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 sperm cell is the male sex cell. All animals (and many other types of organisms) produce what are called sex cells. Sex cells are the cells, that when combined, produce a completely new organism. For example, your mother and every other human female, carry egg cells (female sex cells) in their ovaries. Your father and every other human male carry sperm cells, or male sex cells, in their testes. When an egg cell and a sperm cell unite, the two combine to form an embryo or an unborn, developing organism. At this point, the embryo is able to develop into a fully formed offspring of its parents.