CELL AS BASIC UNIT OF LIFE
•Milestones in Discovery of cell
•The cell theory
•Cell number, size and shape
•Types of cells : Prokaryotic : Bacteria & Blue Green Algae
• Archaea : Methanococcus jannaschii
•Mesokaryotic cells
• Eukaryotic : Plant cell and Animal cell
 Cell organelles : E R,Mitochondria, Golgi body
 Plastids, Lysosomes
 Microbodies : peroxisomes,Glyoxysomes,Sphaerosomes
 Cytoskeleton: Microfilaments and microtubules
 Flagella and Cilia
 Nucleus : Nuclear envelope,Nucleolous
Nucleoplasm,chromatin
By
Prof Ichha Purak
Department of Botany
Ranchi Women’s College,Ranchi11/1/2018 cell as basic unit of life
Mesokaryote
Plant cell

The cell is the smallest unit of living matter.
The cell is the smallest unit having all the properties of life.
All organisms are composed of structural and functional units of life called cells.
The body of some organisms like bacteria, protozoans and some algae is made up
of a single cell ( Unicellular organisms) while the body of fungi, plants and animals
are composed of many cells (Multicellular organisms)
Cells vary in size and structure as they are specialized to perform different
functions.
But the basic components of the cell are common to all cells.

MILESTONES IN DISCOVERY OF CELL
Robert Hooke (1665), an English scientist, discovered and coined the term
cell while examining a thin slice of cork under a self-designed compound
microscope. The term cell was derived from a Latin word cellular (meaning little
room or chamber).
In 1672, Antony Van Leeuwenhoek observed bacteria, sperms and red blood
corpuscles, all of which were cells.
In 1831, Robert Brown, an Englishman observed that all cells had a centrally
positioned body which he termed the nucleus.
The crude microscope employed by
Robert Hook(1665)
Thin slice of cork
showing
chambers/cells

WHAT IS A CELL ? ( DEFINITION OF CELL )
Cell is the structural and functional unit of living organisms, enclosing a bit of
protoplast consisting of numerous micro and macro organic and inorganic
molecules, dissolved or suspended in colloidal or watery matrix.
The molecules are busy in reactions with release or uptake of energy.
The protoplasm of the cell is limited by a membrane.
All types of cells include three major components
1.Cell membrane
2.Cytoplasm and
3. DNA naked in prokaryotes (Bacteria,Archaea and BGA) and covered
by a membrane in all other organisms.
Mature Plant cells have in their cytoplasm large vacuole containing non-living
inclusions like crystals, pigments etc.
The bacteria have neither organelles nor a well formed nucleus.

THE CELL THEORY
The cell theory was jointly put forward by Schleiden and
Schwann (1839) in their paper “Microscopic investigations
on the similarity of structure and growth in animals and
plants” : As follows
1) All organisms are composed of one or more cells .
2) Cells are the basic living units within organisms and the
chemical reactions of life take place within cells.
3) All cells arise from pre existing cells by division and are
not formed de novo
Theodor Schwan
M J Schleiden
In 1855, a German medical doctor
named Rudolph Virchow observed,
under the microscope, cells dividing. He
reasoned that all cells come from other
pre-existing cells by cell division

Modern cell theory includes following features
1. The cell is the fundamental unit of structure and function in living organisms.
2. New cells arise from pre-existing cells through division. All new cells contain the
same amount and degree of genetic information as contained in the parent cell
3. Energy flow occurs within cells.
4. Cells contain hereditary information (DNA) which is passed from cell to cell during
cell division.
5. All cells are basically the same in chemical composition in organisms of similar
species.
Haeckel (1866) established that nucleus stores and transmits hereditary traits.
Cell theory was modified accordingly and was renamed
as cell doctrine or cell principle
Ernst Haeckel (1834-1919)

6. All known living things are made up of one or more cells.
7. Some organisms are made up of only one cell and are known as unicellular
organisms. All life begins as a single cell.
8. Others are multicellular, composed of a number of cells.
9. The activity of an organism depends on the total activity of independent
cells.
10.Depending upon specific requirement, the cells get modified, e.g.
elongated in muscle and nerve cells, loss of nucleus in RBCs or cytoplasm in
outer skin cells.
Modern cell theory includes following features
continued

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
NUMBER, SIZE AND SHAPE OF CELL
Cell Tissue Organ Organ system
Organism

Figure : 1 Living Organisms may be
unicellular /multicelluar
Cosmarium
Spirogyra
starfish
Pedistrum
Volvox
E coli
Nostoc
Chara
Chlorella
Paramaecium
Pinnularia
Plant

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

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

12
CELL SIZE
Typical cells range from 5 – 50 micrometers (microns) in diameter
copyright cmassengale

WHY ARE CELLS 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.

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.
CELL SHAPE

Chlamydomonas Paramaecium
Amoeba Nerve cells
Muscle cells
Acetabularia Caulerpa
Epithelial cells
Onion peel cells
Pinnularia
E. coli
Red blood cells
Figure- 1a Cells of different shapes

TYPE OF CELLS
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.

PROKARYOTIC CELLS
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

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).

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.

