Handout on Energy Flow in an Ecosystem

7 th grade Science Handout on Energy Flow in an Ecosystem What is an ecosystem? All organisms need both living and nonliving things to survive. Bees help the flowering plants reproduce. The flowers have nectar that the bees use to make honey. Flowers and bees, like all living organisms, also need nonliving things to survive, such as sunlight, air, and water. An ecosystem is all the living and nonliving things in a given area. Ecosystems come in all sizes. An entire forest can be an ecosystem. A rotting log, a pond, a desert, and ocean, and your neighborhood are all ecosystems. Biotic factors are the living things in an ecosystem. Plants, animals, fungi, bacteria, and protists are all biotic factors. Abiotic factors are the nonliving things in an ecosystem. Sunlight, water, and rocks are abiotic factors. Biotic factors and abiotic factors depend on each other. If one factor in an ecosystem is disturbed, other parts of the ecosystem are affected. During times of water shortages, or severe droughts, many fish in rivers and lakes will die. Animals that eat fish will have to find other food. This abiotic factor, lack of water, affects the biotic factors in the ecosystem, such as the fish and the other animals that feed on the fish.

How does energy move in an ecosystem? Think of an ecosystem. That ecosystem might seem peaceful. If you visit, though, you will notice that it is full of movement. Birds squawk and beat their wings. Plants sway in the breeze. Insects buzz. Animals run over leaves. An organism requires energy to move. Growth, reproduction, and other life functions require energy. Most of the energy for life on Earth comes from the Sun. Energy does not cycle through ecosystems like matter does. Energy flows in one direction. In most cases, energy flow starts with the Sun. It moves from one organism to another organism. Many organisms get energy by eating other organisms. Organisms can change energy into different forms of energy. Not all the energy an organism gets is used for life processes. Some is released into the environment as thermal energy. Energy cannot be created or destroyed. Its form can change, though. This idea is called the law of conservation of energy.

Producers Producers make things. Living things that make their own food from materials in their environments are called producers. Most of these producers use the process of photosynthesis. Some use the process of chemosynthesis. Photosynthesis is a series of chemical reactions that convert light energy, water, and carbon dioxide into the food energy molecule glucose and give off oxygen. Glucose that is made during photosynthesis is an energy rich carbohydrate. Plants, algae, and some bacteria use photosynthesis to make their food. Chemosynthesis is the process during which producers use chemical energy in matter rather than light energy and make food. Chemosynthesis can occur on the deep ocean floor. Hydrothermal vents are outlets for compounds that contain hydrogen and sulfur, as well as, thermal energy from inside Earth.

Consumers Consumers do not make their own energy-rich food. They get their energy by consuming, or eating, other organisms. Consumers can be classified by the type of food that they eat. The groups of consumers include herbivores, carnivores, omnivores, and detritivores. Herbivores eat only producers. Carnivores eat other animals. Omnivores eat both producers and other consumers. Detritivores get their energy by eating the remains of other organisms. Some detritivores, such as insects, eat dead organisms. Detritivores, such as bacteria and mushrooms, feed on and help decompose dead organisms. They are often called decomposers. Detritivores help recycle nutrients through ecosystems.

Modeling Energy in Ecosystems Organisms use some energy for life processes. Energy might also be stored in the bodies of organisms as chemical energy. When consumers eat these organisms, the chemical energy moves into the bodies of the consumers. Such a transfer of energy can be from a producer to a consumer. It can also be from one consumer to another consumer. With each transfer of energy, some energy changes to thermal energy. Scientist use models to study this flow of energy through an ecosystem. A food chain is a model that shows how energy flows in an ecosystem through feeding relationships. Imagine that you are working on a jigsaw puzzle of a prairie. The food chain is just one piece of the puzzle. It shows just one small part of the prairie. A food chain is like one piece of an ecosystem jigsaw puzzle. It can help you study parts of an ecosystem. It does not show the whole picture, though. Scientists use a food web to study these feeding relationships. A food web is a model of energy transfer that shows how food chains in a community are interconnected. A food web is many overlapping food chains. Arrows show the direction of energy flow. Food chains and food webs show how energy moves in an ecosystem. They do not show how the amount of energy in an ecosystem changes, though. An energy pyramid is a model that scientists use to show the amount of energy available in each step of a food chain. The steps of an energy pyramid are called trophic levels. As you move to a higher level in an energy pyramid, there is less energy available for consumers.

Questions

1. How does energy move within an ecosystem? ______2. How do the movements of matter and energy differ? ______3. How is the movement of energy in an ecosystem modeled? ______4. What food or carbohydrate do producers make during photosynthesis? ______5. During chemosynthesis, what do producers use to make food? ______6. To which group of consumers do most humans belong? ______7. How does the amount of energy change at each trophic level? ______