The document discusses cells and their components. It describes that cells are the fundamental unit of life and contain a nucleus that stores genetic information. The development of the microscope allowed scientists like Hooke and Van Leeuwenhoek to discover and observe cells. Key developments included the identification of plant and animal cells and establishing that all living things are made of one or more cells, leading to the cell theory. The document also describes various cell structures like the cell membrane, cell wall, mitochondria and chloroplasts and their functions.
2. What is a Cell ?
The cell is the fundamental structural and
functional unit of all living beings.
All living things are made of one or more cells.
Every cell has its own life.
Old and weak cells in the body continually die and
are replaced by new cells.
All organisms including ourselves, start life as a
single cell called the zygote.
Cells are so small (microscopic) that they cannot
be seen with the naked eye.
Biswarup Majumder | Bio-World 1
3. The Invention of the Microscope
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The first microscope was constructed by Dutch
scientist Antonie Van Leeuwenhoek (1632-1723).
All his microscopes consisted of a single biconvex
lens and were called simple microscopes.
Some of these microscopes had a considerable
magnifying power up to 200 times.
Lens
Sample
Holder
Focus
Knob
Antonie Van Leeuwenhoek
Leeuwenhoek’s Simple
Microscope
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4. The Discovery of Cell
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Robert Hooke (1635-1703), an English scientist,
develop a microscope by using two lenses for
achieving greater magnification. Such microscopes
were later known as compound microscopes.
Hooke examined a thin slice of cork (the dead cells
of oak bark) under his microscope. He noted small
geometric shapes which he named cells because
they reminded him of the small room monks lived
in at a monastery.
Robert Hooke
Drawing by Hooke
Hooke’s Microscope
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5. An Ordinary Compound Microscope
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The ordinary compound microscope of today is
greatly improved design of the original Hooke’s
microscope.
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6. Electron Microscope
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An electron microscope is a microscope that uses a
beam of accelerated electrons as a source of
illumination.
Electron Microscopes can have magnifications
of ×500000.
Ernst Ruska and Max Knoll built the first electron
microscope in 1931. For this and subsequent work
on the subject, Ernst Ruska was awarded the
Nobel Prize for Physics in 1986.
Pollen Grain
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7. Light vs. Electron Microscope
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Electron Microscope
Light Microscope
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8. Cell Theory
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The three Basic Components of the Cell Theory :
1. All organisms are composed of one or more
cells [Schleiden & Schwann (1838-39)].
2. The cell is the basic unit of life in all living
things [Schleiden & Schwann (1838-39)].
3. All cells are produced by the division of
preexisting cells.[Virchow (1858)].
Matthias Schleiden Theodor Schwann
Rudolf Virchow
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Cells – How Numerous ?
Cells – How Small ?
Mycoplasma gallicepticum, a parasitic bacterium which lives
in the primate bladder, waste disposal organs, genital, and
respiratory tracts, is thought to be the smallest known
organism capable of independent growth and reproduction.
The largest cell found in nature is an Ostrich Egg.
Nerve cells are the longest cell. The longest of nerve cells
in any species are be found in the colossal squid, with some
nerve cells estimated to be over 10 meters in length.
Unicellular Organisms Multicellular Organisms
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Did You Know ?
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Why are cells so small ?
Small cell size is a practical necessity arising from the
decrease in the surface area-to-volume ratio of any
object as it increases in size. As an object increases in
volume, its surface area also increases, but not as
quickly.
This phenomenon has biological significance for two
reasons:
1. The volume of a cell determines the amount of
metabolic activity it carries out per unit of time.
2. The surface area of a cell determines the amount
of substances that can enter it from the outside
environment, and the amount of waste products
that can exit to the environment.
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Cell Wall
Cell wall is a tough, rigid layer that surrounds some types
of cells. It is located outside the cell membrane whose
main function is to provide rigidity, strength, protection
against mechanical stress and infection.
Cell wall is a characteristic feature to cells of plants,
bacteria, fungi, many algae and some archaea. Protozoans
and animals do not have a cell wall.
The composition of the cell wall differs from one species
to the other.
