There are a large variety of organisms on this earth that are all distinct in their

form and structure. However, they all possess similarity in their basic structure
and functions. Just as a building is made up of bricks, similarly, the bodies' of all
plants and animals are made up of cells. From microscopic bacteria, or Amoeba,
to large organisms, like elephants, whales o‹ gigantic trees, all are made up of
'cells'. the basic units of all organisms.

Some cells exist as unicellular organisms (single-celled individuals) while others

are a part of mult iceIIuIar organis ms. Certain b asic functions, like nutrit ion.
respiration, growth, development and reproduction, are performed by the cells
in all organism s. These functions are essential for the survival of the organisms.
We. therefore, regard the Cell as the basic structural as well as functional unit of
all living organisms.

In rhis Chapter, we will study about the variety in the shape, size, structure and
functions of the cells of different organisms.
¥' Discovery of the Cell
Cells are the basic 'structural unit' of all living beings. They remained undiscovered
for a long time because the majorïty of the cells are too small to be seen by the
unaided eye.

lt was only aher the advent of P•'•• irtstru ments, in the seventeenth century. that
the cell wa s discovered and its basic features were studied.

Robert Hooke was the first scientist

who, in 16óS, observed thin slices
of cork (obtained from the bark of
a tree) thro ugh his self-desig ned
microscope. He observed that they
had honey- comb like structures
consisting of litt le compartments
(in Latin, 'ceÍf means 'a little
room’). It was later expl a ined that t
hese 'compartments' were actually
’dead cells', bound by a ’cell wall'.

¥• The Cefl
We now know that living organisms are made up of cells. The cells have the same
basi< structure, but they are different, with respect to their number. shape and size.
in diííerent !ivir+g organsms.

The Outc#mO@ /}& €suz ¥Lza Consists Og Celts Thus Id}& is wild Qdzcdgy id Le re 'face
cell.s. YOu zQ¥}’ bg red IO knQw t@a£ g purse zQ¥¥• /<•< tbQUt foul ki@gKa¥QS Ot Attn
cells eve ar.

Variation in Cell Number, Shape and SiZe in Living Organisms

An Amoe6o and an earthworm are of different sizes. This dñfeence, in the stze
of the organism, is due to the number of cells present in tl+em. While Amoe6o
is a living organism consisting of a single cell. an earthworm has millions of
cells. Hence. on the basis of their 'number of cells', living organisms can be
classified into rwo categories: unkel5ulac and muâticellulae.
 LMng Organisms

Unicellular Mukicellular
,organisms cmslst of a single ‹9*nisms made up of many
celI;i cells;.

The shapes of celh differ not only in different organisms but also in different
organs of the same organism. They may be oval, spherical, cuboidal, fibre-
like or poiygonal. These differences in shapes are due to their location
and function in the tissue. For instance, a nerve cell has to transmit nerve
impulses to o rgans located in different parts of the body. Hence. they
possess a long fibre-like structure.

Cells vary c onsiderably in their s ize. The sma Ilest cell PPLO (Ple uro
pneum onia-like organ ism), also called mycoplasma, is about 0.1 m icron
(denoted as p') in diameter ( 1 p = 10 *m). The ostrich egg. considered to
be the !Iargest cell, is (nearly) 170 mm in diameter.

I
 The hen's egg also represents a single cell; it is big enough to be seen with
the unaided eye.

Take a hen's egg. Cicntly break its shell and n•

transfer the contents to a iJat plate. You
will observe two clear portions. The central
yellow mass is thr yoik. It is surrounded by
a transparent white yelly like tliiid. called
dbumcn. .tIbumcn and yolk represent the
rrrervc food mntcrial in the cytoplasm.
I fen’s egg is a single veil. Its different parts
hax'e been lnbcllcvl in the diagram gix•en here. crest-Gemm m o nen’s e55

The tapproximate) sizes, of some of the plant and animal cells, are given in
Table 1.

Tabfa 1
¢asl
I. Amoebo
2. Hen's egg 60 mm
3. Ostrich egg 170 mm
4. Green alga. Choro 10 cm

The (approximate) sizes. of some celb of human body, are given in Table 2.

TabM 2
Tha cell eftka human bedy S4rc
1. Red blood cell
20 km
2. Liver cell
0.1 mm or 1fX/ jam
3. Human ovum
about 1 m
4. Nerve cell
\Mofia: l km —— 10 metres = 10 ' millimewes)

lftc ' € S}M¥t 4 rcd blood c€ ) is \*out I *0

 1 . ’Io obscrx’e animal iells makr• a temporary mount oi’ ch<•cfi
iells. ’like a clean toothpi< k.
‹ scratch it grntl› on the inner side of your hc‹-)i.
Some frothy material appears on the toothpick.
‹ Rub it in thv• ientre o1’ a clean glass slt‹1v•.

You will oirscrx'e polvgonal, isolated cells, or cills in clusters. Obscrx•e tltc darkly
,stained nucleus in £aih cell.

2 Fol1ov• thru instru‹uions given (u.-low to make a dide of onion pal. ft?nion pr•cd is
the thin memf›ranc like layer pres‹•nt amund tlcshl sca)c lc-a›-cs of onxm. I
+ Put a drop Ot Waler on a glass s$id£“.
Place a small piece of neatl*' cut
cnion Jul ‹rn ii.
‹ Put a drop, or two, of sat(ranin.
+ Stain for a minute.
‹ Pitt a cov-r slip and observe it under on en meet w'ewin i: c•«:
tK- miL rosco c".

hon wilt set thai fhc cell› here arc arranged in run s. t3bserxz 'Weir b'c•undaries. Jherc
is a dark structure in the icntrc o1 cash tell. It is the nuclc•us.

