Cell: The Unit of Life (Cell: Jeevan ki Unit): Class 11 Biology Chapter 8 Hinglish mein

Yeh chapter Unit 3, Cell: Structure and Functions, ki shuruaat karta hai. Isse pehle ke chapters ne dikhaya ki living things form aur body plan mein kitne alag-alag hote hain. Is variety ke neeche ek common plan chhupa hai: har organism cells se bana hota hai. Chapter 8 cell ko khol kar uske parts ke naam batata hai, Chapter 9 poochta hai ki yeh parts kin molecules se bane hain, aur Chapter 10 ek cell ko badhte aur divide hote hue follow karta hai.

Biology mein jaane ka ek doosra raasta bhi hai. Kisi tissue ko pees lo, usmein maujood elements aur compounds ki list banao, aur phir poocho ki har compound kya karta hai: kaun sa enzyme starch ko digest karta hai, kaun sa protein germ ko pehchaanta hai, kaun se molecules memory mein shaamil hain. Aise kai reactions test tube mein bhi chalaye ja sakte hain, ek cell-free system mein. Digestion, defence ya disease ko molecules ke terms mein, physics aur chemistry ke methods se samjhana reductionist biology kehlata hai. Ismein ek puzzle chhupa hai: akele reactions test tube mein chal jaate hain, lekin life ki saari activities ek saath tabhi dikhti hain jab cell ka organisation saboot ho. Isiliye hum poore cell se shuru karte hain.

Ek neem ki patti aur ek kankad ko saath-saath rakho. Dono atoms se bane hain, phir bhi sirf patti badhti hai, khud ko repair karti hai aur ek living parent se aati hai. Fark kisi special substance mein nahi, balki organisation mein hai: patti cells (कोशिका) se bani hai. Kuch organisms, jaise gaon ke talaab ki green alga Chlamydomonas, sirf ek cell ke hote hain aur unicellular kehlate hain. Baaki, jaise neem ka ped ya tum, multicellular hain: bahut saare cells jo zinda rehne ka kaam aapas mein baant lete hain.

8.1 Cell kya hai?

Socho ki ek Chlamydomonas cell kya-kya kar leta hai. Woh tairta hai, apna khaana khud banata hai, salts leta hai, wastes bahar nikalta hai aur divide hokar naye individuals banata hai, aur yeh sab kisi doosre cell ki madad ke bina. Ab ulta karke dekho aur cell ko tod do. Test tube mein alag kiye gaye mitochondria kuch der tak energy chhodte rehte hain, lekin na woh aur na koi doosra tukda apne aap khaana le sakta hai, badh sakta hai ya reproduce kar sakta hai. Poora cell hi sabse chhota package hai jo apne aap zinda reh sakta hai. Isiliye hum ise har living organism ki basic structural and functional unit kehte hain.

Zyaadatar cells naked eye se dekhne ke liye bahut chhote hain, isliye unki khoj lenses ke itihaas ke saath-saath chali (Fig. 8.1). 1670s mein Dutch lens-maker Antonie van Leeuwenhoek talaab ke paani ki boondon mein living cells dekhne aur describe karne wale pehle insaan bane.11Robert Hooke ne 1665 mein cork ki patli slice mein dikhe chhote khaali dabbon ke liye "cell" shabd use kiya tha; woh sirf dead cells ki walls thi. 1831 mein Scottish botanist Robert Brown ne nucleus describe kiya. Uske baad har behtar microscope ne aur zyada dikhaya, aur aakhir mein electron microscope ne woh fine structures saamne laaye jo tum is chapter mein padhoge.

8.2 Cell Theory

Yeh theory do parallel surveys se nikli. German botanist Matthias Schleiden ne ek ke baad ek plants dekhe aur 1838 mein nateeja nikala ki har plant alag-alag tarah ke cells ki ek community hai, jo tissues mein organised hain. Ek saal baad unke hi desh ke zoologist Theodor Schwann ne yeh idea animals par laagu kiya. Unhone dekha ki animal cells mein wall nahi hoti; unhe ek patli outer layer gherti hai, jise aaj plasma membrane kehte hain, aur plant tissue se compare karke unhe yakeen ho gaya ki wall sirf plant cells mein hoti hai. Dono kingdoms ko jodte hue Schwann ne propose kiya ki har plant aur animal body cells se aur cells ke banaye substances se bani hai (Fig. 8.2).

Schleiden aur Schwann ki cell theory ne ek sawaal khula chhoda: naye cells aate kahan se hain? Us samay ke kai biologists sochte the ki cells ek structureless fluid se naye sire se bante hain. 1855 mein German physician Rudolf Virchow ne kaha ki cells divide hote hain, isliye har cell pehle se maujood kisi cell se aata hai; is idea ko unhone Omnis cellula-e cellula mein samet diya. Virchow ke is addition ne theory ko woh roop diya jo hum aaj use karte hain.

