Flow of Energy in Living Systems

Flow of Energy in Living Systems

What are energy roles in an ecosystem?

An ecosystem is a community of organisms that live in a particular area, along with their nonliving environment.  An ecosystem is a living system.  

In an ecosystem, an organism’s energy role is determined by how it obtains food. Each organism fills the role of producer, consumer or decomposer.

  1. A producer is an organism that can make its own food. Most producers make their food by using the sun’s energy in the process of photosynthesis.
  2. A consumer is an organism that obtains energy by feeding on other organisms.
  3. A decomposer is an organism that obtains energy by breaking down once-living material, such as the bodies of dead organisms.

What is a food chain? 

  • A food chain is a series of events in which one organism eats another and obtains energy. The diagram below shows one food chain.
  • In most food chains, the sun is the original source of energy. Producers capture the energy in photosynthesis and make food.
  • In a food chain, energy flows from a producer to a first-level consumer to a second-level consumer.
  • Food chains can have third-level consumers and even fourth-level consumers.

What is a food web?   

  • A food web consists of many overlapping food chains in an ecosystem.
  • An organism may play more than one role in a food web. For example, a first-level consumer may also be a second-level consumer, depending on its food sources.
The diagram shows an example of a food web. The color key identifies producers, various types of consumers, and decomposers and scavengers. (Scavengers are carnivores that feed on the bodies of dead organisms.)  
A food web consists of many interconnected food chains.

What is an energy pyramid?

A diagram called an energy pyramid shows the amount of energy that moves from one feeding level to another in a food web. Energy is measured in kilocalories (kcal).
Organisms use energy to perform life functions, such as movement and growth. Only some of the energy an organism obtains will be available to the next organism in the food web.
  • The most energy is available at the producer level of the pyramid.


  • As you move up an energy pyramid, each level has less energy available than the level below.



Adapted from Pearson Educational products, online Powerpoint.  

  • Energy flows through living systems and is passed from one trophic level to another. It is then returned to the environment through cycles.
  • How does energy transfer in living systems??
  • What happens to the energy in matter that is decaying or decomposing?
  • How is energy returned to the environment through the decay of biomass?   
  • How is matter decomposed?
  • How is energy transferred through the decay of biomass? 



Watch the Video


Play – “Where is all the food?”


V isit – Interactive Art


Read the poem that another student wrote.  Write a short poem about food webs in your journal.