Aim - Study of mitosis in onion root tip (Preparation). lequirements : 2-3 root tips of onion, test tubes, water, beaker, li pound on x , ‘i , glass slides, coverslips, com microscope, spirit lamp, dil HCI, glycerine, acetocarmine stain. ees Theory : Cell division is a process of formation of daughter cells from a single cell. It can be of two () Mitosis or Equational division. i) Meiosis or Reductional division ____ Mitosis : A process by which chromosomes are duplicated and distributed equally to two daughter cells. is known as mitosis. Thus it maintains the chromosome number during growth and repair. Mitotic cycle mainly involves two processes. () Karyokinesis i.e., division of nucleus. (ii) Cytokinesis i.e., division of cytoplasm. Most of the changes take place in nucleus. Nucleus contains a hereditary material known as chromatin which shortens and thickens into countable fragments known as chromosomes. These chromosomes are ‘equally distributed in daughter cells during mitosis.— tosis = daughter cell: it cell are produced. © nePrmasomes aster paren ian a “a nee takes place in somatic cells or vegetative cells. It helps growth one body. (a) Study of Mitosis in onion root tip Procedure : : ‘Observe the permanent slide for various stages of mitosis at low power and high power of microscope, For temporary slide preparation following procedure can be followed : Take a conical flask or a bottle full of water. Select a medium sized onion bulb and trim off the old roots from base. Place the onion bulb on flask, with its base just touching the water. Place the flask aside for a week. New roots will grow. Cut 4-5 mm off the tips of roots. Fix the cells by keeping the cut roots in a mixture of 1: 3 acetic acid and methyl alcohol for 1 hour, Pick up 2~ 3 root tips in a watch glass. Add 3 ~ 4 ml of 1 N Hydrochloric acid. Warm the watch glass NPOpon a till itis just bearable to touch (i.e, about 60°C). 8. Wash the root tips in distilled water. 9. Puta drop of acetocarmine stain on slide. 10. Place a root tip on drop of stain and cover it with coverslip. Tap the coverslip with blunt end of needle till the root tip is squashed into a thin layer. 11, 12. Gently warm the glass slide till it becomes bearable to touch. 18. Observe the slide first under low power of microscope then under high power of microscope. Observations : pm Cell wall 1. Cell is bounded by a cell walll and a cell membrane. ches 2. Thread like chromatin material is scattered in nucleus. Nucleolus 3. Complete and distinct nuclear membrane is present. Nuclear membrane: 4. Duplication of chromosomes has started by thickening Plasma membrane. and shortening, 5. Nucleolus is present. prophase: Cell wall Chromosomes Hf 1. Thick and short chromosomes can be observed, 2. Each chromosome is made uf ip of two chromatid: to each other at centromere. rae Nuclear membrane: Disappearing 3. Nuclear membrane has started disappearing, 4. Nucleolus has disappeared. pn Pr a rophase 1. Proteinaceous threads know! rae Dee piselibes|constvtela i oe ya 2. Chromosomes align at centr 2 of s plate or equatorial plate, Bincle making a metaphasic chr romosome 3. No nuclear membrane is visible. Equatorial plate Metaphas¢ Anaphase : 1. Two chromatids of each pair soy Parate from 2. Daughter chromosomes behave as they ine ao ae 3. Cell shape changes as the cytoplasmic division Sane s.ie , JeSH Practical Manual in Biology-XIl ‘4, Number of countable fragments become double. 5, Daughter chromosomes year as V, ay Telophase : 2. Formation of nuclear membrane has started so It Is reverse of prophase. Nucleoli reappears. ‘Chromosomes start uncolling. Cytokinesis takes place. ‘Acell plate is formed between two daughter cells. ogee stages of mitosis observed are 4. Karyokinesis 2. Cytokinesis. 1. Cell morphology 2. Nuclear morphology 3, Chromosomes/Chromatids Precautions : 4. Root tips should be fixed in mornit 2. Slide should only be warmed gently 4, Careiully entity the stages of mitosis. ‘Two sets of chromosomes have reached opposite poles: ing between 8 to 1 a.m. much above the flame care should be t Colt wall Plasma membrane. separating chromatids ‘Anaphase Now cell wall oll wal ell membrane Chromatin Nuclear membrane reappears! ‘Telophase Fig. 7.1. Various stages of mitosis. erence) aken not to boil the stain.