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 gamete cells produced by males are called spermatozoa, or sperm for short (we tried to call them tozoa instead, but it never caught on). The process by which sperm are produced is called spermatogenesis. The headquarters for sperm production are the testicles or testes. Behold, sperm, the male gamete.