All living organisms are made up of a variety of body parts like roots, leaves, flowers, fruits, wood etc. in plants and bones, flesh, nerves etc in animals. These parts look different from each other, yet they are all composed of tiny units called cells. Moreover, many living organisms like Amoeba, Paramecium, Chlamydomonas etc. consist of only one cell.

1. CELL THE BASIC UNIT OF LIFE: EASY
DRAWING OF CELL
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CELL THE BASIC UNIT OF LIFE
INTRODUCTION
All living organisms are made up of a variety of body parts like roots, leaves, flowers, fruits, wood etc. in
plants and bones, flesh, nerves etc in animals. These parts look different from each other, yet they are all
composed of tiny units called cells. Moreover, many living organisms
like Amoeba, Paramecium, Chlamydomonas etc. consist of only one cell. (CELL – A UNIT OF LIFE)
DEFINITION
A cell is the structural and functional unit of all living beings. A cell is microscopic. In an organism cell is the
minute part of a body. All living beings start their life as a single cell. Every cell has its own life span. (CELL
– A UNIT OF LIFE)
CHARACTERISTICS ( CELL – A UNIT OF LIFE)
Old and worn-out cells are continuously replaced by new cells. It consists of an organized mass of
protoplasm, surrounded by a selectively permeable covering called plasma membrane. In an animal cell, the
plasma membrane is the only limiting membrane. However, in plant cells, fungi and bacteria, the cell is also
surrounded by a cell wall. (CELL – A UNIT OF LIFE)
DISCOVERY OF CELL
Fig#1 first microscope developed by Robert Hooke
The invention of microscope helped in the discovery of cell.
The first microscope was constructed by Anton Von Leeuwenhoek (1632 – 1723). It consist of a single
biconvex lens and was known as the simple microscope. Some of the Leeuwenhoek’s microscopes could
magnify objects up to 200 times.
Robert Hooke (1635 – 1703) developed a compound microscope by using two lenses for achieving greater
magnification. Robert Hooke studied a thin slice of cork under his microscope. He observed that the cork
slice had a large number of compartments as ” cells”. (in Latin: Cella means compartment).

2. CELL THEORY
The cell theory was formulated by two german biologists, Matthias Schleiden (1838) and Theodor Schwann
(1839), their theory stated cell as the basic structural and
functional unit of all living beings.In 1855, Rudolf Vir Chow added a phrase ” omnis cellula-e- cellula”,
meaning all cells arise from pre – existing cells.
Cell theory can be stated as follows:
* The structural and functional unit of all living beings is the cell.
* All living organisms are composed of cells ( CELL – A UNIT OF LIFE)
* All new cells arise as a result of division of pre – existing cells.
* All cells are chemically similar in composition and in biological process. (CELL – A UNIT OF LIFE)
SIZE OF THE CELL
The smallest known cell is Mycoplasma or pplo (Pleuropneumonia –like organism).
It’s size varies from 0. 1 to 0. 5micrometer. The bacterial cell is 0. 5 to 5 micrometre.
Human red blood corpuscles are 7 to 20 micrometre. ( cell)
Human liver and kidney cells are 20 to 30 micrometre. Nerve cells are about 90 to 100 cm in size which are
the longest cell in world. Acetabularia is the longest plant cell having
a length of 10 cm which is a single-celled alga. The largest cells are the bird’s egg. The egg of an
Ostrich is 170x 135 mm which is the largest single cell. ( CELL – A UNIT OF LIFE)
Cell number: ( CELL – A UNIT OF LIFE)
Many organisms are made up only one cell or many cells.
Single-celled: Organisms are made up of only one cell, they are called Single-celled
or unicellular. For example, Bacteria, Amoeba Paramecium, Euglena Chlamydomonas ete.
Multicelled: Most organisms are multicellular
i.e. they are made up of several cells.A newly – born human baby has 2 trillion cells
while an adult man has about 100 trillion cells.
Cell – shape

3. Fig#2 different shapes of cell
Cells show a great variation in their shapes to suit their functions. Most cells have a definite shape.Cells may
be
Spinde – shaped – muscle cells
Elongated – nerve cells
Oval- red blood corpuscles
Branched – osteocytes
irregular shaped – white blood corpuscles
Type of cell
On the basis of their nuclear organizalioncells have been classified into two types
Prokaryotic cells:
Fig#3 structure of a prokaryotic cell
[ pro – before; karvos – nucleus ]Prokaryotic cells having a primitive nucleus. The nuclear material in these
cells is not enclosed by a nuclear membrane. These cells lack several cell organelles like mitochondria,
lysosome, endoplasmic reticulum
chloroplast and nucleolus. Bacteria and blue–green algae are examples of prokaryotic cells.
Eukaryotic cell ( CELL – A UNIT OF LIFE)

