Nucleus and its functions class 9th
Nucleus is the most important cell organelle which directs and controls
all its cellular activities.
It is called as ‘Headquarter of the cell’.
It was discovered by Robert Brown in 1831.
In Eukaryotes, a well-defined nucleus is present while in Prokaryotes, a
well-defined nucleus is absent.
• Prokaryotes contain a primitive nucleus.
• It has double layered covering called as nuclear membrane.
• Nuclear membrane has pores which regulate the movement of materials
in & out of the cell.
• Besides nuclear membrane, nucleus also contains nucleolus and
chromatin material and the substance filled inside the nucleus is nucleolus.
• Chromosomes or chromatin material consists of DNA which stores and
transmits hereditary information for the cell to function, grow and
Functions of Nucleus :
(a)It controls all the metabolic activities of the cell and regulates the
(b)It helps in transmission of hereditary characters from parents to
Cytoplasm was discovered by Kolliker in 1862.
It is the site of both biosynthetic and catabolic pathways.
It can be divided into two parts :
(i)Cytosol : Aqueous soluble part contains various fibrous proteins
(ii)Cell organelles : Living part of the cells having definite shape, structure and function bounded by plasma membrane.
• It is the network of membranes present in the cytoplasm.
• It was discovered by Porter, Claude and Fullam.
• These are present in all cells except prokaryotes and mammalian
• Made of tubules mainly.
• Helps in steroid, lipids and Polysaccharide synthesis.
• Ribosomes are absent.
Helps in membrane biogenesis
• Made of clstemae and vesicles.
• Helps in protein synthesis.
• Contains ribosome on its surface.
• Helps in membrane biogenesis.
Functions of ER :
(a)It is the only organelle which can move within a cell so it serves
as a channel for the transport of materials between various regions