What grade is this for? I am not a plant biologist, but these are straight forward questions.
Hints: If you had no transportation systems in stems, than how would the plant get all of its nutrients?
Look up xylem and phloem.
Look up stomata cells in leaves, they are the control centers of what is absorbed by the leaf tissue and what is expelled. Look up all the tissues in the leaf, and look for the tissue that is on the outside of the leaf. I don’t remember these names, nor do I have the motivation to look it up for you.
Look that stuff up, use your brain a little and you shouldn’t have any problems.