The ribosomes are ribonucleo protein particles measuring 170−230A in diameter and are not bound by any unit membrane. These are the site of protein synthesis. The r-RNA for ribosomes are synthesized by nucleolus. Mitochondria is double layered membrane bound cell organelle. The outer membrane is smooth while the inner membrane folded in matrix to form cristae. Nucleus (control centre of cell) has double layered nuclear membrane which has nuclear pores for the communication between nucleoplasm and cytoplasm. Golgi complex is made up of stack of flat sac-like structures called cisternae, vesicles and tubules.