3. WHAT ARE LIVING BEINGS MADE UP
OF ?
• All living organisms aremadeupof oneor more
cells,whichareconsideredthefundamentalunitsof
life.
• Evenunicellular organismsarecomplex! Inside each
cell, atomsmakeupmolecules, whichmakeupcell
organelles andstructures.
• Inmulticellular organisms,similar cells formTissues.
4. IMPORTANT BIOLOGIST IN CELL
DISCOVERY
• RobertHooke–Thecell was1st discovered byhimin 1665.
Heobserved thecorkslice with aprimitivemicroscope.
• Leeuwenhoek–Withthehelp of theimprovedmicroscope,
hediscovered thefreeliving cells in pondwater in 1674.
• RobertBrown–In1831, hediscovered thenucleus in the
cell.
• Purkinjee–In1839, hecoined theterm‘protoplasm’for the
fluidsubstance of thecell.
5. CELL THEORY
• Thecell theorysaysthat all plantsandanimals are
composed of cells.
• Thecell is thebasic structuralandthefunctional unit of
life.
• This wasexplained bySchlieden (1838) andSchwann
(1839).
• It wasfurtherexpanded byVirchow (1855) that all cells
arisefromthepre–existing cells.
6. LABOUR DIVISION IN CELLS
MulticellularOrganismsalsoshowsdivisionoflabour,
whichmeansthat different partsof humanbody do
differentfunctions.Thehumanbodyhasheart topump
blood, astomachtodigest foodandsoon.
Division oflabour is also seenwithin asingle cell. Each
cell hasaspecific component called Cell Organelles.
Eachcell organelle performsaspecific functionlike
digestion, excretionandsoon.
7. PROKARYOTIC CELLS
ProkaryoticCellsaresingle-celledMicro–Organisms known to
betheearliest onearth.Theyconsists of asingle membraneand
therefore, all thereactions occurwithin thecytoplasm.Theycan
befree-living orparasites. Fore.g.: Bacteria andArchea.
Characteristicsof aProkaryotic Cell :
• It lackaNuclear Membrane.
• OnlyCell Organelle present init isRibosome.
• Thegenetic material is present onasingle chromosome.
• TheHistone Proteins arealsoabsent.
• Their sizeisgenerally small.
8. EUKARYOTIC CELLS
Eukaryoticcells haveanucleusenclosedwithinthenuclear membrane
andformlargeandcomplex organisms.Protozoa,fungi,plants,and
animalsall haveeukaryoticcells.They canperformdifferent activitiesina
singlecell whichallowsthemto carryoutvariousmetabolic reactions.
Characteristicsof aeukaryoticcell :
• It has the nucleus enclosed within the nuclear membrane.AnEukaryote
hasmostof the cell organelle present in it andtheoutermostlayer is the
cell wall.
• Thecell dividebyaprocesscalledmitosis. Thenucleuscontainsa
single, linear DNA,whichcarries thegenetic functions,information.
• Theirsizeis generally large(biggerthanaProkaryote).
9. THE STURUCTRAL ORGANISATION OF
CELL
Everycell consists of :
• PlasmaMembrane
• Cytoplasm
• Nucleus
All chemicalactivities inside thecell arepossible
duetothesefeatures.
10. PLASMA MEMBRANE
• Thisistheoutermost covering of thecell that
separatesthecontents of thecell fromits external
environment.
• ThePlasmaMembraneallowstheentryandexitof
somematerials inandout of thecell. Thecell
membraneistherefore, called theSemi –Permeable
Membrane.
• ThePlasmaMembraneis flexible andmadeupof fat
molecules called Lipids.
11.
12. ENDOCYTOSIS
The flexibility ofthecellmembrane alsoenables thecell
toengulf in foodandothermaterial fromits external
environment. Suchprocesses areknownasEndocytosis.
Amoebaacquires itsfoodthroughsuchprocesses.
Amoebaengulfs foodparticleswiththehelpof
pseudopodia whicharetheprojections of cell
membranes.Afoodvacuole isthenformedaroundthe
foodparticle.Amoebathensecretsdigestiveenzymes
that break downthefoodparticleanddigest it.
13. DIFFUSION
• Substances like CarbonDioxide andOxygencan
moveacrosstheplasmamembranethroughthe
processcalled Diffusion.
• Diffusion isthespontaneous movement of a
substance fromaregionof highconcentrationtoa
regionof lower concentration.
• Thus,diffusion plays animportantrole in exchange of
gasesbetween thecells aswell asthecell andits
external environment.
