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 cells that combine are called sex cells Female â egg Male â sperm Fertilization: an egg cell and a sperm cell join together A new cell is formed and is called a zygote. Sexual Reproduction. A type of reproduction in which the genetic materials from two different cells combine, producing an offspring. The cells that combine are called. sex cells. Female. â egg. Male. â sperm. Fertilization. : an egg cell and a sperm cell join together.