This document discusses cell diversity based on origin, size, shape, and other characteristics. It describes two main types of cells: prokaryotic cells which lack a nucleus and organelles, and eukaryotic cells which have a nucleus enclosed by a nuclear membrane and various membrane-bound organelles. Cell size can vary greatly from 0.1 micrometers in some bacteria to meters in some plant and animal cells. Cell shape also varies significantly between cell types and can change based on cell function.

1. Cell Diversity
Cell size and shape

2. CELL DIVERSITY

3. DIVERSITY OF CELLS IN OURBODY

4. TYPES OFCELL
DIVERSITY
Cell Diversity InOrigin
Cell Diversity In size
Cell Diversity InShape
Some OtherTypes

5. Cell Diversity In Origin:-
Based upon its origin it is basically divided into two types:-
Prokaryotic Cell Diversity - Prokaryotic cells are primitive type of cells. These
cells lacks true nucleus and other cell organelle like mitochondria, chloroplasts,
endoplasmic reticulum, golgi complex, etc. The word prokaryotes is derived
from Greek word ‘pro’ means primitive or old and ‘karyotes’ means nucleus or
main.
e.g.Cyanobacteria,
Bacteria.
Eukaryotic Cell Diversity - Eukaryotic cells have true nucleus and it also contains
cell organelles. The word eukaryotes is derived from Greek word ‘eu’ meanstrue
and ‘karyotes’ means nucleus.
e.g. General green plants,
Starch containing amyloplasts,
Typical AnimalCells,
A live unicellular organism.

6. PROKARYOTIC & EUKARYOTICCELL DIVERSITY

7. NUMBER, SIZE AND SHAPE OF CELL
NUMBER OF CELLS
Some organisms are unicellular i.e. bacteria, yeast, Chlamydomonas, diatoms,
Cosmarium etc whereas most of organisms as plants and animals are multicellular.
Human body is built of about one trillion cells.
In case of unicellular forms single cell is capable of independent existence and to
perform all the essential functions of life
In green alga Pandorina, the coenobium is having a fixed number of cells (8/16/32 )
. Colonies like Volvox ,Nostoc etc have many cells enclosed by mucilaginous
sheath
A multicellular organism is made of many cells
Different cells become specialized for performing different functions. Cells are
grouped into tissues, tissues into organs and organs into organ systems. Organ
systems together form organism
Cell Tissue Organ Organ system
Organism

8. SIZE OF CELL
Generally cell size ranges between 0.2µm-20 µm
Smallest cell : PPLO : Mycoplasma gallisepticum :0.1 µm
Bacteria : Unicellular : About 10 times smaller than Animal cell
Escheritia coli : Rod shaped Bacteria : 1-2 micron long
Protozoa : Amoeba proteus : 220–760 µm
Generally plant cells are larger than animal cell
Generally Animal cell range from 10µm to 30 µm & plant cell 10µm to 100µm
Exceptions : Ostrich egg cell : 75 mm long
Acetabularia a unicellular green alga is about 10 cms in length
Bast fibre (phloem fibre ) of some plants (Ramie) are about 50-55 cm long
A giraffe's nerve cell can reach about two meters
Cell volume The volume of a cell is fairly constant for a particular cell type and is
independent of the size of organism. The difference in the total mass of the organ or
organism depends on the number ,not on the volume of the cells

9. Which Cell Type is
Larger?
11
Plant cell Animal cell Bacteria>
>
>
Generally plant cells are larger than animal cell
Animal cells are larger than bacterial cell

11. WHYARECELLS SO SMALL?
In order to survive, cells must constantly interact with their surrounding
environment and can grow only to a certain size .
If the cell grows beyond a certain limit , enough material will not be able to
cross the
membrane to accommodate with increased cellular volume.
The reason cells can grow only to a certain size has to do with their
surface area to volume ratio.
Here, surface area is the area of the outside of the cell, called
the plasma membrane. The volume is how much space is
inside the cell.
The ratio is the surface area divided by the volume. If the surface area
to volume ratio is small, the cell is very big.
When this happens, the cell must divide into smaller cells with
favourable surface area/volume ratios.
If the ratio is big, the surface area is greater than the volume then the
cell is small

12. Cell Type Size(µm)
Mycoplasma (PPLO) 0.10
Bacteria 0.20-2.50
Small Lymphocytes 4.0
Erythrocytes 7.0-8.0
Amoeba Proteus 1000
Liver Cells 20
Euglena 100-500
Human Oocyte 250
Ostrich Egg 75×103
Neurons (Length) 2×106

