[plt-scheme] is a queue data structure already existing in DrScheme?

Basically I need it to do breadth first search given a graph
, a start node and an end node. Would I convert that graph 
into a tree or would i process it as is? 

This is what I am told to do:
For example,

gt& (bfs graph 'a 'g)
returns
(a b d g)

Also I would require a queue to do branch and bound. 
Thanks