Answer is:
Photosynthesis transforms light energy into chemical energy. Cellular respration releasses the carbon dioxide from food into the air.
hope this helps :)
The best way in handling in this situation is that in order for the astronaut to be able to get back to the shuttle is that he or she should take an object from his or her tool belt and to be thrown out away from the shuttle. This will allow her to weight lightly and safely return to the shuttle and would be easier for his or her to do so.
