5. Why is mitosis called equational division?
6. Name the stage of cell cycle at which one of the following events occur
O Chromosomes are moved to spindle equator.
(1) Centromere splits and chromatids separate.
(WI) Pairing between homologous chromosomes takes place.
(iv) Crossing over between homologous chromosomes takes place.
7. Describe the following
(a) synapsis (b) bivalent (c) chiasmata
Draw a diagram to illustrate your answer.
8. How does cytokinesis in plant cells differ from that in animal cells?
9. Find examples where the four daughter cells from meiosis are equal in size and
where they are found unequal in size.
10. Distinguish anaphase of mitosis from anaphase 1 of meiosis.
11. List the main differences between mitosis and meiosis.
12. What is the significance of meiosis?
13. Discuss with your teacher about
(1) haploid insects and lower plants where cell-division occurs, and
(1) some haploid cells in higher plants where cell-division does not occur.
14. Can there be mitosis without DNA replication in 'S' phase?
15. Can there be DNA replication without cell division?
Answers
5.Why is mitosis called equational division? Mitosis is the process of cell division wherein the chromosomes replicate and get equally distributed into two daughter cells. The chromosome number in each daughter cell is equal to that in the parent cell, i.e., diploid. Hence, mitosis is known as equational division.
6.(i) Metaphase
(ii) Anaphase
(iii) Zygotene of prophase of meiosis I
(iv) Pachytene of prophase of meiosis I
7.(a) Synapsis
The pairing of homologous chromosomes is called synapsis. This occurs during the second stage of prophase I or zygotene.
(b) Bivalent
Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the zygotene stage of prophase I of meiosis.
(c) Chiasmata
Chiasmata is the site where two non sister chromatids have crossed over. It represents the site of cross-over. It is formed during the diplotene stage of prophase I of meiosis.
8.Plant and animal cells both undergo mitotic cell divisions. Their main difference is how they form the daughter cells during cytokinesis. During that stage, animal cells form furrow or cleavage that gives way to formation of daughter cells. Due to the existence of the rigid cell wall, plant cells don't form furrows.
10.Anaphase is the stage during which the centromere splits and the chromatids separate. The chromosomes move apart, toward the opposite poles. ... During anaphase I, the homologous chromosomes separate, while the chromatids remain attached at their centromeres.
11.Mitosis consists of one stage whereas meiosis consists of two stages. Mitosis produces diploid cells (46 chromosomes) whereas meiosis produces haploid cells (23 chromosomes). Mitosis produces two identical daughter cells whereas meiosis produces four genetically different daughter cells.
12.Meiosis is the process by which sexually reproducing organisms make their sex cells, sperm and eggs. During meiosis, a specialized cell called a germ cell splits to make four new sex cells, each with half the number of chromosomes as the original germ cell.
14.Mitotic cell division cannot take place without DNA replication in S phase. ... DNA duplication is important as it maintains the chromosome number in the daughter cells and hence Mitosis is an equational division. Therefore, the duplication of DNA is an essential step and without it, no mitosis can take place.
15.There can be DNA replication without cell division. During cell division, the parent cell gets divided into two daughter cells. However, if there is a repeated replication of DNA without any cell division, then this DNA will keep accumulating inside the cell.
