the corals have a relationship with algae (called zooxanthellae) that live in the tissues of the corals. the coral provides protection for the algae and the algae provides the coral with the compounds they need for photosynthesis
the whole human body is a lever system, that's how muscle work. your joins are the fulcrum, your muscle contracts and hence is the effort. on the other side, whatever you're holding and the weight of your hand is the load. there are all 3 classes of lever system in your body.