Explain why and how theories may be changed or replaced over time.

If new information, evidence or data is obtained that contradicts some part or all of the scientific theory then it would be need to be changed/revised or replaced all together. 

Theories may be changed over time as new information is discovered or new technologies are developed. New developments lead to changes in experimental methods, which provide information that may or may not support the existing theory. If the theory is still supported, it may be updated. If it is not supported, but the results are true and relevant, the theory may be replaced.

Fitness is the ability to perform only very light levels of physical activity.

Answer form flower;