What is the role of temperature, density and air pressure in a convection cell?

Convection is a process which transfers the heat between the temperatures when fluid (i.e. liquid or gas) is in motion. Due to the presence of heat source, water temperature increases and also it will become less dense and rise. Hot air is less dense than cold. When air rises higher in the atmosphere its pressure gets down and it becomes colder.

heat from the core of the earth causes convection currents to occur in the mantle. these currents slowly move the crust around.