The Archean cell wall is made of glycoproteins and
polysaccharides. In fungi cell walls are made of
glucosamine and chitin. In algae it is composed of
glycoproteins and polysaccharides. The plant cell wall is
mainly composed of cellulose, hemicellulose, glycoproteins,
pectins and lignin.
Freely permeable and non-living in nature.
The cell wall is like a fort; it
protects the organelles inside
the cell, and provides strength
and support.
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Plant Cell Wall
The middle lamella - It is first layer formed during cell
division. This layer is rich in pectin. It is the outermost
layer, joins together adjacent plant cells and holds
them together.
The primary cell wall - It is formed after the
middle lamella. It is composed of pectin compounds,
hemicellulose and glycoproteins. The layer consists of a
framework of cellulose micro-fibrils, in a gel-like
matrix. It is thin, flexible and extensible layer.
The secondary cell wall - It is a thick layer formed
inside the primary cell wall. It is extremely rigid and
provides strength. It is composed of cellulose,
hemicellulose and lignin.
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Plant cell wall consists of three layers : the primary cell
wall, secondary cell wall and the middle lamella.
16. Bacterial cell wall :
The gram positive bacteria have a thick cell wall and is made up of many layers of
peptidoglycan and teichoic acids.
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Bacterial & Fungal Cell Wall
The gram negative bacteria have thinner cell walls, and is made up of few layers of
peptidoglycans and is surrounded by a lipid membrane containing lipopolysacccharides and
lipoproteins.
Made up of peptidoglycans also known as murein. The
cell wall of bacteria is essential for the survival of
bacteria.
Cell wall of bacteria is broadly classified into two types:
gram positive and gram negative.
Fungi cell wall consists of chitin and other polysaccharides.
Species of fungi that possess a cell wall have a plasma
membrane and three layers of cell wall material surrounding
it. These layers are made up of chitin, glucans and a layer a
of mannoproteins (mannose containing glycoproteins).
Fungal cell wall :
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Cell Wall - Functions
1. Gives the cell a definite shape and structure.
2. Provides structural support.
3. Protection against infection and mechanical stress.
4. Separates interior of the cell from the outer environment.
5. It enables transport of substances and information from
the cell insides to the exterior and vice versa.
6. Also helps in osmotic-regulation.
7. Prevents water loss.
8. The physiological and biochemical activity of the cell wall
helps in cell-cell communication.
9. It prevents the cell from rupturing due to turgor
pressure.
10. Aids in diffusion of gases in and out of the cell.
Plasmodesmata : The Bridge To Somewhere
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Cell Membrane
It is the boundary, which separates the living cell from
their non-living surroundings.
In animal cells, the plasma membrane is present in the
outer most layer of the cell and in plant cell it is present
just beneath the cell wall.
Very thin, flexible, living membrane, possesses fine pores.
Composed of two layers of phospholipids and embedded
with proteins.
It is a thin semi permeable membrane layer, which
allows only selected molecules to diffuse across the
membrane.
Membrane Transport
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Cell Membrane
Structure :
1. Separates contents of the cell from its surroundings.
2. Regulates the entry of certain solutes and ions.
3. Maintain the shape of the cell (in animal cell).
Chief Functions :
It is the phospholipids bilayer.
Plasma membrane is an amphipathic, which contains both
hydrophilic heads and hydrophobic tails.
It is a fluid mosaic of lipids, proteins and carbohydrate.
It is lipid bilayer, which contains - two layers of
phospholipids, phosphate head is polar (water loving),
fatty acid tails non-polar (water fearing) and the
proteins embedded in membrane.
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Fluid mosaic model of a cell membrane by SJ Singer and GL Nicolson in 1972
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Cell Wall vs. Cell Membrane
Cell Wall Cell Membrane
It is a rigid, thick structure
and visible in light
microscope.
It is delicate, thin structure
and visible only in electron
microscope.
It is outermost layer in plant
cell and occurs as a
protective covering
surrounding the plasma
membrane.
It is the outermost layer in
animal cell and occurs as a
semi-permeable covering
surrounding the protoplasm.
Cell wall is made up of
cellulose in plant cell.
Cell wall is made up of
peptidoglycan in bacteria.
Cell wall is made up of chitin
in fungi.
Plasma membrane is made up
of lipids, proteins and small
amount of carbohydrates.
