CELL:
THE UNIT
OF
LIFE
What is a cell?
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A cell is the smallest unit that is
capable of performing life
functions.
All living organisms are composed
of cells.
Examples of cell:
Amoeba Proteus
Plant Stem
Bacteria
Red Blood Cell
Nerve Cell
Cell Theory
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All living things are made up of cells.
Cells are the smallest working units of all
living things.
All cells come from preexisting cells through
cell division.
Discovery of cell:
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In 1665, Robert Hooke
examined a thin slice
of a cork under a
microscope. He saw
that it was made of
thousands of tiny
chambers. These
chambers reminded
him of the tiny rooms
in a monastery, called
cells.
TYPES OF CELL:
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There are two types of
cells:
Prokaryotic cell
Eukaryotic cell
Characteristics of Prokaryotic cell:
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Cells that lack a membranebound nucleus are called
prokaryotes (from the Greek
meaning before nuclei).
Cells in the monera
kingdom such as bacteria
and cyanobacteria (also
known as blue-green algae)
are prokaryotes.
They don't have a
membrane-bound nucleus
and their genetic
information is in a circular
loop called a plasmid.
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Bacterial cells are very
small, roughly the size
of an animal
mitochondrion (about 12µm in diameter and 10
µm long).
Characteristics of Eukaryotic cell:
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Eukaryotic cells (from the
Greek meaning truly
nuclear) comprise all of the
life kingdoms except
monera.
They can be easily
distinguished through a
membrane-bound nucleus.
Eukaryotic cells also contain
many internal membranebound structures called
organelles. These organelles
such as the mitochondrion
or chloroplast
Following are the Important Cellorganelles:
Cell membrane
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Cell wall
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Endoplasmic reticulum
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Golgi apparatus
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Lysosome
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Vacuoles
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Mitochondria
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Plastids
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Ribosomes
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Cilia and Flagella
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Centrosome and centrioles
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Nucleus
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Microbodies
Let us study about each of them individually………………………………
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Cell membrane:
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Outer membrane of cell that
controls movement in and out of
the cell
Double layer
It is a multipurpose covering
composed of phospholipids and
proteins.
Apart from the plasma membrane,
an eukaryotic cell also shows
intracellular and subcellular
membranes around its organelles
and vacuoles.
A fluid mosaic model was given
by singer and nicholson.
Cell Wall:
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A cell wall is a characteristic feature
of plant cells, bacteria and fungi. The
composition however varies in
different groups.
cell wall is chiefly composed of
insoluble polysaccharides, most
common constituent is cellulose,
pectin, hemicellulose, lignin and
xylan may also be present.
The cell wall is generally deposited
in two layers a primary wall and a
secondary wall.
the cell wall is involved in some
specific functions such as :
Protection against the attack of
pathogens
Providing mechanical support
Allowing movement of materials in
and out of the cell
Cytoplasm:
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The term cytoplasm can be used to describe
the matrix of a cell found between its plasma
membrane and the nucleus. It encloses
various cell organelles and inclusions.
The cytoplasm is a semi viscous jelly-like
substance. It consists of an aqueous, almost
transparent structureless ground substance
called hyaloplasm or cytosol.
Cytoplasm serves the following functions
It is the seat of all metabolic and biochemical processes taking place in a cell.
It is involved in the storage of raw materials
or reserve food required by the cell.
It brings about exchange of materials
between the cell organelles.
It exchanges materials with the surrounding
environment such as extra cellular fluid.
Endoplasmic Reticulum(ER):
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This is a complex network of tubes, the
lumen of which is filled with fluid. Two
types of endoplasmic reticula are seen.
They are:
Tubes with a smooth surface are called
smooth endoplasmic reticula. They
secrete lipids.
Tubes with spherical bodies (ribosomes)
attached are known as rough endoplasmic
reticula.
The functions of the endoplasmic
reticulum are to form the skeletal
framework of the cell, to provide a
pathway for the distribution of nuclear
material from one cell to the other and to
synthesize fats, steroids and cholesterol
with the help of enzymes secreted by the
cell.
Golgi apparatus
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Also known as Golgi Complex
or Golgi Bodies, they consist of
tiny, elongated, flattened sacs
(cisternae), which are stacked
parallel to one another along
with some vacuoles and clusters
of vesicles.
The function of the golgi body is
to secrete certain hormones and
enzymes. It also forms
lysosomes and peroxisomes. The
golgi body is usually found close
to the nucleus.