‘Io s‹•c di1(crcnt tjpe of cdls present in b1t›od

r‹yuesi your tca<h<•r to prepare a diA• of human
Jrl‹md. (âi»u mat' alsn use a permanent slide or e
. Jrlood to study s arious tyJ•cs of (rlor›d cell:s. :'
Abu can observe red blocd cells having their ° ? ”
charactenstiv red colour and thr•ir disc sh.ape.

héDO0CO CnWm DfDhAOOCCdâ

Parts of a Cell
A cell con sist s of a living pro toplasm
s ur rounded b y a cell membrane. The
protoplasm consists of the cytoplasm and
the nucleus.

Cytoplasm contains a number of structures,

which are called cell organelles. Orgar›elles
are, therefore. structures present within a cell
that help it to perform its relevant functions.

Let us learn more about the different parts of a cell.

All living cells are bound by a membrane called the plasma membrane, or
the cctl membrane. It surrounds its inner gel-like material Called pcotoplasm.
The plasma membrane controls the entry and exit of substances as per
the requirements of the cell.
The cells of plants, fungi and bacteria have an additional outer covering

The cell wall is an important covering in plant cells: it provides rigi€lity and
protection to the cell against variations in the environment. It also gives a
deñnite shaPe, size and suppo rt to the cell.

The pa rtio n of the proto pl as m, lying inner to the ceII me mbrane but
outside the nuclear membrar.e, is cal!ed cytoplasm [kyfc‹ th.cll c'a’;, y!a‹ma
l! quidI]. It acts as a ground substance’ for all cell activities. It is made up
of carbohyd rates. proteins, fats. minerals and vitamins. along with a large
proportion of water. All these components work together to provide a
unique living nature to the protoplasm.

It is the most important part of the cell. It generally lies in the centre of
the celi, However, in some cases, it may also occupy peripheral positions. It
controls all the activities of tbe cell.
The nucleus is a dense struct ure bound by a nuclear membrane. The
protop lasm of the nu cleus
is ca I ie d nucleoplacm. It
ha s a thread -like net wo rk
GPIO 0tuD\'ez 0/ CkTOTD0¥0TDc5 ifl a Cek 1ffcF¥
ca lied chromatin. When the in dzJfo I €rgg¥gâi¥tDS. Sfxttc M'e chowtt bK ¥Jw.
cel I is ready to div ide. t his
chromatin condenses to form
thicker, thread- like structures,
called chromosomes. These
chromosomes are rhe structures
responsible for the characters
(g en es ) in h er it ed by one
generation from the earlier generations.
Many small living structures are present in the cell. These are equivalent
to the organs of the body. Hence they are na med as ’cell organelles'

The main cell organelles are:

» Plastids : These are large cell organelles, characteristic of plant cells.
These may contain pigments that provide colour to the cell. The
green-coloured plasmids are called chloroplasts. They manufacture
food for green plants by the process of photosynthesis. The plastids,
associated with the different co’Ioured parts of the plants (like fruits,
vegetables and flowers) are called chzomoplasta They are responsible
for imparting colour (other than green) to the different parts of the
plant. Plants also contain some colourless plastids called leucoplasts:
these provide space to store starch, proteins, oils, etc.
» Mko<hondrta: These are rod-shaped or spherical structures. They are
present in large numbers in cells engaged in different physiological
activities. They are responsible for cellular respiration and for generation
of energy for diPerent activities of life. Hence, they are also called the
powerhouse of the cell.
» Endoplasmic Retkulum (EN): It is a network of membranes. It provides
channels for transport of materials in a ceIL ER is of two types:
Rough ER : Tnis type of ER kas a rough appearance as it is stu¢ide¢i with
ñbosomes. It plays a vital role in synthesis of ;soteins.
Smeoth ER: This type of Eft does not have ribosomes attached to it. it,
therefore, has a smooth appearance. It helps in the synthesis of fats.
Golgi Complex : They are sac-like structures stacked o ne above tke
 otker. They are involved in the processing and packaging of materials
produced by the cell.
• Va<uola: lt appears as an empty space in the cytoplasm. lt is generally
large in plant cells. lt stores excess of water and waste products. In
Amoeóa, food materuls are held in its food vacuoles for digeston.
• Ribosomcs: These are tiny granules present in tbe cytoplasm and on
the rough ER. They help in protein synthesis.
• Cilla and flagella: Some cells have tkese small extensions on their cell
membrane. They help in locomotion and collection of food. Unicellular
organisms, like Paramoecium, have numerous cilia while Eugleno has
a single flagellum.

€u§MB W£Q'*I40C*uWt
All these cell organelles wo rk together to perform different functions of
the cell.

% Levels of Organisation in an Organism

In unicellular o rganisms, like Amoeba, a singIe cell performs all the necessary
functions. It captures and digests food, respites. excretes, grows and reproduces.

Multicellular organisms kave celb that are specialised to perform specific functions.
A group of cells, performing a specialised function, forms a tissue (for example,
nervous tissue). A group of tissues, performing a specific function, fotms an organ
(for example, kidney). A number of such organs work together to fofm an organ
syszem (for example, ¢i›igestive system).

Levels a
Cell Tosue Organ Organ
Organisation Syst - Organism
 li 1 £hgeinre 1.ii l Reipifator}- l iti) Circulatory miv 1 Facretor}' iv 1 Sknletal
1 xâ 1 ht iisciilar fvii l Nerv‹xu l x-iii l Rea,rodiictiiu Lx 1 F.r cÎocm Fxl hi tarv,

All the cells have some common features. However. they can appear different in
different parts of the organism. For example, tke blood and liver cells (in animals),
the root or leave cells (in plants) have different appearances.
The plant and animal cells, however, have some major differences between them.
Let us now, compare the features of the plant and animal cells.

