CELL
PRESENTED BY :
SIMRAN SIGDEL
CONTENTS
• Introduction
• Discovery of cell
• Types of cell
• Shape, size, and structure
• Structure of a cell
• Functions of different cell organelles
• Plant cell and animal cell (typical cell)
• Amoeba And Hydra
WHAT IS CELL ?
Cell is the basic unit of life and that is responsible for
the shape and structure of a living body . As a building
is made up of bricks , a living body is made up of cells .
The work done by a living body is the total work done
by all the cells . So , a cell is the structural and
functional unit of life .
DISCOVERY OF CELL
The word ‘cell’ is derived from the Latin word ‘cellula’ which means ‘a little
room’.
The discovery of cells dates back to 1664 when British botanist Robert
Hooke gave the name cell .to the honeycomb-like structure observed in a
slice of bottle cork under his crude microscope.
In 1840,J.R. Purkenje used the term protoplasm to describe the juicy , slimy
content of the cell . The protoplasm was referred as the physical basis of
life.
Thus, it was clear that all organisms from unicellular to multicellular
organisms are made up of cells and every cell has protoplasm to conduct
life activities like growth , movement , sensitivity , respiration and
reproduction.
TYPES OF CELL
a) Prokaryotic Cell
The cells with primitive or poorly
developed nucleus are called
prokaryotic cells. In such cells, the
nuclear membrane is absent and
the nuclear materials is in direct
contact with the cytoplasm. DNA
is absent in the nuclear material.
Such cells are found in organisms
like bacteria and blue green algae.
b) Eukaryotic Cell
These are the true cells with nucleus
bounded in a nuclear membrane. DNA
is present in the nuclear material. All
higher organisms have eukaryotic cells
The cells with a definite and functional
nucleus are called eukaryotic cell.
SHAPE , SIZE AND STRUCTURE
The structure and shape of cells differ from species to
species and organ to organ of living organisms. Even a
plant cell differs from an animal cell. The shapes of the
cells differ according to the function they have to
perform. Unicellular organisms like amoeba and white
blood cells (WBC) constantly change their shape whereas
nerve cells , red blood cells (RBC) and plant cells have
fixed shape. Cells are too small to be seen through our
naked eyes. Except some big cells like eggs of birds, other
cells are microscopic. The size of a cell ranges from 0.1 to
1 (micron). The smallest cell of a human being is the red
blood cell. The longest cell is the nerve cell ,which may be
up to 3.5 feet in length . A cell may be irregular (Amoeba,
WBC),flat (skin cells),spindle shaped (muscle fibers ),
spherical (RBC) or cubical in shape .
STRUCTURE OF A CELL
A cell has many smaller living cytoplasmic units
suspended in the ground liquid –protoplasm. Such
parts of a cell are called the cell organelles. Besides,
some non- living substances like waste materials, oil
droplets, collectively called cell inclusions, are also
present in the cytoplasm. Some of the cell organelles
are as follows :
1. Cell wall / cell membrane
2. Cytoplasm / protoplasm
3. Mitochondria
4. Nucleus
5. Plastids
6. Endoplasmic reticulum
7. Ribosome
8. Golgi bodies
9. Lysosome
10. Centrosome / centriole
FUNCTIONS OF CELL ORGANELLES
1) Mitochondria : it is the
powerhouse of cell as it
releases and stores energy in
form of ATP.
2) Nucleus : it is the controlling
sector of the cell.
3) Endoplasmic reticulum : it
transports various substances
within the cell .
4) Ribosome : it provides a space
for protein synthesis.
5) Lysosome : they are secret
enzymes (digestive juices).
6) Golgi bodies : They are
responsible for secretion,
synthesis and storage of various
organic compounds.
7) Centrosomes : they helps in cell
division by forming spindle fibers.
8) Plastids : They help in coloring
different parts of a plant
PLANT CELL AND ANIMAL CELL
Plant cell
They are larger and rectangular
in shape. cellulose cell wall is
present. Plastids are present.
Vacuoles are usually large and
centrally placed. Centrosome is
absent. Golgi bodies are
scattered in the cytoplasm and
are called dictyosomes.
Animal cell
They are smaller and oval in shape.
Cellulose cell wall is absent.
Plastids are absent. Vacuoles are
usually absent. If present they are
small and temporary. Centrosome
is present. Golgi bodies are well
developed and are near the
nucleus.
AMOEBA
Amoeba is a unicellular
protozoan animal . Amoeba
is one of the disease
causing organisms. It is
found in water or watery
medium. Many children get
sick due to amoeba
(Entamoeba histolytica).
HYDRA
It is 2- layered metazoan.
It has two layers in the
body with a cavity and is
known As coelenterate.
Hydra is fresh water living
animal. It is multicellular
animal attached on the
surface or leaves of
aquatic plants . It is
available where oxygen
and light is available.
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