Lysosomes:
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These are tiny, spherical,
sac-like structures scattered
all over the cytoplasm. Their
main function is digestion.
They contain powerful
destructive enzymes capable
of digesting all organic
material, and hence called
“digestive bags”.
“suicide bag” is a sobriquet
that is often used for
Lysosomes.
Vacuoles:
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Membrane-bound sacs
for storage, digestion,
and waste removal
Contains water solution
Help plants maintain
shape
Mitochondria:
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These may be cylindrical, rod-shaped
or spherical and distributed in the
cytoplasm.
Each mitochondrion is bound by a
double membrane.
The inner membrane is folded into
ridges called cristae, which increase
the surface area of the membrane.
It is in the mitochondria that the
sugar is finally burnt during cellular
respiration. The energy thus released
is stored as high-energy chemicals
called ATP (adenosine triphosphate).
Hence, mitochondria are termed as
the “power house” or the “power
plant” of the cell.
Plastids:
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These organelles are found only in plant cells.
Plastids are of three types:
Chloroplasts
Chromoplasts
Leucoplasts
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Chloroplasts
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They are green and found in leaves. The green colour is
due to the presence of chlorophyll.
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Chromoplasts
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They are yellow, orange and red, and found in flowers
and fruits.
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Leucoplasts
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They are colourless and found in roots, seeds and
underground stems.
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The function of the chloroplast is to trap solar energy
for photosynthesis. Chromoplasts impart colour to
flowers to attract insects for pollination. Leucoplasts
store food in the form of carbohydrates, fats and
proteins.
Ribosomes:
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These are spherical,
granular particles which
occur freely in the matrix
or remain attached to the
rough endoplasmic
reticulum.
Ribosomes contain RNA
(ribonucleic acid) and
proteins
Their function is to
provide the surface for
protein synthesis.
Cytoskeleton:
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An elaborate network of
filamentous
proteinaceous structures
present in cytoplasm.
They are involved in
many functions as
mechanical support,
motility, maintenance of
shape of cell etc.
Cilia and Flagella:
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Hair-like outgrowths of the
cell membrane
Covered by plasma
membrane
Their core axoneme
possesses a no. of
microtubules parallel to long
axis.
Cilia are small hair-like
structures which work like
oars. Flagella are longer hair
like structures which beat
anteriorly or posteriorly.
Flagella are of two types: 1.)
Whiplash 2.)Tinsel
Centrosome and Centrioles:
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Present only in animal cells
Made up of two centrioles
(cylindrical structures).
The central part of proximal
region of centriole is also
proteinaceous and called
hub.
Function:formation of
spindle fibres.
Nucleus:
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This is a prominent, spherical or
oval structure found at the centre
of the cell. It is the controlling
centre of all cell activities and has
been described as the brain of the
cell. It regulates all metabolic and
hereditary activities of the cell.
The nucleus is composed of the
following structures:
Nuclear Membrane
Nucleoplasm
Nucleolus
Chromatin network
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Nuclear Membrane
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This is a double-layered membrane which separates the nucleoplasm from the
cytoplasm. The nuclear membrane has minute pores which allow the selective
transfer of material between the nucleoplasm and the cytoplasm.
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Nucleoplasm
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Within the nuclear membrane, completely filling up the space, is a clear, semisolid, granular substance or matrix called the nucleoplasm. The nucleolus and the
chromatin network lie suspended in the nucleoplasm.
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Nucleolus
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This dense, spherical granule found in the nucleus contains RNA (ribonucleic acid)
which is responsible for protein synthesis in the cytoplasm.
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Chromatin Network
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These are very fine thread-like, coiled filaments uniformly distributed in the
nucleoplasm. At the time of cell division, the chromatin becomes thick and ribbon
like and are known as chromosomes. The chromosomes contain genes, which are
composed of DNA (deoxy-ribonucleic acid). Genes are responsible for storing and
transmitting hereditary characteristics from one generation to another. A gene is the
functional unit of a chromosome. Genes are arranged in single linear order along
the chromosome. One gene may be responsible for a single characteristic, or a
single characteristic may be transmitted by a set of genes.
Types of chromosomes based on the
position of centromere:
Microbodies:
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Small sac like structures which contain various
hydrolytic enzymes.
1- Nucleus
2- Chromosomes
3- Mitochondria
4- Ribosomes
5- Chloroplasts
6- Vacuoles
7- ER
8- Cell
Membrane
THANK YOU