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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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CELL: THE UNIT OF LIFE
Basic unit of life
...

 Cytology – study of cell and cellular structures
...

 Performing the essential functions of life
...
Hence,
cell is the fundamental structural and functional unit of all living organisms
...
He actually saw cell wall of
dead cells not cell itself
...

Modified by Rudolf Virchow – he explained that new cells develop from pre existing
cells by cell division (Omnis cellula-e cellula)
...

ii)
Cell is structural unit of life
...



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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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

CELL SIZE AND SHAPE
 Smallest cell – mycoplasmas (PPLO – Pleuro Pneumonia Like Organisms)
 Largest cell – egg of an ostrich
...

 Largest cell in human body – Ovum
...

Even shape of cells may vary with the functions they perform
...

 Membrane bound organelles are
absent
...

 Membrane bound organelles are
present like ER, Mitochondria,
Golgibodies, Plastids, Lysosomes
...

Bacteria

on the basis of
their basic shape

Bacillus

coccus

vibrio

spirillum

(Rod shape)

(spherical)

(comma shape)

(spiral shape)

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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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Basic structure of prokaryotes

Cell envelope
and its modifications
Glycocalyx

outermost

Cytoplasm,
cell organelles and
inclusion bodies

Naked genetic material =
genomic DNA (Single
chromosome)

Cell wall
Plasma membrane innermost

If loose sheath

Slime layer

 Glycocalyx

If thick and tough

Capsule

 Cell wall




Determine shape of cell
...

 Mesosomes





Formed by extension of plasma membrane into cell
...

Help in cell wall formation, DNA replication and distribution to daughter cells
...


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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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 Chromatophores
 Membranous extensions into cytoplasm
...

 In cyanobacteria
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 Thin filamentous extensions from their cell wall
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 Pili and Fimbriae
 Pili are elongated tubular structure while fimbriae are small bristle like fibres
...

 Ribosomes
 Associated with the plasma membrane of the cell
...


50S

50S

+

30S

30S
70S



Site of protein synthesis
...


ribosome
mRNA
polysome
 Inclusion bodies
 For storage of reserve material in prokaryotic cells
...

 e
...
, phosphate granules, cyanophycean granules and glycogen granules
...


EUKARYOTIC CELLS

 Include all the protists, plants, animals and fungi
...

 possess an organised nucleus with a nuclear envelope
...


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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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Basic structure of Eukaryotes

Cell envelope
and its modifications

Cytoplasm,
Cell organelles

Nucleus including
chromatin material

Cell wall
Plasma membrane

 Cell wall





non-living, rigid structure
forms an outer covering for the plasma membrane of fungi and plants
...

it also helps in cell-to-cell interaction and provides barrier to undesirable
macromolecules
...
Middle lamella
 Outermost
 Made up of mainly calcium pectate
...

b
...

 Present in young cell
...

 Madeup of cellulose, hemicelluloses
...

c
...

 Hard
...

 Present in sclerenchyma, collenchyma, and vessels, tracheids
...


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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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 Cell membrane
 Mainly composed of bilayer phospholipids, also possess protein and carbohydrate
...

This ensures that the nonpolar tail of saturated hydrocarbons is protected from the
aqueous environment
...

( In human RBC membrane has 52% protein and 40% lipids
...

According to this model the quasi-fluid nature of lipid enables lateral movement of
proteins within the overall bilayer
...


Fluid Mosaic Model



Transport across cell membrane

Passive transport

Active transport

• Energy is not utilised
...

(energy independent)
(energy dependent)
• Movement of substances
• Movement of substances
according to concentration
against the concentration
gradient (from low conc
...

to high conc
...
)

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CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

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Simple
diffusion
Passive
transport



Movement of neutral solute

Facilitate
diffusion

Movement of polar molecule with
the help of carrier protein

osmosis

Movement of water/solvent
Single membrane



Cell organelles

Membrane
bound
Double membrane
Nonmembrane
bound

Endoplasmic Reticulum, Golgi
bodies, Lysosome,Vacuoles,
Cilia, Flagella, Microbodies
...

Outer membrane
Forms continuous
limiting boundary of the
organelle
...

