However, human activities generate additional 'greenhouse gases'. Globally, atmospheric concentrations of two of the main greenhouse gases, carbon dioxide (CO2) and methane (CH4) have increased over the last 150 years. Agriculture has played a significant role in this-up to 35% of anthropogenic CH4 comes from animals and their wastes (Monteny et al. 2006).
sperm, sperm cell, spermatozoan, spermatozoon-the male reproductive cell; the male gamete; a sperm is mostly a nucleus surrounded by little other cellular material. egg cell, ovum-the female reproductive cell; the female gamete.
The Testicular Factory. Sperm are produced in the male testicle (testis). The testis is filled with tiny coiled tubes (seminiferous tubules) through which sperm move as they are produced. Each seminiferous tubule is lined with sperm nurse cells (Sertoli cells) and sperm stem cells (Spermatagonia).utside the tube and between the tubes lie testosterone-producing cells (Leydig cells), whose product is essential to regulating sperm production. Hormones produced by the Leydig cell stimulate sperm production indirectly, by acting on the nurse cells, which in turn regulate the sperm cells.