a. As energy for life processes.
b. For growth and repair of body tissues.
6-2. THE ENERGY CYCLE
The body requires that all of its energy be brought into it from external sources.
a. Solar Radiation. The ultimate source of all energy for living things on Earth
is the Sun. This energy reaches the Earth in the form of solar radiation.
b. Photosynthesis. This radiant energy is stored by plants as the chemical
bonds of glucose molecules. The process for doing this is called photosynthesis.
PHOTO = light
SYNTHESIS = put together
This takes place in the presence of the green substance called chlorophyll.
6CO2 + 6H2O + E ---→ C6H12O6 + 6O2
Carbon Dioxide + Water + Energy YIELDS Glucose + Oxygen
c. Food Consumption. The green plants are then utilized as food by various
animals. Ultimately, either the green plants or the animals that ate the green plants are
consumed by humans.
d. Digestion and Metabolic Oxidation. Through the processes of digestion,
the glucose is released. It is then delivered to the cells of the body by the circulatory
system. Within the cells of the body, the energy is released from the glucose by the
chemical process known as metabolic oxidation:
C6H12O6 + 6O2 ---→ 6CO2 + 6H2O + E
Glucose + Oxygen YIELDS Carbon Dioxide + Water + Energy
e. Production and Use of ATP. The released energy is then used to produce
the compound known as ATP (adenosine triphosphate). This metabolic oxidation and
the production of ATP occur in the mitochondria. For this reason, the mitochondria are
known as the "powerhouses" of the cell. When energy is required for carrying on any of
the life processes, it is obtained from the ATP.
ATP ---→ ADP + P04 + E