% | Comparison Between Plant and Animal Cells

Although all living cells have certain common features, detailed studies reveal some
major differences between plant and animal cells.
Plant cells generally have a def\n ite shape due to a rigxJ cell wall around them. In
compa ‹isor\. anima I cells have a cell mem brane as their outer cover. This provides
flexibility to animal cells; hence they can show a large variation in their shapes.
Moreover, plant ceiis have plasmids, these are absent in aninn ai cells. Plant ceils
generally have large vacuoles. animal cells, on the other hand, either lack vacuoles,
or kave very small vacuoles.
The main points of dtflérence, between a plant cell and an animal cell, kave been
suzrxnarised in the table even below.
Diffazance batwaan a Plazzt anM an AnIma? Call
B0aâ@Aadaa

present absern, or are pesem

pcNe:ca org el s, eut tlua tfe ores shoa« in tie d on thepe«cxa j,age, aze abo
plasods
cell organelles found in plant cells. These may contain pigments
which help in photosynthesis and are responsible for imparting
colour to fruiu, vegetables and f\owers.
protoplnsm gel-like film matter present in»de the cell membrane.
r zosomes tiny granular structures found in the cytoplasm and on the
endoplasmic reticulum: they belp in protein synthesis.
Ossue group of cells performing a specialised function.
sac-like membrane bourx:I Mructures in cells: used for stonng
various materials.

You Must Know

Cell is the basic structural and fur<tional unit of all live ng organisms.
Lix’ir›q organisms show vacation in their cell number. shape and size.
Unic ellular o rganisms, like Amoebo. are made up of a single cell; multicell ular-
organisms, like a mango tree or a parrot. are made up of many cells. Cell sizes may
x’ary from .;nearIy) 0.I micron ;.t/ycop.'o‹mo‘i to 170 mm iOstrich egg; in diameter.
4. A cell consists of lix’ir›q matter. called protoplasm. surrounded by a cell membrane.
Plants. funqi and bacteria have an additional cover. known as the cell wall, outside
their cell membrane.
Protoplasm coruists of cytoplasm and a nucl eus.
6 The nucleus controls all the activities of the cell The cytoplasm contains many cell
organelles: these perform various functions in a cell
Some of the cell organel les. and their functions, are as follows.
Mitochor<sria are responsible for respiration, green coloured plast<Is. or chloropiasts
are the site of photosynthesis: golgi complex processes materials prc<luced by the
cell; vacuoles store excess »'ater and waste ribosomes help in protein synthesis.
and cilia and flagella help in locomooon
8. A tissue is a group of celIs performing a s penalised function.
9. An organ is formed by a group of tissues that perform a specialised function.
\Yhen a number of organs work together. they form an organ system ifor
example, digestive system’i.
Plant and am mal cells show some major differences. Plant cells possess a cell
wall and plastids. these are not found in an animal cell. Also. plant cells contain
large vacuoles. the vacuoles are either absent in animal cells. or if present. hax'e
a small size only.
 I’ . .'IU lieing organism s arc made uy ol".

3. Photosynthesis '! c :' protein s)’nth‹-si s

c. »+x‹x› u« ‹ «»t«a.
1. 4hc cell ‹ rpanellc. » hit h acts as a sts rage Map for a cell, is known as thc—
ñ holt9ropla$t ñ hromoplast
mitoch‹ ndrid 1'acuolc
2. 1 icn’s rytt i; —

a CU OJanellc a llssut"
a single c‹4l an c›rgan

3. d he nucleus is scparat‹€ from the cytoplasm by thc—

cytopl asm nuclear mrwbranc

c‹4l mcmbr anc protoplasm

4. Which of the following; will not be found in an egg cell human liver ccil and
an ztnior6o?
ribosomrs

mitochondria

S. iS'hich of the fol)oo ing represents the correct n uence*

tiisue › cdl › otgan › organ y'strm

org,an › tissue i organ system › cell

éc)1 organ i ti$sttc i organ S3''strm

cell › tissue › organ › organ svstrm

a. i$'hich, amongst th<• following pairs, can be found only in a plam cdl but not
in an anima) cell?

cell wall and plastids

plastuls and cil›a
cdl wall and ‹oil membrane
plzs‹xt› and mi‹ochondri«

1. 1.ist thr (main I factors thal dcterminc thr shape of a cell.

2. Distinguish between uaicehular and mu)ticellular organisms. Give two examples

3. Give reasons for the fo!!owin.g:

I aI Thr yell is called the structural and functional tuiil of life.
fbi elant cells arc more ripid than the animal cells.

4. iS'hich cell organclle is known as the ’Powerhouse of the cdl’? Why is it so

called'

s. Name the rrll organelles msponsiblc for imparting colour to the le•avcs and
fruits of a piant.

6. i$'hat are cilia and l)agcl1a? R’rit«• on«• umilarity and one dissimilarity between
the to or them.
7. tfortiou peel cells and clwek cells are observed through a mioos<ope. state the
two major éñfermces tMt the observer is Iikelv to fin‹L

s.
skin, Psi cell. RBC, blooA ear. tuscle

1. ”All cells in an organism do n‹n have the some due.”

