The endocrine, nervous, and immune systems coordinate and help maintain homeostasis in humans and other organisms.
The natural world is defined by organisms and life processes which conform to principles regarding conservation and transformation of matter and energy. Living organisms use matter and energy to build their structures and conduct their life processes, have mechanisms and behaviors to regulate their internal environments and to respond to changes in their surroundings. Knowledge about life processes can be applied to improving human health and well being.
Organisms respond to internal and external cues, which allow them to survive.