Digital Art, Photo, or 3D Illustration: can you tell the difference?

There are three images below. Can you tell which one is done in Photoshop, which one is a photograph, and which one is done in a 3D program? Click "read the rest of this entry" to see the answers. 

1. 3D - XSIHeart and lung tissue by Jellyfish Pictures
2. Digital Art - PhotoshopLung Tissue by Kate T. Burnett
3. Photograph - 2006 IMI Award WinnerChild heart in situ by Helen Rudd

 It's incredible that artists can achieve similar effects using three different mediums.