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 of a
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)
STRUCTURE OF PPLO

Character Prokaryotic cell Eukaryotic cell
Cell compartments No compartments Distinct compartments in the cell. i.e.
the cytoplasm and the nucleus
Cell wall Present, composed of amino sugars
and muramic acid
Absent in animal cell, present in
plant cell, composed of cellulose
Plasma membrane Present, core of lipid bilayer with
proteins embedded as mosaic
Present,lipid bilayer, with embedded
proteins
Cell organelles Absent, Enzymatic functions are
carried by infoldings of plasma
membrane- mesosomes
Different cell organelles present for
different functions ,bound by
extensions of plasma membrane
Respiratory system Mesosome(part of plasma
membrane)
Mitochondria
Capsule If present , composed of
mucopolysaccharides
Absent
Photosynthetic
apparatus and
chlorophyll
Photosynthetic pigments
chlorophylls and carotenes on
grana lamellae not enclosed by
membrane, no plastid
Pigments present on lamellar
system, enclosed by membrane in
cytoplasm. plastids present in plant
cells
Organization of the
nucleus
Nucleus not distinct , It is in the
form of nuclear zone (Nucloid)
Distinct nucleus
Table-1 Difference between Prokaryotic and Eukaryotic cell

Character Prokaryotic cell Eukaryotic cell
Nuclear membrane Absent Well formed nuclear membrane
Nucleoplasm Undifferentiated from cytoplasm Denser and differentiated from
cytoplasm by nuclear membrane
Hereditory material Single naked strand of DNA / RNA
Circular in shape.DNA not linked
with Histone proteins
More than one strand of DNA &
Histone protein inside nuclear
membrane as chromosomes
Nucleolous Absent Present
Flagellum Single,simple composed of protein
flagellin No 9+2 fibrillar pattern
complex 9+2 fibrillar pattern
composed of tubulin and other
proteins
Cell division Amitosis (Binary fisson) spindle
not formed
Mitosis or meiosis Spindle formed
Ribosomes 70S (30S+50S ) 80 S ( 40S+60S)
Cytoplasmic
movements
Rare or absent Often occurs
Vacuoles Absent Present
Lysosome Absent Present
Growth Can grow both under aerobic and
anaerobic conditions
Can grow only under aerobic
condition
Size 1-10 µm 10-100 µm
Table-1 Difference between Prokaryotic and Eukaryotic cell

STRUCTURE OF A PROKARYOTIC CELL : BACTERIAL
CELL
Average size- 1.25 µm. The smallest bacterium is Dialister pneumosintes which
measures about 0.15 µ to 0.3µ in length and the largest bacterium is Spirillum
volutons which measures about 13 µ to 15µ in length.
A typical bacterial cell consists of three parts
(a) outer coverings,
(b) cytoplasm and its
(c) constituents.
Body of the bacteria is basically prokaryotic type. Outer covering in the bacteria
is made up of three layers namely:
(i) Capsule
(ii) Cell wall &
(iii) Plasma membrane
11/1/2018 Cell as basic unit of life 24

Figure - 2 :Structure of Prokaryotic cell (Bacteria)

Capsule - Most bacterial cells have a slimy capsule outside the cell wall,
composed of polysaccharides. which lies exterior to the cell wall . It acts as a
protective covering and is of uniform thickness.
Cell wall is about 10 µm thick, consisting of carbohydrates,lipids,proteins,
certain inorganic salts along with specific amino acid diaminopimalic acid and a
glucose derivative muramic acid (has oligopeptide and polysaccharide)
On staining properties of cell wall bacteria are of two types Gram positive (+)
and Gram Negative (- ) Appendix Gram staining

Contents of Gram Stain
Dye : Crystal violet stain
Mordant : Gram iodine
Decolourising agent : Ethyl Alcohol
Counter stain : Safarnin
PROTOCOL
Slide with bacterial smear dipped in Crystal violet stain for 1 minute
Washed by water
Slide dipped in Gram iodine (Mordant) solution
Washed by water
Slide dipped in Absolute Ethyl Alcohol
Gram Positive Bacterial Slide retains the stain: not washed out: Bacteria take Violet colour
Gram Negative Bacterial Slide donot retain the stain : washed out
Slide dipped in Counter stain Safarnin : Gram Negative Bacteria take pink colour

The differences in cell wall composition of Gram positive and Gram negative
bacteria accounts for the Gram staining differences.
Gram positive cell wall contain thick layer of peptidoglycan with numerous
teichoic acid cross linking (Figure- 2a) which resists the decolourization with
ethanol
Gram-Positive Bacteria have thicker cell walls with less fatty substances
(lipids) than Gram-Negative bacteria. (Figure- 2b).
When washed with solvent, the cell pores close becoming less permeable
and are able to retain the stain, in this case, purple.
Gram-Negative Bacteria have thinner cell walls with more lipids. The solvent
dissolves the lipids, which combined with thinner cell walls, washes out or
decolorizes the stain.
In order to see the decolorized bacteria, a counter stain (Safranin ) is added
which gives pink colour to Gram-Negative cells.

1a
1b
Figure-2a and 2b
Cell wall components of
Gram positive and Gram
negative Bacteria

Hans Christian Gram(1884) developed the technique to stain bacterial cells .
The Gram stain allows one to distinguish between Gram-positive and Gram-
negative bacteria on the basis of differential staining with a crystal violet-iodine
complex and a safranin counter stain.
The cell walls of Gram-positive organisms retain this complex after treatment
with alcohol and appear purple, whereas gram-negative organisms decolorize
following such treatment and appear pink on treatment with counterstain
safranin.

Plasma membrane is present inner to cell wall, composed of lipoproteins.
usually gets modified as mesosomes/ desmosomes(chondriods)which is
associated with various functions as Electron Transport and DNA replication.
Figure - 3 Diagrammatic representation of fluid mosaic model of
plasma membrane

Gram +ve bacteria Gram –ve bacteria
I Gram +ve bacteria remain coloured
( purple ) even after washing with absolute
alcohol
Gram –ve bacteria do not retain colour when washed
with absolute alcohol
Ii The wall is single layered .Outer membrane is
absent
The wall is two layered.Outer membrane is present
Iii The thickness of the wall is 20-80nm The thickness of wall is 8-12nm
Iv The lipid content of the wall is quite low The lipid content of the wall is 20-30%
V Murein or mucopeptide content is 60-90% Murein or mucopeptide content is 10%
Vi Techoic acid is present in cell wall Techoic acid is not present in cell wall
Vii Porins are absent Porins or hydrophilic channels occur in outer membrane
Viii Example: Staphylococcus,Streptococcus,
Pneumococcus,
Bacillus,Mycobacterium,Strptomyces
Example :Salmonella,E coli, Pseudomonas,E coli,
Rhizobium ,Azotobacter
Table No-2 Difference between Gram +ve and
Gram –ve bacteria

Flagella Generally rod shaped bacteria possess one or more flagella made
up of single fibril (100-200A⁰ thick) Flagellin protein
Pilli (Fimbriae) are stout hair like structures, extra cellular outgrowths,
meant for attachment to host for infection or during conjugation ,made up of
helically arranged subunits of pilin protein
Cytoplasm Dense, colloidal, contain granules of glycogen, protein, fats,
poly β hydroxyl butyric acid, volutin granules and some polymers of glucose
.
Some photosynthetic bacteria possess chromatophores with
bacteriochlorophyll and bacterioviridin pigments.

