Fish and mammals both possess specialized circulatory systems to transport oxygen and nutrients to their body tissues. However, their anatomy and circulatory pathways differ significantly to meet their distinct physiological and metabolic needs.

Compare and contrast the circulatory systems of fish and mammals.

Adipokinetic hormone (AKH) is a key signaling peptide in locusts. It is synthesized and released by neurosecretory cells in the corpora cardiaca (associated with the brain), but acts as a hormone to stimulate the mobilization of lipid reserves from distant fat body cells to fuel flight muscles during prolonged flight.

Explain how it is possible for AKH to exert its effect on fat body cells located far from the corpora cardiaca where it is released.

Sipunculid worms (peanut worms) possess a non-heme, iron-containing respiratory pigment called haemerythrin in their coelomic fluid. During periods of active burrowing, elevated levels of carbon dioxide in the coelomic fluid cause a significant decrease in the oxygen affinity of haemerythrin.

Suggest a chemical mechanism by which carbon dioxide reduces the oxygen affinity of haemerythrin.