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CHAPTER-08 CELL: STRUCTURE AND FUNCTIONS
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CHAPTER-08 CELL: STRUCTURE AND FUNCTIONS
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CBSE Quick Revision Notes (Class-11 Biology)CHAPTER-08 CELL: STRUCTURE AND FUNCTIONS
• Study of form, structure, and composition of cell is called cytology.
• Cell is the structural and functional unit of life. In unicellular organism (amoeba,
paramecium, yeast bacteria) , single cell perform the all essential functions of life.
• In multicellular organism, different kinds of tissues perform different function and have
division of labour.
• Melthias Schleiden and Theodore Schwann( 1938) proposed the cell theory-
a. All living organisms are composed of cells and products of cells.
b. All cells arise from pre-existing cells.
Prokaryotic cells Eukaryotic cells
(i) Membrane bound nucleus is absent. (i) Membrane bound nucleus is present.
(ii) Cells are smaller in size. (ii) Cells are larger in size.
(iii) Single chromosome is present. (iii) More than one chromosome is
(iv) Membrane bound organelles are absent. present.
(iv) Membrane bound organelles are
present.
Shape and size of cells varies greatly according to their position and function. Mycoplasma
is the smallest cell and largest isolated cell is the ostrich egg. The shape of cell may be
cuboid, columnar, polygonal, thread like or irregular.
Prokaryotic Cells
Prokaryotic cells are represented by Bacteria, Blue green algae, Mycoplasma and PPLO.
They multiply rapidly and vary in size greatly.
Bacterial cells may be Bacillus (rod shaped), Coccus (spherical), Vibrio (comma-shaped)
and Spirillum (spiral).
All prokaryotic cells have cell wall surrounding the cell membrane except in Mycoplasma.
Genetic material is naked.
The plasmid DNA, in some bacteria provides some special features like resistance to
antibiotic.
Cell organelles like Mitochondria,
Golgi bodies etc. are absent in
prokaryotes. A specialized
differentiated cell membrane
called Mesosome is the
characteristic of prokaryotes.
In bacterial cell a chemically
complex cell envelope is present,
which consist of three layers. The outermost is Glycocalyx, middle one cell wall and inner
innermost is the cell membrane.
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, Glycocalyax may be as loose sheath in some bacteria called slime layer. In some other
bacteria Glycocalyx may be thick and tough called capsule.
Plasma membrane is semi-permeable having mesosome in form of vesicles, tubules and
lamellae. They help in cell wall formation, DNA replication and distribution to daughter
cells.
Motile bacterial cell contain flagella, which is composed of filament, hook and basal body.
Pili and fimbriae are the other surface structure that help the bacteria in attach with host
and other substance.
In prokaryotes, ribosome are attached with cell membrane having two sub-units – 50S and
30S to form together 70S prokaryotic ribosomes.
Ribosomes are site of protein synthesis. Ribosomes attached with mRNA to form a chain
called polyribosomes.
Reserved materials in prokaryotic cells are present in cytoplasm as cell inclusion bodies,
which may contain phosphate, granules, glycogen granules etc.
Gas vacuoles are found in blue green algae and purple and green photosynthetic bacteria.
Eukaryotic Cell
Eukaryotic cells are present in Protista, plants, Animals and Fungi. Cytoplasm is divided
into compartments due to presence of membrane bounded organelles.
The cells contain well organized nucleus with nuclear membrane. The genetic materials are
arranged in chromosomes.
Plants cells differ in having cell wall, plastids and large central vacuole as compared to
animal cells. Animal cells have centrioles, which are absent in plant cells.
Plant cell
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