Mitochondria are generally known as the "powerhouses" of a cell because it uses the food within the cell to create ATP, or energy. So, if the mitochondria were damaged or prevented from working properly, that means the cell would not be able to convert food into energy as effectively or efficiently as it would if everything were working properly. This could lead to symptoms like low energy, inability to stay warm, inability to think normally, inability to digest and metabolize food efficiently, etc; basically, anything that requires any energy could be affected with damage to mitochondria