Fact 1: Vesicle transport requires energy, so it is also a form of active transport.

Fact 2: Active transport is another form of diffusion.

Given the two facts above, answer the question "What requires energy?" with the following options: 
- diffusion
 - empty space
 - Plants growth
 - nothing
 - salamanders
 - animals
 - passive transport
 - Cooking


 

 diffusion        