In cytoplasm ribosomes (70S) are freely present.
During protein synthesis many ribosomes may attach to same messenger
RNA one after one forming polyribosome.
In bacteria polyribosomes are present free in the cytoplasm whereas in
eukaryotes , polyribosomes are attached to the surface of rough endoplasmic
reticulum.
Prokaryotic Ribosomes contain slightly more RNA than Eukaryotic
ribosomes.

Nuclear material In the interior of cytoplasm, there is light nuclear region or
nucleoid, consisting of single circular DNA molecule ( E coli- 1 nm) (Bacterial
chromosome or genophore) . DNA molecule is folded or packed in the nuclear
region and is not separated from rest of cytoplasm by nuclear membrane.
In addition to nucleoid, bacterial cell may have extra chromosomal circular DNA
called plasmid, which is self replicating unit. Plasmids are of 3 types
F (Fertility),R (Resistance) and Col (colicin) produce toxic material.
Plasmids can be isolated and can be used as tools in Recombinant DNA
Technology to insert foreign genes resulting in chimeric plasmids

Carl Woese (1977) mentioned that prokaryotes can be divided into EuBacteria
and Archaebacteria.
However subsequently it was shown that this group Archaea is distinct from
bacteria and Eukaryotes. Today, these groups are considered to form two out of
three domains of life.
The third domain (Eukarya) includes all eukaryotes, such as plants, animals,
and fungi.
The living cells are therefore now divided into following three domains :
Bacteria, Archaea and Eukarya
This classification came into existence after complete genome sequencing of
Archaeon Methanococcus jannaschii by Bult et al 1996.
Nucleotide sequence determined were compared with that of bacteria and
Eukaryotes . It was found that some of its genes resemble prokaryotes and
other to Eukaryote and some unique genes

Table No 3 Distribution of prokaryotic,Eukaryotic and Novel
unique genes in Archaea
Eukaryotic genes Prokaryotic genes Novel unique genes
1. DNA replication
2. Transcription
3. Translation
4. Histone genes
1. transport of inorganic
ions (Na+,K+) across wall
2. Cell surface structure
1. only one DNA polymerase
2. Several tRNA Aminoacyl
synthetase enzymes missing
3. Numerous inteins are
known that are inserted into
proteins & then are removed
Protein splicing elements (Inteins) are protein sequences that catalyze their own
removal from a longer protein, splicing together the two surrounding protein halves
(exteins) in the process

Table No - 4 Comparison of Archaea, Bacteria and Eukarya

Holger Jannasch (1982) discovered Methanococcus jannaschii from a hot spot of
deep sea ( 3 km deep pacific ocean ) as Methane producing organism
Following are some of the novel features of this Archaean, to create new Domain
Archaea
1. 56% of the genes of Methanococcus are new to science.
2. It lives in temperature ranging from 48⁰C →94⁰C and pressure 200 atm
3.It is killed by oxygen
4.It is autotrouph using CO2, N2 and Hydrogen
5.Produces methane and is a methanogen
6. Some of its genes resemble prokaryotes and other to Eukaryotes
It has also been shown that Archaeal system is more likely a Eukaryotic system. In
fact scientists now believe that common ancestor of all living creatures was a
thermophile, which branched off more than 3.6 billion years ago into 3 major life
forms Prokaryotes(bacteria) ,Archaea and Eukarya.

Figure- 5 Evolution of three major life forms ( Prokarya,Archaea and
Eukarya) from a common ancestor (a thermophile/Archaeon}
Common ancestor

ANOTHER PROKARYOTE : CYANOBACTERIA
(BLUE GREEN ALGAE)
Flagella and cilia are
absent, have capacity
of movement by
gliding.
Figure-6 Generalized structure of cell of
Blue Green Algae
(under electron microscope)
Examples are
Nostoc,Anabaena,Oscillitoria,
GleocapsaTrichodesmium,Spirulina,
Microcystis

Blue green algae are found in diverse habitats as fresh water, terrestrial, marine
and hot springs.
STRUCTURE OF BLUE GREEN ALGAL CELL (CYANOBACTERIA)
BGA may be unicellular, filamentous or colonial.
Mucilaginous sheath is always present around the cell/cells.
Cyanobacteria have primitive( prokaryotic) cell organization. Cell wall consists of
cellulose, pectic substances, lipoproteins, lipopolysaccharides and mucoproteins.
Plasmamembrane Lipoproteinous,invaginates as mesosomes

contains chlorophyll, carotenes, myxoxanthophyll, phycocyanin and
The cytoplasm can be distinguished into central colourless region-centroplasm and
an outer blue green pigmented region chromoplasm
phycoerythrin along with oil drops, glycogen and few spherical bodies
called cyanophycean granules evenly distributed in chromoplasm located as small
granular chromophores (cyanoplasts)
Both blue and red pigments are collectively called as phycobilins, which are
covalently bound with proteins forming phycobilisomes (cyanosomes) Each
cyanosome measures about 400A⁰ in diameter and contain about
10 subunits.
Photosynthetic pigments chlorophyll and cartenoids are present on flattened disc,
lamella are arranged concentrically in chromoplasm.