8.3 Cell ka Overview

Class 9 mein tumne shayad microscope ke neeche onion peel aur cheek cells dekhe honge. Dono ko saath-saath imagine karo. Kinaare par woh alag hain: box jaisa onion cell ek sakht cell wall se ghira hota hai, aur uski cell membrane wall ke andar ki taraf dabi rehti hai, jabki chapte cheek cell ki membrane ke bahar kuch nahi hota. Beech mein dono ek jaise hain: dono mein ek ghana, membrane se lipta nucleus hota hai, jo chromosomes ka ghar hai aur isliye cell ke DNA ka bhi.

DNA membrane-bound nucleus ke andar hai ya nahi, isi baat par saare cells do groups mein bant jaate hain. Jinke paas nucleus hai woh eukaryotic hain (Greek eu, true, aur karyon, kernel); jinke paas nahi hai woh prokaryotic hain (pro, before). Dono groups mein ek semi-fluid matrix, cytoplasm, cell ko bharta hai. Cell ki zyaadatar activity cytoplasm mein hi hoti hai: hazaaron chemical reactions jo cell ke zinda rehne tak kabhi nahi rukte, aur jo use living state mein rakhte hain.

Organelles do tarah ke hote hain. Zyaadatar membranes mein lipte hote hain, aur yeh sirf eukaryotic cells mein milte hain: nucleus ke alawa is list mein mitochondria, vacuoles, lysosomes, microbodies, Golgi complex aur endoplasmic reticulum (ER) aate hain. Prokaryotic cell mein inmein se koi nahi hota. Kuch organelles mein membrane bilkul nahi hoti. Centrosome, jo animal cells mein cell division ko organise karta hai, inmein se ek hai. Doosre hain ribosomes, aur yahi ek organelle hai jo har cell mein hota hai, chahe prokaryote ho ya eukaryote; eukaryotic cell mein yeh chaar jagah milte hain: cytoplasm mein free, rough ER par, aur mitochondria aur chloroplasts dono ke andar.

Cells ke size mein bahut fark hota hai (Fig. 8.1). Sabse chhote known cells, Mycoplasma, sirf lagbhag 0.3 µm lambe hote hain22NCERT text ki kuch printings mein yeh 0.3 mm likha hai; sahi value 0.3 µm hai, yaani ek micrometre ka teen-dasvaan hissa., aur bacteria kuch micrometres ke hote hain (NCERT 3–5 µm batata hai). Hamare apne body mein red blood cell lagbhag 7.0 µm across hota hai, jabki nerve cells sabse lambe known cells mein aate hain. Agar hum sirf un cells ko ginein jo apne aap exist karte hain, to record ostrich ke egg ke naam hai.

Shapes bhi utne hi alag hote hain: disc jaise, polygonal, columnar, cuboidal, thread jaise ya irregular. Cell ka shape shayad hi kabhi ittefaq hota hai. Aam taur par woh cell ke kaam ke hisaab se hota hai (Fig. 8.3).

8.4 Prokaryotic Cells

Bacteria, blue-green algae (cyanobacteria), bina wall wale Mycoplasma aur unse jude PPLO (pleuro-pneumonia-like organisms) milkar prokaryotes banate hain. Eukaryotic cells ke comparison mein yeh aam taur par chhote hote hain aur tezi se reproduce karte hain: achhi conditions mein kuch bacteria har 20 minute mein divide hote hain. Inke forms alag-alag hote hain, phir bhi zyaadatar bacteria chaar basic shapes mein se kisi ek mein fit hote hain (Fig. 8.4): rod jaisa bacillus, gol coccus, comma jaisa vibrio aur spiral spirillum.

Is variety ke neeche, har prokaryotic cell ek hi basic tareeke se organised hota hai (Fig. 8.5):

• Koi true nucleus nahi hota. Genomic DNA, yaani ek single circular chromosome, bina kisi nuclear membrane ke cytoplasm mein naked pada rehta hai.
• Kai bacteria genomic DNA ke bahar DNA ke chhote circles bhi rakhte hain, jinhe plasmids kehte hain. Plasmid par maujood genes bacterium ko extra traits dete hain; antibiotics ke against resistance iska ek common example hai.
• Mycoplasma ko chhodkar saare prokaryotes mein cell membrane ke bahar ek cell wall hoti hai, aur cytoplasm, ek semi-fluid matrix, cell ko bharta hai.
• Ribosomes ke alawa, eukaryotic cells ka koi bhi organelle maujood nahi hota. Iski jagah prokaryotes mein inclusions hote hain, yaani reserve material ke stores, aur ek mesosome, jo cell membrane ka andar ki taraf muda hua hissa hai aur inki khaas pehchaan hai.

