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Energy from the Sun

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

Energy in Everyday Life

In ordinary language, people speak of “producing” or “using” energy. To produce energy typically means to convert some stored energy into a desired form. For example, the stored energy of water behind a dam is released only when the water flows downhill and drives a turbine generator (Fig. 1A). Similarly, windmills allow us to store energy when the wind is blowing (Fig. 1B).

<p>Fig 1A. This dam in Japan can store energy when the water passes and spins a turbine generator.</p><br />
<p>Fig 1B. The Kama'oa Wind Farm on the Big Island of Hawaii stores enery when the wind is blowing and converts it to electricity for future use.</p><br />

A system does not destroy energy when carrying out a process. Most often some or all of it has been transferred as heat to the surrounding environment - in the same sense that paper is not destroyed when it is written on, it still exists but is not readily available for further use. The same idea can be applied to the energy our bodies need to survive.  

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. 2).

<p>Fig 2. &nbsp; &nbsp;Limu (algae) →&nbsp; Wana (sea urchin) →&nbsp; He'e (octopus) →&nbsp; Puhi (eel) → Ulua (trevally)</p><br />

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. 3). Food webs give a more realistic picture of feeding relationships.

Consider, for example, the food chain described above. In reality, the is algae 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.

<p>Fig 3. A combination of different food chains make up a food web of a given ecosystem.</p><br />

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. 4). 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. Therefore 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. 

<p>Fig. 4. An energy pyramid shows that all energy in an ecosystem began as energy stored in plants from the sun.</p><br />

Energy in Your Food


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.
  • 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
  • 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.

NERRS: Energy from the Sun


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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.