Biology Class 11 NCERT Solutions: Chapter 10 Cell Cycle and Cell Division Part 2
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Q: 7. Describe the following:
(A) synapsis
(B) bivalent
(C) Chiasmata
Draw a diagram to illustrate your answer.
Answer:
(A) Synapsis
The pairing of homologous chromosomes is called synapsis. This occurs during the second stage of prophase I or Zygotene.
Q 7 a Image of Synapsis
Q 7 A Image of Synapsis
(B) Bivalent
Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the Zygotene stage of prophase I of meiosis.
Q 7 B Image of Bivalent
Q 7 B Image of Bivalent
(C) Chiasmata
Chiasmata is the site where two sister chromatids have crossed over. It represents the site of crossover. It is formed during the diplotene stage of prophase I of meiosis.
Q 7 C Image of Chiasmata
Q 7 C Image of Chiasmata
Q: 8. How does cytokinesis in plant cells differ from that in animal cells?
Answer:
| Cytokinesis in plant cells | Cytokinesis in animal cells | ||
| (i) | The division of the cytoplasm takes place by cell plate formation. | (i) | The division of the cytoplasm takes place by cleavage. |
| (ii) | Cell plate formation starts at the centre of the cell and grows outward, toward the lateral walls. | (ii) | Cleavage starts at the periphery and then moves inward, dividing the cell into two parts. |
Difference between Cytokinesis in Plant and Animal Cells
Difference between cytokinesis in plant and animal cells
Q: 9. Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.
Answer:
(A) Spermatogenesis or the formation of sperms in human beings occurs by the process of meiosis. It results in the formation of four equal-sized daughter cells.
(B) Oogenesis or the formation of ovum in human beings occurs by the process of meiosis. It results in the formation of four daughter cells which are unequal in size.
The Formation of Ovum in Human Beings
The formation of ovum in human beings
Q: 10. Distinguish anaphase of mitosis from anaphase I of meiosis.
Answer:
| Anaphase of mitosis | Anaphase I of meiosis |
| Anaphase is the stage during which the centromere splits and the chromatids separate. The chromosomes move apart, toward the opposite poles. These chromosomes are genetically identical. | During anaphase I, the homologous chromosomes separate, while the chromatids remain attached at their centromeres. Hence, in anaphase I, the chromosomes of each bivalent pair separate, while the sister chromatids remain together. |
 Q 10 1 Image of Anaphase Q 10 1 Image of Anaphase Anaphase |  Q 10 2 Image of Anaphase I Q 10 2 Image of Anaphase I Anaphase I |
Q: 11. List the main differences between mitosis and meiosis.
Answer:
| Mitosis | Meiosis | ||
| 1. | In mitotic division, a single division results in two daughter cells. | 1. | Meiotic division involves two successive divisions – meiosis I and meiosis II. These divisions result in four daughter cells. |
| 2. | Mitosis is known as equational division. This is because the daughter cells have the same diploid number of chromosomes as the parent. | 2. | Meiosis I is known as reductional division. This is because the chromosome number is reduced to half. Meiosis II is known as equational division. This is because the sister chromatids separate and the chromosome number remains the same |
| 3. | Prophase is short and does not comprise any phase. | 3. | Prophase I is very long and comprises 5 phases-leptotene, Zygotene, Pachytene, diplotene, and diakinesis. |
| 4. | There is no pairing of chromosomes, crossing-over, or Chiasmata-formation during prophase. | 4. | In the zygotene stage of prophase, the pairing of chromosomes occurs. During pachytene, the crossing-over occurs. The chiasmata are formed in the diplotene stage. |
| 5. | Synaptonemal complex is not formed. | 5. | Synaptonemal complex is formed during the zygotene stage of prophase I. |
| 6. | Anaphase involves the separation of the chromatids of each chromosome. | 6. | During anaphase I, the homologous chromosomes separate, while the chromatids remain attached at their centromeres. During anaphase II, the chromatids separate as a result of the splitting of the centromere. |
| 7. | Mitosis plays a significant role in the healing, repair, and growth of a cell. | 7. | Meiosis brings about variation and maintains the chromosome number from generation to generation. |
| 8. |  Image Shows the Structure of Mitosis Image shows the structure of mitosis | 8. |  Image Shows the Structure of Meiosis Image shows the structure of meiosis |