Solar
Energy
Solar energy accounts 99.9798 percent of our total
energy income. This amounts to 13 x 1023
gram-calories/year or a continuous power supply at the rate of 2.5 billion,
billion horsepower. Between .4% - 5% of solar energy is used
in photosynthesis to feed the metabolism of the biosphere.
Plants
use ± 1/6 of the energy they take up for their own metabolism—making about 5/6
available for animals and other consumers.
About 5% of this net energy is dissipated by forest and grass fires and
by man’s burning of plant products as fuel.
When
an animal or other consumer eats plant protoplasm, it
1. uses some of the substance for energy to fuel
its metabolism and some as raw materials for growth.
2. discharges
in brokendown form metabolic waste products, e.g. animals excrete urea; yeast
(anaerobic) ethyl alcohol. Other
consumers may use this waste—flied and dung.
3. passes
some ingested plant material through the body undigested.
Of
the plant protoplasm herbivores succeed in extracting only about 50% of the
calories but only 20-30% is built into protoplasm
(meat)—net efficiency 10-15%. Meat eaters do a little better—carnivores can use
about 70% of the meat for internal chemistry since there is less indigestible
matter. But only about 30% goes into
building tissue—hence net efficiency about 20%.
1000
calories stored by the algae in
The
lower on the food chain we eat the greater the number of calories
available. The longer the food chain the
greater the mass necessary to sustain large organisms.
Lamont Cole, The Ecosphere,
Scientific American, April 1958