Load and Unload Texture Atlas

I want to know that when texture atlas are loaded and unloaded in Unity 2D?
I am experience 2d programmer of AndEngine in that I have way to handle manually each texture atlas. But in Unity 2D I don’t know same thing.

Basically as per my consideration new graphics are loaded when new scene is created and unloaded when scene is destroyed.

I know that it is pretty broad question but I want to know about basic working of the engine so that I can define my further work strategy.

I think you must use the Assets/Resources folder to manually control load and unload. See in the doc the special folder name “Resources” is not auto loaded at start of unity scene.