?iñ the tbove Astemem drswisgaAle**t Uwee J fferenCceM CypecfouDd
ah«m*m g.
2. W'liere, and how, are chroriu›somm famed? State their significance.
W'ith the help of well labelled diegrarnn highbght three differences betmen a
plant ceÏI and aa soîmd ceIL
V’rite due functions perfzmned by the fdlowizig cell organeÏles.
(a) EnMplasmic ReticuJuza
(b) Go@ Gozaplez
(c) Nudeus
(d) chroœoplaes
(e) Vacuoles
(f) 3dJtochooürîa
S. The ceil membrane is a very important component of a cell. How is damye to
«i« cat rm•»d.rane lika¡ to i«ip»<i il» mici»i. of the ce0r
6. Def\oe the term 'cell”, for plants/zaimaJs. Name the ddferent organelles that
make e cell. Ezplaio why ncxse of these is caMd time sDtxtural and fñnctioual
unit of life.
ce a also wo1 pzopezly as their different psrts work as a ’teazn’ aad do tbetz specific
faatiocs. Sbe advised ker stadeats to tazblbc tke ’teaza spiztt' aad do tbetr specific
Laacfifio as ax recpoaatble zneznbers afaay ’team’ tMy azay be a pazt of.
l. Name two of the vs)ues that the tether spoke of in her clasi.

2. Have a group discussion in o-hich indents suggee how. 'working si a team‘ can
improve the ‘oizra)1 working‘ of a home or a school.

3. Have a ’play’ in the class in which a group of students give themselves names
corresponding to the different cell organelles of a plant/animal cell. Eadi ’name'
has to then explain herfhis rde th the working of the vetl.

e into r ape
em. En& gru p wit prepare n she 'I
eport o• tbr topkxfquecthini gleen
rim. Two ctnde ti firm erred group may
pres«crt the report to die whole ctasc.
(aJ R'heri u›zre cdls discoszred' YYWe they discovered before or after the invention
of the compound microscope*

(b) Ozs the size and number of celli depend upon the size of the nganism?

(c) List the functions où cell organelles and dso mention ike organYorgan sjrsteza,
tMt 1e orgnzielle is sùnilar tu in the hum8n body’.

(di List the adnntcges o( hnving a ceil wall as the outermost boundary in cells.
 crt›s9
3. storage structures of a cell.
S. regulates the mtry aad ezit of 2. structure that helps io protein
material in and nut of the
cell.
4. help plant cells in converting
7. impart colour to flowers and solar energy into usKle fern.
fruiu.
6. control centre of ter cetL
9. responsible for trnnsferriug traits
hnmonegeoersMoo to nen.
We see a large number of plants and animals around us. Besides these. there
are a large number of small organisms which cannot be seen with our unaided
eye. However, they can be easily observed through the microscope. These living
organisms, that are invisible to the naked eye but are visible under the microscope,
are called microorganisms; their study is known as miCrobioTogy. Microorganisms
include viruses and singie-celled organisms like bacteria, yeast, protozoans and
algae. Each of these groups of microorganisms includes some harmful organisms
(foes) and some useful organisms (friends).
The discovery of microorganisms was possible due to the invention of the
microscope. Anton von Leeuwenhoek was the first person to establish tke
existence of bacteria. Now, with the help of modern microscopes and other r›ew
techniques, we have come to know a lot more about microorganisms.

% t Types of Microorganisms
Microorganism s are the ol dest forms of life on earth. Certain varieties of
microorganisms have existed for millions of years. They affect us in many ways.

On the basis of their cell structure, microorganisms can be divided into four groups.
These groups are: bacteria, fungi, protozoa and (some) algae.

Some of these organisms have been shown in the following pictures.

% t Viruses are Unique

Viruses are unique: they can e1ibit the characteristics of both living organisms
and non- living things. When they are floating in air, or are settled on a door
 knob, they are non-living like, say, salt and sugar. In fact, tkey can be
crystallised and stored in jars for years. However, when they come in contact
with a suitable plant, animal or bacteria, they show the characteristics of living
organisms. They infect the cell and quickly mukiply inside it. Viruses are,
therefore, regarded as beir›g on the borderline between living and non-living
entities.

% | Where do MiCroorganisms Live?

Microorganisms are found in almost all kinds of environment: in ice-cold water, in hot
springs, in dry, marshy or saline areas. Some of them need oxygen for their growth
while others do not. They are found in soil. on the ocean floor, high in the atmosphere
and deep inside rocks within rhe earth's crust. Microorganisms are also found in the
human body Jg !Fi the bodies of othe piants and an!maIs. Our mouths throat. nose
and the alimentary canal are all inhabited by a large number of microorganisms. Thus,
microorganisms are found everywhere.

b'JuODophlle• Are ri4ictoorgafiiimi whtch XnAV adapted t)sem$€)ves la thnt thcy can stlr8kYC,
And fl¥cn thrive, l£t ccK2Jititms txt be GOrma v fata to fDost life fOrTOs.
IJ q>crtIsczmopkflcs arc orgeu•ms that «azt ¢kn•-c coca at temperatures bctweea 8U”1— I Z2-L.
ooh w tkosc found in k}xfrot ezmC s} trnas.
)J} Lit)ts Ave \csi3c ro•zks ie cold clx <zts.
C Op gT' BtCF it t pCr¥tt$2'OG 01 I \* 0€ tQweP'. C£ TLZEiO¥T IO COC kQt/S Dad pQi¥F iCc-
cof‹t +>zoan watts.
% Role of Microorganisms in Our Life
Microorqarñsms play an important role in our
lives as well as in the overall
environment. They help in the deco.-
nposition process and in maintaining the
biogeochemical cycles (like the carbon and
nitrogen cycles). They are useful and
beneficial for mankind in many ways.
However, some of them are harmful as
they spoil our food and cause diseases.

Microbial Population in the

Human Body
U nder nor rna I c o nd it i o n s, o ur
bodies house a large population of
microorganisms; they are, however,
kept in ba lance and are u su ally
harmless. These microorganisms are
important lot our f›ody: they form an
essential rystem that helps our body.

% Microorganisms as Our Friends

Microorganisms are friendly to us in many ways.

