient (i.e. from
- Chemical studies on human RBCs show that cell membrane
lower to the higher concentration) with the expenditure of
is composed of a lipid bilayer, protein & carbohydrate.
energy (ATP is utilized). E.g. Na+/K+ pump.
- Lipids (mainly phosphoglycerides) have outer polar head
and the inner hydrophobic tails. So the non-polar tail of 2. Cell Wall
saturated hydrocarbons is protected from the aqueous - It is a non-living rigid structure found outer to the plasma
environment. membrane of fungi and plants.
- Ratio of protein and lipid varies in different cells. E.g. In - Cell wall of Algae is made of cellulose, galactans, mannans
human RBC, membrane has 52% protein and 40% lipids. and minerals like CaCO3. In other plants, it consists of
- Based on the ease of extraction, membrane proteins are 2 cellulose, hemicellulose, pectins and proteins.
types: - Cell wall of a young plant cell (primary wall) is capable
o Integral proteins: Partially or totally buried in membrane. of growth. It gradually diminishes as the cell matures and
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