Energy in Ecosystems

Energy in Ecosystems 

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All organisms need energy, and many get it from eating other organisms. Can you guess how each of the living things in this picture gets the energy it needs?

How does energy move in ecosystems?

When you see a picture of an ecosystem , it often looks quiet and peaceful. However, ecosystems are actually full of movement. Birds squawk and beat their wings, plants sway in the breeze, and insects buzz.

Each movement made by a living thing requires energy. All of life’s functions, including growth and reproduction, require energy. The main source of energy for most life on Earth is the Sun. Unlike other resources, such as water and carbon, energy does not cycle through ecosystems. Instead, energy flows in one direction, as shown in Figure 1. In most cases, energy flow begins with the Sun, and moves from one organism to another. Many organisms get energy by eating other organisms.

Sometimes organisms change energy into different forms as it moves through an ecosystem. Not all the energy an organism gets is used for life processes. Some is released to the environment as thermal energy. You might have read that energy cannot be created or destroyed, but it can change form. This idea is called the law of conservation of energy.

1. Key Concept Check How do the movements of matter and energy differ?

Energy moves in a flow, and matter moves in a cycle.

Figure 1 Matter moves in a cycle pattern, and energy moves in a flow pattern.

Producers

People who make things or products are often called producers. In a similar way, living things that make their own food are called producers. Producers make their food from materials found in their environments. Most producers are photosynthetic (foh toh sihn THEH tihk). They use the process of photosynthesis (foh toh SIHN thuh sus), which is described below. Grasses, trees, and other plants, algae and some other protists, and certain bacteria are photosynthetic. Other producers, including some bacteria, are chemosynthetic (kee moh sihn THEH tihk). They make their food using chemosynthesis (kee moh SIHN thuh sus).

Photosynthesis Recall that in the carbon cycle, carbon in the atmosphere cycles through producers such as plants, into other organisms, and then back into the atmosphere. This and other matter cycles involve photosynthesis, as shown in Figure 2. 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.

Figure 2 Most producers make their food through the process of photosynthesis.

Chemosynthesis As you read earlier, some producers make food using chemosynthesis. Chemosynthesis is the process during which producers use chemical energy in matter rather than light energy and make food. One place where chemosynthesis can occur is on the deep ocean floor. There, inorganic compounds that contain hydrogen and sulfur, along with thermal energy from Earth’s interior, flow out from cracks in the ocean floor. These cracks are called hydrothermal vents. These vents, such as the one shown in Figure 3, are home to chemosynthetic bacteria. These bacteria use the chemical energy contained in inorganic compounds in the hot water and produce food.

2. Reading Check What materials do producers use to make food during chemosynthesis?

Producers use chemical energy in inorganic compounds to make food during chemosynthesis.

NOAA

Figure 3 The producers at a hydrothermal vent make their food using chemosynthesis.

Consumers

Some consumers are shown in Figure 4. Consumers do not produce their own energy-rich food, as producers do. Instead, they get the energy they need to survive by consuming other organisms.

Consumers can be classified by the type of food that they eat. Herbivores feed on only producers. For example, a deer is an herbivore because it eats only plants. Carnivores eat other animals. They are usually predators, such as lions and wolves. Omnivores eat both producers and other consumers. A bird that eats berries and insects is an omnivore.

Another group of consumers is detritivores (dih TRI tuh vorz). They get their energy by eating the remains of other organisms. Some detritivores, such as insects, eat dead organisms. Other detritivores, such as bacteria and mushrooms, feed on dead organisms and help decompose them. For this reason, these organisms often are called decomposers. During decomposition, decomposers produce carbon dioxide that enters the atmosphere. Some of the decayed matter enters the soil. In this way, detritivores help recycle nutrients through ecosystems. They also help keep ecosystems clean. Without decomposers, dead organisms would pile up in an ecosystem.

(l to r) Digital Vision/PunchStock, SA Team/ Foto Natura/Minden Pictures, David Young-Wolff/PhotoEdit, Colin Young-Wolff/PhotoEdit, Mark Steinmetz

Figure 4 Organisms can be classified by the type of food that they eat.

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WORD ORIGIN

Ask: What words do you know that begin with photo-?

Students will likely mention the word photograph. Explain that the root -graph means “write.”

Ask: What is the meaning of photograph?

A photograph is an image created using light energy.

Ask: How does light relate to photosynthesis?

The energy from light powers the processes that create food through photosynthesis.

WORD ORIGIN

photosynthesis
from Greek photo, meaning “light”; and synthese, meaning “synthesis”

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How can you classify organisms ?