Uses in Food

Lactobacillus is a bacterium that helps in the formation of curd. At favourable

temperatures, it mulhplies in milk and converts it into curd. Some
bacteria and fungi are also involved in the making of cheese.

Fungi, like yeast, reproduce rapidly and produce carbon dioxide. This gas,
when trapped in dough, or batter tused for idlies, dosas , causes it to increase
in volume and makes it fluffy and soft The is known as farmentntlon.
 Many microorganisms are used in the manufacture of alcohol, wi.ne and
acetic acxs. Fungi, like yeast, convert natural sugars, ;xesent in cereal’s and
fruits, into alcohol: this alcohol is then used to make alcoholic beverages.
Acet ic acid, comm only known as vinegar, is also produced by a s imi›Ia r

Take five t›rakrts and la(rl them as A, B. C, D and E. You may UI them with a
marker pm. Pvt 200 ml of milk in each of the five beakers. 11c.at the milk in th‹-
first four beakers to the temperatures mentioned in the tall• given below. .add a
teaq•mnful of card in ezci•. beaker and cox•cr cach hcaK•r with an ir.ser•md pctndish.
Put thc beakers in separate cardhonrd boxes or insulated containers. You may wrap
each t›eaker in a thick towd to help maintain thrir rcspcctis'c temperatures. Put the
filih beaker in thr retrigcraior. again alter mixing a teaspoonful or card in it. I.cave th-
hcakrrs undisturbed fa fi-4 hours. Rrcord your obsewx aiions in the gis'en table.
Teaspezstureattkettzao Obserw£ion (tasthe azifkbeea
of.asiziag cuzd wi& z•iIk converted to c•zd) YmfNo

ñ tnd micrr›rirganisms exhibit mnximum gr‹iwth in thr temperature range 30°G -4S°C
It is for this r<•ason that use store y<•rcshahIc materials in tic refrigerator.
ñ lilk tastes swcrtish because of thr pretence of a sugnr called lnrtoce. Lnctohecillitr
converts this lactose lot the mdkl Euro lactic acid in curd. Jhe lnnger you leave curd
at rmm temperature, the more s‹rur it tastes: this is t›ccausc of increased growth o(
hact<•ria and the rmuJting production of more lactic acid.

Sewage Treatment
Some bacteria are used in the biological treatment of sewage and industrial
waste, called e’ff?uenL This process is known as bioaugmentation.
l. Many microorganisms. present in the alimentary canal of some animals
ilike cows’l help in digestion and absorption of food. The bacteria,
present in our large intest me. help in bowel movement.
2. Microorganisms are also used in production of antibiotic s. Antibiotics
are chemicals that inhibit the growth o( {other t harmful microorganisms
by affecting their life processes. For example.. penicillin is an antibiotic
obtained from a fungus, Pen,iciI!i’um no.•atu.m. Streptomycin, tetracycline
an d eryt hromyc in a re s ome anti biotics o bta ined from fu ngi and
bacteria.
Antibiotics are extreme!y effective in treatment cf various microbial
infections.’diseases. like. tuberculosis, cholera. etc. However antibiotics
should be taken only on the advice of a qualified doctor and that
too only in the prescribed dosage and for the prescribed duration.
Not completing the prescribed course may make them ineffective
when used in future. If they are taken when not really required th.ey
may kill some of the useful bacteria in the body.

3. When microorganisms, like bacteria or viruses. enter our body, they are
rec oqnised by special kind of blood cells. These cells get stimulated
to produce antibodies. Antibodies identify and destroy su ch disease
ca us ing organisms.

During this process the body ’remembers’ the type of microorganisms. if

the same microorganism enters the body again, it gets recognised
and destroyed much faster. This is called 'immunity. Immunity is,
therefore, the natural ability of an organism to have an inbuilt mechanism
to resist, and destroy, the infection that some microorganism may
cause

Immunity through Vaccination

Vaccinat on is an important way to build immunity. A vaccine produces

immunity to a disease by stimulating the production of antibodies.
Vaccines are suspensions of killed, or weakened microorganisms ior
products, or derivatives, of such microorgan sms i. The most common
method of administering vaccines is by inoculation: However, some
vaccines are given orally also.
F.dward !enner was on English elector who pioneered tire vaccination
g•r css. leaner s ducal cry la 1796 - inoculaMon wrdt cowg•ox gas c
immunity to uUdJlpox - was 4n t2omcnxc medtCf.1 br fhrott;g s And
hai saved counde•i 1›re•. Smallpox has now been eradicated from

Some bacteria, and blue-green algae lcyanobacteria), are able to ’fix'

(for use by plants) atmospheric nitrogen irfto usable forms of saks of nitrogen.
They are called bloTogfcal nitrogen fixers. Rhizobium lives in symbiotic
association in the root nodules of ieguminous piants and enriches the soil
with nitrogen compounds. Some cyanobacteria do the same in rice fields
and in association with the roots of Cycos plant.

Probiotice I Jictar y ¥upp)emeDt$ of iVc baCtcria or ’1 cost hc$p prcvcDt. and treat Ji$cA8cs
throttgh a DtlH 'Rf Of fTteC)lAD umt. ODS Was t$ b}’ tDtcf4s-tiog dtreC t)9 with tic di C- cAf4zlDg
mIc robcs making tt harder tor tJcm to cauJc d$ $'caSc. .In cx4 p Ot UI A iA thC in cstion of
ptGbtxitm bACt0FlA to ptcvCot. £f IO WcAt. JiaZEh ThcVe Of tSfftA kRlp ficlntorCc tic GAttfral
)?ucteriAl Arricr thai existi oD Use liDlog of tkr Jigcitivc tract; they thus. provtdc additiooal
proiectiim agunit paihogeniv orgent emu thai van cause diarrhoea.

