Its so that migrating fish can get by a dam that is in the way.. Usually its a dam sometimes its a different sort of barrier
Blank 1: Inner membrane of the Mitochondria
Blank 2: matrix of the mitochondria
Blank 3: their own nucleus
Blank 4: DNA
Hope this helps.
The answer is weathering.
Treat animals gently under all conditions. You don’t want to hurt them at all.
The molten material moving in the mantle due to circulation moves the lithospheric plates