Class 12 mein tum plasmids ko kaam karte dekhoge: biotechnologists inka use foreign DNA ko bacteria mein le jaane ke liye karte hain, aur yeh track karne ke liye ki kaun se bacteria ne woh DNA le liya hai (transformation).

8.4.1 Cell Envelope aur iske Modifications

Bacterium teen layers mein lipta hota hai jo itni kaske judi hoti hain ki ek protective coat ki tarah behave karti hain; yeh chemically complex cell envelope hai. Ise bahar se chheelo to pehle glycocalyx milta hai, phir cell wall, phir plasma membrane. Yeh layers chemistry aur apne-apne kaam mein alag hain; saath milkar yeh cell ki raksha karti hain.

Is envelope ke differences ek staining test mein dikhte hain jise Danish scientist Hans Christian Gram ne banaya tha. Jo bacteria Gram ka stain pakde rehte hain unhe Gram-positive kehte hain; jo use kho dete hain woh Gram-negative hain. Hospital laboratory mein bacteria ko pehchaanne ke pehle steps mein yeh test aaj bhi shaamil hai.

Glycocalyx har bacterium mein alag hota hai, is baat mein ki woh kis cheez se bana hai aur kitna mota hai.

Talaab ke paani mein bacterium phool kar phat kyun nahi jaata, ya sikud kar dhah kyun nahi jaata? Uski cell wall itni mazboot hai ki rok sake, aur yahi cell ko uska rod, sphere ya spiral shape bhi deti hai. Wall ke andar ki plasma membrane kaafi had tak eukaryotic cells ki membranes jaisi bani hoti hai; yahi woh selectively permeable layer hai jiske through cell apne aas-paas ke maahaul se deal karta hai.

Mesosome ke kaam hairaan karne wale had tak zyada hain: building (cell wall banane mein madad), copying (DNA replicate karne aur har daughter cell ko ek copy dene mein madad), energy aur export (respiration aur secretion) aur space (extra membrane area, isliye enzymes ke liye zyada jagah).33Kai cell biologists ab maante hain ki electron micrographs mein jo mesosomes dikhe the, unmein se zyaadatar samples ko prepare karte samay ban gaye the. Exams ke liye mesosomes ko waise hi seekho jaise yahan bataya gaya hai. Cyanobacteria mein andar ki taraf membrane ka ek doosra extension hota hai, chromatophore, jismein unke pigments hote hain.

Kuch bacteria tairte hain aur kuch nahi. Tairne wale flagella use karte hain, jo cell wall se nikalne wale patle filaments hain, aur species mein inki sankhya aur jagah alag hoti hai: ek sire par ek, ek guchha, ya poore surface par bahut saare. Har flagellum ke teen parts hote hain: envelope mein motor mount ki tarah laga basal body, joint ki tarah kaam karne wala chhota muda hua hook, aur filament, jo sabse lamba part hai aur bahar latakta hai. Do aur surface structures ka movement se koi lena-dena nahi. Pili ek special protein ki lambi tubes hain. Fimbriae surface se nikalne wale kaafi chhote baal hain; kuch bacteria mein yeh cell ko stream ke pattharon ya host ke tissues se chipka kar rakhte hain.

8.4.2 Ribosomes aur Inclusion Bodies

Proteins ribosomes par bante hain, aur prokaryote ke ribosomes uski plasma membrane se jude hote hain. Har ribosome ek chhota particle hai, lagbhag 15 nm by 20 nm, jo 50S aur 30S subunit se milkar 70S ribosome banta hai (unit S ko Section 8.5.6 mein samjhaya gaya hai). Jab protein jaldi chahiye hota hai, to ek messenger RNA (mRNA) ko ek saath kai ribosomes padhte hain, jo uspar motiyon ki tarah piroye hote hain. Is string ko polysome (polyribosome) kehte hain, aur uspar har ribosome mRNA ko protein mein translate karta hai.

Aur stores ka kya? Prokaryote apne reserves ko inclusion bodies ke roop mein rakhta hai: phosphate granules, cyanophycean granules (cyanobacteria mein) ya glycogen granules, jo bina kisi membrane ke cytoplasm mein free pade hote hain. Kuch photosynthetic prokaryotes, jaise blue-green algae aur purple aur green bacteria, mein gas vacuoles bhi hote hain jo unhe paani par tairte rakhte hain.

