A mechanical wave is a type of wave that needs a medium to propagate or transfer its energy to.
An example of a mechanical wave is a sound wave.
Sound waves are not capable of going through vacuum.
Mechanical waves travel faster through solids than liquids because they move with the oscillations of the particles they go through and solid particles are denser and have stronger bonding forces, the mechanical waves pass through quicker than liquids that have weaker bonding forces.
Complex organisms need cells that can perform many different functions. they need to be supported on a cellular level. Without specialized cells you they won't be able to perform different functions.
