If you want an animation of the organelle going back to the origin when placed in an incorrect spot;
1) make an copy of the organelle in the correct spot with outlining collision points, and then make it invisible.
2) Make an event; that if the organelle overlaps it's invisible counterpart while the mouse button is released, then "yay... a kid wins a gold star" .... but... if else then goto bullet point three
3) As ArcadEd suggested; record the X:Y coordinates. Also record the X:Y of where the organelle was dropped. Make a "for:next" loop stepping one: from 1 to 10 (sorry if I used the wrong terminology)
4) Subtract the origin coordinates from the the coordinates of where it is dropped. Divide the difference by ten and multiply by the step of the for/next loop.
5) Display the organelle each step
It would be a little choppy, but that number 10 could be adjusted for that.