In this activity (on page 142 of the PDF), learners will compare breathing rates before and after hyperventilation to explore how reduced carbon dioxide levels in the blood lower the need to breathe. This activity also includes information about how microgravity conditions in space affect sleep and breathing rates of astronauts. This activity can be enhanced by sharing the "Astronaut's Sleep" Podcast with learners (see related resource link). This resource guide includes background information and sample evaluation questions. Note: learners with respiratory ailments, such as asthma or allergies, should not participate in the breath-holding part of this activity.