Write the functions of the following

(a) Centromere It is required for proper chromosome segregation. The centromere consists of two sister chromatids. It is also necessary at the point chromosome attaches to the spindle apparatus during mitosis and meiosis. 

(b) Cell wall It gives a definite shape to the cell and protects the cell from mechanical injury and infections. It also helps in cell to cell interaction and act as a barrier for undesirable macromolecules. 
(c) Smooth ER It helps in synthesis of lipids, metabolism of carbohydrates, regulation of calcium concentration, drug detoxification and attachment of receptor on cell membrane proteins.
The smooth ER also contain enzymes-glucose 6 phosphatase, which converts glucose 6 phosphate to glycogen, essential in glucose metabolism. 

(d) Golgi apparatus It is the important site for the formation of glycoprotein and glycolipids. It is also involved in the synthesis of cell wall materials and also play an important role in formation of cell plate during cell division.

(e) Centrioles They form the base body of cilia and flagella and spindle fibres that gives rise to spindle apparatus during cell division in animal cells. They help in formation of microtubules and sperm tail. They also help in cell division by forming asters, which acts as spindle pole.