2. CELL
•
•
•
•
Cell is the fundamental unit of life
All the living organisms are made up of cell
It is the structural and functional unit of life
because whole body is made up of cells
It is known as the fundamental unit of life
because regulates all the functions inside an
organisms
History of Cell
•
•
•
Robert Hooke (1665) discovered Cell in a thin
slice of Cork under primitive microscope.
He observed “Honeycomb” like structure and
name them CELLS
The cell is a Latin word for “ a little room”
•
•
•
•
1665- Robert Hooke, discovered the Cell
1674- A.Van Leeueenhoek, studied living Cell in
pond water
1831- Robert Brown, discovered nucleus in the
Cell
1839- Purkinje , coined the term protoplasm (for
the fluid substance in the Cell
Discovery of Cell
3. Organisms On The Basis Of CELL NUMBER
Multicellular Organism
•
•
•
Composed of Single Cell
Single Cell constitute the structure and entire
function of the organisms
E.g Amoeba, Paramoecium, Euglena
•
•
•
Composed of Many cells
Division of labour can be seen in these organisms
e.g. plants, animals, human beings
Unicellular Organism
4. CELL- Shape and Size
•
•
•
•
•
Shape and size of cells vary but all of these are
ultimately determined by the specific function.
Some Cell can change their shapes amoeba,
WBC but plants and animals have almost fixed
shapes.
Smallest cell- PPLO( mycoplasma)
Largest Cell- Ostrich egg.
Longest animal Cell- Nerve Cell
Red Blood Cell
Muscle Cell
Paramoecium
Guard Cell
Nerve Cell
5. CELL THEORY
To know more about cell, few scientists sum up their views about
cell as cell theory. It was given by volunteers: Scheldon &
Schwann(1839)
According to this theory: -
Cell is the structural unit of life.
Cell is functional unit of life.
All cells arise from pre-existing cells. Every organism starts life as
a single cell. (It was given by R. Virchow ,1855)
6. Types of cells
There are two main types of cells depending upon their basic and
important difference in their structures. The types are:
Prokaryotic (primitive cell)
Eukaryotic (advanced type)
Prokaryotic and eukaryotic cell: The basic difference between the
two is: In prokaryotic, the nuclear material lies naked in cytoplasm
that is no special membrane is present that separates it from the
cytoplasm. It is present as such in cytoplasm.
In eukaryotic, the nuclear material is well protected and enclosed
by special membrane that is nuclear membrane .
7. Structure of cell
cells have three things in common:
Cell membrane
Nuclear material
Metabolic machinery
8. Cell membrane
Cell membrane (Plasma membrane)
This gives a covering to all cells.
* It is present in both plant & animal cell
* It is an outer covering of cell
* It is living, thin and delicate membrane.
* It is semi-permeable – “allows selective particle to pass through.”
* It is made up of lipids & proteins.
It allows only selected substances to move through it .The movement of
substances takes place by activities like: -
Diffusion – “movement of molecules from higher concentration to lower
concentration”. It is mostly seen in case of Gases. For example: Cell
respire i.e. intake of O2 & giving out CO2 take place through diffusion.
Osmosis: “movement of solvent molecules from higher cone. to lower
conc. across the semipermeable membrane.
9. Types of solution
Osmosis can occur in hypertonic solutions, hypotonic solutions and
isotonic solutions. Sometimes cell can even undergo the phenomenon
called as plasmolysis.
Hypotonic solutions are the ones which have a lower concentration of
solute than the cell. Water diffuses into the cell to balance the solute
concentration on either side (outside and inside) equal. Here the cell
swells up due to entry of water.
Hypertonic solutions are the ones which have higher solute
concentration than the cell. Water moves out of the cell through cell
membrane to balance the concentration of the solute on either side. It
results in cell shrinking .This may also lead to desiccation of the cell.
Isotonic solutions have the same concentration of the solute as the cell.
Water moves in and out of the cell with no net change.
Plasmolysis-When a living plant cell loses its water through osmosis and
get shrink.This phenomenon is called Plasmolysis.
10. Functions of plasma membrane are as follows-
a) It provides support to cell
b)It allow exchange of materials.
c) It provides shape to the cell.
*Flexibility of cell membrane also enables cells to engulf food
from it's external environment.Such process is called
Endocytosis for eg.in amoeba
In plant cells outer to cell membrane another layer or covering is
present called as cell wall. It is present in all plant cells .It is
somehow different from cell membrane .
11. Cell wall
It is outer to cell membrane
It is dead
It is present only in plant cell
It is made up of cellulose (in fungus it is made of chitin)
It is freely permeable
Functions of cell wall are as follows -
It provides mechanical support to cell.
It allows materials to exchange.
It maintains the shape of cell
12. cell consist of cell membrane and it encloses a living material
called protoplasm. Protoplasm is defined as living material of cell.
The term protoplasm was coined by: J.E Purkinjee.
It is further divided into two parts:
Nucleus (discovered by Robert Brown)
Cytoplasm
Nucleus
Like we have brain, the cell has a nucleus. All the activities are
controlled by nucleus. It is located in the centre of the cell.
13. Nuclear membrane: -It is the membrane that separates the
nucleus from the cytoplasm. The membrane has pores in it which
allow only selected exchange of materials. It is therefore called
semi permeable in nature.
Nuclear material: It contains thread like structures which further
condense at the time of cell division to ribbon like structures
called chromosomes. These chromosomes are made up of DNA
and proteins. There are segments of DNA that are responsible for
characters in a body or transfer of characters from parents to
offspring and are called genes. They act as hereditary vehicles.
14.
15. Functions of nucleus are as follows-
It regulates the cell cycle.
It controls metabolic activities of cell.
It contains genes that help in transmission of characters from
parents to offspring .
*Nucleoid-In some organisms like bacteria the nuclear region is
poorly defined due the absence of nuclear membrane.such an
undefined nuclear region is called Nucleoid
16. Cytoplasm
It is the fluid content in side the plasma membrane.
Its soluble part is called cytosol. It contains organelles.
These organelles perform necessary functions for the cell like
some organelles help in cleaning the cell, some help in
synthesizing certain substances for the cell, some perform
catabolic function like breakdown of food,.
*Viruses lack any membrane hence do not show any
characteristics of life until they enter a living body and uses
host machinery.
17. Difference between prokaryotic and
Eukaryotic cell
Prokaryotic cell
•
•
•
•
•
•
•
Small in size
Nuclear material lies naked in
cytoplasm
Contain single chromosome
Organelles absent
Nucleolus absent
Cell division by fission etc
Eg : bacteria blue green algae etc.
Eukaryotic cell
•
•
•
•
•
•
•
Large in size
Nuclear material is surrounded by
nuclear membrane
Contain more than one
chromosome
Organelles presents
Nucleolus present
Cell division by mitosis or meiosis.
Eg. Human etc.
