cell, cell types, structure &function

1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai
Cell
Dr. Sonia Bajaj
(Head of Department)

2. Introduction
Cytology: (G.k. kyios = cell ; logas = study) is the branch of biology which comprises the study of cell
structure and function.
• All the living organisms are made up of fundamental unit of life called “ cell”.
• The cell is a Latin word for “a little room”.
• The scientist Robert Hooke (1665)-saw a little room in the cork (the bark of a tree)
resembled the structure of a honeycomb. The use of the word “Cell” to describe these
units is used till this day in Biology as” Cell Biology”.
• Robert Brown in 1831 discovered the nucleus in the cell.
• The scientist Leeuwenhoek saw free living cells in the pond water for the first time.
• (father of microbiology)
• The cell theory states that all the plants and animals are composed of cells, it
was proposed by Schleiden and Schwann.
• The cell theory was further expanded by Virchow by suggesting that “all cells arise from
the pre-existing cells”.
• Cells are the basic structural and functional unit of life. Cell was discovered by Robert
Hooke. A number of cells can work together to form tissues and organs.
Cell is termed as the structural unit of life as it provides structure to our body.
Cell is considered as the functional unit of life as all the functions of the body take place at
cell level.

3. Scientist name Year Discovered By
Robert Hooke 1665 noticed the presence of cells in a cork slice
Leeuwenhoek 1674 found the presence of living cells in the pond water
Robert Brown 1831 recognized the existence of a nucleus in the cell
Purkinje 1839 invented the term ‘Protoplasm’ which is the liquid
present in a cell
Schleiden and
Schwann
1838,
1839
presented the cell theory that all organisms are
actually made up of cells
Virchow 1855 suggested that all cells come from cells that already
exist in nature

4. • The Size and shape of the cell may vary
depending upon the type of function they
perform in an organism. They may be oval,
spherical, rectangular, spindle shaped, or
totally irregular like the nerve cell.
• Types of cells: Onion cells, Smooth
muscle cell, Blood cells, Bone cell, Fat cell,
Nerve cell, Ovum, Sperm etc. Each kind of
cell performs specific function.
• A single cell may constitute a whole
organism as in Amoeba, Chlamydomonas,
Paramecium and Bacteria; these are called
as unicellular organisms. Whereas in
multi-cellular organisms (Human beings)
division of labor is seen.
• The feature in almost every cell is same-
Plasma membrane, nucleus and
cytoplasm.
Cells can have different Shaped and Sizes

5. Two Types of Organisms on the Basis of Number of Cells
(i) Unicellular Organisms: The organisms that are made up of single cell and may
constitute a whole organism, are named as unicellular organisms.
For example: Amoeba, Paramecium, bacteria, etc.
(ii) Multicellular Organisms: The organisms which are composed of a collection of
cells that assume function in a coordinated manner, with different cells specialized
to perform particular tasks in the body, are named as multicellular organisms.
For example: Plants, human beings, animals, etc.

6. Plant cell Animal cell
Cell wall present. Cell wall absent.
Nucleus usually lies near periphery due to
vacuole.
Nucleus present near the centre.
Centrosome is usually absent from higher
plant cells, except lower motile cells.
Usually centrosome is present that helps in
formation of spindle fibres.
Plastids are present, except fungi. Plastids are absent.
Single large central vacuole is present. Many vacuoles occur, which are smaller in
size.
Number of mitochondria from 200 – 2000. Number of mitochondria is approximately
1600 – 16000 in liver cells.
Cytoplasm during cell division usually
divides by cell plate method.
Cytoplasm divides by furrowing or cleavage
method.
There is no contractile vacuole. Contractile vacuole may occur to pump
excess water.
Spindle formed during cell division is an
astral.
Spindle formed during cell division are
amphi astral.
Lysosomes present in less number. Lysosomes present in more number.
Chromosomes are larger in size. Chromosomes are smaller in size.

8. Types of Cells
The cells can be categorized in two types:
1. Prokaryotic Cell 2. Eukaryotic Cell
1. Prokaryotic cell
• Prokaryotic cells are cells in which true nucleus is absent. They are primitive and
incomplete cells.
• Prokaryotes are always unicellular organisms.
• These cells are small and multiply at a faster rate.
• For example, Mycoplasma and PPLO (Pleuro Pneumonia Like Organisms).
archaebacteria, bacteria, blue green algae are all prokaryotes.
• 2. Eukaryotic Cell
Eukaryotic cells are the cells in which true nucleus is present. They are advanced
and complete cells.
• Eukaryotes include all living organisms (both unicellular and multicellular
organisms) except bacteria and blue green algae.

9. Characteristics of Prokaryotic Cell
• Prokaryotic cells are the cells that do not have
a true nucleus and membrane-bound
organelles.”
• They lack a nuclear membrane.
• Mitochondria, Golgi bodies, chloroplast, and
lysosomes are absent.
• The genetic material is present on a single
chromosome.
• The histone proteins, the important
constituents of eukaryotic chromosomes, are
lacking in them.
• The cell wall is made up of carbohydrates and
amino acids.
• The plasma membrane acts as the
mitochondrial membrane carrying respiratory
enzymes.
• They divide asexually by binary fission. The
sexual mode of reproduction involves
conjugation.