Extension

How can you classify organisms?

Prep: 10 min Class: 15 min

Purpose
To classify organisms as producers or consumers.

Materials
Student: magazine photos of ecosystems with several different organisms

Before You Begin
You will need old magazines for this lab. Ask students to bring in nature magazines from home. Students can also download photographs from the Internet. You might also need to provide magazines. Make certain the magazines provided contain many images of ecosystems with clear images of a variety of organisms. Students will be asked to note how the organisms are interacting with one another and with their environment, so the images in the magazines should clearly depict these types of scenes.

Guide the Investigation
• Provide reference materials to help students identify unfamiliar organisms.
• Help students look for clues in the photographs that indicate whether an organism is a producer, a consumer, or a decomposer. For example, is the organism a plant or an animal? Is it found on decaying organic matter? Does it have sharp teeth? Is it stalking prey?

Extension

Have each student create a chart to further classify the consumers in the photos as herbivores, carnivores, omnivores, or detritivores.

MiniLab: How can you classify organisms?

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Most organisms get their energy from the Sun or by consuming other organisms. In this lab, you will use photographs to classify organisms based on their feeding relationships.

1. Search through a magazine for photographs of ecosystems. Select a photograph that shows several different organisms.

2. In your Science Journal, identify the organisms. Include a description of their environment.

3. Describe how the organisms are interacting with one another and with their environment.

Analyze and Conclude

1. Classify the organisms as producers or consumers. Use details from the photograph to support your classification scheme.

Answers will vary, depending on students’ photographs. Producers include organisms that make their own food, such as algae, most plants, and some bacteria. Consumers include organisms that eat other organisms or break down the remains of dead organisms.

2. Key Concept  How do the producers in your photo obtain energy? How do the consumers get their energy?

Producers obtain energy by using light energy or chemical energy to make food. Consumers get their energy by consuming other organisms.

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Modeling Energy in Ecosystems

Food Chains

Visual Literacy : Figure 5

Differentiated Instruction

Teacher Demo

Modeling Energy in Ecosystems

Students might find it difficult to understand what a model is and why scientists use models.

Ask: What is a model?

A model is a description or way of showing a natural process.

Food Chains

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Have students read Food Chains and examine Figure 5. Draw another food chain on the board, using familiar organisms such as grass, a grasshopper, and a bird. Discuss the feeding relationships among the organisms. Use the questions below to assess student understanding.

Guiding Questions

What is a feeding relationship?

It is an interaction between two organisms where one organism eats the other.

Key Concept Check How does a food chain model energy flow?

Arrows in a food chain show how energy is transferred from one organism to another through a feeding relationship.

What might happen if a group of organisms that ate hawks were added to the end of the food chain in Figure 5? Explain.

The hawk-eating organisms would have to eat many hawks to survive. This is true because the amount of available energy decreases every time it is transferred from one organism in a food chain to another.

Visual Literacy: Figure 5

Because the steps in Figure 5 appear to be arranged in a circle, students might think the energy flow in the food chain is circular. Point out the arrows that indicate the transfer of energy. Explain that each arrow can be read as “energy transfers into.” Use the questions below to assess student knowledge of energy flow in a food chain.

Differentiated Instruction

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Building a Food Chain Distribute four images of organisms in a food chain, one to each of four students. Then, using their images, have the students come to the front of the class and stand in an order that correctly depicts a food chain. Initiate a discussion about the organisms in the food chain, making sure students recognize that the chain must begin with a producer.

Teacher Demo

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Humans in Food Chains Ask student groups to draw two food chains, both with a human at the top of the chain. For one chain, have students depict a human who eats meat. For the other chain, have students depict a vegetarian.

Modeling Energy in Ecosystems

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Unlike matter, energy does not cycle through ecosystems because it does not return to the Sun. Instead, energy flows through ecosystems. Organisms use some energy for life processes. In addition, organisms store some energy in their bodies as chemical energy. When consumers eat these organisms, this chemical energy moves into the bodies of consumers. However, with each transfer of energy from organism to organism, some energy changes to thermal energy. The bodies of consumers emit excess thermal energy, which then enters the environment. Scientists use models to study this flow of energy through an ecosystem. They use different models depending on how many organisms they are studying.

Food Chains

A food chain is a model that shows how energy flows in an ecosystem through feeding relationships. In a food chain, arrows show the transfer of energy. A typical food chain is shown in Figure 5. Notice that there are not many links in this food chain. That is because the amount of available energy decreases every time it is transferred from one organism to another.

1. Key Concept Check How does a food chain model energy flow?

Arrows in a food chain show how energy is transferred from one organism to another through a feeding relationship.

