This is why growing plants in space will be so important. Plants can serve many uses on a long space journey. They are a renewable food source. Astronauts will welcome the addition of fresh fruits and vegetables to their diet of dry foods. Also, because plants use carbon dioxide and produce oxygen, they can help improve air quality. Currently all oxygen is taken aboard in tanks and then caught again so it can be reused. Plants can help extend the capabilities of the air inside the spacecraft—the only air that the astronauts can breathe.