Eukaryotic cell is bounded by plasma membrane which encloses a bit of protoplast.
The major components of the cell are (1) cell membrane, (2) cytoplasm, and (3)
nucleus.
In eukaryotes, a complete set of genetic instructions is found on the DNA
molecules, which exist as multiple linear structures called chromosomes that are
confined within the nucleus.
Eukaryotic cells also contain other membrane bound organelles within their
cytoplasm (the region between the nucleus and the plasma membrane). These
subcellular structures vary tremendously in structure and function.
STRUCTURE OF EUKARYOTIC CELL

Plant cells have special
features as cell wall,
plasmodesmata, large
vacuole and plastids
Animal cells possess Centrosome
and centriole
Common features
Plasma membrane
Cytoplasm
Endoplasmic reticulum
Golgi body
Mitochondria
Lysosome
Microbodies
Nucleus
In animal cell, outer most boundary is cell membrane, plant cell have additional
outermost covering out side plasma membrane, this is cell wall. Because of cell
wall plant cells has definite shape, animal cells have no definite shape.
Figure :-7 A typical plant cell and A typical animal cell

S N Plant cell Animal Cell
1 Cellulosic cell wall present around cell
membrane
Cell wall is absent
2 Vacuoles are usually large Generally vacuoles are absent and if
present, are usually small
3 Plastids are present. Except Euglena ,no animal has Plastids
4 Golgi body present in the form of many
units known as dictyosomes.
Single highly complex and prominent Golgi
apparatus .
5 Centrosome and Centriole absent Centrosome and Centriole present
Table No- 5 Difference between plant cell and animal
cell

Plant cells differ in several key features from cells of other eukaryotic
organisms
A cell wall composed of cellulose and hemicellulose, pectin and in many cases
lignin, is secreted by the protoplast on the outside of the cell membrane.
This contrasts with the cell walls of fungi (which are made of chitin), and of
bacteria, which are made of peptidoglycan.
Cell wall is rigid, transparent, permeable ,having pits or pores. Cell wall protects
the protoplast against loss of water, excessive heat and foreign attacks and
provides mechanical strength to cell
Cell wall is differentiated into 3 layers
a) Primary wall – Cellulosic, delicate, 1-3µm thick. first deposition product of
protoplasm, parenchyma, merismatic cells, unicellular forms have only primary
wall.

b) Secondary wall is more than 4 µm thick, consists of cellulose, hemicelluloses and
lignin. It is not deposited uniformly leave unthickened areas(pits) .
Through pits fine cytoplasmic strands known as plasmodesmata pass from one cell
to another cell and connect endoplasmic reticulum and cytoplasm of two
neighbouring cells.
This is specialized cell-cell communication through cell junctions or pits. Besides the
cell junctions, some protein molecules are there in between the cells of a tissue for
binding cells together. These protein molecules are called Cell Adhesion Molecules
(CAMs).
c) Middle lamella – is the cementing layer present between two cells, consisting Ca
and Mg pectinate and cellulose. It is sticky gel like, swells with water and join two
cells

In mature plant cell a large central cavity or vacuole enclosed by delicate
membrane (tonoplast) is present .Vacuole is filled with sap and help in excretion
of waste and excess water. Cell sap has many organic and inorganic substances
Young plant cells are completely filled by cytoplasm ( Cytosol) ,having many
small vacuoles and nucleus in the centre. These small vacuoles later on fuse to
form a single large vacuole, pushing aside cytoplasm and nucleus towards cell
wall (Figure-8 )
Figure : - 8 Young and mature plant cell

THE CYTOPLASM AND THE CELL ORGANELLES
Cytoplasm is the protoplasm outside nucleus . Cytoplasm has two parts
1) Cytosol
2) Cell organalles
Cytosol is jelly like, optically clear, homogenous, colloidal or viscous fluid in which
granules and fibrils are suspended . It is the living part of the cell, most reactions
take place in cytosol.
Chemical composition of cytosol
Water- 90%
proteins -7%
carbohydrates – 1.5%
Lipids and inorganic ions – 1.5%

Plasma membrane is present between cell wall and cytoplasm.
It is delicate, semi permeable – permeability depends on physiological state of cell
and size and nature of molecules .
Plasma membrane regulates flow of water and other organic and inorganic
molecules through it.
Fluid Mosaic Model
SJ Singer and G L Nicolson(1972) proposed the fluid mosaic model for describing
the structure and thermodynamics of plasma ( cell ) membranes
a) Bilayer of phospholipids form core of plasma membrane
b) Proteins are embedded randomly on peripheral or integral portion of bilayer
c) Bilayer has fluid consistency ( not rigid ) due to number of unsaturated fatty acids
in phospholipids

Figure : 9 Structural detail of Plasma membrane according to Fluid Mosaic Model

By courtsey

Cell organelles of cytoplasm are related with different
functions
Those that trap and release energy e.g. Plastids and mitochondria
Those that are secretory or are involved in synthesis and transport e.g
Endoplasmic reticulum,ribosomes and Golgi apparatus
The organelles related with motility – Flagella and Cilia
 Suicidal bags – Lysosome
Microbodies – Peroxisomes,Glyoxysome and Sphaerosomes
Related with cell division Centrosome and centriole
Cytoskeleton- Microfilaments and Microtubules
Nucleus which controls all activities of the cell, and carries the hereditary
material

Plastids – Largest cell organelle present only in plant cell (Except BGA and
Fungi). Plastids are not found in animal cell. Plastids are of three types
a) Leucoplast – Colourless plastids, Store starch , present in cells of underground
parts such as tuber, roots
b) Chromoplast – Coloured plastids (red, orange, yellow or violet) due to presence
of carotene, xanthophylls and Anthocyanin, are present in petals of flowers and
fruits
c) Chloroplast – green plastids , present in mesophyll cells of leaves and green
stems contains pigments as chlorophylls and carotenoid for light harvesting and
photosynthesis
Chloroplast is enveloped by double membranous sac. It encloses proteinaceous
matrix ( stroma).
Lamellar structure run in matrix, it is denser at certain places due to pigments
(grana) stacked in a group of many.

