Adaptations of Gas Exchange Surfaces Crossword Puzzle

QUESTIONS LIST: counter current : fluids flowing in opposite directions, operculum : bony plate covering the gills, tracheae : rigid tubes that connect spiracles to tracheoles, chitin : polysaccharide that supports tracheae in insects, simple diffusion : gas exchange process across body surface in single-celled organisms, spiracles : pores in the exoskeleton segments that allow air to enter an insect, tracheoles : highly branched tubes where gas exchange takes place in insects, gill filament : branched structure connected to gill arch (also known as primary lamellae), secondary lamellae : structures on gill filaments where gas exchange takes place in fish