14. OSMOSIS
• Wateralso obeys the lawof diffusion.Themovement
ofwatermoleculesthroughthesemi–permeable
membraneiscalled Osmosis.
• Osmosisis thepassage ofwater fromaregion of
higher waterconcentration toaregion of lowwater
concentration till theequilibrium isreached.
• Osmosiscanbeofthree types : Hypotonic Solution,
Isotonic SolutionandHypertonic Solution.
• Unicellular organismsandmostoftheplant cells tend
togainwaterthroughosmosis.
• Absorption of waterbytherootsof theplants is also
anexample of osmosis.
15. HYPOTONIC SOLUTION
If themediumsurrounding thecell hasahigher water
concentration thanthecell, meaningthat theoutside solution
is verydilute, thecell will gain waterbyosmosis.Sucha
solutionisknownasaHypotonicSolution.Water molecules
arefreeto passacrossthecell membranein bothdirections,
but morewater will comeintothecell thanwill leave. Thenet
(overall) result is thatwater entersthecell.Thecell is likely to
swell up.
19. CELL WALL
Cell Wallis foundin plant cells outside theplasmamembrane.
It isarigidcovering madeupof cellulose whichacomplex
substance is providing structuralsupport totheplants.
Functions of Cell W
all inPlants:
• Renders mechanical strength.
• Serveasfoodreservoir.
• It maintains theshapeof thecell.
• It regulates theintercellular transport.
• It regulates theexpansion of cells.
• Provides protectionagainst pathogens
20. PLASMOLYSIS
Whenaliving plant cell loses water through osmosis there is
shrinkageorcontractionofthe contents ofthe cellaway
fromthecell wall. Thisphenomenon isknownas
Plasmolysis.
21.
22. CYTOPLASM
TheCytoplasmisthefluidcontent inside the
plasmamembrane.It alsocontainsmany
specialized cell organelles. Eachof these
organelles performsaspecific functionfor the
cell. Cell Organelles areenclosed by
membranes. Inprokaryotes, besidetheabsence
ofadefined nuclear region, the membrane-
boundcell organelles arealsoabsent. Onthe
otherhand, theeukaryotic cells havenuclear
membraneaswell asmembrane-enclosed
organelles.
23. ENDOPLASMIC
RETICULUM
TheEndoplasmic Reticulum(ER)is alargenetworkof membrane-bound
tubesandsheets.It lookslike longtubulesorroundoroblongbags
(vesicles).TheERmembraneis similar in structuretotheplasma
membrane.TherearetwotypesofER–RoughEndoplasmicReticulum
(RER)and Smooth Endoplasmic Reticulum(SER).RER looksrough
underamicroscopebecauseit hasparticlescalled Ribosomesattached to
its surface.Theribosomes, whicharepresent in all activecells, arethe
sitesof Proteinmanufacture.Themanufacturedproteinsarethensentto
variousplacesinthecelldepending on need, usingtheER.The SER
helps in themanufactureof Lipids, importantfor cell function. Proteins and
lipidshelpinbuildingthecell membrane. This processisknownas
MembraneBiogenesis. Someother proteinsandlipidsfunctionas
enzymesandhormones.
24. FUNCTIONS OF (ER)
• Thus, onefunction of the ERis to serveaschannels for the
transport of materials (especially proteins) between various
regions of the cytoplasm or between the cytoplasm and the
nucleus.
• TheERalsofunctions asacytoplasmic frameworkproviding a
surface for someof thebiochemical activities of thecell.
• Intheliver cells of thegroupof animals called vertebrates, SER
plays acrucial role in detoxifying manypoisons anddrugs.
25. GOLGI APPARATUS
TheGolgiApparatus, first described byCamillo Golgi, consists
ofasystemofmembrane-boundvesicles(flattenedsacs)
arranged approximately parallel toeachother in stacks called
Cisterns.Thesemembranesoftenhaveconnectionswiththe
membranesofERandthereforeconstituteanotherportionofa
complexcellularmembranesystem.Thematerialsynthesized
near theERispackaged anddispatched tovarioustargets
inside andoutside thecell through theGolgi apparatus. Its
functions include thestorage, modification andpackaging of
productsinvesicles.Insomecases,complexsugarsmaybe
madefromsimple sugarsin theGolgi apparatus.TheGolgi
apparatus isalsoinvolved intheformationof Lysosomes.
26. LYSOSOMES
Structurally,Lysosomesaremembrane-boundsacsfilled
withDigestiveEnzymes,madebyRER.Lysosomesarea
kindof wastedisposal systemof thecell. Thesehelpto
keep thecellclean by digesting any foreignmaterialas
well asworn-out cell organelles. Lysosomesbreak complex
substances intosimpler substances andareabletodothis
becausetheycontainpowerfuldigestiveenzymes.During
thedisturbance in cellular metabolism,whenthecell gets
damaged,lysosomesmayburstandtheenzymes digest
their owncell. Therefore, lysosomes arealsoknownasthe
‘Suicide Bags’of acell.
