Cell Organelles: Nucleus - Cell Biology | Science Grade XI

Science Notes

Cell Organelles: Nucleus, Cell Biology


It is an important cell organelle, which controls all the activities of the cell. It also carries the hereditary information of the cell. Its structure is spherical or oval. It is present one or more in number in a cell.

The nucleus is doubling membraned. The outer membrane is rough and inner membrane is smooth. The nuclear membrane is porous and selective permeable. The pores help in the exchange of substance between cytoplasm and nucleoplasm.

The nucleoplasm is semi liquids bounded by nuclear membrane within nucleoplasm DNA RNA enzymes are found. In nucleoplasm there is round structure of ribonucleoprotein, which is called nucleolus. Nucleolus forms ribosomes. In nucleoplasm there is net like structures of fine thread, which is called chromatin network or simply called as chromatin. During cell division, this network gives fine separate thread like structures called chromosome.

There are two types of chromatin: 



  • Densely packed region of chromatin.
  • It remains tightly coiled and they are condensed during interphase.
  • Deeply stained.
  • It possesses large amount of RNA and less amount of DNA.
  • Due to small amount of DNA present they are genetically inactive
  • Loosely packed region of chromatin.
  • It remains loosely coiled and diffused during interphase.
  • Loosely stained.
  • It possesses large amount of DNA and less amount of RNA.
  • Euchromatin is genetically active.

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