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Class 11 Biology Chapter 10 Cell Cycles And Division
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Cell Cycles And Division
Chapter – 10
VERY SHORT ANSWER TYPE QUESTIONS
Q.1. What is cell cycle ?
Ans :- The sequence of events by which a cell duplicates its genomes, synthesises the other constituents of the cell and eventually divided into 2 daughter cells is termed cell cycle.
Q.2. Name the phases of inter phases.
Ans :- G₁ phase (Gap 1)
S phase (synthesis)
G₂ phase (gap 2)
Q.3. What is karyokinesis ?
Ans :- Nudear division of M-phase is also termed as karyokinesis.
Q.4. What is cytokinesis ?
Ans :- Division of cyto plasm is also termed as cytokinesis.
Q.5. What is M-phase ?
Ans :- It is the phase when actual cell division occurs.
Q.6. What is cell division ?
Ans :- Cell division is the process by which new cells are formed from the pre existing cells.
Q.7. Name the 2 cell division that occur in sexually reproducing organism.
Ans :- Mitosis and Meiosis.
Q.8. Why mitosis cell division is also termed as equation division ?
Ans :- The number of chromosomes remain some in both parent and daughter cells so cell division is also termed as equation division.
Q.9. Name the 1st and last phase of mitosis.
Ans :- 1st phase – Anaphase.
Last phase – Telophase.
Q.10. In which phase kinesis occurs ?
Ans :- Telophase.
Q.11. What is chiasmata ?
Ans :- Chiasmata are the ‘X’ shaped structures formed at the site of crossing over.
Q.12. What is metaphase plate ?
Ans :- The plane of alignment of the chromosomes at metaphase is termed as metaphase plate.
Q.13. What is Go (quiescent stage) phase ?
Ans :- Cells that do not divide further exit G 1 phase and enter an inactive stage called Go phase of the cycle.
Q.14. What is crossing over ?
Ans :- Crossing over is the exchange of genetic material between two homologous chromosomes.
Q.15. Name the 1st phage of mitosis.
Ans :- Prophase.
SHORT ANSWER TYPE QUESTIONS
Q.16. Why Meiosis is also known as reduction division ?
Ans :- Meiosis is also known as reduction division because the number of chromosomes get reduced to half.
Q.17. Distinguish between G₁ phase and G₂ phase.
Ans :- G₁ phase
(i) 1st substage of interphase.
(ii) Certain cell may stop dividing and enter G phase.
G₂ phase
(i) Last substage of interphase.
(ii) All cells enter into the M-phase.
Q.18. What happens in S phase of interphase ?
Ans :- During this phase DNA synthesis or replication of DNA occurs. Amount of DNA per cell doubles but there is no increase in chromosomal number even the duplication of the centriole too take place.
Q.19. Mention the characteristic events of prophase.
Ans :- (i) Chromosomal material condenses to from compact mitotic chromosomes. Chromosomes are to be composed of 2 chromatid attached together at the centromere.
(ii) Initiation of the assemble of mitotic spindle, the microtubules, the proleinaccous component of the cell cytoplasm help in the process.
Q.20. Mention the key features of metaphase.
Ans :- (i) Spindle fibres attach to kinetochores of chromosomes.
(ii) Chromosomes are moved to spindle equator and get aligned fibres to both poles.
Q.21. What is synapsis ? In which stage this process occurs.
Ans :- The process of pairing of similar chromosomes are termed as synapsis.
It occurs during the second stage of prophase I called Zygotene.
Q.22. Mention the various phases of prophase I. In which phases crossing over starts ?
Ans :- Leptotene, zygotene, pachytene, diplotene and diakinesis. During pachytene stage crossing over starts.
Q.23. What happens in Anaphase I.
Ans :- The homologous chromosome separate, while sister chromatids remain associated at their centromere remain associated at their centromere.
Q.24. Explain what happens in Diakinesis.
Ans :- (i) Terminalisation of chiasmata.
(ii) Chromosomes are fully condensed.
(iii) Meiosis spindle formation starts.
(iv) Nuclear membrane and nucleolus totally disappear.
Q.25. With the help of diagram show the Various stages of Meiosis I.
Ans :-
Q.26. What is the difference between Anaphase I and Anaphase II of Meiosis.
Ans :- In Anaphase I homologous chromosome separate, while the sister chromatid remain associated at their centro mere but in Anaphase II splitting of the centromere of each chromosome takes place.
Q.27. Mention the key events that occurs in telophase.
Ans :- Chromosome cluster at opposite spindle poles and their identify is lost as discrete elements.
Nuclear envelope assembles around the chromosome clusters.
Nucleolus, golgi complex and Er reform.
Q.28. How cytokines is takes place in.
(a) Animal cell
(b) Plant cell
Ans :- (a) In animals cell a furrow appears in the plasma membrane. The furrow gradually deepens and ultimately joins in the centre dividing the cell cytoplasm into two.
(b) In plant cells, wall formation starts in the centre of the cell and grows outward to meet the existing lateral walls.
Q.29. Draw the various stages of Mitosis.
Ans :-
Q.30. Mention the significance of mitosis.
Ans :- (i) It helps in growth by increasing the number of cell.
(ii) It helps in repairing of cell.
(iii) Mitotic division in the meristematic tissue result in continuous growth of the plant through out their life time.
Q.31. Mention the significance of Meiosis.
Ans :- (i) It helps in maintaing the number of chromosome constant among the organism (where sexual reproduction occurs) belonging to the same species.
(ii) It also bring variation which is very important for the process of evolution.
Q.32. Draw the various stages of meiosis II.
Ans :-
5 Marks :-
Q.33. Distinguish between mitosis and meiosis.
Ans :- Mitosis :-
(i) Mitosis takes place in the vegetative cell.
(ii) Mitosis division is also known as equational division as the number of chromosome remain same.
(iii) Mitosis division give rise to 2 cells.
(iv) Crossing over doesn’t take place.
Meiosis :-
(i) Meiosis takes place in the germ cells.
(ii) Meiosis is also known as reduction division as the number of chromosome reduced to half.
(iii) Meiosis division give rise to four daughter cell.
(iv) Crossing over takes place.
Q.34. Mention the various event that occurs in interphase. Give a diagram to show the various stages of interphase.
Ans :- interphase is divided into 3 phases G₁ phase here the cell is metabolically active and continuously grows but does not replicates its DNA.
S phase :- DNA synthesis, replication of DNA take place.
G₂ phase :- Proteins are synthesised in preparation for mitosis while cell grows continues some time it some cell do not divide it exit g phase and enter in an inactive 3laye G0 phase. In G0 phase cells are metabolically active but doesn’t proliferate.
Q.35. Explain in detail the various event of prophase I of meiosis division.
Ans :- Prophase I is divided into 5 subphases ie –
(i) Leptotene :- Chromosome becomes visible.
(ii) Zygotene :- Pairing of homologous chromosome takes place which is accompanied by the formation of complex structure called synaptonemal complex.
(iii) Pachytene :- Bivalent chromosomes now clearly appears as tetrad. Two chromatid of non sister chromosome meet at a point (chiasmata) where crossing over take place.
(iv) Diplotene :- Dissolution of the synaptonemal complex take place and the tendency of the recombined homologous chromosomes of the bivalent to separate from each other except at the site of crossover.
(v) Diakinesis :- (i) Terminalisation of chiasmata.
(ii) Chromosomes are fully condensed.
(iii) Meiosis spindle formation starts.
(iv) Nuclear membrane and nucleolus totally disappear.
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