1. Cell:The fundamental Unit of Life
By Dr.Juhee Bhatia

2. Contents
 Discovery of Cell
 Prokaryotic and Eukaryotic
 Multicellular organisms
 Cell Membrane and Cell Wall
 Cell Organelles: Chloroplast, Mitochondria,
Vacuoles, Endoplasmic Reticulum, Golgi
Apparatus and Nucleus.
 Chromosomes ( Basic structure and Number)

3. Introduction of Cells
 Cell is a latin word for “little room”.
 Cell is the fundamental and structural unit of
living organisms and basic unit of life.
 Cell biology: Study of cell in all respect of
structure and function.

4. Discovery of cells
 1. Robert Hooke-(1665) He observed dead cell
which resembled honeycomb like structures in
cork. He called these boxes cell.
 He published what he observed under
microscope in his book Micrographia.

5.  2. Antony Von Leeuwenhoek-(1674) He as
first to observe living cell in pond water
(Algae-Spirogyra)
 3. Robert Brown-(1831) He discovered
nucleus.
 4. J.E. Purkinjee-(1839) he used the term
protoplasm. It is living matter present inside
the cell.
 5. Rudolf Virchow-(1855) German
pathologists established that all cells arise
from pre existing cells.

6. Cell Theory
 The cell Theory was formulated by two
German biologists, M.J.Schleiden in 1838,
German Botanist and T.Schwann, German
physiologists in 1839. According to them, The
cell is the functional and structural unit of all
living beings. The cell theory was further
expanded by Virchow.

7.  Cell Theory stated that:
 Bodies of the living beings are made up of
cells.
 Activities of an organisms are the sum total of
activities of its cells.
 Cell develops from pre existing cells.

8. Size and shape of the cell
 Size of the cell: Normal size in human-20µm
to 30µm in diameter
 Largest Cell: In animals- Ostrich eggs(15cm)
In Plants- Acetabularia(6-10cm)
 Longest Cell: In animals- Nerve cell
In Plants- hemp fibre
 Smallest Cell: PPLO- Pleuro Pneumoniae Like
Organisms (Mycoplasma)

9. Shape of the cell

10. Unicellular vs Multicellular organisms
 The organism which are made of single cell
are called unicellular organisms. Example
bacteria, Amoeba, Paramecium,
Chlamydomonas.
 The single cell is able to perform all life
processes, like obtaining of food, respiration,
excretion, growth and reproduction.

11.  The organisms which are made up of number
of cells are called Multicellular organisms.
E.g. (except yeast), Plants and animals.
 All the cells of muticellular organisms have
basic structure and under take similar basic
functions.

12. Question??
 Which property of multicellular organisms
differentiate them from unicellular organisms?
Due to the property of division of labour the
cell in multicellular oragnisms are specialised
to perform different functions of the body and
in unicellular organisms only a single cell has
to perform all activities.

13. Basic structure of cell
Structure of cell
Cell Membrane Protoplasm
Cytoplasm Nucleus
Mitochondria Nuclear membrane
Choroplast Nucleoplasm
Endoplasmic reticulum Nucleolus
Golgi body Chromatin threads
Lysosomes
Centrosomes
Vacuole

14. Plasma Membrane or Cell membrane
All living cells, prokarytic and eukaryotic, have a plasma membrane that
encloses their contents and serves as a semi-permeable or selectively
permeable barrier to the outside environment. The plasma membrane
is permeable o specific molecules, however, it allows nutrients and
other essential elements to enter the cell and waste materials to leave
the cells. Small molecules such as oxygen, carbon dioxide and water
are able to pass freely across the membranebut the passage of larger
molecules, such as amino acids and sugars, is carefully regulated. The
plasma membrane is flexible and made up of organic molecu;les
called lipids and proteins. Flexibility enables the cell to engulf in food
and other materials (endocytosis). E.g. Amoeba.

15. Fluid Mosaic structure

16. Important points
 A living organisms is made up of one or more cells.
Therefore, cell is structural and functional unit of life. All
life functions of an organism reside in its cells. Cells may
also become specialized to perform specific functions like
contraction in muscle cell or impulse transmission in
nerve cell. Therefore, cells are functional unit of life.

17. Transport across plasma membrane
 Substance may pass across the membrane with or without
expenditure of energy.
Transport
Diffusion Osmosis
 Diffusion: The process of movement of substance (solid,
liquid& Gas) from the region of its higher concerntration
to the region of its lower concerntration so as to spread
uniformly in the given space is called Diffusion.

18. *DiffusionAcross Cell Membrane*
 Metabolic gases (CO2 and O2) move out and into the cells
through diffusion. Respiration of the cell produces carbon
dioxide. As the concerntration of CO2 increases inside the
cell into the external medium. Similarly concerntration of
oxygen is always higher in the external medium as
compared to the cell where it is being consumed in
respiration. Therefore oxygen diffuses from outside to the
inside of cell.

19.  Osmosis: Osmosis can be defined as the diffusion of
water or solvent across semi permeable membrane from a
region of its higher concentration to the region of its lower
concentration. Plasma membrane function as semi
permeable membrane.
 Example of osmosis:
 Absorption of water by plant roots.
 Absorption of water by unicellular fresh water organisms.
 Types of osmosis- Osmosis is of two types: Endosmosis
and exosmosis.
 Endosmosis is the osmotic entry of water into a cell or
system.
 Exosmosis is the osmotic withdrawal of water from a cell
or system.

20. Cell when placed in solution
 Plant and animal cells placed in salt or sugar solution will
behave in one of the following ways depending upon the
concentration of external solution.
 Hypotonic solution- The external solution is dilute as
compared to cell contents. Is has more water content while
the water content is lower inside the cell. The cell
membrane allows passage of water in both direction. Due
to difference in concentration of water moelcules, tere is
net flow of water molecules into the cells. The
phenomenon is called endosmosis.