8.5 Eukaryotic Cells

Yeast cell, Amoeba, leaf cell aur tumhare apne cells mein kya common hai? Sab eukaryotic hain, aur inka main design feature hai compartmentalisation: membrane-bound organelles cytoplasm ko alag-alag kamron mein baant dete hain, har ek ki apni chemistry ke saath, taaki bilkul alag reactions saath-saath chal sakein. Protists, fungi, plants aur animals sab apne cells isi tarah banate hain. Inka DNA ek organised nucleus ke andar, nuclear envelope ke saath, chromosomes mein pack hota hai, aur inmein movement aur shape banaye rakhne ke liye kai complex structures hote hain (cytoskeleton).

Is common plan ke andar, plant aur animal cells kuch khaas tareekon se alag hain. Sirf plant cells mein cell wall, plastids aur ek bada central vacuole hota hai. Doosri taraf centrioles animal cells mein milte hain lekin lagbhag saare plant cells mein nahi hote. Table 8.1 teen main cell types ko saath-saath rakhta hai; neeche diya explorer tumhe har ek ko khol kar dekhne deta hai.

8.5.1 Cell Membrane

Membrane ko koi dekh pata, usse pehle hi chemists ne pata laga liya tha ki woh kis cheez se bani hai. Unka favourite material tha human red blood cell: ikattha karna aasaan, aur andar koi membranes nahi, isliye isse pure plasma membrane milti hai. Analysis se pata chala ki ismein zyaadatar lipids aur proteins hain. 1950s mein electron microscopes ke aane ke baad hi membrane ki structure ko detail mein study kiya ja saka.

Phospholipid, jo membrane ka main lipid hai, ko ek sir aur do poonchh wala imagine karo. Head polar hai aur paani pasand karta hai; hydrocarbon tails non-polar hain aur paani se door rehti hain. Membrane mein yeh molecules do sheets banate hain, tails beech mein milti hain aur heads dono taraf ke paani wale fluid ki taraf hote hain, taaki tails paani se door rahein: yeh hai lipid bilayer. Phospholipids ke beech cholesterol ke molecules bhi fit hote hain.

Membranes mein kaafi protein aur thoda carbohydrate bhi hota hai, haalaanki alag cell types mein inka balance alag hota hai; human red blood cell ki membrane mein lagbhag 52 % protein aur 40 % lipid hota hai. Biochemists membrane proteins ko is hisaab se sort karte hain ki unhe bahar nikalna kitna mushkil hai. Integral proteins bilayer mein aadhe ya poore dabe hote hain aur mushkil se nikalte hain; peripheral proteins uske surface par baithe hote hain aur aasani se alag ho jaate hain.

In findings ko jodne wali picture 1972 mein S. J. Singer aur G. L. Nicolson ne di: fluid mosaic model (Fig. 8.7). Iska main idea yeh hai ki lipid bilayer quasi-fluid hai. Proteins ek jagah fixed nahi hote balki usmein sideways tairte rehte hain, jaise lipid ke samundar mein icebergs, aur is movement ki aasani hi membrane ki fluidity hai. Fluidity zaroori hai: growth, cell division, secretion, endocytosis aur cells ke beech junctions banana, in sab ke liye aisi membrane chahiye jo beh sake aur phir se jud sake.

Traffic control membrane ka sabse zaroori kaam hai, aur yeh selective hai: kuch molecules andar aa jaate hain, kuch nahi (membrane selectively permeable hai). Zyaadatar traffic dhalaan ki taraf chalta hai. Koi substance zyada concentration wali jagah se kam concentration wali jagah jaata hai, apne concentration gradient ke saath neeche, aur cell ismein koi energy kharch nahi karta; yeh passive transport hai. Oxygen jaise chhote uncharged (neutral) solutes seedhe lipid bilayer mein ghul kar paar ho jaate hain: simple diffusion. Paani bhi yahi dhalaan wala rule maanta hai, aur membrane ke across uske diffusion ka apna naam hai, osmosis.

Glucose alag hai. Polar hone ki wajah se yeh bilayer ke oily, non-polar core mein ghul nahi sakta, isliye yeh sirf membrane mein maujood carrier protein ki madad se paar hota hai; jab tak yeh dhalaan ki taraf jaata hai, transport passive hi rehta hai. Chadhaai wala movement, kam concentration se zyada ki taraf, alag baat hai. Ise active transport kehte hain, aur cell iske liye ATP se energy kharch karta hai. Textbook example hai $\mathrm{N}\mathrm{a}{\phantom{X}}^{+}$/$\mathrm{K}{\phantom{X}}^{+}$ pump, jo tumhare cells ke andar sodium kam aur potassium zyada rakhta hai.44Pump ka har cycle ek ATP use karke teen sodium ions bahar dhakelta hai aur do potassium ions andar laata hai.