It is completely permeable to
ordinary macromolecule.
It is selectively permeable
i.e. allowing only certain
molecules to pass.
It occurs in plant cell,
bacterium and fungus.
It occurs in all cells.
It is metabolically inactive
and non-living.
It is metabolically active and
living.
It determines the cell shape
and offers protection.
It protects protoplasm and
maintains a constant internal
environment to the
protoplasm.
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Protoplasm
✓ The living component of a cell.
✓ Protoplasm = Cytoplasm + Nucleus.
✓ Surrounded by the plasma membrane.
✓ Plant cells have an outer boundary called the cell wall.
Cytoplasm
✓ Jelly like substance enclosed by cell membrane.
✓ Contains organelles to carry out specific jobs.
✓ Provides a medium for chemical reactions to take place.
Nucleus
✓ The cell nucleus acts like the brain of the cell.
✓ Contains genetic material.
Components
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Structure of Nucleus
Nuclear Envelope
▪ It is a double-layered membrane that encloses the
contents of the nucleus during most of the cell’s
lifecycle.
Nuclear Pores
▪ The nuclear envelope is perforated with holes called
nuclear pores.
▪ These pores regulate the passage of molecules between
the nucleus and cytoplasm, permitting some to pass
through the membrane, but not others.
Nucleoplasm
▪ Also called nuclear sap or karyoplasm, is the fluid
usually found in the nucleus of eukaryotic cells.
▪ The fluid contains primarily water, dissolved ions, and a
complex mixture of molecules.
▪ Its primary function is to act as a suspension medium
for the organelles of the nucleus.
Nucleolus
▪ The nucleolus is a membrane-less organelle within the
nucleus that manufactures ribosome, the cell’s protein-
producing structures.
Chromatin
▪ Fibres of DNA and protein, stores information for
synthesis of proteins.
▪ When cell prepares to divide, chromatin fibres coil up
as separate structures, chromosomes.
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Nucleus
▪ It regulates and coordinates various life processes of
the cell.
▪ It plays an important part in cell division.
▪ It contains factors (genes) which determine heredity.
Structure
Chief Functions :
The nucleus is called the "brain” of the cell because it holds the
information needed to conduct most of the cell's functions.
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A gene is the
basic physical and
functional unit of
heredity. Genes,
which are made up
of DNA, act as
instructions to
make molecules
called proteins.
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27. Chromosome Number
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Like the fingerprints, the DNA pattern helps in ascertaining the identify of a
person and hence the term DNA fingerprinting. The technique can even
testify the percentage of an individual. In a woman’s murder case in Delhi in
July 1995 the DNA from her unidentifiable charred dead body was matched
with the DNA from the body cells of her parents to confirm that they really
were the father and mother of the murdered woman. That was one of the
earliest cases. Now, DNA fingerprinting has become very common.
DNA - Fingerprinting
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30. Mitochondria - Structure
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Outer membrane
▪ It is smooth and is composed of equal amounts of
phospholipids and proteins.
▪ It has a large number of special proteins known as
the porins.
▪ The porins are integral membrane proteins and they
allow the movement of molecules that are of 5000
daltons or less in weight to pass through it.
▪ The outer membrane is freely permeable to nutrient
molecules,ions, energy molecules like the ATP and
ADP molecules.
Inner membrane
▪ The inner membrane of mitochondria is more
complex in structure.
▪ It is folded into a number of folds many times and is
known as the cristae.
▪ This folding help to increase the surface area inside
the organelle.
▪ The cristae and the proteins of the inner membrane
aids in the production of ATP molecules.
▪ Various chemical reactions takes place in the inner
membrane of the mitochondria.
▪ Unlike the outer membrane, the inner membrane is
strictly permeable, it is permeable only to oxygen,
ATP and it also helps in regulating transfer of
metabolites across the membrane.
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31. Mitochondria - Structure
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Intermembrane space
▪ It is the space between the outer and inner
membrane of the mitochondria, it has the same
composition as that of the cell's cytoplasm.
▪ There is a difference in the protein content in the
intermembrane space.
Matrix
▪ The matrix of the mitochondria is a complex
mixture of proteins and enzymes. These enzymes
are important for the synthesis of ATP molecules,
mitochondrial ribosomes, tRNAs and mitochondrial
DNA.
