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 sperm are produced inside these tubules, where they stay until they're mature. Sperm cells have their own guardians, the Sertoli cells, also known as nurse cells, which help protect and nourish the sperm until they're mature.he sperm are produced inside these tubules, where they stay until they're mature. Sperm cells have their own guardians, the Sertoli cells, also known as nurse cells, which help protect and nourish the sperm until they're mature.