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 name sperm is taken from the Greek word sperma meaning seed. An animal sperm cell is capable of movement, as it has to get to the uterus to meet with the ovum. Animal sperm cells (including humans) have small 'head' and a long tail called a flagellum. The flagellum acts like a motor to propel the sperm cell through the female reproductive system.