let us know about the unit of life itself

1. Cell Biology
Presentation By
Smita Amit –M.Sc (Botany ) M.Ed
PGT Biology & pre medical faculty
for more than 20 years in various schools and institutes
including Sacred Heart Sr Sec School , Chandigarh , Ace
academy Chandigarh , Sumermal Jain Public School ,
New Delhi, Adhar Academy , Jodhpur
(1)

2. CELL – THE BASIC BUILDING BLOCK OF ALL LIVING
THINGS
 Why study –cells
 What are cells ?
 Development of our understanding of cells.(the story behind it )
In this introductory lecture we will throw
light on

3.  Provide structure for the body.
Why study -the cell
As a student of biology - --to gain knowledge about life
itself
 Energy production for use in all life
functions’

4.  All the functions of a living being are dictated by cell function and carried out
individually in a single cell as well as collaboratively in an organism.
 Carry out specialized functions.
Why study -the cell
As a student of biology - --to gain knowledge about life
itself

5.  Often, interactions and processes that impact health and disease occur at the
cellular level.
 Essential for therapeutic approach.
Why study -the cell
As a student of biology - --to gain knowledge about life
itself

6.  Contain the body’s hereditary material and can make copies of themselves
Why study -the cell
As a student of biology - --to gain knowledge about life
itself

7. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
A bit of history
Discovery of cells
1. 1665 (Robert Hooke ) First Seen In Cork He actually saw the dead cell walls
of plant cells –cork, as it appeared under the microscope. **Micrographia .
He remarked that it looked strangely similar to cellula or small rooms which monks
inhabited, thus deriving the name.

8. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
2. 1674 (Anton van Leeuwenhoek): The first to witness a live cell under a self
made microscope(300x magnification ), he described the algae Spirogyra. Van
Leeuwenhoek probably also saw bacteria from his teeth scrapping.
A bit of history
Discovery of cells

9. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
3. Formulation of the Cell Theory
 Credited to Schleiden 1838, (studied plant cells) & Schwann ( studied animal
cells 1839 ).
 Both gave separate observations
 . In 1839, Schleiden suggested that every structural part of a plant was made up of
cells or the result of cells
 Tenets given by Schwann who published a book on animal and plant cells in 1839
 All living beings are made up of cells.
 The cell is the unit of structure, physiology and it retains a dual existence as a
distinct entity and a building block in the construction of organisms.
 Cells form by free-cell formation, similar to the formation of crystals
(spontaneous generation).
A bit of history
Discovery of cells

10. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
3. Formulation of the Cell Theory( ( Schleiden 1838 & Schwann 1839 )
contd..
Schleiden did not agree to the third tenet . . He also suggested that cells were made
by a crystallization process either within other cells or from the outside. Now we
know that it is clearly wrong. The correct interpretation of cell formation by division
was enunciated in Rudolph Virchow’s powerful dictum.
• Omnis cellula e cellula,: “All cells only arise from pre-existing cells”
A bit of history
Discovery of cells

11. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
The generally accepted tenets of Modern
Cell Theory
1. All known living things are made up of one or more cells[

12. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
The generally accepted tenets of Modern Cell Theory (contd..)
2. The cell is the fundamental unit of structure and function in all living
organisms.
3. The activity of an organism depends on the total activity of
independent cells.

13. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
The generally accepted tenets of Modern Cell Theory (contd..)
4.All cells are basically the same in chemical composition i.e
fundamentally in organisms of similar species.

14. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
The generally accepted tenets of Modern Cell Theory (contd..)
5. Energy flow (metabolism and biochemistry) occurs within cells.

15. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
The generally accepted tenets of Modern Cell Theory(contd..)
6. Cells contain DNA which is found specifically in the chromosome
and RNA found in the cell nucleus and cytoplasm.
** We will discuss these in greater detail later on

16. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
The generally accepted tenets of Modern Cell Theory(contd..)
7.All living cells arise from pre-existing cells by division.

17. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
Caveats to the Cell Theory
Certain types of cells / tissues do not conform to a standard notion of what
constitutes a cell:
Virus: Non living (passive , crystalline) outside the host , living inside (take over
the host cell's role to replicate themselves, which in turn leads to the death of the
host.)
Prions : Are only proteinaceous infectious particles—smaller than viruses.
Viriods :Small, single-stranded, circular RNA particles that are much simpler than
a virus
Challenges the idea that cells arise from pre existing cells, and that all
living beings are made up of cells .
At best they can be defined as the non-cellular organism.
Prions
Virus

18. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
Caveats to the Cell Theory
Coenocytic organisms.
The Coenocytic organisms like Vaucheria and some fungi(Aseptate fungal
hyphae) are not partitioned by septa and hence have a continuous cytoplasm
along the length of the hyphae) are said to be filamentous with incessant
protoplasm and considerable nuclei numbers. The filament is not separated
archetypally into cells.
Challenges the idea that living structures are composed of discrete cells

19. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
Caveats to the Cell Theory
Striated muscle fibres:
Muscle cells fuse to form fibres that may be very long (>300mm)
Consequently, they have multiple nuclei despite being surrounded by a single,
continuous plasma membrane
Challenges the idea that cells always function as autonomous units

20. CELL – THE BASIC BUIDING BLOCK OF ALL LIVING
THINGS
Caveats to the Cell Theory
Giant Algae
Certain species of unicellular algae may grow to very large sizes
(e.g. Acetabularia may exceed 7 cm in length)
Challenges the idea that larger organisms are always made of many
microscopic cells

21. Trivia:
o Schwann did not acknowledge anyone else’s contribution, including that of
Schleiden with whom he had purportedly discussed the observations on cells
in 1838.
o The crystallization process suggested by Schleiden was not his original idea .
Though he claimed this theory as his own, Barthelemy Dumortier had stated
it years before him.
o Virchow’s powerful dictum (which was itself borrowed from a Jewish
scientist’ Robert Remak work.)
o And finally ** Rishi Parashar spoke of cells in plants in his book
‘vriksh ayurved’? Who knows ?

22. SMITA AMIT