sentences: bark is a protective covering around the trunk of / branches of a tree & protecting is a kind of function ->  bark is used to protect the tree  a cell wall provides support / protection / shape / structure for a plant cell & protecting is a kind of function ->  a cell wall is used to protect a plant cell  bark is used to protect the tree & a cell wall is used to protect a plant cell -> a cell wall has a similar function to the bark of a tree