Many microorganism s produce ethanol by fermentat ion of sugars and

produce methane in the biogas reactors. Both ethanol and methane are
used as fuel for production of energy.

When a plant or animal dies, it leaves behind nutrients and energy in the
organic material that formed its body structure. Decomposers eventually
convert all such organic matter into carbon dioxide and nutrients. These
nutrients (like nitrogen, phosphorous, magnesium, etc.) become a part of
the soil. This process eventually replenishes nutrients back to the ecosystem,
thereby, allowing tke plants to grow.

Bactena and fungi are some of the common decomposers.

% Microorganisms — The Foes
So me microo rganisms are harmfuI in diffe ren t ways. They cau se diseases in
hum an being s, plant s and anim als. Such disease caus ing organisms are known
as pathogens. Some m icroorqanisms also cause spoi lage of food. Some grow on
leather and c lathes and have an a dverse affect on their quality.

Bacteria also grow on food particles that may get lodged in beMeen our teeth.
Acids produced by these bacteria, corrode the tooth enamel and cause cavities.
Many microorganisms grow in water bodies and decrease their oxygen level. This
is harmfuI to the othef organisms living in these water bodies.

Microorganisms causing diseases in Humans

During our lifetime, we come in contact with many microo rgani sms. Som e
of these microorganism s leave undesirable effects on our body. They inva de
a ur body and mult ipl y inside it. They release so me harmful materials. called
toxins, in our body. The se toxins adverse Iy affect our body and can make us
suffer (rom disea ses.

Diseases, which can spread from an

infected person to a healthy person,
are called communicable diseases.
Com mu nic able d i seases s prea d
from one perso n to anoth•er through
air, water, food, physical contact or
insects. In diseases, like tuberculosis
and pne umoni a. whe n a pat ie nt
sneezes o r coughs, sm all droplets
carrying germs. are released in the
air. These germs. if inhaled, can infect
a healthy person. The consumptio n
of contaminated food can result in disea ses like cholera, typhoid or hepatitis.
DiPerent types of insects can also spread various diseases. For example, malaria is
spread by the female Aoopheles mosquito. dengue by Aedcs mosquito and plague
by rat flea. Diseases, like common cold and conjur›ctivitis. can spread through
direct, or indirect, contact with a patient.
 Given below ›s information about some commo n human diseases and rhe way
they get transmitted.
Infect iv u s D is ease s Ca used by f•t ieru v›r ga ni

snas Microozganbms Diseases Caused

Bacteria Tuberculosis, diphtheria, cholera, tetanus, typhoid

Viruses Common cold, influenza, mumps, polio, chickenpo< AIDS

Fungi Ringworm. athlete’s foot

Protozoans Malana, amoebic dysentery, sleeping sickness

h1o de s of Tra n s n is s io n of Pa IN og e ns

Modas of Transrnbsion Rotated Diseases

Air (actions like sneezing, coughing) Tuberculosis. common coId. influenza,

swine flu
Watar (using contaminated water) Typhoid, amoebic dysentery, cholera

Soil (consuming food items that are Tetanus

not washed/cleaned properly; wounds)

Animals (direct contact {e.g. being Rabies, malaria

bitten by a rabid dog); through vectors
that spread disease)

t#O•OUTtO O72
Prevention of Diseases
Various ways that can help in preventing diseases are given in tJ'›e following table.

prevezsMen Désaases dent may be $N'evented

Vaccination Tuberculosis, polio, mumps, tetanus

Using mosquito nets and mosquito Malaria. dengue

repellents. controlling mosquito
population

Proper disposal of waste and using Cholera

disinfected water
fvtaintaining good personal hygiene Ringworm and athlete’s foot

Microorganisms Causing Diseases in Animal5

Microorganisms also cause diseases in animals. You must have heard about rabies
(a disease that affécts animals like dogsj, and foot and mouth disease (that affects
cattle). Such diseases may affect domest< animab. Peu and human beings may
also get infected if they come in contact with the infected animals.

The following table tells us about some diseases caused by the

microorganisms in animals.

Anth.rax Bacteria Cattle

Foot and mouth Virus Cattle
disease

Rabies Virus Dogs. monkeys

Tuberculosis
Bacteria Cattte, poultry
Ringworm
Fungi Cattle, poukry
Aspergillosis
Fungi Poukry

Canine distemper Virus Dogs

Mic roorganisn s Causing disease s in Plants
You must have observed some plants with wrinkled leaves, or plants and trees
having an abno rmal branching pattern or having abnormal fruits. These plants
may have been affected by a pathogen. Most plant disea ses are ca used by
fungi, bacteria and viruses. These mic roorganis ms may reduce crop yield and,
at times, cause total destruction of the crops. The Irish Famine in 174D-41 was
caused because of complete destruction of the potato crop due to the disease.
late blight', caused by a fungus.
The following table gives information about some commo n plant diseases that
are caused by different microo rganisms.

Related Plant disaasa

Viru s Tobacco mosaic virus
lappearance of uneven spots and discolouration on the
leaves)
Bacteria Citrus canker
Ilesions on leaves. stems and fruit. with raised brown
water soaked margins l
Fungus Rust of wheat
Idiseased plants show ru st-coloured orange patches on
the infected plant parts)
F ungus Smut of rice
Ism ut balls in grains that become greenish black. then
burrt and infect other grains;i
Fung us Red rot of sugarcane
|the infected stems have a dull red colour interrupted
by occasional whitish patches across the stall and,'’or
elongated red lesions on rhe midribs of leaves)

”OD6'CCO m OSS C
Food Poisoning
Food poisoning, as the n ame su gges ts, is a disea se that result s from the
consumption of contaminated food. Symptoms of food poisoning are vomitting,
nausea, severe pa in in the abdominal region. diarrhoea and dehydration. It may
also cause weakness, fatigue and damage to the nervous system.

