I'm not sure what context you are asking the question in. However, passive transport occurs when an item needs a vehicle to be transported from one area to another or when an item requires an external agency to move it and the item does nothing on it's own to move. I hope this helps.

Actually... what you just described is active transport and not passive transport.

Passive transport are the processes where substances do not need energy to be transported. Examples include diffusion and osmosis.

My apologies! You are quite right, I had the two completely mixed up. Thanks for correcting me, perhaps I'm a little dyslexic in the brain these days, too much time in front of the computer!

It's okay, it happens to me too sometimes :)