Rough Endoplasmic Reticulum (RER) is easily observed in the cell

Explanation:

Rough Endoplasmic Reticulum (RER) is observed in the cells that are actively involved in the protein synthesis and secretin. SER is also present in secretory cells. SER is involved in lipid synthesis.

Golgi apparatus is present in secretary cells.

Secretory granules are not formed in nucleus.