Transcript Click on image to content

• The cells are structural and
functional units of life.
• In 1665, an English
scientist Robert Hooke,
while examining thin
sections of cork, observed
many hexagonal chambers,
like a honey comb, which
had no living matter.
• He named these
compartments as cells.
ONION PEEL CELL
• There are different types of
cells depending on their shape
and size. It may be spherical,
rod shaped, star shaped and
from microscopic to very large
cells. The largest cell is the
ostrich egg and the smallest cell
is mycoplasma gallisepticum.
The longest cell is fibre cell in
plants and nerve cell in
animals.
• Robert Brown (1831) observed a
dense spherical body named as
nucleus.
• Dujardin observed a jelly-like
living substance in the cell which
was named protoplasm by
purkinje in 1839.
• In 1838-39 Schleiden, a German
botanist Schwann, a German
zoologist, founded the cell
theory.
• They postulated that cell is the
basic unit of structure in life.
• STRUCTURE OF A
CELL:
• Structurally the cell is
formed of three parts:
1. Plasma membrane
2. Cytoplasm
3. Nucleus
• Plasma Membrane or Cell
Membrane:
• Each cell is bounded by an
extremely delicate, thin, elastic,
trilaminar living membrane, called
plasma membrane.
• It is made up of two layers of
lipid molecules with protein
molecules sandwiching it. It is
selectively permeable membrane
which allows the flow of some
substances into the cell and out of
the cell.
• Cell Wall: The plant cells have
an additional protective wall
outside the plasma membrane,
called a cell wall.
• It is thick, rigid and non-living
envelope. It is made of cellulose.
It prevents desiccation of cells.
• It protects the plasma
membrane
and
internal
structure of the cell.
• Protoplasm: All the
components of a cell
including the cell
membrane is known as
protoplasm.
• It is colourless, jelly-like,
viscous,semifluid
substance which can be
distinguished into a
centrally located
nucleoplasm and
surrounding cytoplasm.
• Cytoplasm: Protoplasm around
nucleus is called cytoplasm.
• It is formed of proteins, lipids,
carbohydrates, nucleic acids and
certain inorganic substances. Many
small membrane bound living
bodies called cytoplasmic organelles
are found inside the cytoplasm.
• These organelles are the actual sites
for various metabolic functions of
the cells.
• Endoplasmic
Reticulum(ER): It was
described by an American
biologist, Porter.
• ER is a network of tube-like
structures distributed extensively
throughout the cytoplasm.
• It may be rough, if ribosomes are
attached to it or smooth, when
ribosomes are not attached.
• It increases the surface area of
cell for various metabolic
activities.
• Ribosomes: These are
extremely small, rounded
bodies found either in free
state in the cytoplasm or
attached to the surface of
ER.
• They are composed of RNA
and protein. It helps in
protein synthesis.
• Mitochondria: It was first
described by Altman, but named by
Benda in 1898.
• Each mitochondrion is bounded by
two membranes-outer and inner.
• Inner membrane is pushed inwards at
intervals called cristae which lie in a
ground substance called matrix.
• It possess enzymes for the oxidation
of carbohydrate and thus release
energy in the form of ATP.
• For this reason mitochondria is
called as power house of the cell.
• Golgi Bodies: Camilo Golgi
in 1898 observed the
structure for the first time.
• Golgi bodies are membranebound organelles which
occur in the form of tubules,
vesicles or cisternae.
• They help in the formation
of cell plate during cell
division.
• Plastids: They are doublemembraned organelles found in
plant cells only.
• A plastid shows two distinct
regions –grana and stroma. Grana
are stacks of membrane-bound,
flattened, discoid sacs containing
chlorophyll molecules.
• These molecules are responsible
for the production of food by the
process of photosynthesis. They are
therefore are called kitchen house
of the cell.
• Lysosomes:
Lysosomes
were first described by de
Duve.
• They are small, enzymecontaining, single membranebound vesicles.
• They
function
as
intracellular
digestive
systems and are called
demolition squads or suicidal
bags.
• They help in destruction of
other foreign food materials.
• Centrioles: Centrosome is
a slightly differentiated
region of cytoplasm close to
the nucleus of animal cells.
• It has usually two central
granules called centrioles. It
helps in the process of cell
division.
• centrioles and in the
formation of cilia and
flagella of the cells.
• Vacuoles: They are small or
large sized organelles which are
filled with liquid or sap and are
membrane-bound.
• In animal cells, vacuoles are
smaller in size and lesser in
number as compared to plant
cells.
• The cell sap is a watery solution
rich in sugar, proteins, amino
acids, metabolic wastes and
minerals.
• Nucleus: It is surrounded
by a double membrane called
nuclear membrane. Inside the
nucleus
thread like
structures called chromatin is
present which appears as
short, thick, rod-like bodies
called chromosomes at the
time of cell division. The
chromosomes
contain
stretches DNA called genes.
PLANT CELL
PLANT CELL
PLANT CELL
BLOOD CELL
NERVE CELL