Maintenance of life
3.1 Internal transport : circulatory system
3.2 Obtaining and digesting of food: digestive system
3.3 Gas exchange: respiratory system
3.4 Excretory system
3.5 Chemical control: endocrine system
3.6 Nervous system and the senses organ
3.7 The control of internal environment and homeostasis
3.8 Animal locomotion