Write the functions of the following:
$(a)$ Centromere
$(b)$ Cell wall
$(c)$ Smooth $ER$
$(d)$ Golgi apparatus
$(e)$ Centrioles

(N/A) Centromere: It is the site where two sister chromatids are held together. During cell division,it serves as the attachment site for spindle fibers via the kinetochore.
$(b)$ Cell wall: It provides a definite shape to the cell,protects it from mechanical injury and infection,facilitates cell-to-cell interaction,and acts as a barrier to undesirable macromolecules.
$(c)$ Smooth $ER$: It is the major site for lipid synthesis,carbohydrate metabolism,and the storage of $Ca^{++}$ ions. It also plays a crucial role in the detoxification of drugs and poisons.
$(d)$ Golgi apparatus: It is involved in the packaging of materials to be delivered to the intracellular targets or secreted outside the cell. It is the site for the formation of glycoproteins and glycolipids.
$(e)$ Centrioles: They form the basal body of cilia or flagella and facilitate spindle fiber formation during cell division in animal cells.