"a type of root vegetable"
GO GO GO YOU GOT THIS
Basically appositive phrases are phrases you can take out from these comma infested sentences and still have the sentence make sense. SO, in this case where it says , "The potato, a type of root vegetable, is high in starch" You can take out the phrase "a type of root vegetable" and still have it be a complete, comprehensible sentence = "The potato is high in starch"
HOPE YOU LEARNED SOMETHING ! :)