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Chapter-08
Cell – The unit of Life
KEY TERMS
Cell: The structural and functional unit of life.
Cell theory: States that (i) all living organisms are composed of cells. (ii) all cells arise from preexisting cells.
Cell Organelles: The membrane bound structures in the cells that perform specific functions.
Endocytosis: Transport of material into the cell by an in folding of the cell membrane forming a
vesicle.
Active transport: Movement of molecules across membrane by expending energy from ATP.
Passive Transport: Movement of molecules across membrane depending upon concentration gradient
of molecules without any requirement of energy.
Osmosis: Movement of water molecule across semi permeable membrane from a region of their higher
concentration to a region of their lower concentration.
Facilitated Diffusion: Diffusion of some ions and polar molecules across membranes through special
transport proteins.
Vesicles: Round, spherical sac like structures.
Cisternae: Elongated, flattened irregular structures.
Tubules: Branched, tubular irregular structures.
Chloroplasts: Plastids that contain chlorophyll.
Amyloplasts: Leucoplasts (a type of plastid) that store carbohydrates
Elaioplasts: Leucoplasts (a type of plastid) that store oils and fats.
Aleuroplasts: Leucoplasts (a type of plastid) that store proteins.
Histones: Packaging proteins associated with chromosomes.
Microbodies: Enzyme bearing membrane bound minute vesicles.
Polyribosome: A chain of ribosomes.
Cytoskeleton: Network of protein filament in the cell that gives support to the cell.
Chromatin: Coiled nucleo-protein fibres present in the nucleus of cell.
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Chromosomes: The network of nucleoprotein condenses into small rod like
structures called
chromosomes during cell division.
Chromatids: Two parts of a chromosome.
Centromere: The primary constriction in a chromosome that holds two chromatids together.
Metacentric chromosome: Centromere at the centre.
Sub-metacentric chromosome: Centromere near the centre.
Acro centric chromosome: Centromere sub terminal.
Telocentric chromosom : Centromere terminal.
Satellite: Chromosomes with a secondary constriction, show a smaller part of chromosome called
satellite.
Prokaryotic cells: A cell with naked genetic material and lacks all membrane bound organelles.
Eukaryotic cell: A cell with well organizsed membrane bound nucleus and number of membrane
bound organelles.
DISCOVERIES
Year
Name of Scientist
Discovery
1665
Robert Hooke
Examined cork under microscope and termed
the word ‘cell’.
1650-1700
Leeuwenhoeck
Used simple lens and observed bacteria.
1831
Robert Brown
Discovered nucleus.
1838
1838 - Mathias Schleiden
Proposed cell theory.
1839- Theodore Schwann
1855- Rudolf Virchow
1840
Purkinje
Gave the term protoplam
1898
Camillio Golgi
Discovered Golgi apparatus
1953
George Palade
Observed Ribosome
1972
Singer Nicholson
Proposed fluid
membrane
mosaic
model
of
cell
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Cells
 Prokaryotic Cell
Bacteria
 Eukaryotic Cell
Plant
Blue green Algae
Animal
PPLO
Fungi
 Nucleus without
nuclear membrane
 Nucleus enclosed
within
nuclear
membrane
1. Capsule
1. Cell wall (Plant Cell)
2. Cell wall
2. Plasma Membrane
3. Plasma Membrane
3. Cytoplasm
4. Cytoplasm
4. Mitochondria
5. Genetic Material (DNA)
5. Endoplasmic Reticulum
6. Ribosomes
6. Golgibodies
7. Plastids (Plant Cell)
8. Lysosome
9. Ribosomes
10.Vacuoles
11. Microbodies
12. Centrosome (Animal Cell)
13. Cilia
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Prokaryotic Cell Structure:
S.N.
1.
Struc`ture
Cell envelope
Description
Function
Cell envelope of different bacteria are Act together as
of different types.
protective unit
a
Capsule : Tough envelope
Slime Layer : Loose Layer
2.
Cell wall
It is present beneath the slime layer
Gives shape to the cell,
Protection
against
mechanical
and
chemical injury.
3.
Plasma
membrane
It is a thin membrane beneath the cell Controls entry an exit
wall
of molecules
It is semi - permeable
4.
Mesosome
Extension of plasma membrane in to Increase surface area
the cell.
Secretion
Respiration
DNA replication
5.
Ribosome
Several ribosome form a chain called Protein synthesis
polyribosome
70 S type with two sub units
50S + 30S
6.
Cytoplasm
Appears granular due to presence of Store house for food,
Ribosomes
lipids,
glycogen
granules
7.
Genetic
Material
(Nucleoid)
It is composed of DNA, (not enclosed Hereditary Material
by membrane).
8.
Plasmid
Non chromosomal, Circular DNA
9.
Flagella
Thin, filamentous extension from the Helps in locomotion
cell wall
Composed of three parts.
Filament, Hook, Basal body
10.
Pilli or
Fimbrae
Elongated tubular structures made of Helps in attachment of
special protein are called pilli
the bacteria to the host
Small bristle like structures are called structure.
fimbrae
11.
Inclusion
body
Reserve material like phosphate Stores material
granules, glycogen granules
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Eukaryotic Cell Structure
Cell or plasma Membrane
(Fluid Mosaic Model) Fig. 8.4
Page 131 NCERT Biologic
Textbook for Class-XI
Outermost
covering
of (i)
Provides
and
animal cells that provides maintains shape of the
and maintains shape of the cell.
cell. It is composed of lipids
that are arranged in a bi
layer.
Cell
possess
(ii)
Regulates
transportation
the
of
materials in a out of
membrane
proteins
also the cell because it is
and semi-permeable
carbohydrates
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Different types of cells
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