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.
A Sertoli cell (a kind of sustentacular cell) is a nurse cell of the testicles that is part of a seminiferous tubule and helps in the process of spermatogenesis; that is, the production of sperm.unctions [edit]. Because its main function is to nourish the developing sperm cells through the stages of spermatogenesis, the Sertoli cell has also been called the mother or nurse cell. Sertoli cells also act as phagocytes, consuming the residual cytoplasm during spermatogenesis.