Partial preview of the text
Download Cell cycle and cell division and more Essays (high school) Biology in PDF only on Docsity!
7 Cell Cycle and Cell Division Chapter Gy nIRcouSr CO wrenmnse ; 2 Divtdedtuthernt tree phases | Allcls raprosuc by dividing inte te, with sach parenal Caiguingoe lowe daughter col ech trey Sve. () G,phase (Gap 1) (0) Sphase Synthesis) 2 Growth and reproduction are characteristics of calls, Indaedofallining organisms. 2 Such cycles of growth and division allows single calltofarm . 2 sructure consisting ofmilions afcall. > Some calls do not divide further, exit G, phase to enter an e—_—er— inactive stagecalled quiescent stage (G;) of thecellcycte, @eeu crue © Calls in this stage remain metabolically active but no longer Dh ge EPI Iec ih @ pwotfersto unlees caled on io co co. depending on the ecm; Spuhosioes the cine conetrents ofthe cal ned @g Dy ate oars ca Heatests (Gi) G,phase(Gap2) ‘everiualy divides intotwo daughter coll, 2 Call growth results in disturbing the ratio between the ‘nucleus and cytoplasm. It therefore becomes essential for theccllto divide to restore the nucleo-cytoplasmicrati. 9. Gell gronth (in terms of cytoplasmic increase isa continous, process Interval between mitosis andinitation of DNA replication. Calls metabotcally active and continuously grows but doas not replicaio ts DNA Mostof the callorganelles dupicate (© Duration of cell cycle can vary ftom organism to organism {and also from cel ype to calltype. “This phase marks the phase of DNA replication and .9., Yeast-celloycle duration - 80 minutes, yomosome duplication, ch 2 Amauntof DNA per cell doubles but theres noincrease nina ‘chromosome number 2 Inanimat cali, centriole dupicatesin cytoplasm. > DNAreplication beginsin nucleus. ‘© Proteins are synthasised in preparation for mitosis while call ‘growth continues Human cell cycle duration-24 hours bt call division proper lasts foronly aboutan hour. @ PHASES OF CELL CYCLE oe Tn animal calls mitotic division fs only seen in diploid somatic calle, Plant calls show mitotic division in both haploid and iplosd cole. ‘Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Cell Cycle and Cell Division NCERT Maps 2, Mostdramaticperiodtcal eye @ wenase qnrosis) \Chromosnma rumserin parent and progeny co ite sarsshencs needs toued oquctoel chason i OYTOKINESIS ‘untangled, 2 Gentrosome starts to mave towards opposite poles. 2 Wis aivision of cytoplasm at the fend af which cell division gets| ‘completed. 2 Inanimal cols itis achieved by the| ‘appearance of a furrow in the membrane, Im plant calls cytokinesis is! ‘achieved by wall formation, which referred to as daughter theirindividualty. ‘ehromosomebagin heirmigratien ., Nuclear envelope develops 2 They af canbe 2 ‘marked by- itis pase around the chromosome starts in he centre of the celland The centromere of each custeral cach pole forming grow outward to mast the Chi condense to form compact mitotic 2 All the chromosome coming to fe at remain directed ‘nucle. ‘existing latoralwall towards the pole and armstraling , Nucleolus, Golgi camplex 2 The formation af new coll wall bebind. (leading to different ang eR begins with the formation of a simple precursor, called the call and ‘out called asters. The two asters together with spindle fibres form miteticapparatus. {A the end of prophase celis do not ‘show Golgi complex, ER, nucteolus ‘andruciear envelope. chromosome. Esch controsomereachatpole 2 Eath chromosome connactod by Late Prophase: ®) ‘Mata plate that represents the middle lamella between the wall of two ‘agjacentcells. @ SIGNIFICANCE oF urTosis. Mitosis usualy esuts neni genaiccomplerentn daughter cts CGrowhotmulicobererganisms Calirepai io dvsioninaicalanllerl mercer rests coninsoun pron of planks troughoul het Be. Insome ower plants and in some socal nsectshaploccets alsochvide by mitosis. ‘Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph, 011-47623456 Cell Cycle and Cell Division NCERT Maps MEIOSIS {Equational Phase) -Resembles a normal mitosis, + ¥ 7 PROPHASE!! METAPHASE I ANAPHASE I TELOPHASE I o hist nests 3h alignattheequator 2 Splitting of centromere allowing 2 Meiosis endswith telophase I © The nuclear by theo ‘tom poles of the fo move towards 2 Two groups of chromosomes once again get ‘enidof prophase spindle gt. ‘ote ot pales ofthe cll by shriening bya © Ghromosomes become compact. sister chromatids of microtubules attached to the 4 Gytokiness follow resulting inthe formation of kinetochore. totadofcol, @ signincance of meiosis By cere spec cutis ato fst pci csi ci Gini nly ening ly tak 12 Increases gonotic variabiityin th of organisms whichis forthe of ‘Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph, 011-47623456 
