Lesson 20
Energy in the Natural World
Building directly on Lesson 17, learners connect the principles of kinetic and potential energy to all living things. Starting with the student's own body, the lesson traces the path of energy from sunlight to plants to animals to heat and ultimately out into space. Students discover that every food chain on Earth is really an energy chain, that life depends on a continuous supply of incoming solar energy, and that fossil fuels and renewable energy sources are both forms of stored or incoming sunlight.


Key Ideas
  • Every living thing needs a continuous supply of energy to keep going. Without fresh energy coming in, life stops.
  • Sunlight is kinetic energy entering Earth's system. Plants capture it through photosynthesis and store it as potential energy inside their bodies.
  • Animals get energy by eating plants, either directly or through food chains. Every food chain on Earth traces back to a plant, and every plant traces back to the sun.
  • When animals digest food, they release stored potential energy as kinetic energy that powers muscles, nerves, the brain, and every body process.
  • Used energy becomes low-level heat. Heat flows toward cooler places, eventually leaving Earth into outer space. Life cannot recycle this energy, which is why it depends on fresh sunlight every day.
  • Fossil fuels are stored solar energy from ancient plants and animals buried in the Earth millions of years ago. Burning them releases that ancient potential energy.
  • Renewable energy sources such as solar cells, wind turbines, and water-powered generators are all different ways of capturing the same solar energy that is arriving today.


Vocabulary
  • Photosynthesis: The process by which plants use sunlight, water, and carbon dioxide to build their bodies and store energy as chemical potential energy.
  • Food Chain: The path that energy follows as it moves from plants to the animals that eat them and then to other animals further up the chain.
  • Fossil Fuels: Coal, oil, and natural gas. These formed from ancient biological material buried in the Earth for millions of years. They hold potential energy originally captured from the sun.
  • Renewable Energy: Energy from sources that are constantly replenished by the sun: solar cells, wind turbines, and hydroelectric generators.


Hands-On Activity: Trace Your Lunch to the Sun

Supply List
  • Paper and pencil or colored markers
  • The student's actual lunch, a photo of it, or a written list of what they ate
  • Optional: index cards for building a physical food chain


Instructions
  • Write down or draw everything you had for one meal today. This is your starting point.
  • For each food item, ask: did this come from a plant or an animal? Write it down.
  • For any animal-based food, ask: what did that animal eat? Write that down and keep going until you reach a plant.
  • For every plant in your chain, ask: where did the plant get its energy? The answer is always the sun.
  • Draw arrows connecting each step: food item to source to source, all the way back to the sun. Label each arrow with either kinetic or potential to show what form the energy is in at each step.
  • Discuss: how many steps did it take to get from the sun to your plate? Which food had the shortest chain? Which had the longest?
  • Extension: look up what a typical food calorie represents in joules. Discuss what that unit measures and connect it back to the idea of stored potential energy in food.

Sources
L19 Energy in the Natural World by Selene
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