1. What gas do humans and animals exhale? Write the formula for this exhaled gas. (CO₂)
2. List two important 'sinks' (things that store carbon), two important 'sources' (things that release carbon), and one important 'release agent' (things that trigger sources) for carbon.
3. We are currently worried that CO₂ sources are out of balance with CO₂ sinks. If sources produce more CO₂ than sinks can remove, CO₂ in the atmosphere increases, possibly leading to global warming. What might happen if the reverse were true and sinks took up more CO₂ than sources? (Answers will vary but students may note that less CO₂  would be available for plant growth or that less atmospheric CO₂ might result in a slightly cooler atmosphere.)
4. Explain how understanding the carbon cycle helps atmospheric scientists understand and prepare for global climate changes.