13. There is great variability in cell shape i.e. spherical, polygonal, disc like, cuboidal,
columnar,spindle like or fibre like.
Generally cells are spherical but in multicellular forms due to pressure become
polyhedral . In plants as cells have cell wall appear hexagonal or polygonal .
Cells some times change shape because of function as Amoeba and leucocytes .
While animal cells tend to have irregular shapes, plant cells are typically
rectangular or cube shaped.
CELLSHAPE

15. Cell shape Example
1. Variable cells Amoeba, Leucocytes, Myxomycetes.
2. Fixed cells
(i) Spherical cells eggs of many animals.
(ii) Flattened cells Squamous epithelium,
endotheliums,
and upper layer of epidermis.
(iii) Cuboidal cells Thyroid gland follicles
(iv) Columner cells The cells lining the intestine.
(v) Discoidal cells Red Blood Cells Or Erythrocytes
(vi) Spindle shaped cells Smooth muscle fibres
(vii) Elongated cells Nerve cells or Neurons
(viii) Branched cells Chromatophores Or Pigment
cells of
skin.
(ix) Polyhedral (with 8,12 or14
sides)
Squamous Epithelium

16. Dougherty (1957) classified cells into prokaryotic (Pro
meaning primitive, karyon meaning nucleus) and eukaryotic
(Eu meaning true, Karyon meaning nucleus) types on the
basis of structural organization of their nucleus.
The cells which possess a primitive type of nucleus devoid of
nuclear membrane are the prokaryotic cells. On the other
hand, eukaryotic cells are those which possess a true, well
organized nucleus having typical chromosomes and nuclear
membrane.
Dodge et al (1966) proposed a third type (Mesokaryotic)
which can be placed in between prokaryotic and eukaryotic
cells.
TYPE OF CELLS

17. There is primitive type of nucleus which is not bounded by nuclear
membrane as true nucleus and is termed as nucloid
There are no membrane bound cell orgalleles, infolding of plasma
membrane called mesosomes take their function The nuclear material
lies diffused in central part of the cell, the genetic material
consists of DNA, but it is not associated with
proteins (Histones).
Prokaryotic cells are generally smaller than eukaryotic cells.
The cells of bacteria, Archaea, blue green algae,
Mycoplasma, rickettsiae are included in this type
PROKARYOTIC CELLS

19. EUKARYOTIC CELLS
Eukaryotic: In this type of cell organization, there is
definite or true nucleus surrounded by definite nuclear
membrane.
The genetic material consists of DNA complexed with
histone proteins to form well developed chromatin/
chromosomes. Nucleus has nucleolous.
There are different membrane bound cell organelles such
as mitochondria, Endoplasmic Reticulum, Golgi body
,plastids etc for different functions. Plastids are presents
in the plants cell only.
This types of cells are in general larger and more
organized than prokaryotic cells
Most of the plants and animal cells fall under this
category except Blue Green Algae(BGA).

21. MESOKARYOTIC CELLS
In some organisms ( the Dinoflagellates ) the genetic material
is surrounded by a nuclear membrane
( Eukaryotic character) but histone protein is not
associated with DNA ( prokaryotic character)
The nucleus is larger in size and has been named as
mesokaryon by Dodge (1966).
These types of cells which are intermediate between
prokaryotic and eukaryotic are called mesokaryotic cells. In
these types of cells, the mitotic spindle is not formed.
The cells of certain algae like Gymnodinium
and Peridinium are the example of such type.

22. Some cells are even smaller than prokaryotic cell
Smallest known cell is of
Mycoplasma gallisepticum
(PPLO-Pleuro Pneumonia like
organism- a bacterium prokaryote ) Size – 0.1 µm -
0.3 to 0.5
µm . The size of this cell may not be more than
1000 to 5000 times that ofa
hydrogen atom.
W. V. Iterson (1969) placed PPLOs with bacteria in the
group Mycoplasmata.
Novikoff and Holtzman (1970) have
excluded them from bacteria and
considered them as simplest prokaryotic cells.
OTHER CELL TYPES
1. Absence of cell wall and mesosomes
2. Selectively permeable plasma
membrane
(75A⁰ in thickness ), composed of
lipoproteins
3.The cytoplasm has ribosomes
and
enzymes required for protein synthesis and ATP
metabolism
4.Nucleus is absent and instead there occurs
double stranded DNA molecule of circular or fibrillar
type.
5. It does not need a host cell (can live
freely)