Sunday, September 8, 2013

Reproduction

A cell does not go on growing indefinitely in size but at a certain optimum point divides into two daughter cells. Further, certain cells will undergo division to replace worn-out cells or those destroyed by disease. This kind of cell division is called mitosis or karyokinesis.

Activity begins in the nucleus. The nuclear membrane disappears and the chromatin changes character and becomes long filaments called chromosomes.

The centrosome divides and the two new centrosomes move away from each other to each end of the nucleus called the poles.

The chromosomes are then attracted to the poles and lie near the new centrosomes. The chromatin of which nucleus is formed now comes to rest and two new nuclei exist. Finally the protoplasm of the cell constricts and divides and the two new cells are complete.
Each new daughter cell resulting from mitosis contains forty six chromosomes, so that during mitosis each chromosome must duplicate itself. The process of chromosomal duplication is one of the least understood of the cell’s activities.

However, mitosis is not the only kind of cell division. In the sex organs, the ovary and testis, another kind of cell division occurs called meiosis. During the formation of the sex cells, or gametes, the number of chromosomes is halved, so that the spermatozoon contains only twenty-three chromosomes and the egg-cell or ovum, twenty three.

When fertilization occurs, that is when spermatozoon and ovum fuse to form the cell (zygote) which develops into a new individual the normal chromosomal complement of forty six is restored. By this means a mixing of the hereditary determinants or genes, from male and female is achieved.

Friday, August 23, 2013

Abou ben Adhem (Summary)


James Henry Leigh Hunt
This poem has been written by James Henry Leigh Hunt. In this poem the poet says that Abou ben Adhem was a pious man. He was the leader of his tribe. He was very kind and gentle to his people. One night he woke up from a sound sleep. As he woke up, he found straight light in his room. An angel was writing some thing in a golden book. Abou picked up courage and asked the angel what he was writing. The angel replied that he was writing the names of those persons who loved God. Abou asked him if his name was there. The angel replied in negative. Abou did not loose heart and asked the angel to write his name as a person who loved his fellow men. The angel did so and went away. Next night the angel came again and showed Abou the names of those person whom God had blessed. Abou was very much surprised and overjoyed to see his name at the top of the list.
Abou ben Adhem and the Angel

Lines from the Lay of the Last Minstrel (Summary)


Walter Scott
In this poem the poet Sir Walter Scott says that the man who has no love for his country is quite worthless. If he does not feel an excitement as he comes back from a foreign country, he is dull fellow. No body loves such a man and no singer sings in his honor though he has a lot of wealth and holds a high office. He is a selfish mean fellow, and always thinks about his interest only. He will be completely forgotten after his death and will be totally ignored in poetry and songs.
The Lay of the Last Minstrel