How Enlightening

What is a tree made of? Where do the matter and energy in a tree come from? As you studied Earth's living systems you have certainly learned about food chains through which matter and energy move. Click here to review ideas about food chains. Early in the school years, students learn that a plant needs light and water to grow. Most students might even be able to tell you that plants take in carbon dioxide and give off oxygen, which animals then breathe. This lesson will attempt to help you understand what happens to matter and energy as they are stored in living systems. Look around you and find something made of wood. Wood is just one example of the substances that plants can produce. A tiny seed can grow to be a large tree by producing structures from wood. Most of the matter in wood, and most other materials in plants , begins as carbon dioxide in the atmosphere and water in the soil. Let's trace the flow of matter and energy in plants.

Look closely at the diagram above. Notice that sunlight strikes the chlorophyll and is captured in the leaves. The energy from the sunlight is used to create chemical bonds to hold the glucose molecules together. In this way, the sun's energy is stored as chemical energy. If the chemical bonds holding glucose together are broken, the energy will be released.

The matter to form glucose comes from carbon dioxide and the hydrogen in water. The oxygen from water is released into the atmosphere. Glucose and other molecules produced in this process called photosynthesis are used to create the structures of plants. Can you answer the question, "What is a tree made of?" If you answer sunlight, matter from carbon dioxide and hydrogen from water, you are correct! Other elements are necessary, too, but most of the solid mass and all of the energy in a plant come from these things.

What happens to energy that is stored in plants? Review the food web diagram below.

Plants capture the sun's energy and store it in chemical bonds. As animals eat the plants, both the matter and energy stored in the plant are passed on. Each time the matter and energy are passed to another organism, much is lost. If plants or animals are preserved, the energy and matter are preserved as well. Fossil fuels form when large amounts of plant (and sometimes animal) matter is preserved in Earth's rocky layers.

Essay:

Write a short essay describing the pathways for coverting and storing light energy as chemical energy. Share your essay with a parent, teacher, friend, or classmate.