One functional characteristic necessary to maintain life in humans is nutrients. Nutrients contain the chemical substances used for energy and cell building. Carbohydrates, vitamins, and minerals are found in plant-derived foods. Proteins and fats are found in animal products. Cells receive the majority of their energy from carbohydrates. Proteins are essential to build cell structures. Fats also cushion body organs, form insulating layers, and provide a reserve of energy-rich fuel. Mineral and vitamins are necessary for chemical reactions to occur in cells and for oxygen transport in the blood.

Normal body temperature is a necessity to maintain human life. When the body temperature drops below 37°C (98°F), metabolic slow down and finally stop. When body temperature is too high reactions happen at frantic rates and body proteins lose their characteristic shape and stop functioning. It is necessary that body ehat remains constant through the muscular system to avoid death.

Another functional characteristic necessary to maintain life is oxygen. Chemical reactions that release energy are oxidative reactions and require oxygen. Cells without oxygen will not survive. 20% of what humans take in is oxygen. The cooperative efforts of the respiratory and cardiovascular system make it available to the blood and body cells in the human body.

Water is also a functional characteristic needed to maintain life in humans. 60 to 80% of body weight is water. It is the single most abundant chemical substance in the body. Water provides the watery environment needed for chemicals to occur in the human body. It is also the fluid base for body secretions and excretions. Humans obtain water through ingested foods or liquids and is lost from the body by evaporation of the lungs and skin and I'm body excretions.

Survival Needs

Atmospheric pressure is the final functional characteristic needed to maintain life in humans. Atmospheric pressure is the force that air exerts on the surface of the body. Breathing depends on appropriate atmospheric pressures. When in high altitudes atmospheric pressure tends to be lower and results in thin air, which leads to inadequate support to cellular metabolism.