The most conspicuous organelle in a living cell is usually round, surrounded by lipo-protein made membrane which contains chromosomes and regulates all the activities of a cell is called nucleus.
Discovery: In 1831, Robert Brown discovered nucleus in the cell.
Position: True nucleus is formed in all eukaryotic cells.
Number: Usually, a single nucleus present in a typical cell Prokaryotic cells do not have am nucleus. Few eukaryotic cells, in matured stage do not contain nucleus, such as sieve cell. R B C of humans etc. There are a few cells which may have more than one nucleus.
Shape: The shape of nucleus depends on the shape of cell, usually they are round. Nucleus may be also, oval and disc shaped.