A place where 2 geologic units meet is called contact .
hope this helps
I do think that they close to not allow too much of either water or air from entering.
the hollow tube allows water to flow easily.
https://www.bbc.co.uk/bitesize/guides/z28g7p3/revision/1
<span> Biotic components or biotic factors are any living organisms that affect another
organism. These components shape an ecosystem which includes animals that
consume organisms in question and its living food that the said organisms
consume. Biotic components include human influence. Producers, consumers and
decomposers usually comprise biotic components.</span>
<span> </span>
