Class 11 Biology · Chapter 10
Short answer:
Cell Cycle cell ke life mein hone wale sequential events ka set hai jisme cell grow karta hai aur divide hota hai. Yeh chapter Interphase (G1, S, G2), M Phase, Mitosis ke stages, Meiosis ke stages, aur dono divisions ki significance cover karta hai.
Growth, repair aur reproduction ke liye cells ko divide hona padta hai. Is chapter mein hum Cell Cycle ke phases — Interphase aur M Phase — detail mein padhenge, saath hi Mitosis (equational division) aur Meiosis (reductional division) ke stages, unki significance, aur dono ke beech ke differences samjhenge.
Chapter 10 Summary — 5 Minute Revision
Cell cycle do major phases mein bata hai — Interphase (jisme G1, S aur G2 sub-phases hote hain, aur DNA replication S-phase mein hota hai) aur M Phase (jisme actual cell division — mitosis ya meiosis — hota hai, jiske baad cytokinesis hoti hai). Mitosis ek somatic cell division hai jisme ek parent cell se do genetically identical daughter cells banti hain (chromosome number same rehta hai — isliye ise equational division kehte hain). Mitosis ke four stages hain — Prophase, Metaphase, Anaphase aur Telophase.
Meiosis reproductive germ cells mein hota hai aur do successive divisions — Meiosis I aur Meiosis II — involve karta hai, jisse chromosome number half ho jaata hai (reductional division). Meiosis I ka Prophase I sabse complex hota hai, jisme paanch sub-stages hote hain — Leptotene, Zygotene, Pachytene, Diplotene aur Diakinesis. Zygotene mein synapsis hota hai (homologous chromosomes pairing) aur Pachytene mein crossing over hota hai, jo genetic variation ka main source hai. Meiosis genetic diversity maintain karta hai aur sexual reproduction ke dauran chromosome number ko generation dar generation constant rakhta hai.
In-Text Questions — Solutions
Interphase ko 'resting phase' kyun kaha jaata tha, aur kya yeh sahi hai?
Purane time mein microscope ke neeche koi visible division dikhai nahi deta tha is phase mein, isliye ise 'resting' bola gaya. Lekin actually yeh naam galat hai — G1 phase mein cell grow karta hai aur proteins/organelles synthesize karta hai, S-phase mein DNA replication hota hai, aur G2 phase mein cell division ke liye zaroori proteins aur energy prepare hoti hai. Matlab cell is poore time metabolically bahut active rehta hai, resting bilkul nahi hota.Ek cell ka DNA content G1 phase mein 2C hai. S phase ke baad aur G2 phase mein DNA content kya hoga, aur kyun?
G1 mein DNA content 2C hota hai (unreplicated diploid set). S-phase mein DNA replication hoti hai to content double hoke 4C ho jaata hai — lekin chromosome number same (2n) rehta hai kyunki har chromosome ab do sister chromatids mein badal jaata hai jo ek hi centromere se judi hoti hain. G2 phase mein further replication nahi hoti, isliye content 4C hi rehta hai; cell sirf division ke liye prepare hoti hai. Mitosis complete hone ke baad daughter cells mein content wapas 2C ho jaata hai.Prophase I ke Pachytene stage mein crossing over kyun important hai?
Pachytene mein synapsed homologous chromosomes (bivalents) ke non-sister chromatids ke beech recombination nodules ke through genetic material exchange hota hai — isse naye gene combinations bante hain jo parent mein nahi the. Iska visible proof Diplotene stage mein Chiasmata (X-shaped structures) ke roop mein dikhta hai. Yehi process meiosis se bane gametes mein genetic variation laata hai, jo evolution ke liye zaroori hai.Anaphase I aur Anaphase (mitosis) mein chromosome movement ka basic difference kya hai?
Mitosis ke Anaphase mein centromere split hota hai aur sister chromatids alag hoke opposite poles ki taraf jaate hain — har chromatid ab ek independent chromosome ban jaata hai. Meiosis ke Anaphase I mein centromere split NAHI hota — puri homologous chromosome pair (do chromatids sahit) separate hoke opposite poles ki taraf jaati hai, sister chromatids sath judi rehti hain. Yehi wajah hai ki Meiosis I ko reductional division kehte hain.
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Exercise Questions — Solutions (Q1–Q14)
Mammalian cell ka average cell cycle span kitna hota hai?
Ek typical mammalian cell mein cell cycle complete hone mein lagbhag 24 hours lagte hain. Isme se G1 phase ~11 hours, S phase ~7-8 hours, G2 phase ~4-5 hours, aur M phase sirf ~1 hour leta hai. Matlab interphase hi total cycle time ka bahut bada hissa cover karta hai, actual division (M phase) bahut chota time leta hai.Cytokinesis aur karyokinesis mein fark batao.
Karyokinesis nuclear division hai — isme nucleus divide hoke do daughter nuclei banata hai (mitosis ke Prophase se Telophase tak ka process). Cytokinesis cytoplasm ka division hai jo karyokinesis ke baad hota hai, jisme cell membrane (animal cells mein cleavage furrow) ya cell plate (plant cells mein) form hoke ek cell ko do separate daughter cells mein baant deta hai. Karyokinesis pehle hoti hai, cytokinesis uske baad.Interphase ke events describe karo.
