Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle.
Neptune's atmosphere, like Jupiter's and Saturn's, is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen; it contains a higher proportion of ices such as water, ammonia, and methane.
Right, referring to Uranus and Neptune as gas giants has really fallen out of favor in the scientific community, since they really are something different. The term ice giant is used almost exclusively now - since, by mass, they are made of mostly ice (or ice-like stuff) - and not as a subcategory of gas giants. With that said, it's currently believed that beneath the weather layer, both Uranus and Neptune have a very deep, slushy ocean of ionic water and ammonia.