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Energy from the Sun

Clarification Statement: Examples of models could include diagrams and flow charts.

Table of Contents

This activity builds on the content below. For more information on plant growth, check out the content in Materials for Plant Growth.

Energy in Everyday Life

In ordinary language, people speak of “producing” or “using” energy. However, we when we say "produce energy" we actually mean to convert energy from one form into another. For example, the stored energy of water behind a dam is released when the water flows downhill and drives a turbine generator (Fig. 1A). Similarly, windmills allow us to capture energy when the wind is blowing (Fig. 1B).


Energy in Your Food


All of the energy we get from food can be traced back to the sun! Plants use energy from the sun to convert water and carbon dioxide into usable sugars, a process called photosynthesis. Those plants may then be eaten by bugs, who are eaten by animals, who are then eaten by larger animals. So, the whole process is powered by the sun!


The food we eat fuels our body to grow, heal, stay warm, and gives us energy throughout the day. In our everyday lives, we might eat a chicken that ate a caterpillar that ate a leaf that grew through photosynthesis. The labels on our food provide an ingredient list and nutrition facts to help us know what we are eating (Fig. 2).

Food Chains

Food chains are simplistic models that describe the feeding relationships among various species of organisms in an ecological community. Food chains are useful tools for understanding the trophic levels of organisms in an ecological community. Arrows are used to represent the transfer of energy from each level in a linear way (Fig. 3).


In this food chain example, the algae represent the primary producers, which are autotrophic organisms that make their own food by converting the energy from sunlight into food energy. Consumers are heterotrophic organisms that cannot produce their own food and must obtain food by eating other things. The sea urchin is a herbivore, an eater of plants or algae, and is a primary consumer in this example. Carnivores eat herbivores and other types of carnivores. The octopus is a carnivore, and because it is the first carnivore in the food chain, it is also a primary carnivore. The eel is a secondary carnivore. And finally, the ulua is the top predator in this food chain example because no other consumer eats it.

Food Webs

In a given ecosystem or community, many different food chains can be combined into a food web (Fig. 4). Food webs give a more realistic picture of feeding relationships.


Consider, for example, the food chain described above. In reality, the algae is eaten by sea urchins as well as by a variety of different species of fish and other invertebrates. In a food web diagram, many arrows can be used to point from the algae to multiple different organisms that feed on it. Likewise, other types of consumers eat sea urchins and octopus and eels. Many arrows can be drawn to account for the feeding relationships of the various organisms in the coral reef community.


This Fish Life handout was produced by the Division of Aquatic Resources and funded by the Federal Aid in Sport Fish Restoration Program. Others like this are indexed and dowloadable on this NOAA site.

The Transfer of Energy

Plants capture energy directly from the sun. All food sources can be traced back to plants. As the primary producers, plants sit at the base of the energy pyramid (Fig. 5). The different parts of the pyramid are called trophic levels. Only a fraction of energy actually gets transferred from one trophic level to the next. Most often, some energy is used to do work and some energy is lost as heat to the surrounding environment. The same idea can be applied to the energy our bodies need to survive. Each successively higher trophic level has less and less energy available. In a majority of communities, the drop in energy available at each trophic levels is reflected as a drop in the relative abundance (number of organisms) and total biomass (amount of living matter per unit area) of organisms. This is depicted by the smaller and smaller trophic levels within the pyramid. 


Conservation of Energy

Energy is conserved over time. Although some energy is lost as heat when animals digest their food, heat is also a form of energy. And, heat is an important type of energy for keeping mammals, like humans, warm. But, even when energy is lost as heat to the environment, the energy itself is not destroyed.


For example, when wood burns, most of the energy in the wood matter is converted into heat. Some of that heat will escape, and some may be captured to do work, like cooking or warming a house. And, some of the energy and matter from the wood will be left over in the form of ash (which can be added to soil and the remaining energy used by some organisms).

Energy from the Sun Vocabulary

  • Autotrophic: any organism capable of self-nourishment by using inorganic materials as a source of nutrients and using photosynthesis or chemosynthesis as a source of energy, as most plants and certain bacteria.
  • Carbon dioxide (CO2): a colorless, odorless gas made of one carbon atom and two oxygen atoms bonded together. CO2 is produced by plants and animals during cellular respiration. CO2 is also producedby burning carbon and organic compounds. CO2 is naturally present in air and is absorbed by plants during photosynthesis.
  • Carnivore: animals that feed primarily or exclusively on animal matter.
  • Consumers: an organism requiring complex organic compounds for food which it obtains by preying on other organisms or by eating particles of organic matter
  • Energy Pyramid: a graphical model of energy flow in a community.
  • Food Chain: simplistic linear models that describe the feeding relationships among various species of organisms in an ecological community.
  • Food Web: The combination of many different food chains in a given ecosystem or community that give a more realistic picture of the feeding relationships.
  • Herbivore: animals that eat only plants
  • Heterotrophic: organisms that obtain nourishment from the ingestion and breakdown of organic matter, such as plants and animals
  • Photosynthesis: the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a byproduct.
  • Predator: an organism that primarily obtains food by the killing and consuming of other organisms
  • Primary Consumer: an animal that feeds on primary producers; herbivore.
  • Primary Producers: any green plant or any of various microorganisms that can convert light energy or chemical energy into organic matter.
  • Secondary Consumer: an animal that feeds only upon herbivores; carnivore.
  • Trophic Levels: any class of organisms that occupy the same position in a food chain, as primary consumers, secondary consumers, and tertiary consumers.

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.