27. MITOCHONDRIA
Mitochondria are known as the Powerhouses of the Cell.
Mitochondria have two membrane coverings. The Outer
Membrane is porous while the Inner Membrane is deeply folded.
These folds increase surface area for A
TP generating chemical
reactions. The energy required for various chemical activities
needed for life is released by mitochondria in the form of A
TP
(Adenosine Triphosphates) molecules. A
TP is known as the
Energy Currency of the Cell. The body uses energy stored in A
TP
for making new chemical compounds and for mechanical work.
Mitochondria are Strange Organelles in the sense that they have
their own DNA and Ribosomes. Therefore, mitochondria are able
tomakesomeof their ownproteins.
28. PLASTIDS
Plastids arepresent only in plant cells.Therearetwotypesof
plastids–Chromoplasts(ColouredPlastids)andLeucoplasts
(WhiteorColourlessPlastids).Chromoplastscontainingthe
pigment chlorophyll areknownaschloroplasts. Chloroplasts are
importantforphotosynthesisinplants.Chloroplastsalsocontain
variousyellowor orangepigmentsinaddition tochlorophyll.
Leucoplasts areprimarilyorganelles inwhichmaterialssuchas
starch,oilsandproteingranulesarestored.Theinternal
organizationoftheChloroplastconsistsofnumerousmembrane
layersembeddedinamaterialcalledtheStroma.Theseare
similar tomitochondria in external structure.Like the
mitochondria, plastids also havetheir ownDNAandRibosomes.
29. VACOULES
Vacuoles arestorage sacsfor solid orliquid contents.
Vacuoles aresmall sized in animalcells while plant cells
haveverylarge vacuoles.Thecentral vacuole of someplant
cellsmayoccupy50-90%ofthecellvolume.Inplantcells
vacuolesarefull ofcellsapand provideturgidity and rigidity
tothecell. Manysubstances of importanceinthelifeof the
plant cell arestoredin vacuoles.Theseinclude aminoacids,
sugars, various organic acids andsomeproteins. Insingle-
celled organisms likeAmoeba,thefoodvacuolecontains the
fooditemsthat theAmoebahasconsumed. Insome
unicellular organisms,specialized vacuoles also play
importantrolesinexpellingexcesswaterandsomewastes
fromthecell.
30. NUCLEUS
TheNucleushasadoublelayeredcoveringcalled
NuclearMembrane.Thenuclearmembranehaspores
which allow thetransfer ofmaterial frominside the
nucleus toitsoutside. Thenucleus contains
Chromosomes, whicharevisible asrod–like
structures.ThenucleusplaysacentralroleinCellular
Reproduction –theprocessbywhichasingle cell
divides andformstwonewcells. It also plays acrucial
part, along with theenvironment, in determining theway
thecell will develop andwhat formit will exhibit at
maturity,bydirecting thechemicalactivities of thecell.
31. ORGANIZATION OF
NUCLEUS
TheNucleus contains Chromosomes,which arevisible asrod-
shapedstructuresonly whenthecell is aboutto divide.
Chromosomes contain information for inheritance ofcharacters
fromparents tonext generation in theformof DNA(Deoxyribo
NucleicAcid)molecules.ChromosomesarecomposedofDNA
andProtein.DNAmoleculescontaintheinformationnecessary
for constructing andorganizing cells. Functional segmentsof
DNAarecalled Genes.In acell which is not dividing, this DNA
is present aspart of chromatinmaterial. Chromatin Material is
visibleasentangledmass ofthreadlikestructures.Whenever
thecell is about todivide, thechromatin material gets organized
intochromosomes.
33. MITOSIS AND MEIOSIS
• Mitosis – The process of cell division bywhich most
of thecells divide for growthiscalled Mitosis. Inthis
process, eachcell called mother cell divides toform
twoidentical daughter cells. Thedaughter cells have
thesamenumberofchromosomesasmothercell.It
helps in growthandrepairof tissues in organisms.
• Meiosis–Specific cells of reproductive organsor
tissuesinanimalsandplantsdividetoformgametes,
whichafter fertilizationgiverise tooffspring. This
process is called Meiosis it involves twoconsecutive
divisions. Whenacell divides bymeiosis it produces
four newcells andhavehalf thenumber of
chromosomesthanthat of themother cells.