8.5.2 Cell Wall

Plants aur fungi plasma membrane ke bahar ek aur layer jodte hain: ek sakht, non-living cell wall. Yeh cell ka shape fix karti hai aur use chot aur infection se bachati hai. Yeh anchahe bade molecules ko bhi bahar rakhti hai, aur phir bhi padosi cells ko aapas mein interact karne deti hai.

Wall kis cheez se bani hai, yeh organism par depend karta hai. Algal walls mein cellulose, galactans aur mannans hote hain, aksar calcium carbonate jaise minerals ke saath. Baaki plants mein wall cellulose, hemicellulose, pectins aur proteins se bani hoti hai. (Fungal walls, jaise tumne Chapter 2 mein dekha, zyaadatar chitin se bani hoti hain.)

Do padosi plant cells ke beech ki wall ko beech se bahar ki taraf banao (Fig. 8.9). Pehli layer hai middle lamella, jo zyaadatar calcium pectate se bani hai, yaani cells ke beech ka gond. Iske dono taraf ek young cell patli primary wall banata hai jo cell ke saath khinch aur badh sakti hai. Cell ke mature hone par yeh growth dheemi ho jaati hai, aur tab andar ki taraf, membrane ke paas, ek secondary wall jodi jaati hai. In saari layers mein se patle channels, plasmodesmata, guzarte hain, jo ek cell ke cytoplasm ko agle se jodte hain.

8.5.3 Endomembrane System

Ek factory socho jahan ek workshop parts banata hai, agla unhe finish karta hai aur teesra unhe pack karke bhejta hai. Eukaryotic cell ke andar ER, Golgi complex, lysosomes aur vacuoles aisi hi ek chain banate hain: har ek dikhne aur kaam karne mein alag hai, lekin unke kaam coordinated hain aur material unke beech behta hai. Saath milkar yeh endomembrane system hain. Mitochondria, chloroplasts aur peroxisomes mein bhi membranes hoti hain, lekin unka kaam is chain ke saath coordinated nahi hai, isliye unhe ismein nahi gina jaata. Fig. 8.10 is chain mein ek protein ko follow karta hai.

8.5.3.1 Endoplasmic Reticulum (ER)

Naam hi sab batata hai: endoplasmic, yaani cytoplasm ke andar, aur reticulum, yaani ek chhota jaal. Electron microscope mein endoplasmic reticulum patli tubes aur chapti theliyon ke network jaisa dikhta hai jo poore cell mein phaila hota hai. Iski membranes cell ke andar ki jagah ko do spaces mein baant deti hain: ER ke andar ka luminal compartment, aur uske bahar sab kuch, yaani cytoplasm, jo extra-luminal compartment hai.

ER do roopon mein milta hai. Jahan iske outer surface par ribosomes jade hote hain, wahan yeh daanedar dikhta hai aur rough ER (RER) kehlata hai; ribosomes ke bina yeh chikna dikhta hai aur smooth ER (SER) hai. RER un cells mein bahut hota hai jo proteins banane aur secrete karne mein lage rehte hain, jaise digestive enzymes chhodne wale pancreatic cells, aur yeh nuclear envelope ki outer membrane se juda hota hai. SER cell mein lipid synthesis ki main jagah hai. Animal cells mein lipid jaise steroid hormones SER mein bante hain, isliye adrenal glands aur gonads ke hormone banane wale cells mein yeh bahut hota hai.

8.5.3.2 Golgi apparatus

Is organelle ka naam Italian scientist Camillo Golgi ke naam par hai, jinhone 1898 mein nerve cells ko silver salts se stain karte samay nucleus ke paas dark, jaal jaisi bodies dekhi thi. Dhyaan se dekho to chapti, disc-shaped theliyon ka ek dher dikhta hai, cisternae (har ek 0.5–1.0 µm across), jo plates ke stack ki tarah parallel rakhi hoti hain; inki sankhya alag-alag hoti hai. Stack nucleus ke charon taraf muda hota hai, isliye iske do faces hain jo dikhne aur kaam mein alag hain lekin jude hue hain: ubhra hua (convex) cis ya forming face aur dhansa hua (concave) trans ya maturing face.

Iska main kaam packing aur dispatch hai. Material ER se chhote vesicles mein aata hai jo cis face se fuse hote hain, isiliye Golgi hamesha ER ke paas hota hai. Material stack se hote hue trans face ki taraf badhta hai. Raaste mein ER ke ribosomes par bane kai proteins modify hote hain, aur zyaadatar glycoproteins aur glycolipids yahin bante hain. Trans face par taiyaar products naye vesicles mein nikalte hain, jo ya to cell ke andar kisi jagah ke liye hote hain ya bahar ke liye (secretion).

