Nucleus:-

                                The nucleus is an oval-shaped membrane-bound organelle present in all eukaryotic cells. It is present both in plant and animal cells. It is large and present in the center of a cell. It is a structure that contains the cell's hereditary information and helps in controlling the growth and reproduction of the cell. It is the most integral component of the cell and contains DNA which controls the growth and function of the cell and helps in coordinating the cell activities. The nucleus here is similar to the brain in it's functions and hence known as the "Brain of the cell"

                 It was first discovered by "Robert Brown" in 1831 when he was scrutinizing the epidermis in a collection of orchids with his microscope.  He identified a small opaque spot in the cell and later he noted that this spot can be observed in the early stages of pollen formation. He then further realized that this part is an important component in the cell and named it as "Nucleus". 

Structure of Nucleus:-

                      It is a typically membrane-bound structure and the most prominent organelle in a cell. It is present in all eukaryotic cells except in few cells like mammalian cells etc. The nucleus may be round, oval, or disc-shaped depending on the type of cell. Structurally, the cell nucleus consists of the following parts. They are as follows;-

1.  Nuclear membrane
2. Nucleoplasm
3. Nucleolus
4. and chromosomes 

1.Nuclear membrane:-

•  It is a double layered membrane that surrounds the nucleus and protects it from any mechanical injuries.
•  As it encloses the nucleus, it is also called a "Nuclear envelope". 
• It helps in the entry and exit of material into the nucleus and also separates the nucleus from the other parts of the cell.
•  A liquid-filled space is present between the two layers of the membrane called the 'perinuclear space'.
• The nuclear membrane is perforated with numerous pores called "nuclear pores". 
• The "Nuclear pores" are the sites for the exchange of large molecules between the nucleus and cytoplasm.

2.Nucleoplasm:-

•  The liquid-filled matrix present in between the two layers of the membrane is called as 'nucleoplasm'.
•  It is also called the  'karyoplasm'

3.Nucleolus:-

• It is a small, spherical-shaped structure found in the nucleus of both plant and animal cells.
• It plays a vital role in the synthesis of RNA and in the formation of ribosomes.
  
• Some of the eukaryotic cells have nucleus consisting of more than 4 nucleoli.
• The nucleolus disappears when a cell undergoes cell division and again reforms after the cell is formed.

4. Chromosomes:-

• Chromosomes consist of DNA that contains hereditary information and promotes cell growth, cell development, and reproduction.
• These are self-reproducing thread-like structures packed with DNA located in the nucleus.
• When a cell is resting, ie, not dividing the chromosomes are organized into long structures called 'chromatin'.

    (for more details on this topic, refer to the chromosomes and chromatin page in the blog)

Nucleus in plant cell:-

                                  The nucleus in the plant cells can be different in different plants. The various forms of nucleus present in the plant can be given in the following way;-

• Uninucleate cell: Plant cell which contain only a single nucleus and also referred to as monokaryotic cell
• Binucleate cell: Plant cell which contains two nuclei at a time and also referred to as dikaryotic cell. For eg; paramoecium
• Multinucleate cell: Plant cell which contains more than 2 nuclei at a time and also referred as polynucleate cell. For eg; latex cells in plants, bonemarrow cells in animals
• Enucleate cell: Plant cell without a nucleus. For eg; mature sieve tubes of phloem, RBCs of mature mammals.

Functions of Nucleus:-

1. The nucleus is responsible for cell division, growth, differentiation, and protein synthesis too.
2. It helps in the exchange of DNA and RNA between the nucleus and the other parts of the cell.
3. It is the control centre of the organism as it regulates the integrity of the gene and gene expression.
4. It controls the hereditary characters of a cell organism.
5. The nucleus is the site of transcription where mRNA is produced for protein synthesis.

Robert brown

• Courtesy by google images