Nucleus

Nucleus, Parts and Functions

The nucleus is much denser than cytoplasm. It is a spherical or an oval body usually located in the center of the cytoplasm. In young cell, it lies in the center while in older cells, it comes to lie in the peripheral region.
The cell may be uninucleate or multinucleate. The average diameter of nucleus varies from 10µ to 15µ. It is regarded as the ‘brain’ of the cell as it is the controller and regulator of all the activities of the protoplasm. It controls all the function of the cell, and a cell without a nucleus cannot live for long and ultimately dies.

It consists of four parts:

a)    Nuclear membrane
b)    Nucleoplasm
c)    Nuclear reticulum
d)    Nucleolus

 a) Nuclear Membrane:

It is the outer layer surrounding the nucleus and separating it from the cytoplasm. It has pores and is semipermeable, through which molecules can move in and out, thus, controlling the passage of materials.

Nuclear membrane

* Nuclear membrane

b) Nucleoplasm :

Inside the nuclear membrane, there is a clear mass of protoplasm, known as the nucleoplasm, which is also called cell sap, or karyolymph. It is a clear and transparent homogeneous fluid having variable consistency. It is denser than cytoplasm and makes up the body of the nucleus.
Nucleoplasm

Nucleoplasm

c) Nuclear Reticulum:

Inside the nucleoplasm, there are numerous threads of chromatin forming a network called nuclear reticulum. These chromatin thread are made up of a substance, known as chromatin. The nature of this substance is the nucleo protein, which is a phosphorous containing protein. During nuclear division, this chromatin network becomes more clear and visible as a definite number of individual chromosomes.
Nuclear Reticulum

Nuclear Reticulum

d) Nucleolus:

In nucleoplasm, there is a spherical body called nucleolus, which is composed of RNA and protein. It participates in protein synthesis.
Nucleolus

Nucleolus

Function of Nucleus: 

  1.  The nucleus is regarded as the controlling center of vital activities of the cell like assimilation of food, respiration and reproduction, etc.
  2.  It takes direct part in reproduction. In sexual reproduction, the nucleus usually divided twice to give rise to a   group of four cells, called spores, whereas for sexual reproduction, two reproductive nuclei, called gametes, fuse together, to rise to an oospore.
  3. It takes the initiative part in cell division, i.e. it is the nucleus that divides first and is followed by the division of the cell.
  4. It is regarded as the bearer of hereditary characters. The characteristics of the parent are transmitted to the offspring through nucleus.
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