Answer:
Are you referring to symbiotic relationships between organism? If so, the answer would be parasitism.
One organism, a parasite, takes advantage of another organism at the expense of the host organism.
Ex. A tick bites a dog for blood to use as food. The dog gets an uncomfortable bug bite and the dog might catch a tick borne disease.
The exoskeleton of an arthropod is chitin.
Pacific Coast. As this area is in the bottom left and therefore has the highest hazard according to the key.
