All life on Earth that we know of ultimately exists because of our sun — our source of energy. The sun gives off incredible amounts of energy in the form of light that makes the transit to the earth in about 8 minutes. This light is captured by some organisms and used for their own metabolism. Those organisms are then fed upon by other organisms that cannot capture the light. Still other organisms feed on these organisms for their energy requirements. Each time another step is made in this energy transfer, 90 % of the incoming energy is lost, usually in the form of heat.
Those organisms that capture the sun’s light are referred to as producers (or autotrophs) because they produce their own food. They have evolved a process called photosynthesis (“make with light”) in which carbon dioxide and water are combined in the presence of a specific pigment called chlorophyll to produce a sugar, usually glucose, oxygen and heat.
These producers store any excess captured energy for others to use. Excess glucose is hitched to other glucose molecules and formed into starch – think of a potato. Some glucose is hitched with other glucose molecule, only backwards, which is stored as cellulose in trees, a building material called wood.
So the photosynthesis process results in a waste product called oxygen; that’s going to be critical for the next group of organisms.
The consumers (also referred to as heterotrophs), mostly animals and the fungi, take sugars, water and oxygen from the environment and rearrange them into carbon dioxide and water along with some energy and heat. The energy we harvest (you and I are consumers) is transferred to a very high energy molecule and then is sequentially used to power our muscles, our brains, etc.
There are many kinds of consumers; the herbivores that only eat plants (think of rabbits and deer), the carnivores only eat some kind of meat (think of tigers and lions) and then omnivores, which eat everything. We are omnivores since we eat plants (carrots, lettuce and wheat), we eat animals (like a steak or bacon) and we eat fungi (in the form of mushrooms and yeast) that are found in the next major group.
Traditionally, the last group are the decomposers. If there were none of these organisms on Earth, we would quickly be knee-deep in crickets and other carcasses throughout the world. The decomposers are composed primarily of the fungi (think yeast for making bread, and morels and Shiitake mushrooms) and bacteria. These critters break down the animals AND plants AND other fungi into their mineral components and make them available for the plants to start the whole cycle over again.
The diagram below might help you understand this whole process. Please remember that there are many cycles on Earth such as the carbon cycle, the water cycle and many others. But energy does not cycle. It’s a one way path to eventual decline.
About the Author
Charlie Belin is a retired professor and biological oceanographer. He taught five courses in the University of Georgia system for many years from his home base in Savannah, Georgia.
Charlie loves hiking at Reflection Riding, teaching children about the ecology of the area, and interacting with the Reflection Riding staff. They are GREAT!