10. Prokaryotic Cell Structure
A prokaryotic cell does not have a nuclear membrane. The genetic material is present in a
region in the cytoplasm known as the nucleoid. They may be spherical, rod-shaped, or
spiral. A prokaryotic cell structure is as follows:
Capsule– It is an outer protective covering found in the bacterial cells, in addition to the cell
wall. It helps in moisture retention, protects the cell when engulfed, and helps in the
attachment of cells to nutrients and surfaces.
Cell Wall– It is the outermost layer of the cell which gives shape to the cell.
Cytoplasm– The cytoplasm is mainly composed of enzymes, salts, cell organelles and is a
gel-like component.
Cell Membrane– This layer surrounds the cytoplasm and regulates the entry and exit of
substances in the cells.
Pili– These are hair-like outgrowths that attach to the surface of other bacterial cells.
Flagella– These are long structures in the form of a whip, that help in the locomotion of a
cell. Ribosomes– These are involved in protein synthesis.
Plasmids– Plasmids are non-chromosomal DNA structures. These are not involved in
reproduction. Nucleoid Region– It is the region in the cytoplasm where the genetic material
is present. A prokaryotic cell lacks certain organelles like mitochondria, endoplasmic
reticulum, and Golgi bodies.

11. Reproduction in Prokaryotes
A prokaryote reproduces in two ways:
1. Asexually by binary fission
2. Sexually by conjugation
Binary Fission
The DNA of an organism replicates and the new copies attach to the cell membrane.
The cell wall starts increasing in size and starts moving inwards.
A cell wall is then formed between each DNA, dividing the cell into two daughter cells.
Recombination
In this process, genes from one bacteria are transferred to the genome of other bacteria. It
takes place in three ways-conjugation, transformation, transduction.
• Conjugation is the process in which genes are transferred between two bacteria through
a protein tube structure called a pilus.
• Transformation is the mode of sexual reproduction in which the DNA from the
surroundings is taken by the bacterial cell and incorporated in its DNA.
• Transduction is the process in which the genetic material is transferred into the bacterial
cell with the help of viruses. Bacteriophages are the virus that initiates the process.

12. Characteristics of Eukaryotic Cells
Eukaryotic cells are the cells that contain a
membrane bound nucleus and organelles.”
The features of eukaryotic cells are as
follows:
• Eukaryotic cells have the nucleus
enclosed within the nuclear membrane.
• The cell has mitochondria.
• Flagella and cilia are the locomotory
organs in a eukaryotic cell.
• A cell wall is the outermost layer of the
eukaryotic cells.
• The cells divide by a process called
mitosis.
• The eukaryotic cells contain a
cytoskeletal structure.
• The nucleus contains a single, linear
DNA, which carries all the genetic
information.

13. Eukaryotic
Cell Structure
Eukaryotic cell
diagram
mentioned
below depicts
different cell
organelles
present in
eukaryotic cells.
The nucleus,
endoplasmic
reticulum,
cytoplasm,
mitochondria,
ribosomes,
lysosomes are
clearly
mentioned in
the diagram.

14. Prokaryotic cell Eukaryotic cell
It is a single membrane system. It is a double membrane system.
Cell wall surrounds the plasma membrane. Cell wall surrounds the plasma membrane in
some protists, most fungi and all plant cell.
Animal cell lack it.
Cell wall composed of peptidoglycans.
Strengthening material is mureir.
It is composed of polysaccharide. Strengthening
material is chitin in fungi & cellulose in others
plants.
Cell membrane bears respiratory enzymes. It lacks respiratory enzymes.
Cytoplasm lacks cell organelles e.g., Mitochondria,
ER, Golgi body etc.
Cytoplasm contains various cell organelles.
Ribosomes are 70 S type. Ribosomes are 80 S type.
There are no streaming movements of cytoplasm. Cytoplasm show streaming movements.
Mitotic spindle is not formed in cell division. Mitotic spindle is formed in cell division.
Nuclear material is not enclosed by nuclear
envelope and lies directly in cytoplasm. It is called
nucleoid.
It is enveloped by nuclear envelope. Nucleus is
distinct from cytoplasm.
DNA is circular and not associated with histone
proteins.
Nuclear DNA is linear and associated with histone
proteins extranuclear DNA is circular and protein
free.
Replication of DNA occurs continuously
throughout cell cycle.
Replication of DNA occurs during S- Phase of cell
cycle only.
Sexual reproduction absent but parasexuality
present.
Sexual reproduction is present.
Plasmids and pili occur in many prokaryotes
Example – E. coli
There are no plasmids and pili in eukaryotic cells
Example – Spirogyra, Chlorella
Cell division mostly amitotic. Cell division is typically mitotic.