The photosynthetic pigments are chlorophylls and carotenoids. The stroma of
chloroplast has DNA, RNA , ribosomes, fat globules, starch and a number of
enzymes.(Figure- 10) Main function of chloroplast is photosynthesis
Figure :- 10 Structure of Chloroplast

Mitochondria (Chondriosome) Power house of the cell
Mitochondria are .0.5 – 1.0 µm long, appear spherical or rod shaped
under compound microscope .
Particles present on inner membrane are oxysomes( Respiratory particles/F1
particles ) . These particles play important role in electron transport.
Matrix of mitochondria has enzymes for TCA ( Krebs) cycle, ATP synthesis, protein
and fat synthesis and contains DNA, RNA and Ribosomes.
(Figure- 11)
Mitochondria appears to be surrounded by two membranes.
Inner membrane is folded inwards deep in matrix, even upto opposite side forming
cristae.
Intermembranous space is filled with a liquid. Inner membrane has large surface
area than outer membrane .

Figure : 11 Structure of Mitochondria
Drawn By Prof Ichha Purak
Mitochondria contain 70% enzymes of the
cell and is mainly connected with respiration
which gives energy so is termed as power
house of cell. Mitochondia possess in total
70 enzymes and 14 coenzymes.

In 1970, American biologist, Lynn
Margulis, provided evidence that
some organelles within cells were
at one time free living cells
themselves
Supporting evidence included organelles with their
own DNA
Both chloroplast and mitochondria are semi autonomous
as they have DNA
( genetic material), RNA and Ribosomes ( Protein
synthesizing machinery) are considered as
endosymbionts ( Intracellular parasites)

Endoplasmic Reticulum (E R )
Porter et al (1945) reported and described structure of Endoplasmic Reticulum for
the first time
Plasma membrane is folded ( extended) inwards into the cytoplasm in the form of
double membranous system of thousands of tiny tubules
( branched/unbranched )
This membranous system extends from plasma membrane upto nuclear
membrane or plasma membrane to cytoplasm or nuclear membrane to
cytoplasm . Endoplasmic reticulum keeps on changing
Space enclosed by tubules is cisternae, two cisternae are connected by inter
cisternal connection. On sides of cisternae spherical bodies are present. These
are known as vesicles.
Endoplasmic reticulum is of two types
Smooth E R - no particles present on its surface
Rough E R - On surface of Endoplasmic Reticulum , Ribosomes and Microsomes
( Particles ) are present ( Figure -12 )

Figure : -12 ENDOPLASMIC RETICULUM &
RIBOSOMES

Functions of Endoplasmic Reticulum
Mechanical support and act as endoskeleton(cytoskeleton) of the cell
1) Divides cytoplasm into a number of compartments for different enzymatic
biochemical reactions
2) Cisternae (Channels) provide space for transport of metabolities from
cytoplasm to nucleus and in between two cells through pits.
3) Help in synthesis of sterols and phospholipids
4) Excretion of metabolites outsides Plasma membrane
5) Holds ribosomes for synthesis of secretory proteins

Ribosomes
RNA and Protein non membranous particles , present free in cytoplasm or
attached to outer surface of nuclear membrane or on Endoplasmic Reticulum.
Ribosomes are also present in chloroplast and mitochondria.
Ribosomes are site for protein synthesis
Ribosomes present free in cytoplasm or attached to E R are 80S particles
having two subunits 40S and 60S,whereas ribosomes present in chloroplast and
mitochondria are 70S having two subunits 30S and 50S.(Figure-12 )
Svedberg unit- Components of cell after centrifugation, sediment or settle down
at different speeds depending upon their mass and size. The coefficient of
sedimentation is represented in Svedberg unit and depicted as S.

Golgi bodies (Apparatus) Dictyosome / Lipochondria
discovered by Camillo Golgi (1898) in animal cell
Stacks of flat sac like structures – cisternae ( 4-10 ), surrounded on sides , above
and below by swollen structures the vesicles.
Margins of cisternae are curved to cup or bowl like appearance.
Structure of golgi apparatus continuously changes, some discs appear to grow
others shrink.
Some cisternae are formed on Cis( forming ) face and some are destroyed on trans
face ( Maturity).
Cis face lies towards nucleus and Endoplasmic Reticulun , trans face lies towards
Plasma Membrane .
On cis face small vesicles fuse and add to Golgi Body while vesicles are destroyed
from trans face .(Figure-13 )

In plant cell, groups of cisternae, are attached to other similar groups with the help
of Inter cisternal tubules. Each group is reffered as dictyosome, collectively form a
golgi complex.
Figure :- 13 Structure of Golgi body
Functions of Golgi body
Helps in secretion of polysaccharides, enzymes, proteins etc, cell
plate formation during cell division, vesicles separate and in cell plate region fuse
with each other and storage and secretion of cellular products.

