They let things in and out
" Up " or " against " a concentration gradient means from low concentration to high concentration. Moving in this direction requires some sort of en else.
This is Circulation !!
Pathway of the blood from Heart to Lungs to Heart then the whole body !!
the base would be the beginning of a thing right?
and if it is then plants would be the base
but if it's not then I'm sorry,
but if it's the thing that all the things can eat (except plants) then maybe lizards
srry if I'm wrong ;-;
<span>Post-medieval people did not take the best care of their teeth. Poor diet combined with poor hygiene practices lead to tooth decay and tooth loss. Many people of the time were wholly unaware that poor oral hygiene can lead to other health problems so taking care of them was not a priority.</span>