1 (c) Energy Pyramids
Energy Roles
An organism’s energy role is determined by how it obtains energy and how it interacts with other organisms. Each of the organisms in an ecosystem fills the energy role of producer, consumer, or decomposer.
Producers
Energy enters most ecosystems as sunlight. Some organisms, such as plants, algae, and some bacteria, capture the energy of sunlight and store it as food energy. These organisms use the sun’s energy to turn water and carbon dioxide into food molecules in a process called photosynthesis.
An organism that can make its own food is a producer. Producers are the source of all the food in an ecosystem. In a few ecosystems, producers obtain energy from a source other than sunlight. One such ecosystem is found in rocks deep beneath the ground. How is energy brought into this ecosystem? Certain bacteria in this ecosystem produce their own food using the energy in a gas, hydrogen sulfide, that is found in their environment.
Consumers
Some members of an ecosystem cannot make their own food. An organism that obtains energy by feeding on other organisms is a consumer.
Consumers are classified by what they eat. Consumers that eat only plants are herbivores. Familiar herbivores are caterpillars and deer. Consumers that eat only animals are carnivores. Lions and spiders are some examples of carnivores. Consumers that eat both plants and animals are omnivores. Crows, bears, and most humans are omnivores.
An organism’s energy role is determined by how it obtains energy and how it interacts with other organisms. Each of the organisms in an ecosystem fills the energy role of producer, consumer, or decomposer.
Producers
Energy enters most ecosystems as sunlight. Some organisms, such as plants, algae, and some bacteria, capture the energy of sunlight and store it as food energy. These organisms use the sun’s energy to turn water and carbon dioxide into food molecules in a process called photosynthesis.
An organism that can make its own food is a producer. Producers are the source of all the food in an ecosystem. In a few ecosystems, producers obtain energy from a source other than sunlight. One such ecosystem is found in rocks deep beneath the ground. How is energy brought into this ecosystem? Certain bacteria in this ecosystem produce their own food using the energy in a gas, hydrogen sulfide, that is found in their environment.
Consumers
Some members of an ecosystem cannot make their own food. An organism that obtains energy by feeding on other organisms is a consumer.
Consumers are classified by what they eat. Consumers that eat only plants are herbivores. Familiar herbivores are caterpillars and deer. Consumers that eat only animals are carnivores. Lions and spiders are some examples of carnivores. Consumers that eat both plants and animals are omnivores. Crows, bears, and most humans are omnivores.
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Decomposers
If an ecosystem had only producers and consumers, the raw materials of life would stay locked up in wastes and the bodies of dead organisms. Luckily, there are organisms in ecosystems that prevent this problem. Decomposers break down wastes and dead organisms and return the raw materials to the ecosystem.
You can think of decomposers as nature’s recyclers. While obtaining energy for their own needs, decomposers return simple molecules to the environment. These molecules can be used again by other organisms. Mushrooms and bacteria are common decomposers.
Energy Pyramids
When an organism in an ecosystem eats, it obtains energy. The organism uses some of this energy to move, grow, reproduce, and carry out other life activities. This means that only some of the energy it obtains will be available to the next organism in the food web.
A diagram called an energy pyramid shows the amount of energy that moves from one feeding level to another in a food web. You can see an energy pyramid in Figure 3. The most energy is available at the producer level of the pyramid. As you move up the pyramid, each level has less energy available than the level below. An energy pyramid gets its name from the shape of the diagram—wider at the base and narrower at the top.
If an ecosystem had only producers and consumers, the raw materials of life would stay locked up in wastes and the bodies of dead organisms. Luckily, there are organisms in ecosystems that prevent this problem. Decomposers break down wastes and dead organisms and return the raw materials to the ecosystem.
You can think of decomposers as nature’s recyclers. While obtaining energy for their own needs, decomposers return simple molecules to the environment. These molecules can be used again by other organisms. Mushrooms and bacteria are common decomposers.
Energy Pyramids
When an organism in an ecosystem eats, it obtains energy. The organism uses some of this energy to move, grow, reproduce, and carry out other life activities. This means that only some of the energy it obtains will be available to the next organism in the food web.
A diagram called an energy pyramid shows the amount of energy that moves from one feeding level to another in a food web. You can see an energy pyramid in Figure 3. The most energy is available at the producer level of the pyramid. As you move up the pyramid, each level has less energy available than the level below. An energy pyramid gets its name from the shape of the diagram—wider at the base and narrower at the top.
In general, only about 10 percent of the energy at one level of a food web is transferred to the next higher level. The other 90 percent of the energy is used for the organism’s life processes or is lost to the environment as heat. Since about 90 percent of the energy is lost at each step, there is not enough energy to support many feeding levels in an ecosystem.
The organisms at higher feeding levels of an energy pyramid do not necessarily require less energy to live than do the organisms at lower levels. Since so much energy is lost at each level, the amount of energy available at the producer level limits the number of consumers that the ecosystem is able to support. As a result, there are usually few organisms at the highest level in a food web.
When an organism in an ecosystem eats, it obtains energy. The organism uses some of this energy to move, grow, reproduce, and carry out other life activities. This means that only some of the energy it obtains will be available to the next organism in the food web. The most energy is available at the producer level of the pyramid.
Decomposers are organisms that break down large chemicals in dead organisms into small chemicals. Decomposers are “nature’s recyclers.” They return basic chemicals to the environment for other living things to reuse. For example, the leaves of many trees die in autumn and drop to the ground. Decomposing bacteria spend the next months breaking down the chemicals in the dead leaves. The broken-down chemicals mix with the soil and can then be absorbed by the roots of nearby plants.
