[Biology] Nucleus

DISCOVERY:

• Robert Brown in 1831 was the first individual to observe nucleus.
• The discovery of nucleus was a revolutionary step which disregarded the concept of cell being an empty compartment bound by thick walls

PLACEMENT:

• In animal cell, the nucleus occupies a central position.
• In plant cell, the nucleus is pushed towards the periphery by the central vacuole.

NUCLEI PER CELL:

• Generally, cells contain a single nucleus and are termed as mono-nucleate cells.
• Cells containing two or more nuclei are termed as multi-nucleate cells.

VISIBILITY:

• Nucleus is only visible under the microscope when cell is in non-dividing stage. It contains chromatin material and soluble sap called nucleoplasm.
• In dividing cell, the nucleus disappears and the chromatin material in it is replaced by chromosomes.