Endoplasmic reticulum:

• Fist observed by Porter, Claude and Fallum (1945) under EM.

Structure:

• In young meristematic cells it form a continuous system extending from the nuclear envelope to the cell membrane and even to the cell wall.
• In old cells it may be less prominent and is represented by discontinuous vesicles.
• It occurs in the form of cisternae, tubules and vesicles.
• The morphology of the ER depends upon the physiological and development stage of a cell.
• The main components of the endomembrane system is ER with its three portions (The nuclear envelope, the RER and the SER) and the Golgi complex.
• The RER has ribosomes attached to its outer surface.  The tubular and cisternal cavities of the ER may be closed, but more often contain material that has been systhesized on the ribosomes.
• The ribosomes  are bound by their 60S (large) subunits. There are two proteins (ribophorins I and II) in RER that are absent in SER.
• The SER is devoid of ribosomes.

Microsomes are small spherical vesicles formed from disrupted endoplasmic reticulum.

Functions:

Intracellular transport of substances; Storage of glycogen. Glycosidation or synthesis of glycoprotein, glycolipids etc. Provides skeletal framework to the cell and gives rise to membrane organelles like Golgi bodies, spherosomes.