8.5.3.3 Lysosomes

Lysosome cell ki digestive thaili hai: ek chhota membrane-bound vesicle jise Golgi enzymes se bhar kar pack karta hai. Cells se alag kiye gaye lysosomes mein lagbhag har tarah ke hydrolases hote hain (lipases, proteases, carbohydrases aur doosre), isliye saath milkar yeh bade molecules ki chaaron major classes ko tod sakte hain: carbohydrates, proteins, lipids aur nucleic acids. Yeh enzymes acid mein sabse achha kaam karte hain, aur lysosome apne andar acidic pH banaye rakhta hai.

8.5.3.4 Vacuoles

Cell ki har jagah chemistry mein busy nahi hoti. Vacuole ek membrane-bound space hai jo zyaadatar storage ke liye use hota hai: paani, sap, excretory products aur doosre substances jinka cell ko koi use nahi. Isko gherne wali single membrane tonoplast hai. Plant cell ka vacuole bahut bada ho sakta hai, cell ke volume ka 90 per cent tak, jo cytoplasm ko wall ke saath ek patli layer mein daba deta hai.

Tonoplast asli kaam karta hai. Plant cells mein yeh kai ions aur doosre materials ko unke concentration gradients ke against vacuole mein le jaata hai, isliye woh cytoplasm ke comparison mein sap mein kahin zyada concentrated ho jaate hain. Doosre vacuoles ke doosre kaam hain. Amoeba ka contractile vacuole extra paani ikattha karke bahar pump karta hai, jo osmoregulation aur excretion ke liye zaroori hai. Kai cells, khaas kar protists, food particles ko nigal kar food vacuoles banate hain.

8.5.4 Mitochondria

Special stain ke bina mitochondria (singular mitochondrion) light microscope mein mushkil se dikhte hain. Ek cell mein kitne honge, yeh is par depend karta hai ki cell kitna kaam karta hai, kuch se lekar busy heart-muscle cell mein hazaaron tak, aur inka shape aur size bhi alag hota hai. Typical mitochondrion ek sausage ya cylinder jaisa hota hai, 0.2–1.0 µm chauda (average lagbhag 0.5 µm) aur 1.0–4.1 µm lamba.

Har mitochondrion do membranes mein lipta hota hai (Fig. 8.11). Chikni outer membrane iski continuous boundary hai. Inner membrane mud kar cristae (singular crista) banati hai jo andar tak jaati hain aur iska surface area kai guna badha deti hain. Membranes do paani wale compartments banati hain: unke beech ek sankara outer compartment (intermembrane space), aur inner compartment, jo ek ghane, uniform fluid, matrix, se bhara hota hai. Har membrane par organelle ke kaam ke liye enzymes ka apna set hota hai.

Mitochondrion ka kaam hai aerobic respiration: yeh khaane mein chhupi energy ko nikal kar ATP ke roop mein pakadta hai, jo cell ki energy currency hai, isiliye mitochondria ko cell ka powerhouse kehte hain. Ek khaas baat yeh hai ki mitochondrion apne kuch proteins khud bana sakta hai: iske matrix mein ek circular DNA molecule, kuch RNA molecules, 70S ribosomes aur protein banane ka baaki saaman hota hai. Naye mitochondria tab bante hain jab maujood mitochondria do mein toot jaate hain (fission).

8.5.5 Plastids

Patti ka hara rang, gaajar ka orange aur aaloo ka safed, sab plastids se aate hain, jo har plant cell aur euglenoids mein milne wale organelles hain. Bade hone ki wajah se yeh microscope mein aasani se dikhte hain. Inke pigments ke hisaab se inhe chloroplasts, chromoplasts aur leucoplasts mein classify kiya jaata hai (Table 8.2). Rangheen leucoplasts, jo kai shapes aur sizes ke hote hain, food stores hain: amyloplasts starch rakhte hain (jaise aaloo mein), elaioplasts oils aur fats rakhte hain, aur aleuroplasts proteins rakhte hain.

Hare plant mein pattiyon ke mesophyll cells mein zyaadatar chloroplasts hote hain, har cell mein 20–40, jabki alga Chlamydomonas sirf ek se kaam chala leta hai. Chloroplast aam taur par 5–10 µm lamba aur 2–4 µm chauda hota hai, aur iska shape lens jaisa, oval, spherical, disc jaisa ya ribbon jaisa bhi ho sakta hai.