These symptoms arise due to the presence of bacteria or other microbes, in

food. They may also be due to ingestion of toxins contained in (ood |including
those produced by bacterial. Some bacteria. like Clostricii’um and S.*aphylocccci
and fungi, like AspergJl/us, cause food poisoning.
Food must be properly prepared and stored to prevent food poisoning. Food
pa isoning can occur when food is left unrefngerated fo r lo ng per rods of time.
This often happens at picnics and large parties. Sometimes, mishandling
also causes food pa isoning. Persons who handle or prepa re food, sLro uld wash
ther hands to present contaminat on of food.

Food Preservanon
Food preservation is the process of treat ng and handling food so as to sto p, or
greatly slow down. spoilage lloss of quality, edibility or nutritive valueI ca used,
or accelerated, by microo rganisms.

Preservation usually involves preventing the growth of bacteria, fungi and other
microorganisms as well as retarding the oxidation of fats which cau se rancidity.
(Ran cidity means having disagreeable odour, or taste due to decomposih on of
oils or fats.I

Tom e preservation methods require the food to be sealed after treatment to

prevent recontamination with microbes. other methods. such as drying, allow
food to be stored wrthout any special containment for Dnq periods.
A brief descnption of some of the methods usod for ’food preservation' is given

. Drying: This method reduces water content s ufficiently and, thereby.

prevents. or delays. bacterial growth Drying also reduces weiaht. makina
food more portable. Some common food stuffs that are preserved by drying
are: apples. pears. bananas. mangoes, papaya, apricot and coconut. Dry
ng is also the normal means of preservation for cereals |grains I, such as
wheat, maize. oats barley roe. millet and rye.
2 Preservation udng sugar and salts Sugar and salt
reduce the water content and make it unavailable
for rhe growth of microorganisms. As a result, the
food pets preserved. Meat and fish are covered
with salt to che<k bacterial growth. Some pickles are
also preserved by the addition of specific
quantities of salt. Jams and jellies are usually
preserved by
addition o( supar.

3. Preservation using a<etk acid: Acetic acid. in the form of vinegar, is used in
the manufacture of several pickled products. Vinegar also stops the growth
of microorganisms. Crtric acid and phosphor›c ac‹d are also used, in carbonated
beverages and fruit drinks, for both flavouring and preservation.

Preservation using chemical preservatives: Chemical preservatives. like

sodium benzoate and potassium metabisulfite are used to preserve jams,
jellies and pickles. These chemicals inhibit the growth of microorganisms.
s. heat and cold tmatments: Some food items, like milk, are usu ally boiled,
before their use. or storage. Boiling kills many microorganisms.
Several foo¢i stuffs are also stored in the refrigerator; the low temperature
inhibñs the growth of micrc•o rganisms.

ó. Pasteurisation: Pa steurisation is 'pressurised heating' for a short time: it

may be considered as a mild form of heat treatment. The temperature, used
during pasteurisation, is below 3 1 2”F I‘ I 00"C). Milk is pasteurised to destroy
microorganisms. However, tbere are m any mo re heat-resistant organisms
in it that only get reduced in number. Hence, pasteurised milk needs to be
stored under refrigeration to keep bacterial growth in check.

In addition to destroying so me m ic roorganis ms, pasteu risation also

inacuvates some enzymes; that, at times, can be a disadvantage.
7. Vacuum pack in g: Vac uum packing
sto res food in a vacuum enviro nment:
usually an air-t ight ba g or bottIe. The
vaccum environment deprives bacter ia
of the oxygen needed for their s urv ival:
it, thereto re, sl ows ’s poiling’. Vac uum
pack ing is com m onIy used for stor ing
nuts: it helps to redu ce t heir loss of
flavour caused by their oxidation.
8. €azzzd It irwolves cooEJng Ized and sealizzg "zt in sterile cans or}ars;tfñs is
féllo«ed4boiBngtfmentaina«tokiIowesken any+emainag b«teria
(a fomi of sterilisation).However, food preserved by earning, oz boMng, is
at knrrmdiate ñsk of spoibge once the cms or bottle has been openezL

shoukl never be consumezL

9. Fza•slag: When foods are kept at below freezing temperatures, most

are noticeable even alto long periods of storage , zrñcromgarzisms

aze germra¥y more to cold thnn to heat. Although some are
IéMed by freezing, most bacterial spores and a brge rnimbw of organisms
survive and get revitaliswJ when the fozxJ is thawwL
ranod an unpleasant taste or odour Sof food containinq fats and oils
causod by chemical changes, or decomposition.
a poisonous substance produced by living organisms.
vaccine
a suspension of killed. or weakened, micr‹>orqanisms. administered
to increase protection againu a disease, i.e. to bolster immunity.

YOU Mci s t K now

Li 'ing organisms, a'hich are not visible to the unaided eye and can be seen only
through a microscope are known as microorganis ms. Microbiology is the study
of microorgani sms.

Depending upon their cell structure. microorganisms are classified into Bactena.
Fur+qi, Protozoa. : somel Alpae.
3. Viruses are m›cros‹opic bodies which can reproduce only inside the cells of some
host orpanums, like a bacterium, plant or animal however, tbey can be crystallised,
’,I ike salt and s ugari, when they are o utside a living organism.

4. Microorganisms are 1éund everywhere in air, in water. in rocks ithin the earth’s
crust. insicI•e human beings. piant and animal bodies, and even in cold deser:s and
hot springs.
Some microorganisms are useful to us in many »’ays: they help us in preparing
foods, like curd. cheese and alcoholic beverages they are useful in treatment of
sewage. in energy production. and in cleaning of the en 'ironment. They also help
in production of antibiotics and vaccines. Some of them even enrich the soil and
beIp in agriculture.
See' other microorgani sms are quite harmfuI They 'pathogens \ cv se dise'ases in
humans, plants and animals. Some of them cause spoilage of c lolla and leather.
Some microorganisms grow in water bodies and decrease their oxygen levels: tbey
thus, cause harm to other organisms live ng therein.

