CBSE Class 11-science Answered

describe amitosis,mitosis.meiosis and their significance briefly(long question carring 8 marks)

Asked by hrushikesh.barik | 21 Feb, 2018, 09:03: PM

Expert Answer

Mitosis

Mitosis is the division of the parent cell into two identical daughter cells, each with a nucleus which has the same amount of DNA, same number and kind of chromosomes and same hereditary information as in the parent cell. Hence, mitosis is regarded as equational division.
It occurs in the somatic cells and gonads of animals. In plants, it takes place in the meristematic tissues and during the growth of leaves, flowers and fruits.
There are two main events in mitosis—karyokinesis or duplication of the nucleus, followed by cytokinesis or division of the cytoplasm
Karyokinesis is divided into four stages—prophase, metaphase, anaphase and telophase
Karyokinesis results in the formation of two nuclei inside a cell. It is followed by the division of the cytoplasm or cytokinesis to form two daughter cells, each with one nucleus

Significance of Mitosis

1. Maintenance of cell size

2. Maintain equal chromosome number

3. It provides new cells to replace the old worn out and dead cells.

4. Plays an important role in multiplication and sexual and asexual reproduction.

Meiosis

Meiosis is a reductional division which occurs only in diploid cells for the formation of haploid cells in which the number of chromosomes and the nuclear DNA content are reduced to half and there is a recombination of hereditary material.

Meiosis takes place only in certain types of cells and occurs only at a particular time.
Sexually reproducing organisms undergo meiosis and some special cells in multicellular organisms undergo meiosis instead of mitosis at a specific time in the life cycle

The two divisions of meiosis are called the first and second meiotic divisions or meiosis-I and meiosis-II.

Meiosis I consists of four stages—prophase-I, metaphase-I, anaphase-I, and telophase-I.

Meiosis-II consists of four stages—prophase-II, metaphase-II, anaphase-II and telophase-II.

Significance of Meiosis

1.Meiosis produces gametes for sexual reproduction in plants and animals.

2.The chromosome number of the gametes reduces to half through meiosis so that fertilization may restore the original diploid chromosome number in the zygote.

3. Abnormal meiotic divisions may result in chromosomal mutations, some of which may be advantageous for the organism

Amitosis

Amitosis is the cell division by cleavage of the nucleus and division of the cytoplasm without spindle formation or chromosomes.

Answered by Sivanand Patnaik | 22 Feb, 2018, 09:46: AM