The Energy Cycle
GSource of EnergyG
All energy on Earth comes from the sun. The fusion of hydrogen atoms into helium atoms releases a tremendous amount of energy that is thrown from the sun and some of this energy reaches the Earth. Through the process of photosynthesis, plants take advantage of this energy converting it to a form of energy that is useful to them. The plants take in 6CO2 + 6H2O and using Chlorophyll and light energy convert it to 6O2 + C6H12O6. (Oxygen and Glucose). Oxygen is the waste product created in this process.
Animals then eat these plants, or other animals that have eaten these plants, and convert the chemical energy of the glucose that they eat into mechanical energy. The mechanical energy in the bodies of animals is also called muscular energy.
Eventually these plants and animals die. After many many years the remains are transformed into things like petroleum and coal. Humans then use these to run powerplants and create electricity.
The energy that has come from the sun is ultimately transformed into a useless form. Energy can not be created or destroyed, it only changes forms. At each step in the energy cycle some energy is lost as it is turned into a form of energy that can not be destroyed. The end of the energy cycle comes when the energy is no longer in useful form.
Human Energy Conversion
Humans convert energy much the same way as a power plant. In a power plant chemical energy in the form of coal is burned this heats water that turns to steam to turn a turbine creating mechanical energy. In the human body chemical energy in the form of the glucose in our food is turned into mechanical energy in the process of movements such as running or lifting heavy objects. The muscles serve as a transducer, through muscle contraction energy is transformed from chemical to mechanical energy.
The way in which energy is taken from food in the human digestive process is quite complicated. The many vitamins that we are told we have a daily recommended dosage of all play a part. All of the nutrients we consume are converted into Andenosine Triphosphate (ATP), an energy-rich compound. This is the fuel used to fill the energy requirements of the body. ATP is created in the body as it is needed. Excess energy can be stored as fat. ATP does not require oxygen to function. This makes it possible for us to perform short bursts of movement such as sprinting. ATP is stored in very limited quantities. Only about 3 ounces of ATP are stored in body fat at any given time. This only provides enough energy to run at full speed for a few seconds. ATP must be constantly produced in the body to provide continuous energy.
Food energy is used to reform the compund ATP in the body. Enzymes control the speed at which the chemical reactions take place in the digestive process.
When a power plant burns coal there are many waste products released including CO2 and heat. Humans also create many waste products, including: CO2, heat and the ones that we leave in the toilet. Only about 40% of the energy in the foods we consume is captured and stored for use later in the bonds of ATP. (Katch, p.49) In contrast, the steam engine is only about 30% efficient.
The amount of energy a person needs varies greatly from individual to individual. While a sendentary person needs about 1800 kcal per day depending on body size, the amount of exercise a person does can quickly make a much higher level of calories necessary. The author, at 160 lbs consumes 5000 kcal per day. That is equal to 20,930,000 J/day = 2.208115*10^10 BTU/day = 269,666,044 W.
For me to eat as much energy as is believed to be contained in ANWR (6.96*10^16 BTU) I would need to live for 8635.6 years. Of course I would consume this energy in the form of food, not oil.