PDD Practice Exam Form 1 Question 12 - Sun Space vs. Isolated Gain

An architect is designing a passive solar building. This particular design uses a nearby south-facing slope. The slope will have a specially designed collector where air will be warmed by the sun and then rise to serve as the heat for the building. Cooler air will simultaneously be pulled from a chamber below the floor, creating a convection loop.

What is this type of passive solar system called?
The correct answer is Isolated Gain.
What is the difference between sun space vs isolated gain? I googled the definitions and learned that sun space is a form of isolated gain. Can anyone help to clarify?