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32. Mitochondria - Functions
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The most important function of the mitochondria is to
produce energy. The simpler molecules of nutrition are
sent to the mitochondria to be processed and to produce
charged molecules. These charged molecules combine with
oxygen and produce ATP molecules. This process is known
as oxidative phosphorylation.
Mitochondria help the cells to maintain proper
concentration of calcium ions within the compartments of
the cell.
The mitochondria also help in building certain parts of
blood and hormones like testosterone and estrogen.
The liver cells mitochondria have enzymes that detoxify
ammonia.
The mitochondria also play important role in the process of
apoptosis or programmed cell death. Abnormal death of
cells due to the dysfunction of mitochondria can affect
the function of organ.
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Cellular
Respiration
33. Plastid - Types
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Chloroplasts are elongated disc shaped organelles which contains
chlorophyll. Chlorophyll is present in green plants which helps
them make food by the process of photosynthesis, which uses
energy from the sunlight is converted into chemical energy.
Chromoplasts are plastids which are found in fruits and are
yellow, orange and red in color.
Lecuoplasts are colorless plastids. They found in roots, seeds and
underground stems.
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34. Chloroplast - Structure
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They have a double membrane structure.
They have their own DNA (circular and naked) and ribosomes
(70S).
Thylakoids – flattened discs have a small internal volume to
maximise hydrogen gradient upon proton accumulation
Grana – thylakoids are arranged into stacks to increase SA:Vol
ratio of the thylakoid membrane
Photosystems – pigments organised into photosystems in
thylakoid membrane to maximise light absorption.
Stroma – central cavity that contains appropriate enzymes and
a suitable pH for the Calvin cycle to occur.
Lamellae – connects and separates thylakoid stacks (grana),
maximising photosynthetic efficiency.
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35. The Endosymbiotic Theory
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Endosymbiosis (Greek: endon = "within", sym =
"together" and biosis = "living").
An endosymbiont is any organism that lives within the
body or cells of another organism.
The endosymbiosis theory attempts to explain the
origins of organelles such as mitochondria and
chloroplasts in eukaryotic cells.
According to Endosymbiosis theory :
Modern eukaryotic cells evolved from simple, phagotrophic
cells that ingested bacteria and cyanobacteria; the prey was
not digested, and physiological processes of the
endosymbionts were used by the host.
36. Endoplasmic Reticulum
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The endoplasmic reticulum (ER) is a network of
interconnecting membranes distributed throughout the
cytoplasm.
The internal compartment, called the lumen, is a separate
part of the cell with a distinct protein and ion composition.
At certain sites, the ER membrane is continuous with the
outer nuclear envelope membrane.
Depending upon the presence or absence of ribosomes on
the surface, there are two types of E.R.
1. Rough E.R. – presence of ribosomes on its surface.
2. Smooth E.R. – devoid of ribosomes on its surface.
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Structure :
38. Golgi apparatus was discovered in the year 1898 by an
Italian biologist Camillo Golgi.
In plant cells, the Golgi apparatus is called dictyosome.
It is located in the cytoplasm next to the endoplasmic
reticulum and near the cell nucleus.
Golgi Apparatus
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Structure :
The Golgi apparatus organelle consists of three
membranous components that can be clearly identified
through the electron microscope. These are lamellae or
cisternae, vesicles and vacuoles.
The flat sacs of the cisternae are stacked and is bent
and semicircular in shape.
The Golgi complex is polar in nature : One end of the
stack is known as the cis face, it is the 'receiving
department" while the other end is the trans face and is
the "shipping department“.
Vesicles are minute spherical structures of the Golgi
apparatus that originate from cisternae by budding or
“pinching off” process. They are found singly or in
clusters.
Vacuoles are spherical, comparatively larger secretory
granules adjacent to cisternae. They also lie at maturing
face and contain electron-dense material.
A Golgi Body is like a “Post Office” because a Post Office
collects and packages packages just like how a Golgi Body
modifies, collects and packages.
39. Golgi Apparatus
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The principal function of golgi apparatus organelle is
secretion that occurs in the form of secretory granules.I
t also has a role in neurosecretion secreting
neurosecretory materials.