Outer compartment

Inner compartment

Peri Mitochondrial Space/
Inter membranous space




Matrix

Mitochondria are site of aerobic respiration
...

The matrix also possesses single circular DNA molecule, a few RNA molecules,
ribosomes (70S) and the components required for the synthesis of proteins
...

The mitochondria divide by fission and produce new mitochondria
...
Anurag mittal
Mob
...
wordpress
...

They bear some specific pigments, thus imparting specific colours to the plants
...
Gives the part of the
plant a yellow, orange or red colour
...


Elaioplasts

Store Oils and Fats
...


Chloroplasts are mainly found in the mesophyll cells of the leaves
...

Double membrane bound Cell organelle
...

Chloroplast

Grana
• Stake of Thylakoids
...


Stroma
• Limited by inner membrane
• Contains enzymes for the
synthesis of carbohydrates or
proteins
...
Anurag mittal
Mob
...
wordpress
...

Stroma also contains small, double-stranded circular DNA molecules and ribosomes
(70S)
...


 Endoplasmic Reticulum
 a network or reticulum of tiny tubular structures scattered in the cytoplasm that is
called the endoplasmic reticulum (ER)
 Hence, ER divides the intracellular space into two distinct compartments, i
...
,
luminal(inside ER) and extra luminal(cytoplasm)
...

• Major site for synthesis of lipid
...


Endoplasmic Reticulum

Rough
(RER)
• bear ribosomes on their surface
proteins
...

• are extensive and continuous with
the outer
• membrane of the nucleus
...
Anurag mittal
Mob
...
wordpress
...

 They consist of many flat, disc-shaped sacs or cisternae stacked parallely
...

 The golgi apparatus principally performs the function of packaging materials
...

 A number of proteins synthesised by ribosomes on the endoplasmic reticulum are
modified in the cisternae of the golgi apparatus before they are released from its
trans face
...

The isolated lysosomal vesicles have been found to be very rich in almost all types of
hydrolytic enzymes (hydrolases – lipases, proteases, carbohydrases) optimally active
at the acidic pH
...


 Vacuoles







Membrane-bound space found in the cytoplasm
...

It contains water, sap, excretory product and other materials not useful for the cell
...

In plants, the tonoplast facilitates the transport of a number of ions and other
materials against concentration gradients into the vacuole
...

In many cells food vacuoles are formed by engulfing the food particles
...

They are composed of ribonucleic acid (RNA) and proteins
...

The eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S
...


60S

60S

40S
40S
80S

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11

CHAPTER 8: CELL: THE BASIC UNIT OF LIFE

https://biologyaipmt
...
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 Cytoskeleton



An elaborate network of filamentous proteinaceous structures present in the
cytoplasm
Functions are mechanical support, motility, maintenance of the shape of the cell
...

 Cilia are small structures which work like oars, causing the movement of either the
cell or the surrounding fluid
...

 Eukaryotic cilium and flagellum are covered with plasma membrane
...
The axoneme usually has nine pairs of doublets of radially arranged
peripheral microtubules, and a pair of centrally located microtubules
...


 Centrosome and centriole
 Centrosome is an organelle usually containing two perpendicularly lying centrioles
surrounded by amorphous pericentriolar materials
...
They are made up of nine evenly
spaced triplet peripheral fibrils of tubulin
...

 The centrioles form the basal body of cilia or flagella, and spindle fibres that give
rise to spindle apparatus during cell division in animal cells
...

They are present in both plant and animal cells
...
Anurag mittal
Mob
...
wordpress
...

the material of the nucleus stained by the basic dyes was given the name chromatin
by Flemming
...

the nuclear envelope is consists of two parallel membranes with a space inbetween
called perinuclear space
...

At a number of places the nuclear envelope is interrupted by minute pores
...

Normally, there is only one nucleus per cell
...
g
...

The nuclear matrix or the nucleoplasm contains nucleolus and chromatin
...
It is non-membrane
bound
...

During cell division, chromatin network condenses into chromosomes
...

Every chromosome essentially has a primary constriction or the centromere on the
sides of which disc shaped structures called kinetochores are present
...
This gives the appearance of a small fragment called the satellite
...
Anurag mittal
Mob

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