chapter 1 Manned and Unmanned Missions -- chapter 2 Manned Space Flights -- chapter 3 Space: An Extreme Environment -- chapter 4 Gravity and Weightlessness 26 / chapter 5 7 The First American Tests -- chapter 6 The Skeletal System and Weightlessness -- chapter 7 The Muscular System -- chapter 8 The Vestibular Apparatus and Balance System -- chapter 9 The Other Effects of Weightlessness -- chapter 10 Space Cell Biology -- chapter 11 The Effects of Gravity and Weightlessness on Plants -- chapter 12 Developmental Biology -- chapter 13 Cosmic Radiation -- chapter 14 Extraterrestrial Life.