Lysosomes are called “suicidal bags” as enzymes contained in them can digest
the cell’s own material (can perform intracellular digestion). Lysosomes are about
0.2-0.8 µ in diameter, generally present in animal cells and some lower plants as
fungi.
Lysosome is sac enclosed by unit membrane. It encloses various digestive
enzymes, which when released break down various organelles, help in digestion
of food particles and extracellular substances ( Bacteria , Virus)
Lysosomes enable the cell to process bulk material taken by endocytosis
( along with water current )
Lysosome contains 30 different types of hydrolytic enzymes break down cell
organelles and cell itself.(Figure-14 )

Centrosome and centriole It is generally present in animal cell, but in some
algae, fungi, moss and fern, the cells have centriole, near the nucleus. It has a
pair of dots ( granules) surrounded by transparent cytoplasm centrospheres,
whole structure is known as centrosome . centrioles have astral rays and are
functional in cell division in formation of spindle.
Figure :-15 Structure of centriole and centrosome

Cilia and flagella (the organelles for mobility)
Cilia and Flagella: - Cilia and Flagella are hair-like micro-tubular organelles
projecting from the cell surface into the extracellular medium and are concerned
with cell motility.
i) Some unicellular organisms like Paramaecium and Euglena swim in water with
the help of cilia and flagella respectively.
(ii) In multicellular organism some living tissues (epithelial tissues) have cilia.
They beat and create a current in the fluid in order to move in a given direction
e.g. in the wind pipe (trachea) to push out the mucus and dust particles.
iii) Reproductive cells as spores and gametes bear one, two or many cilia or
flagella for movement.
Human sperm Isogametes Cladophora
Chlamydomonas

(iv) Cilia beat like tiny oars or pedals (as in a boat) and
flagella bring about whip like lashing movement.
(iv) Both are made up of contractile protein tubulin in
the form of microtubules.
(v) The arrangement of the microtubules is 9 + 2, that is,
two central microtubules surrounded by nine peripheral
ones.
(vi)The cilia and flagella appear to arise from the basal
bodies.
(vii) Cilia are shorter and more numerous on cells
Flagella are longer and fewer (usually 1-3) on cells
C
P

Microbodies are spherical bodies 0.5-1.5 µm, single membrane bound
organelles having granular interior of proteins. Some of these bodies are
associated with chloroplast, mitochondria, E R and golgi bodies. On the basis of
enzymes present and tissue in which microbodies are present, they are
classified as
a) peroxisomes – Discovered by Tolbert (1969) . Found both in plant and animal
cells. They are found in leaves of higher plants, are present closely associated
with chloroplast. They takes part in photorespiration in plant cells along with
chloroplast ant mitochondria. They also bring about fat metabolism in cells. They
participate in oxidation of substrates resulting in the formation of hydrogen
peroxide

b) Glyoxysomes – Discovered by Beevers ( 1961), found in plant cell, present
in cotyledons and endosperm of seeds are also surrounded by unit membrane
and possess the enzymes required for conversion of fats into carbohydrates
during germination of seeds, the enzymes are aconitase, citrate synthetase,
glycolate oxidase, malate dehydrogenase, catalase and lipase etc.
Glyoxysomes have not been reported in animal cells.
c) Sphaerosomes – spherical (0.5- 2.0 µm) bodies bounded by half of unit
membrane, contain fatty materials, act as centres for synthesis and storage of
fats.
Cell inclusions – Life less substances in the cell called ergastic matters. These
may be stored food ( Strach, oil, proteins) or waste materials deposited as
crystals, Calcium carbonate, Calcium oxalate, gums, mucilage. Latex, tannin,
nector (help in fertilization)

Microfilaments and Microtubules (Cytoskeleton) The cytoskeleton is a structure
that helps cells maintain their shape and internal organization, and it also provides
mechanical support that enables cells to carry out essential functions like division
and movement and is located near membrane
Microfilaments are solid structures (5-7nm in length) rods made up of a proteins
called actin , generally present in muscle cell of animals.
Microtubules are the largest type of filament, with a diameter of about 25
nanometers (nm), and they are composed of a protein called tubulin
Intermediate filaments, as their name suggests, are mid-sized, with a diameter of
about 10 nm.
Unlike actin filaments and microtubules, intermediate filaments are constructed
from a number of different subunit proteins.

Nucleus : the hereditary organelle. It is the largest cell organelle. It is
present in Eukaryotic cells but not present in prokaryotic ( Bacteria & BGA)
cells- In these cells nuclear material is not bounded by nuclear membrane.
The eukaryotic cells may be uninucleate (higher plants) or multinucleate (
Algae and Fungi ). Multinucleate cells may be syncytium or coenocytes
Nucleus is spherical and denser organelle in the cell. It is bounded by double
layered porous nuclear membrane. Nucleus always remains surrounded by
cytoplasm and never touches cell wall or vacuole.
Chemically nucleus consists of approximately 72% protein, 20% DNA, 5%
RNA and 3% Lipids.

Figure :- 16 Structure of Nucleus .The outermost
boundary of the nucleus is the nuclear envelope.
Nuclear envelope consists of two phospholipid
bilayers (membranes)—an outer membrane and an
inner membrane
(credit: modification of work by NIGMS, NIH)
Figure -17 Structure of Nucleus

Nuclear membrane is double membrane of lipo-proteinous nature like plasma
membrane. It separates the nucleoplasm from cytoplasm. Outer nuclear membrane
continues with ER through pores and also has ribosomes attached on the outer
surface which make the outer membrane rough.
Nuclear envelope consists of two phospholipid bilayers (membranes)—an outer
membrane and an inner membrane ,in contrast to the plasma membrane, which
consists of only one phospholipid bilayer.( Figure -16)
Structually nucleus consists of nuclear membrane, having nuclear pores,
nucleoplasm, chromatin (karyolymph) and nucleolous. The pores allow the
transport of large molecules in and out of nucleus
Nucleoplasm consists of two parts
a) A structure less phase the nuclear sap which is made up of phospholipids,
proteins and enzymes
b) Structural phase consisting of chromatin network and nucleolous
(Figure-17)

Chromatin network changes with stages of cell division, form thread like
structure known as chromosomes on which genes are located in linear fashion.
On staining with feulgen stain chromosomes show bands of dark stained
regions known as heterochromatin is more condensed and is genetically
inactive and light stained regions known as euchromatin is less condensed and
is genetically active.
Chromatin contains DNA, bound to basic proteins( Histones) and small amount of
RNA
Nucleolous – interphase nucleus may have 1-2 or many nucleoli. The nucleoli are
organized by the activities of certain specific areas of some chromosomes. Those
chromosomes which take part in formation of nucleolous are known as Nucleolar
organizer (N O ) chromosomes.

