Help please science (7th grade)

What provides structure to the human body?

Particles vibrate in a rigid structure and do not move relative to their neighbors.

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?