Chapter 10: Cell Cycle and Cell Division

Ans: Meiosis is called reduction division because the number of chromosomes in daughter cells becomes half of the number of chromosomes in mother cells. In spite of this, meiosis enables the conservation of specific chromosome numbers of each species. In fact, if there has been no meiosis, organisms would not have been able to evolve to sexual mode of reproduction. We know that fertilization involves fusion of male and female gametes.Hence,the zygote gets the chromosome pool from two cells and the number of chromosomes in a zygote becomes double that of the gametes. To  maintain the specific no. of chromosomes  after fertilization, it is necessary that the gametes should have half the number of chromosomes compared to what it is in somatic cells.

Ans: This happens in mammalian oocytes. In female mammals, the egg formation begins while the female is still inside the womb. But meiosis gets arrested in the diplotene stage itself. This pause remains till the female attains sexual maturity. Once she enters the adolescence phase , meiosis gets resumed but this does not happen to all the oocytes. This happens in the phased manner because in each ovulation cycle; only a certain number of eggs are released by the ovary. For example; in human beings, only one egg is released roughly once in a month. The whole process continues till the cessation of reproductive capability in the female.

Ans: The difference between cytokinesis in plant cells and in animal cells are as follows:-