CLEAN > Teaching Climate Literacy > Teaching Energy > 3. Energy in Biological Processes

Energy Principle 3. Biological processes depend on energy flow through the Earth system.

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Teaching this principle is supported by six key concepts:






What does this principle mean?

This principle addresses the flow of energy through life on Earth. The Sun is the primary source of energy for nearly all biological systems. Sunlight allows plants, algae and cyanobacteria to use photosynthesis to convert carbon dioxide and water into organic compounds like carbohydrates. This process is the fundamental source of organic material in the biosphere. There are a few exceptions to this, such as ecosystems living around hydrothermal vents on the ocean floor, which derive their energy from the chemical compounds such as methane and hydrogen sulfide.

This principle also illustrates the role of energy in food webs. Plants use energy from the Sun to create organic matter. Plants are then eaten by primary consumers who are in turn eaten by secondary consumers, and so on. In each step, the energy that was originally emitted by the Sun is consumed, but energy also dissipates with each step. Animals use up 90% of the energy contained in the foods they eat for their normal activities. This leaves just 10% of the original energy available for the next consumer. These concepts illustrate several important points, such as that the overall productivity of an ecosystem is controlled by the total energy available, and that the efficiency of the food chain decreases as you go upward. It is most efficient to eat at the bottom of the food chain; this has implications for humans as we strive to keep a growing human population adequately nourished.

Why is this principle important?

This principle is important in two ways. First, it illustrates how energy flows from the Sun to nearly all living things and describes how energy moves through a food web or ecosystem. Second, it points out a critical factor in the distribution of energy in foods. Eating producers (plants) is most energy efficient. This same basic principle of energy apply to our food system too; eating at the bottom of the food chain is still the most efficient way for humans to acquire energy for living. The continual input of energy, mostly from sunlight, sustains the process of life.

This principle also introduces the origin of organic matter that later can become fossil fuels and biofuels. These ideas are further explored in Energy Principle 4.

What makes this principle challenging to teach?

While many students can readily identify with the idea of the terrestrial food web, the marine food web may be less familiar to them. Students may be surprised to learn that about half the Earth's primary productivity of organic material comes from the oceans.

Strategies for teaching this principle


Related teaching materials

Teaching about Food with teaching materials for college students

Fisheries Unit from EarthLabs

In middle school and high school, food webs are commonly taught with concept maps, such as this example Oceanic Food Web. The video The Ocean's Green Machines further explores the marine food web by examining phytoplankton These organisms form the base of the marine food web, are the source of half of the oxygen on Earth, and are an important means to remove CO2 from the atmosphere. This video is suitable for a middle school or high school audience.

How Cheeseburgers Impact the Oceans asks students to calculate the carbon emissions of cheeseburger production (middle school).

How Much Energy is on my Plate? leads students through a sequence of activities that highlight the embodied energy that is necessary to produce various types of food (high school or introductory-level college).


College students can delve deeper into the concepts of energy in biological systems. Possible pathways include:

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