7. Mishandling. and improper storage of food.. causes microbes to contaminate it

and produce toxi ns in it. Consuming such food causes food poisoning: this can
result in omitting. nausea. dehydration: it may even damage the nervous system.
8. Food preserx'ation is the process of gix'ing an appropriate physi cal. or chemical
treatment to food in order to prevent, or slow down, its s po‹ lage.
9. Some of the methods used to preerve food are: Drying Use of salt and supar, Use
of preservatives, Pasteurisation, Can ning, Freezing and Vacuum packing
 Something To Know

1. The study of microorganisms is known as

Ohr bread dough rises bcxaus<• of the production of

3. are the microorganisms that cause diseases.

4. altd arC tWO chClTtlCal pftMr¥'atfVeS.

S. is a fungus that vauscs food poismiing.

I. Ringworm ‹at food poimninp

CJostridiuJn

3. Antfirax

4. Lactobac illus ldi catle

s. stethan‹•

C. TicL (/) the comet optio•.

1. The process. that hdps milk to last longer but As not kill all mlcmbcs present
in it, is known as—
bioaugmcntatlon

fermentation

*. Rust of wheat is caused by—

fungus

@FO#OEO8

3. $lcdicinm. containing killed or weakened pathogens, and utsd to prevent

infections diseases, are called—
disinfr•ciants

antibiotics va‹vfinn
4. H'hich of the following reproduce only insi‹)r a host ceh?
mms d

S. A disease. caused by a virus. and spread by on insect, is—

polio dengue
rabies niumps

1. M'liy are viruses considered as being at the Borderline' between living and
now-living things?
Yt'hat is fermentation * How is this process useful in the food and beverage
induitriei?

3. ’In the absence of microorganisms the ewth would become n heap of dead
plants and animals.' Justify this statement.
4. Munna observes that the yield of wheat, growing in his field, has ceduced
in the current year. He gets the soil tested and the report confirms the
deficiency of one particular nutrient. Accordingly, he is advised to grow
peer after harvesting wheat.
(i) Home the nutrient found insuf(icient.
(ii) How do you think growing pear will help in replenishing the soil?
S. Yt’liy does it take tess time to prepare curd iii summers or compwed to
preparing it in winters*
6. Hoc- are the following diseases transmitted:
(al Stalnria (bi Common cold (cJ To (NJ Typhoid
M’liat are antibiotics? How are they produced? Give two examples of these.

I. ’Microorganisms zre very usefuJ in mazzutact uz fiag diiereat loco! items’.

Explain tJx' above statement.

2. t)ivc reasons for the following.

I”b ł lt is im§•ortant to brush on<•’s tc<°th Wforc go›ng la hc°1

I. c, R£ ktcing Urz“ QuantitS’ of salt in plCk)e Can 'iai4s£“ it to go bad soon.

1. ‹i1 Foods, from ptiffcM or cnlarg •d cans, should not R• onsum‹H

I <•/› \S’hcn using irozcn food items one shoulil take o ut onlj‘ th<• required
quantities; thawed food shoul‹l nr•ser b<• refroz‹m.

I)£IW’ dn C€Immuni'ra le dlxrascM sprt?ad ? 'tuggcll ways trt pTr¥’en,t t hc“ I llrlWk ng

‹. is'hai are pathogrms? Name two path‹›gens caih that catisc dn.cascs in ii 1 płants
zna ( ii i animais

Slohan irought oimoses from a road- side x cndor and ate it. .¥ń ‹-r somruimc hc
łch nausca and starte‹i vnmitting. I Ie lud sever‹- pain in thc aMomina) rrqion
and stillcrc€ frum ‹łiziih‹›ca. vtfiat cou)d hc thr• rcason for his condition? ¥¥’hat
is it call‹Hi I lov• ioiild it dc prr•xcnt‹H?

Whiih discascs the following children are most likcly to sufer from ?

k3mu Orinks watcr l"rom a mark›' laLt”. “IhJs y”af<°r ls nr”itżic°r hoilcd nor
‹lisinfccte‹i.

Ashu docs not take a bath ‹-vcr›da›. He maintains poor prison.at hygiene.

I.J I
SohAn is )J ’Eng in an area whr•rc the o{ uJation is › ‹r1 htgh. Itc docs
not use a mosquito net I »h ilc sleeping,', or insect r<•pclJ<°nt creams l/whiIc
playlng in thc cpc n ..

siohw was with tv•o of his fri<-niis who were roughing and sneezing 1 th‹-y
were- sulf‹-ring fmm common cold 1. t3ne of these friends did not i.cup a
handk‹-rchn.•l in front of‘ his mouth whil • c‹mghing and sn‹•‹-zing.
 z« t¥«z tM ckild I es a la•g «d Ma/thy bG.

I. Was Soizaza right io supporting his wzfe’s deciszoa? List aziy two values tMt are
demoastzated kis belzaytour.
2. How does yacctnat@n help io providing immuaxy?
3. Find ‹:iut the mimes of any five dioceses thet eel be prevented by timely vaccinati‹:ni
of children.

Ozooe Tre meat

5. Find out about tbe teraprraturcs at wki<2 tkc following occur.•'exist.’‘work:

i d 1 Rcl‘ri crater

Bred on the infc›rmation

pmvided in the pi‹uurr, predict
the cboncei of growth arid
suri4vd of microbes in eech
of