Answer:
This means that some cells are able to letter molecules pass through them and this makes it easier for the molecules to pass through.
It is a cold Artic air mass over Siberia. Air masses are altered because it doesn't stay in one place and changes as it moves due to the temperature of environment that can be caused by moisture. The cold Artic Mass from Siberia will go to the North Pole, Canada then moves further to the South area.
