Question

With the help of labeled diagram give an account of the cell organelle which is generally referred as Cell brain.

Answer 1

Ans: Nucleus is the controlling centre of the cell that consists of chromosomes. Structurally it has four parts known as Nuclear envelope, Nucleoplasm, Nucleolus and Chromatin.

 

Nuclear envelope: It is covering of nucleus present around the nucleoplasm. It has two unit membranes called outer membrane and inner membrane between which a cavity called perinuclear space is present. It has pores called nuclear pores which control the exit and entry of materials into the nucleus. Outer membrane is in contact with endoplasmic reticulum. Nuclear envelope disappears during prophase and reappears during anaphase.

Nucleoplasm: It is protoplasm of nucleus. It is homogenous semisolid substance. It has glycoproteins, ribonucleoproteins, hydrolases, DNA polymerase, RNA polymerase and chromatin material.

Chromatin material: The deeply stained network like substance found in nucleoplasm is called chromatin material. It has DNA and histone proteins. During division, the chromatin transforms into thick structures called chromosomes.

Nucleolus: These are spherical, deeply stained bodies found in the nucleoplasm. These were discovered by Fontana. These are also called as Plasmosomes. Chemically these are composed of RNA, proteins and little DNA. It forms ribosomes. It is associated with chromosome at secondary constriction. It also disappears in Prophase and reappears in telophase.