The word that means "the smallest part of an organism that can survive by itself" is CELL.
CELL is the word that means "the smallest part of an organism that can survive by itself."
The word that means "a special quality or feature of something" is CHARACTERISTIC.
CHARACTERISTIC is the word that means "a special quality or feature of something."
EXTERNAL is the word that means "outside."
The word that means "outside" is EXTERNAL.
The word that means "to sort things into groups" is CLASSIFY.
CLASSIFY is the word that means "to sort things into groups."
The word that means "an organism that has a backbone" is VERTEBRATE.
VERTEBRATE is the word that means "an organism that has a backbone."