It's the mitochondrion. It it the powerhouse of the cell and deals mainly with energy.
I think the answer is reversible. Reversible reaction is a kind of reaction which can react in both direction at the same time. And when the both side reactions get the same speed, the reaction is at a equilibrium state.
Igneous rocks are found where plates diverge, as lava rises and fills the gap between the plates. Igneous rocks also form where plates converge. The subducting plate melts as it sinks into the crust of the Earth, and the melt rises into the overriding plate forming volcanoes.
