Part A shows a photo of a freshwater fish and states that many invertebrates and aquatic species excrete ammonia. The chemical structure of ammonia is NH3. Part B shows a photo of a wood rat and states that mammals, many adult amphibians, and some marine species excrete urea. The chemical structure of urea is shown. Urea has two NH2 groups attached to a central carbon. An oxygen is also double-bonded to this central carbon. Part C shows a photo of a pigeon and states that insects, land snails, birds, and many reptiles excrete uric acid. The chemical structure of uric acid is shown. Uric acid has a six-membered carbon ring attached to a five-membered ring. Each ring has two NH groups embedded in it. An oxygen is double-bonded to each ring.
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