Interphase teen sub-phases mein bata hai. G1 phase mein cell size mein badhta hai aur RNA/protein synthesis karta hai, division ke liye prepare hota hai. S-phase mein DNA replication hoti hai — DNA content 2C se 4C ho jaata hai lekin chromosome number same rehta hai. G2 phase mein cell continue growth karta hai aur division ke liye zaroori proteins (jaise tubulin) synthesize karta hai.G0 phase (quiescent phase) kya hai?
Kuch cells jo actively divide nahi karte (jaise mature neurons, ya temporarily non-dividing cells), G1 phase se bahar nikal ke ek inactive stage mein chale jaate hain jise G0 kehte hain. Yeh cells metabolically active rehte hain lekin cell cycle mein aage nahi badhte jab tak koi signal na mile unhe wapas cycle mein enter karne ke liye.Mitosis ko equational division kyun kaha jaata hai?
Mitosis mein parent cell (2n) se do daughter cells banti hain jo dono genetically aur chromosome number ke hisaab se identical hoti hain (2n hi rehta hai) — parent aur daughter cells ka chromosome number barabar (equal) hota hai, isliye ise equational division kehte hain.Cell cycle ke kis stage mein ye events hote hain: (i) chromosomes spindle equator par move hote hain (ii) centromere split hoke chromatids separate hote hain (iii) homologous chromosomes ke beech pairing hoti hai (iv) homologous chromosomes ke beech crossing over hota hai?
(i) Metaphase — chromosomes spindle fibres se attach hoke cell ke equator (metaphase plate) par align hote hain. (ii) Anaphase — centromere split hota hai aur sister chromatids opposite poles ki taraf move karte hain. (iii) Zygotene (Prophase I of meiosis) — homologous chromosomes pair karte hain, is process ko synapsis kehte hain. (iv) Pachytene (Prophase I of meiosis) — non-sister chromatids ke beech crossing over hota hai.Kya somatic animal cell mein division hamesha ke liye chalta reh sakta hai?
Nahi. Normal somatic cells mein ek limit hoti hai jitni baar woh divide ho sakte hain, jiske baad cells senescence mein chale jaate hain ya apoptosis ho jaata hai. Har division ke saath telomere shortening hoti hai jo eventually division ko rok deti hai. Sirf cancerous ya kuch stem cells hi is limit ko bypass karke unlimited division kar paate hain, jo ek abnormal condition hai.Cytokinesis ke dauran cell mein kya changes hote hain?
Animal cells mein plasma membrane cell ke centre mein andar ki taraf pinch hoti hai (cleavage furrow) jab tak cell do parts mein completely separate nahi ho jaata. Plant cells mein, jinme rigid cell wall hoti hai, cell plate cell ke centre se shuru hoke periphery ki taraf grow karta hai — yeh Golgi vesicles se material deposit hoke banta hai aur eventually naya cell wall ban jaata hai jo do daughter cells ko separate karta hai.Meiosis ki significance briefly discuss karo.
Meiosis chromosome number ko half (diploid se haploid) kar deta hai jo sexual reproduction ke dauran fertilization ke time chromosome number ko generation dar generation constant rakhne mein help karta hai. Crossing over (Prophase I mein) genetic recombination create karta hai jisse offspring mein genetic variation aati hai — yeh variation evolution aur adaptation ke liye zaroori hai.Discuss karo — agar (a) meiocytes meiosis na karein, (b) anaphase mein chromatids separate na ho, (c) karyokinesis ke baad cytokinesis na ho — to kya hoga?
(a) Agar meiocytes meiosis nahi karenge to gametes diploid (2n) reh jaayenge, aur fertilization ke baad zygote ka chromosome number har generation mein double hota jaayega — jo abnormal aur usually non-viable hota hai. (b) Agar anaphase mein chromatids separate nahi honge, to daughter cells mein asymmetric ya extra chromosome number ho jaayega (aneuploidy), jo cell function ko disrupt kar sakta hai. (c) Agar cytokinesis na ho to cell mein multiple nuclei ban jaayenge (multinucleate condition), jaise coenocytic cells mein dekha jaata hai.Synapsis, Bivalent aur Chiasmata describe karo.
Synapsis: Zygotene stage mein homologous chromosomes ka pairing process, jo synaptonemal complex ke through hota hai. Bivalent: ek pair of synapsed homologous chromosomes (total 4 chromatids) ko bivalent ya tetrad kehte hain. Chiasmata: Diplotene stage mein dikhne wale X-shaped structures jo crossing over ke points ko represent karte hain, jaha non-sister chromatids ke beech genetic material exchange hua tha.Spindle fibre organisation ki significance kya hai cell division mein?
