Energy Flow Characterizes Systems

Many elements are required for proper growth and development of living beings.

These materials require energy to flow between living and non-living systems in a cyclic manner that are called biogeochemical cycles.

These biogeochemical cycles include:

Sedimentary cycles: elements found in rocks and soil, like the phosphorus cycle and the sulfur cycle.
Gaseous cycles: the oxygen cycle, the carbon cycle, the nitrogen cycle.
Hydrologic (water) cycle: evaporation, transpiration, cloud formation and precipitation.

Energy Drives Who Survives in Ecosystems

Energy is evident in all living and nonliving beings in an ecosystem and in the interactions between them.

Sunlight and wind are energy resources
Potential energy is present in plant and animal matter
Temperature is related to thermal energy
Moisture content in soil and air is influenced by temperature

Energy influences which types of plants and animals live in an ecosystem because of the survival requirements of each of these beings.

Food Chains

Would you like some sunshine for dinner?

The energy for almost everything you eat can be traced back to the sun through food chains.

A food chain consists of a series of beings in which the first being is eaten by a second, and the second is eaten by a third.

Nutrients and energy in a being are transferred to the being who eats it.

Most of the food we eat comes from simple food chains derived from human-controlled agricultural ecosystems.

Beef we eat comes from a cow
The cow ate corn
The corn received its energy from the sun

In some Indigenous traditions, humans are not viewed as the "apex" predator or consumer, but have the role of a being who is completely dependent on the sun, earth, plants, and animals for their survival.

Natural Food Chains

Because the primary source for all life on Earth is the sun, we begin our natural food chain with beings that "consume" the sun.

Producers

Producers are beings such as green plants that can make their own food.
Through photosynthesis, producers convert solar energy to chemical energy.
Of all the energy a plant receives from the sun, only about three percent is converted into chemical energy.
The amount of chemical energy varies depending on the plant species and the location of the plant.

Consumers

Plants are eaten by consumers, which are beings that cannot make their own food.
Herbivores are consumers that eat only producers.
Consumers that eat other consumers are called carnivores.
If an animal can get its energy by eating either producers or consumers, it is an omnivore.

Decomposers

Decomposers, such as bacteria, fungi, ants and worms, eat nonliving organic matter.
Decomposers cycle nutrients back into food chains, and the remaining potential energy in unconsumed matter is used and eventually dissipated as heat.

Energy in Food Chains

We often use an energy pyramid like the one pictured above to show the flow of energy in food chains.

The steps get smaller further up the pyramid because some of that energy is changed to a form that cannot be consumed by beings at the next higher step in the food chain.

Another reason energy obtained by one being isn’t completely passed on in the food chain is that it has already been used by the first being. For example:

A plant uses some of the energy it receives to grow and function.
An herbivore uses its energy to grow, look for food, and run away from predators.
A predator uses large amounts of energy to chase after its food in addition to its regular life processes (e.g., breathing, digesting food, moving).
The energy these beings use eventually leaves their bodies in the form of waste materials and heat.

The amount of energy that is transferred from one being to the next varies in different food chains.

Generally, about ten percent of the energy from one level of a food chain makes it to the next.

In natural ecosystems, these food chains have many alternate routes through which energy can flow, creating integrated, complex food webs.

Food Chains and the Carbon Cycle

The transfer of energy between beings also includes the transfer of matter, specifically carbon-based matter.

Unlike energy, however, carbon and other elements of matter cycle within ecosystems, being used again and again as they travel through food chains, the atmosphere, soil, and water.

Energy enables carbon to move through these different components of an ecosystem. However, it is important to note that carbon cycles within a system, and energy flows through an ecosystem.

Carbon Transfers and Human Societies

It is possible to make food/energy chains out of other fuel usages besides food. For example:

How we power our homes and run our cars are types of food chains.
The fuel sources are mainly fossil fuels, and these are burned to provide our society with energy.

Like food chains, using energy to power our homes or run our cars involves the flow of energy and the cycling of carbon.

And, as with food chains, energy is “wasted” or “lost” with each transfer.

Other waste products of energy use associated with burning fossil fuels have contributed to climate change.

What kind of food chains have you been a part of today? Send an email to keep@uwsp.edu with details on how the sun's energy got to ONE of the following:

To your body via your food
To your home via electricity or other heat/air conditioning
To your car
To any other way that you can identify