The golgi apparatus organelle acts as a packaging
organelle and transports various materials like proteins,
polysaccharides out of the cell.
The golgi apparatus takes part in the formation of plasma
membrane, cell wall, lysosomes (primary lysosomes),
acrosome (head cap) of sperm.
Functions :
Structure
40. Lysosome
Biswarup Majumder | Bio-World 39
The cytoplasm of both plant and animal cells contain
many tiny regular shaped membrane bound vesicles
known as lysosomes.
They contain various (at least 50 types) hydrolytic
enzymes.
Lysosomes of injured or dead cells rupture together
and release enzymes which lyse the useless cells.
These are membranous sacs budded off from Golgi
apparatus.
Lysosomes help in digestion. Lysosomes can digest the entire cell
.This takes place during formation of human appendages and
during natural death of cells. Hence it is termed as "Suicidal
bag“.
41. Lysosome - Types
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Primary lysosomes: The newly produced lysosomes are
called primary lysosomes ,which is a virgin particle in that
its digestive enzymes have not yet taken part in hydrolysis.
Secondary lysosomes: The lysosomes that is formed by
fusion of primary lysosome and phagosomes is termed
secondary lysosomes.They are of two types - Hetero
Phagosomes are secondary lysosomes formed by
endocytosed phagosomes and primary lysosomes. Lysogenic
digestion of endocytosed material is
termed heterophagy. Auto phagosomes are formed by
fusion of cellular particles and primary lysosomes.The
process of digestion of portion of a cell's own cytoplasmic
constituents by its lysosomes is termed autophagy.
Residual bodies: Hetero Phagosomes and auto phagosomes
after digestion and absorption are left with only residues
and denatured enzymes within the vacuole ,which are
termed residual bodies.
On the basis of function of lysosomes ,they are
classified into three types :
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Endomemebrane System
Divides cell into compartments.
Includes :
Endoplasmic Reticulum (and vesicles).
Golgi Apparatus (and vesicles).
Lysosomes.
Vacuoles.
Responsible for production of various macromolecules,
including proteins and some lipids.
Important note : The endomembrane system does not
include mitochondria, chloroplasts, or peroxisomes.
43. Ribosomes contain equal amount of proteins and rRNA. So
they are also known as ribonucleoprotein.
Ribosomes functions in two cytoplasmic locations.
Free Ribosomes : They are suspended in the cytoplasm.
Bound Ribosomes : They are attached to the outside of the
endoplasmic reticulum.
Each ribosome has two subunits.
The ribosomes of prokaryotes are smaller than eukaryotes.
They are different in their molecular composition.
Ribosome
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44. Ribosome - Function
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The ribosome plays a key role in translating the genetic
message. This genetic message is carried by mRNA from
the nucleus to the cytoplasm. This message is translated in
the ribosomes. It forms specific primary structure (amino
acid sequence) of a polypeptide chain.
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45. Centrosome
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The centrosome is an organelle made up of two mutually
perpendicular structures known as centrioles.
Each centriole is composed of 9 equally spaced peripheral
fibrils of tubulin protein and the fibril is a set of
interlinked triplets. The core part of the centriole is known
as a hub and is proteinaceous in nature. The hub connects
the peripheral fibrils via radial spoke which is made up of
proteins.
The centrioles form spindle fibers during cell division.
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(a) How centrioles are a component
of centrosomes.
(b) How centrosomes are involved in
cell division.
(c) Ultrastructure of centrioles as
seen in T.S.
(C)
47. Vacuoles
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The term “Vacuole” literally means empty space.
Vacuoles are formed by the fusion of small multiple
membrane vesicles.
They have no basic shape or size, and their structure
varies according to needs of cell.
Plant and fungal cells usually consist of large vacuoles
although there number is less, on the contrary animal and
bacterial cells might contain large number of small
vacuoles.
Tonoplast a term commonly associated with vacuoles
refers to a very active and dynamic membrane that
surrounds the plant cell vacuole.
Functions
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49. Cytoplasmic Inclusions
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Types
These are diverse intracellular non-living substances
that are not able to carry out any metabolic activity
and are not bound by membranes.
These structures were first observed by O. F. Müller in
1786.
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