The main contents of Nucleolous are RNA and proteins ( diffuse from cytoplasm),
rRNA and proteins pack to form ribosomal precursors. Nucleolous is ribosome
producing machine. Nucleoous is not bounded by a membrane.
In chromatin network of some nuclei, here and there deeply stainable groupings
or lumps are present knowns as chromocentres, these are formed due to close
coiling of chromonemata.
Nucleolous functions for synthesis of RNA and as store house of RNA
The cell cannot survive without nucleus. It controls the metabolic activities of the
cell and also carries hereditary material from one generation to next and helps in
division of the cell, therefore it is known as control centre of cell.

REFERENCES
Bult C J I et al (1996 )Complete genome sequence of the methanogenic archaeon,methanococcus
jannaschii. Science : 273(5278) : 1058-73
Cooper, T. G., and Beevers, H. (1969) Mitochondria and Glyoxysomes from Castor Bean Endosperm.
Enzyme Constituents and Catalytic Capacity J. Biol. Chem. 244, 3507-3513
D ODGE , J. D. (1965). Chromosome structure in the dinoflagellates and the problem of mesokaryotic
cells.Excerpta Medica, International Congress Series 91: 339–345
Doughtery, E. C. (1957). Neologism needed for structures of primitive organisms. 1. Types of nuclei. J.
Protozool. 4:14
Gram, H.C. (1884). "Über die isolierte Färbung der Schizomyceten in Schnitt- und
Trockenpräparaten". Fortschritte der Medizin (in German). 2: 185–189.
Haeckel, E. (1866). Generelle Morphologie der Organismen, Allgemeine Anatomie der Organismen Vol.
I, Reimer, Berlin
Jannasch HJ, Wirsen CO, Taylor CD (1982) Dark sea Bacteria. Isolation in the absence of
decomposition . science 216: 1315-1317
Mazzarello, Paolo (1999). "Camillo Golgi's Scientific Biography". Journal of the History of the
Neurosciences. 8 (2): 121–131.
Porter KR, Claude A, Fullam EF (1945). “ A study of Tissue Culture Cells by Electron Microscopy”.J Exp
Med. 81 (3) : 233-246.

Schleiden, M. J. (1839). “ Beitrage Zur Phytogenesis”. Archiv für Anatomie, Physiologie und
wissenschaftliche Medicin: 137–176.
Schwann, Theodor (1839). Microscopical Researches into the Accordance in the Structure and Growth of
Animals and Plants. Berlin
Singer SJ and Nicolson GL ( 1972). "The fluid mosaic model of the structure of cell membranes". Science.
175 (4023): 720–731.
Tolbert NE, Oeser A, Yamazaki RK, Hageman RH, Kisaki T (1969) A survey of plants for leaf
peroxisomes. Plant Physiol 44: 135–147
Woese, C. R., and G. E. Fox. (1977). Phylogenetic structure of the prokaryotic domain: the primary
kingdoms. Proc. Natl. Acad. Sci. USA 74:5088-5090.
Books referred
1.The Cell A molecular approach By G M Coopoer and R E Hausmen 6th edition
2.Cell and Molecular biology By P K Gupta: Rastogi Publications
3. Cell Biology (Cytology,Biomolecules and Molecular Biology) By Verma PS and Agarwal V K )
S Chand & Company Pvt Ltd.
4. Biocyclopaedia Is online for students and researchers in Biology biocyclopedia.com
5. Cell Biology by Dr S P Singh and Dr B S Tomar Rastogi Publication,Meerut,U P ,India

Questions/Problems
Select correct choice for following MCQs on cell structure and function
1. Which is differentially permeable
a) Cell wall b) Middle lamella
c) Cell membrane d) cuticle
2. Which one of the following cell organelle remains enveloped by single membrane
a) Mitochondria b) Plastid
c) Ribosome d) Lysosome
3. Which one of these give mechanical support to cell ?
a) Cilia b) Lysosome
c) Endoplasmic reticulum d) Golgi bodies
4. The unit for measurement of sedimentation of ribosome is
a) Svedberg(S) b) Angstrom (A⁰) c) Micron (µ) d) Nanometre (nm)
5. Extranuclear DNA is found in
a) Lysosome b) Golgi bodies c) Mitochondria d) None of these
6. The ribosome of 70S sediment coefficient breaks into 2 subunits
a) 50S and 20S b) 50S and 40S c) 50S and 30S d) 60S and 40S
7. Lysosomes are called suicide bags because of
a) Phagocytic enzymes b) Hydrolytic enzymes
c) Proteolytic enzymes d) Respiratory enzymes
8. A cluster of ribosomes held together on a messenger RNA is called
a) Mesosome b) Dictyosome c) Polysome d) Microsome

9. The oxysomes are made of
a) Glycoproteins b) Lipoproteins c) Phosphoproteins d) None of these
10. Mitochondria are called power house of the cell because these
a) contain enzymes b) Release ATP c) contain ribosomes d) Contain RNA and DNA
11)Which is not a membrane bound structure ?
a) Centriole b) Nucleus c) E R d) None of These
12) Non-living substance of cells are collectively known as
a) Cytoplasm b) Plasmagel c) Mesoplasm d) Deutoplasm
13) Centromere is also called
a) Secondary constriction b) Primary constriction
c) Satellite body d) Locus
14) Plastids contain
a) Cristae b) microtubules
c) Porous membrane d) thylakoids
15) Which of the following is semi-autonomous ?
a) Lysosome b) Sphaerosome C) peroxisome d) mitochondria
16) Sphaerosomes are associated with
a) Protein metabolism b) Liptd metabolism
c) Nitrogen metabolism d) Glycolate metabolism
17) Smallest cells so far observed are of
a) Bacteria b) virus
c) PPLO d) yeast

