It is used in measuring the humidity in the air or in gas
Answer: They move against the concentration gradient
Explanation: This is because, with active transport, the molecules go from a low concentration to a high concentration.
A proposed explanation for a wide range of observations and experimental results that is supported by a wide range of evidence. ... Most factors are held constant in a scientific experiment because you can only change one factor in an experiment so if you notice something, you'll know what caused it.