Biology [3 marks Question Answer]

(i) A - Duplicated chromosomes
B - Centromere
(ii) The structure C is Spindle fibre. Its function is to help in the movement of chromosomes.
(iii) The type of cell division is mitosis because all chromosomes appear to be same as there is no crossing over.
(iv) Metaphase.
(v) Prophase occurs before metaphase and after metaphase anaphase takes place.

(i) Anaphase in a plant cell
(ii) A - Spindle fibre
B - Cell wall
(iii) The homologous daughter chromatids or chromosomes begin to move towards opposite poles.
(iv) This type of cell division occurs usually in the somatic cells.
(v) Two daughter cells are formed from this type of cell division.
(vi) The dividing cell shown is a plant cell because of the presence of cell wall and the absence of centriole.

(i) If four cells undergo mitosis, eight daughter cells will be produced.
(ii) Sixteen daughter cells will be produced.
(iii) Eight daughter cells will be produced if four cells undergo amitosis.

Mitosis is important because:
(i) It helps in the growth of tissues, organs and thus the entire organism.
(ii) It helps in the repair of damaged tissues and organs.
(iii) It is the method by which lower organisms reproduce.
(iv) It helps in the maintenance of the hereditary characters by the replication of chromosomes.

In an animal cell, the cytoplasm between the two daughter nuclei constricts i.e. a furrow starts forming in the plasma membrane at the middle. This deepens towards the interior of the cell and the cytoplasm splits into two similar daughter cells.
In plant cells on the other hand, the constriction is not observed during cytokinesis. Instead a new cell wall is laid down along the equatorial region of the spindle network beginning at the centre. Thus, two distinct, daughter cells are cut off.

Significance of Meiosis:
(i) Due to meiosis, chromosome number is reduced to half in gametes and chromosome number of species is maintained.
(ii) Genetic variations occur due to meiosis.
(iii) The zygote on fertilization gets one maternal and one paternal chromosome in each homologous pair.

Few important characteristics of Meiosis are:
(i) Meiosis occurs in germ cells only.
(ii) It results in the formation of gametes.
(iii) Chromosome number of the parent cell is halved.
(iv) Daughter cells differ from the parent cell.

Some characteristic features of mitosis are:
(i) It takes place in somatic cells.
(ii) Chromosome number is preserved.
(iii) Daughter cells produced are identical to the parent cell.
(iv) It results in increase in the number of cells.