We were sitting in the Q in-line in EWR and were wondering what the 4 Yellow strakes under the tip of each wing are for on the ERJ?

Also on most jets, just happened we saw on a 757, what is the door that opens just under the captains side rear elevator, is it a back up air vent for the APU? I am pretty sure the one on the FOs side above the elevator is.

thanks ! If you got any Q400 questions Ill try to answer in return !