Biomass
Suppose you take a walk in the forest one day and you look around you at all the trees and think, "That's a lot of wood, I wonder how much all these trees weigh?" Biologists ask the same question. Biomass is the total mass of all the trees (after the water has been taken out).
The term "biomass" is actually applied to three related but slightly different concepts. The total dry weight of all living organisms that can be supported at each trophic level in a food chain is known as the biomass. The term is also applied to the dry weight of all living organic matter in an entire ecosystem. Finally, people interested in alternative sources of energy use the term to apply to the total mass of all plant materials and animal wastes that can be used as fuel.
Plants use a complex chemical process known as photosynthesis to combine carbon dioxide, water, and sunlight to produce carbohydrates (sugar and cellulose), fats, and proteins. The solar energy that drives photosynthesis is stored in the chemical bonds of these molecules. These carbohydrates, fats, and proteins make up biomass. Biomass, then, can be considered to be stored solar energy.
The energy stored in carbohydrates and other compounds by photosynthesis can be released by burning or by metabolism. When animals eat plants, their bodies slowly release the energy stored in the chemical bonds and this energy becomes available to the animals for muscular activity or maintaining body temperature. When biomass is burned, the water and carbon dioxide are released back into the atmosphere. Therefore, biomass is a renewable energy resource.
The total amount of biomass produced each year is about eight times the world's energy consumption. However, the energy density of each unit of biomass is much smaller than the energy content of fossil fuels ("old" biomass), so much more mass must be burned to produce the same amount of energy. Also, the world's biomass is widely distributed, so concentrating and transporting the biomass remains a problem. There are experimental projects that convert biomass into alcohol or natural gas. But worldwide, only about 7 percent of the biomass produced each year is used as fuel, so this energy resource remains underutilized.
The amount of biomass generally decreases at each higher trophic level. In a temperate grassland, for example, the amount of biomass at each trophic level is only about 10 percent of the biomass of the level below it. If there are 10,000 kilograms (22,000 pounds) of producers (grasses and other plants), there will be only 1,000 kilograms of primary consumers (grasshoppers, voles, bison), 100 kilograms of secondary consumers (shrews, hawks, small cats), and only 10 kilograms of tertiary consumers (large cats, wolves, humans).
The remaining 90 percent of the available energy from biomass at each level is converted to waste heat. This energy loss at each trophic level generally limits food chains to no more than four or five levels.
Marine environments usually reverse the amounts of biomass in the first two trophic levels. The mass of primary consumers (small fish and shrimp) is generally much larger than the mass of producers. This happens because the primary producers are tiny phytoplankton that grow and reproduce rapidly instead of large plants that grow and reproduce slowly.
American Bioenergy Association
This interest group located in Washington D.C., works to promote the use of bioenergy resources as alternative energy sources. The ABA strives to gain support through the federal government by proposing policies such as tax incentives, increased budget allocations, and research funding. The ABA argues that using biomass would cut U.S. dependence on oil from the Persian Gulf, and fuel the nation's economy.
Biomes; Food Web.
Bibliography
Curtis, Helena, and N. Sue Barnes. Biology, 5th ed. New York: Worth Publishing, 1989.
Miller, G. Tyler, Jr. Living in the Environment, 6th ed. Belmont, CA: Wadsworth Publishing Company, 1990.
Purves, William K., and Gordon H. Orians. Life: The Science of Biology. Sunderland, MA: Sinauer Associates, 1987.
This is the complete article, containing 649 words
(approx. 2 pages at 300 words per page).
