The Earth is always the same distance from the planet Mars. Would hope to see reliability between these two questions. Oxygen is essential for life to exist. This is not true. Anaerobic life existed on Earth for millions of years, and, in fact, at one point oxygen was actually a deadly poison to the existing anerobic life on Earth.
Gravity helps muscles stay healthy.
A very serious health concern of any extended human mission is what happens to muscle tissue after long periods of reduced gravity. As the unit progresses and the students investigate more of the physiological aspects of long-term space flight, responses will change substatially. Once a rocket has reached full speed in space, its engines can be shut off and the rocket will continue at full speed. This is a test on Newton's First Law of Motion. A very difficult concept for children to master, this law of inertia has been fairly resistant to change and is somewhat counter-intuitive to the child's experiences here on earth.