Andar se chloroplast membranes ke andar membranes ka set hai (Fig. 8.12). Mitochondrion ki tarah do envelope membranes ise gherti hain, inner membrane kam permeable hoti hai, aur yeh ek fluid se bhari jagah, stroma, ko gherti hain. Stroma mein membrane ki chapti theliyan hoti hain, thylakoids. Yeh dabbe mein rakhi rotiyon ki tarah ek ke upar ek jama hokar grana (singular granum) banate hain, aur stroma lamellae naam ki chapti membrane tubules alag-alag grana ke thylakoids ko jodti hain. Har thylakoid ki membrane apni ek chhoti jagah gherti hai, lumen.

Chlorophyll pigments thylakoids mein hote hain, jahan light energy pakdi jaati hai; grana light reactions ki jagah hain. Stroma mein carbohydrates aur proteins banane wale enzymes hote hain (dark reactions yahin hote hain), saath hi chhote double-stranded circular DNA molecules aur ribosomes bhi. Chloroplast ke ribosomes 70S hote hain, jo cytoplasm ke 80S ribosomes se chhote hain.

8.5.6 Ribosomes

Ribosomes mein membrane nahi hoti: har ek ribonucleic acid (RNA) aur protein ka ek granule hai. George Palade ne 1953 mein inhe pehli baar electron micrographs mein ghane particles ke roop mein describe kiya.

Har ribosome ke do subunits hote hain, ek bada aur ek chhota (Fig. 8.13). Eukaryotic ribosomes 80S hote hain, jinke subunits 60S aur 40S hain; prokaryotic ribosomes 70S hote hain, jinke subunits 50S aur 30S hain. S ka matlab hai Svedberg unit, jo sedimentation coefficient ki unit hai: yeh naapta hai ki bahut tez speed par ghumane par koi particle kitni jaldi neeche baithta hai. Kyunki yeh particle ki density aur size dono par depend karta hai, yeh size ka sirf indirect measure hai.55Ek Svedberg unit $1\times {10}^{-13}\mathrm{s}$ hai. Iska naam Theodor Svedberg ke naam par hai, jinhone pehle ultracentrifuges banaye.

8.5.7 Cytoskeleton

Cell parts ka koi dheela thaila nahi hai. Protein filaments ka ek jaal, cytoskeleton, iske cytoplasm mein phaila hota hai, jo teen tarah ke filaments se bana hai: microtubules, microfilaments aur intermediate filaments.66Microfilaments lagbhag 7 nm mote hote hain, intermediate filaments lagbhag 10 nm aur microtubules lagbhag 25 nm. Yeh values sirf interest ke liye hain. Tent ke bamboo, rassiyon aur khoontiyon ki tarah yeh cell ko mechanical support dete hain aur uska shape banaye rakhte hain, aur movement ko bhi mumkin banate hain. Microtubules cilia, flagella aur centrioles ka core banate hain, jo aage aate hain.

8.5.8 Cilia aur Flagella

Kai eukaryotic cells cell membrane se dhake baal jaise ubhaaron se khud move karte hain, ya apne aas-paas ke fluid ko move karte hain. Chhote aur bahut saare, jo chappu ki tarah chalte hain, cilia hain (singular cilium): yeh Paramecium ko paani mein aage badhate hain, aur tumhari windpipe mein mucus ko upar ki taraf saaf karte hain. Lambe wale, aam taur par har cell mein ek ya do, flagella hain (singular flagellum); yeh human sperm jaise cell ko chalate hain. Bacterial flagella ka naam same hai lekin banawat nahi (Section 8.4.1).

Ek ko aade kaato aur electron microscope se dekho. Membrane ke andar core hota hai, axoneme: lambai mein chalne wale microtubules ka ek bundle. Cross-section ko bahar se andar ki taraf padho (Fig. 8.14):

• Nau outer doublets. Jude hue microtubules ke nau jode membrane ke theek neeche ek ring banate hain; har doublet agle se ek linker (interdoublet bridge) se bandha hota hai.
• Ek central pair. Do single microtubules beech mein chalte hain, ek bridge se jude hote hain aur ek central sheath se ghire hote hain.
• Nau radial spokes. Ek spoke central sheath se har doublet ke ek tubule tak jaata hai, isliye kul nau hote hain.

Do singles ke charon taraf nau doublets: yeh hai 9 + 2 array. Neeche, har cilium aur flagellum ek basal body se nikalta hai, jo centriole jaisi bani structure hai.

