(i)Middle piece in human sperm contains several mitochondria which produces energy for the motility of the sperm. (ii) Tapetum in anthers It is the innermost layer of the anther. The main function of tapetum is to provide nourishment to the developing pollen grains. (iii) Leuteinising hormones in human male stimulates the Leydig cells to produce testosterone, necessary to complete the process of spermatogenesis.