Spindle fibres (microtubules) kinetochores se attach hoke chromosomes ko cell ke equator tak le jaate hain (Metaphase) aur phir Anaphase mein chromosomes/chromatids ko opposite poles ki taraf khichte hain. Bina proper spindle organisation ke, chromosomes equally aur accurately daughter cells mein distribute nahi ho payenge, jisse aneuploidy ho sakti hai.Mitosis ke Anaphase aur Meiosis ke Anaphase I mein fark batao.
Mitosis ke Anaphase mein centromere split hota hai aur sister chromatids alag hoke opposite poles ki taraf jaate hain. Meiosis ke Anaphase I mein centromere split nahi hota — puri homologous chromosome (dono chromatids sahit) separate hoke opposite poles ki taraf jaati hai, sister chromatids sath judi rehti hain. Isliye Anaphase I ko reductional aur Anaphase (mitosis) ko equational movement kaha ja sakta hai.Animal aur plant cell division mein main differences list karo.
(1) Centrioles: Animal cells mein centrioles spindle formation mein help karte hain, most plant cells mein centrioles absent hote hain aur spindle bina centrioles ke organize hota hai. (2) Cytokinesis: Animal cells mein cleavage furrow (membrane pinching) se hoti hai, plant cells mein cell plate formation se (kyunki rigid cell wall hoti hai). (3) Cell shape: Animal cells division ke time round ho jaate hain, plant cells ka shape wall ki wajah se largely fixed rehta hai.Important Equations — Ek Nazar Me
| Feature | Mitosis | Meiosis |
|---|---|---|
| Occurs in | Somatic cells | Germ cells (reproductive) |
| Number of divisions | One | Two (Meiosis I and Meiosis II) |
| Daughter cells produced | 2, diploid (2n) | 4, haploid (n) |
| Genetic identity | Identical to parent cell | Genetically variable (due to crossing over) |
| Crossing over | Absent | Occurs in Pachytene of Prophase I |
| Homologous pairing (synapsis) | Absent | Occurs in Zygotene of Prophase I |
| Biological significance | Growth, repair, asexual reproduction | Maintains chromosome number across generations, creates genetic variation |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Students often confuse Anaphase of mitosis with Anaphase I of meiosis — mitosis ke anaphase mein centromere split hota hai aur chromatids separate hote hain, jabki anaphase I mein centromere split NAHI hota, sirf homologous chromosomes separate hote hain.
- Synapsis (Zygotene) aur Crossing over (Pachytene) ko same stage samajh lena — yeh dono Prophase I ke alag-alag sequential substages hain.
- G0 phase ko active cell cycle ka hi part (jaise G1) samajh lena — G0 asal mein cell cycle se bahar ek quiescent state hai.
- Cytokinesis aur karyokinesis ko same process samajh lena — karyokinesis nuclear division hai, cytokinesis cytoplasmic division hai, dono alag events hain.
- Plant cell cytokinesis mein bhi cleavage furrow bolna — plant cells mein rigid cell wall hone ki wajah se cell plate banta hai, cleavage furrow sirf animal cells mein hota hai.
- DNA content aur chromosome number ko confuse karna — S phase ke baad DNA content double (4C) ho jaata hai lekin chromosome number same (2n) rehta hai, kyunki sister chromatids ek hi centromere se judi hoti hain.
Board-Style Important Questions
- Cell cycle ke phases aur unki duration describe karo.
- Mitosis aur meiosis mein differences likho (table format mein).
- Prophase I ke sub-stages ka sequence aur unki key events likho.
- Meiosis ki biological significance explain karo.
- Anaphase aur Anaphase I mein fark spashtikaran ke saath likho.
Aksar Poochhe Jaane Wale Sawaal
Cell cycle mein kitne phases hote hain?
Cell cycle do main phases mein divide hota hai — Interphase (jisme G1, S aur G2 sub-phases hote hain) aur M Phase (jisme mitosis ya meiosis hoti hai, uske baad cytokinesis hota hai).
Mitosis aur meiosis mein basic difference kya hai?
Mitosis ek division hai jisme 2 genetically identical diploid daughter cells banti hain (somatic cells mein), jabki meiosis do successive divisions ke through 4 genetically variable haploid daughter cells banata hai (germ cells mein).
G0 phase kya hota hai aur kaunsi cells isme rehti hain?
G0 ek quiescent (resting) state hai jisme cells actively divide nahi karti par metabolically active rehti hain — jaise mature neurons ya kuch differentiated cells.
Crossing over kis stage mein hota hai aur iska kya fayda hai?
Crossing over Prophase I ke Pachytene stage mein hota hai, jisme non-sister chromatids genetic material exchange karte hain — isse offspring mein genetic variation aati hai, jo evolution ke liye important hai.
Mitosis ko equational division kyun kehte hain?
Kyunki mitosis mein daughter cells ka chromosome number parent cell ke barabar (2n) rehta hai — koi reduction nahi hota.
Plant aur animal cells mein cytokinesis kaise alag hota hai?
Animal cells mein cleavage furrow (membrane pinching) se cytokinesis hoti hai, jabki plant cells mein rigid cell wall hone ki wajah se cell plate formation ke through hoti hai.
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