4. Fig#4 simplified structure of plant cell
Fig#5 simplified structure of animal cell
[eu-true; karyon-nucleus] Eukaryotic cells mean cells having a properly defined nuclear membrane. In these
cells , the genetic material is made of two or more DNA molecules which form chromatin fibres . The nuclear
material is enclosed in a nuclear membrane. These cells have a well-organised nucleus and have well-
developed membrane-bound organelles,such as mitochondria, endoplasmic reticulum, lysosome, chloroplast
and nucleolus. Eukaryotic cells occur in plants, animals,fungi and protozoa. (cell)
AN OVERVIEW OF CELL ( CELL – A UNIT OF
LIFE)
CELL
ORGANELL
E
KEY
CHARACTERISTICS
KEY
FUNCTION
DIAGRAM

5. 1) Cell wall
a)Found only in plant
cell
b)Composed of
cellulose c)Rigid,
protective, supportive
in nature
a)It provides
shapes and
rigidity to the
cell
b)freely
permeable
c)protects
plasma
membraneand
internal
structure of
the cell
2)Plastid
a)Double-layered
proteinaceous
containing DNA
b)Three types of
organelles:-
Chloroplast,
Chromoplast,
Leucoplast
c)Found only in plant
cell
a)Chloroplast
helps in
photosynthesi
s
b)chromoplas
t imparts
colour to
flower and
fruit
c)Leucoplast
helps in the
storage of
food
3)Centrosome
a)Found only in
animal cell.
b)Small, naked,
protoplasmic structure
present near the
nucleus.
c)Consists of two
small granules called
centrioles.
a) Initiates
and regulates
cell division.
b)Helps in
cell division.

6. 4)Cell
membrane
a)Found in both the
cells.
b)selectively permeabl
e.
c)Made up of lipids
and proteins in the
bilayer.
a)Allows
only selective
substances to
pass through
it.
b)protects the
cell from
injury.
5)Cytoplasm
a)Amorphous,
transluscent, colloidal
liquid.
b)Contains inorganic
molecules,
water, organic
compounds.
a)Helps in
exchange of
material
between
different
cells.
b)Biosynthesi
s of
protein,fatty
acid takes
place.
6)Endoplasmi
c reticulum
a)Interconnected
system of membrane
lined channels.
b)It may be rough for
the presence of
ribosome.
a)Acts as
skeletal
framework of
cell.
b)Helps in
synthesis and
transport of
proteins and
fats.
7)Ribosome
a)Small granules
found either floating in
cytoplasm or attached
to the outer surface of
rough endoplasmic
reticulum.
b)Found in
mitochondria and
plastid.
a)Helps iin
protein
sysnthesis.

7. 8)Mitochondri
a
a)sausage-shaped.
b)double-walled. (
CELL – A UNIT OF
LIFE)
c)Inner membrane
given into folds.
d)Matrix contains
lipids,
proteins,DNA,RNA.
a)Oxidizes
food to
release
energy in the
form of ATP.
b)Synthesizes
respiratory
enzymes and
many amino
acids.
9)Golgi bodies
( in animal);
Dictyosome
(in plant)
a)Stacks of flattened
sacs or cisternae.
b)Contains vesicles,
vacuoles, tubules.
a)Helps in
secretion of
mucus,
enzymes and
hormones.
b)Helps in
storage.
10)Lysosome
a)Membranous sacs
budded off from Golgi
bodies. ( CELL – A
UNIT OF LIFE)
b)Having a resistant
membrane.
a)Helps in
intracellular
digestion.
b)Provides
energy during
starvation.
11)Nucleus
a)Dense, spherical,
cylindrical body at the
centre.
b)Contains chromatin
which contains DNA.
a) Helps in
cell division.
b)Regulates
all functions
within cell.
c)Possesses
all genetic
informations
in gene.

8. 12)Vacuole
a)Fluid-filled
membrane bound
space.
b) Large in plant cell.
c) Small in animal cell.
a)Helps cell
to remain
turgid.
b)Helps in
cell
elongation.
c)Helps in
storage of
water and
other
substances.