Enzymes are proteinous biochemical molecules that serve as catalyst in living systems. They speed up the rate of biochemical reactions by lowering the activation energy of the reaction they are involved in.
As this question describes, enzymes possess an active site, which the substrate binds to yield products. The enzymes make the reaction faster by reducing the activation energy of the reaction, which is the energy needed to start a reaction.
Mitochondria are made from the process called binary fission. This is the cell division utilized by the prokaryotes. It also has circular DNA that is similar in both size and structure in prokaryotic cells. Mitochondria also has its own DNA different than the DNA found in the nucleus of a cell.
Hypotonic solution is a specific type of solution in which the concentration of water molecules is high than that of solute molecules present within that solution.