Plants and animals depend on each other and their physical environment for survival. All organisms have basic needs: food, shelter, water, and space. Other organisms provide some of these needs and some are filled by the non-living environment.

Energy (food) is essential for all living things. There are several ways organisms obtain energy. Some organisms get energy from other organisms. That is they eat or consume plants or other animals. Still others get energy by breaking down dead or decaying organic matter. Most plants, such as grass or alfalfa, get their energy from the sun. Instead of eating other organisms, plants use the sun’s energy to convert water and carbon dioxide into sugar, which the plant then uses for energy. Other organisms, like cows, eat the plants for their energy. Still other organisms, like humans, might eat the cow for their energy. This progression of consumption is called a food chain.

In order to understand the fragile balance in an ecosystem it is important to recognize how energy flows from organism to organism. Stating with the sun, there is a transfer of energy from one organism to the next in a food chain. But not all of the energy available at one level of the chain is available to the next level; much of it is lost as heat.

To illustrate, let’s look at a typical food chain in the area. Clover (a type of plant) grows and is eaten by a rabbit. The rabbit is eaten by a hawk. The hawk dies and begins to decay. Fungi, like mushrooms, then break down this organic matter. From one level to the next, only about 10% (1/10) of the energy is made available.

To help visualize this concept even more, try this. Imagine the energy of the sun as a 1-meter length of paper. The first organism in the food chain, the clover, has 10% of the sun’s energy available. On the strip of paper, that would be 10 centimeters. The rabbit in turn, only has 10% of the clover’s energy available to it. That would be 1 centimeter. The hawk has 10% of that or about 1 millimeter. Finally, the fungi get 10% of what is left, about .1 millimeters. All of the rest is lost to the atmosphere as heat.

To review:
Sun – clover – rabbit – hawk – mushrooms
100% - 10% - 1% - 0.1% - 0.01%
1 m – 10 cm – 1cm – 1mm – 0.1mm

Vocabulary
Organism – a living thing
Consumer – an organism that gets energy by eating (consuming) other organisms
Producer – an organism that gets energy from the sun through photosynthesis
Decomposer – an organism that gets its energy by breaking down dead or decaying organic matter
Photosynthesis - the process by which many plants use sunlight to produce energy. Sunlight, carbon dioxide, and water combine with chlorophyll to produce sugar.
Food Chain – a model of how food (energy) passes from organism to organism in an ecosystem
Ecosystem – a community of all living things in an area and their interactions with each other and the non-living environment
Organic – anything that may have once been living or is derived from an organism

Review
1. How much of the Sun’s energy is available to the producer?
2. Which organism received the least energy? Which received the most?

Think about it
1. How much of the sun’s available energy was lost as heat?
2. Since there is so little energy available from one level to the next, how might that impact on the number of organisms at each level?