CBSE Class 9 Answered

Nucleus is the most prominent and important structure in a cell. It acts as the control centre of the cell because of the following reasons:

• It regulates cell functions.
• It regulates the cell cycle.
• It contains chromosomes, made of genes, which control hereditary characteristics.
• The cell dies in the absence of nucleus.

Centrosome present in animal cells forms the aster of a spindle.

• It contains one or two centrioles.
• Centrioles are surrounded by radiating microtubules to form an aster.
• Centrosome initiates and regulates cell division.
• It forms spindle fibres with the help of asters.