18) Which is exoskeleton of plant cell ?
a) Endoplasmic reticulum b) Golgi bodies
c) Plasma membrane d) cell wall
19) ‘Fluid Mosaic Model’of plasma membrane was given by
a) Du Praw b) Danieli
c) Robertson d) Singer and Nicolson
20) Semi-autonomous nature of chloroplast is due to
a) DNA b) DNA and RNA polymerase
c) Ribosomes d) All of the above
21) Ribosomes of chloroplast are of the type
a) 60S b) 70S c) 80S d) 120S
22) Ribosomes are attached to endoplasmic Reticulum through
a) r-RNA b) t-RNA c) Hydrophobic interaction d) Ribophorins
23) Largest cell organelle is
a) Golgi bodies b) Peroxisome
c) Chloroplast d) Mitochondria
24) Which one of the following is known as store house of RNA ?
a) Nucleus b) Chromosome c) Nucleolous d) None of the above
25) The longest plant cell is
a) Fibre b) tracheid c) Vessel d) companion cell

26. Single envelope system is characteristic of
a) Prokaryotic cell b) Eukaryotic cell c) None d) Both
27. Cell boundary of animal cell is
a) Cell wall b) Plasma membrane c) None of these d) Both
28. The granular structure found attached with endoplasmic reticulum are
a) Ribosomes b) Lysosomes c) Desmosome d) Kinetosome
29. The power house of the cell
a) Golgi complex b) Chloroplast c) Mitochondria d) Lysosome
30. Prokaryotes and eukaryotes have the common
a) Mitotic apparatus b) Histone c) Genetic code d) Mitochondria
31.What is the name of fluid part of the cytoplasm of the Eukaryotic cells ?
a)Protoplasm b)Cytokine c) Cytoplasmic inclusions d) Matrix
32.Which of the following is not available in animal cells?
a) Plastid b)Mitochondria c)Lysosomes d)Centrosomes
33. Which part of the cells are concerned with respiration?
a)Ribosome b)Golgi body c) Mitochondria d) Nucleus
34.Which part of the cell contain hydrolytic enzyme?
a)Flagella b)Centrosome c)Ribosome d) Lysosomes
35. Microfilaments are made of:
a) RNA b)Protein c)DNA d) Enzyme
Answers : Note : Options in red colour are correct choice

Fill in the blanks of the following
1) The fluid-mosaic model of plasma membrane was propsed by ---------------------- Sanger and Nicolson
ii) Most abundant lipid in plasma membrane is ---------------------------------phospholipid
iii) Golgi complex plays a major role in ---------------------------post translational modification of proteins
iv) --------------------------- organelle is enclosed by single membrane lysosome
v) colchicines treated cells are arrested in ---------------------------.spindle formation
vi) Plant cell wall contain --------------------.cellulose
vii) ------------------------ is known as power house of the cell Mitochondria
viii) Peroxisome contains ---------------------- enzyme. Oxidative enzymes
ix) Histone proteins are enriched in ---------------- amino acid Histidine/Lysine/Arginine(Basic amino acids)
x) Kinetochore is the attachment site for ---------------------------. Spindle fibres

Short Answers Questions
1Apart from nucleus which two other cell organelles have their independent DNA ?
2.Summarize important diagnostic features of prokaryotes
3.Write a short notes on PPLOs
4.Write short note on prokaryotic cell
5.Give the structure of eukaryotic cell
6. Describe the factors which control the shape of the cells .
7. What are the conditions which set upper limit in cell size?
8. Differentiate between cell wall and cell membrane.
9.Draw Singer and Nicholson’s model of cell membrane.
10.Draw structure of mitochondria or chloroplast as seen by electron microscope.
11. List functions of mitochondria or chloroplast.
12. Name the self – duplicating cell organelles? Why are they called so?
13. Differentiate between functions of ER, ribosomes and Golgi bodies.
14. Most organelles are membrane – bound. What is the advantage of such arrangement.
15. Differentiate between the structure and function of centriole and cilia/flagella.

Long Answer Questions
1.Describe the structure of a prokaryotic cell
2.Describe generalised structure of bacterial cell
3.Describe the structure of a cyanobacterial cell
4.Give electron microscopic structure of PPLO cell.
5. Give a well labelled diagram of a eukaryotic animal cell.
6. Define the cell.
7. Describe the structure of eukaryotic cell.
8. Describe the general shape,size and number of cells in living organisms
8.Describe the detailed structure of a plant cell with the help of labelled diiagram.
9. Describe the structure of eukaryotic cell . Enumerate the differences in plant cell and animal cell.
10. What are differences between prokaryotic and eukaryotic cells ?

Justify the statement that mitochondrion is semi-autonomous cell organelle
Mention components of prokaryotic cell
Give an account of different phases of cell cycle
Write short note on nuclear envelop and nucleolous
Give an account of structure and function of peroxisome
Explain structure and function of smooth and rough Endoplasmic reticulum.
Explain the structure of flagella and cilia with examples
Describe the structure of cell membrane.
Describe the structure of typical animal cell. Mention the differences between plant cell and animal cell .
Describe different kinds of plastids. Describe the structure of chloroplast as observed under electron
microscope.
Describe different types of ribosomes ? Mention their role in protein synthesis
Describe briefly the cell theory mentioning contribution of important scientists .
Describe the structure and function of plant cell wall
Defferentiate between prokaryotic cell structure and eukaryotic cell structure with labeled diagrams
Explain structural features of mitochondria
Why lysosome is known as suicidal bag of the cell ?
Briefly describe Fluid mosaic model of plasma membrane with a suitable diagram.
Discuss about the structure and function of Golgi complex.
Explain the cytoskeletal system for eukaryotic cell.
Discuss about the following a) Nucleosome model b) euchromatin and heterochromatin .
Describe signal molecule and their role in cellular signaling.
Answer the following questions