1. _______________ are needed by living things and are cycled back and forth on Earth. A. Limited molecules B. Organic molecules C. Finite molecules 2. The brainstem controls A. emotion and mood B. complex analysis C. heartbeat and breathing D. reflexes 3. Living things produce new individuals through the process of ________________. A. metabolism B. responsiveness C. reproduction D. organization 4.A double circulatory system is important for A. large animals B. fast metabolism C. an emergency backup 5. Fluid within capillary beds of tissues is A. lymph B. plasma C. interstitial .