8.5.9 Centrosome aur Centrioles

Centrosome ek organelle hai jismein aam taur par chhote cylinders ki ek jodi hoti hai, centrioles, jo pericentriolar material ke ek bedaul baadal mein ek doosre se right angle par rakhe hote hain (Fig. 8.15). Centriole ko aade kaato to ek cartwheel dikhta hai. Iska rim protein tubulin ke nau barabar doori par rakhe peripheral fibrils se bana hai, har ek microtubules ka ek triplet hai jo agle se juda hai. Proximal (paas wale) sire par centre mein ek protein hub hota hai, jo protein radial spokes se triplets se juda hai. Ismein koi central pair nahi hota, aur yahi centriole ko axoneme se alag pehchaanne ka ek tareeka hai.

Centrioles ke do kaam hain. Yeh basal bodies banate hain jinse cilia aur flagella nikalte hain, aur animal cells mein yeh spindle apparatus ke spindle fibres banate hain jo cell division ke dauraan chromosomes ko alag karta hai (Chapter 10).

8.5.10 Nucleus

Nucleus sabse pehle jaana gaya organelle hai: Robert Brown ne ise 1831 mein describe kiya. Iske stain hone wale contents ko naam baad mein mila, jab Walther Flemming ne basic dyes lene wale material ko chromatin kaha (Greek chroma, rang).

Do divisions ke beech cell interphase mein hota hai. Interphase nucleus mein teen cheezein hoti hain: chromatin, jo bahut lambe nucleoprotein fibres ke ek dheele, elaborate network ki tarah phaila hota hai; ek nuclear matrix; aur ek ya zyada gol nucleoli (singular nucleolus) (Fig. 8.16).

Iski boundary nuclear envelope hai, aur electron microscope dikhata hai ki yeh double hai: do parallel membranes jinke beech 10–50 nm ka gap hai, perinuclear space. Envelope nucleus ke contents ko cytoplasm se alag karta hai, lekin yeh band nahi hai. Kai jagah iski do membranes fuse ho jaati hain, aur bahut chhote nuclear pores chhod deti hain, jinse RNA aur protein molecules nucleus ke andar aur bahar aate-jaate hain. Cytoplasm ki taraf outer membrane aam taur par aage endoplasmic reticulum se jud jaati hai, aur rough ER ki tarah uspar ribosomes hote hain.

Nucleolus mein membrane nahi hoti; iska material aas-paas ke nucleoplasm (nuclear matrix, jismein chromatin bhi hota hai) mein ghul-mil jaata hai. Yahan ribosomal RNA (rRNA) tezi se banta hai. Jo cell bahut protein banata hai use bahut ribosomes chahiye, isliye usmein bade aur zyada nucleoli hote hain.

Chromatin aur chromosomes

Chromatin DNA, RNA aur do tarah ke proteins ka mixture hai: basic proteins jinhe histones kehte hain, aur doosre, non-histone proteins. Jab cell divide hota hai, to dheela chromatin lipat kar alag-alag chromosomes ban jaata hai, aur kuch der ke liye yeh jaane-pehchaane nucleus ki jagah le lete hain. Ek single human cell mein lagbhag do metre DNA hota hai, jo uske 46 chromosomes (23 pairs) mein bata hota hai; itna lamba dhaaga kaise pack hota hai, yeh Class 12 ka topic hai.

Dividing cell mein koi bhi chromosome dekho (sirf isi samay chromosomes dikhte hain), to tumhe ek patli kamar milegi, primary constriction ya centromere. Yeh chromosome ke do chromatids ko saath pakad kar rakhta hai, aur iske bagal mein disc-shaped kinetochores hote hain (Fig. 8.17). Chromosome par centromere kahan hai, iske hisaab se chaar types hote hain:

• Metacentric: centromere beech mein, isliye dono arms barabar.
• Sub-metacentric: centromere beech se thoda hat kar, jisse ek arm chhoti aur ek lambi hoti hai.
• Acrocentric: centromere ek sire ke paas, jisse ek arm bahut chhoti aur ek bahut lambi hoti hai.
• Telocentric: centromere bilkul chromosome ke sire par.

Kuch chromosomes mein ek doosra pinch bhi dikhta hai. Yeh secondary constriction stain nahi leta aur hamesha same jagah dikhta hai, isliye uske aage ka tukda ek alag chhote knob jaisa dikhta hai: satellite.

8.5.11 Microbodies

Plant aur animal dono cells mein bahut saari microbodies bhi hoti hain: bahut chhote vesicles, har ek mein single membrane aur andar enzymes bhare hue. Peroxisomes, jo hydrogen peroxide ko todte hain, aur ugte hue oily seeds ke glyoxysomes, jo store kiye fat ko sugar mein badalne mein madad karte hain, iske do examples hain.