Figure 5 Energy moves from the Sun to a plant, a mouse, a snake, and a hawk in this food chain.

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Food Webs

Visual Literacy : Figure 6

Differentiated Instruction

Differentiated Instruction

Real - World Science

Technology Activity

Food Webs

Students might be confused by the many arrows in a food-web diagram. Simplify Figure 6 by drawing some of the individual food chains in the web. Then as you circle shared organisms, discuss ways some chains overlap. Use the questions below to assess students’ understanding.

Guiding Questions

Key Concept Check What models show the transfer of energy in an ecosystem?

The transfer of energy in an ecosystem is shown with food chains and food webs.

What kind of organism must be at the bottom of a food web? Why?

A producer must be at the bottom of a food web because energy must flow into the food web from an outside source, such as the Sun.

What advantage does a food web have over a food chain in nature?

If one organism dies out, the organisms that eat it will still have a food source.

Visual Literacy: Figure 6

Use Figure 6 and the questions below to assess student knowledge of food webs.

Ask: Is the portion of the food web shown below a complete food chain? Explain.

No, it is not a complete food chain because it has no decomposers.

Ask: Do any organisms pictured in the portion of Figure 6 below get energy from the leopard seal?

No.

Ask: If the leopard seal has no predators in a given area, do any organisms get energy from it?

Yes, decomposers get energy from the leopard seal.

Differentiated Instruction

Building a Food Web Distribute at least eight images of organisms to student groups, one per student. Have students bring their images to the front of the class and stand in an arrangement to build a food web. Invite the class to discuss the food web. Tell students to hold a long piece of string that “connects” them to other organisms in the food web.

Differentiated Instruction

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Interpreting a Food Web After a food web has been assembled, have ELL students move through the web, describing the flow of energy.

Real-World Science

Terrarium Have student groups draw a sketch to design a terrarium. Prompt them by mentioning a group of organisms they might include, such as grass, crickets, and a lizard.

Technology Activity

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Digital Photography Tell students to use a digital camera to record examples of organisms interacting in nature as part of a food web. Examples might include a bird feeding on an insect, a bee on a flower, or a human eating a meal.

Food Webs

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Imagine you have a jigsaw puzzle of a tropical rain forest. Each piece of the puzzle shows only one small part of the forest. A food chain is like one piece of an ecosystem jigsaw puzzle. It is helpful when studying certain parts of an ecosystem, but it does not show the whole picture.

In the food chain above, the mouse might also eat the seeds of several producers, such as corn, berries, or grass. The snake might eat other organisms such as frogs, crickets, lizards, or earthworms too.

The hawk hunts mice, squirrels, rabbits, and fish, as well as snakes. Scientists use a model of energy transfer called a food web to show how food chains in a community are interconnected, as shown in Figure 6. You can think of a food web as many overlapping food chains. Like in a food chain, arrows show how energy flows in a food web. Some organisms in the food web might be part of more than one food chain in that web.

1. Key Concept Check  What models show the transfer of energy in an ecosystem?

The transfer of energy in an ecosystem is shown with food chains and food webs.

Figure 6 A food web shows the complex feeding relationships among organisms in an ecosystem.

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Energy Pyramids

Visual Literacy : Figure 7

Math Activity

Careers in Science

Energy Pyramids

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Invite volunteers to discuss the foods eaten at their most recent meal. Use an energy pyramid to trace the flow of energy from the Sun to each kind of food.

Guiding Questions

What is an example of a producer in the trophic level at the bottom of the pyramid?

plants

Can carnivores occupy trophic level 1? Explain.

No, carnivores get energy by eating meat. The only available energy in trophic level 1 comes from the Sun.

Visual Literacy: Figure 7

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Point out the significance of the fading blue arrow at the side of the image, which depicts the decrease in available energy at each level.

Ask: Visual Check How does the amount of available energy change at each trophic level?

The amount of available energy decreases at each trophic level.

Ask: Which trophic level contains the fewest organisms? Why?

Trophic level 3 contains the fewest organisms because it has the least energy available.

Ask: What kind of organism is in trophic level 1?

Trophic level 1 contains producers that get energy from an outside source, usually the Sun.

Math Activity

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Transferring Energy Choose four students to represent four trophic levels. Give 100 beans to the student representing trophic level 1. Ask this student to transfer energy to trophic level 2. (Student should transfer 10 beans.) Ask the student representing trophic level 2 to transfer energy to trophic level 3. (Student should transfer 1 bean.) Ask if there is enough energy for trophic level 4.

Careers in Science

Nutritionist Nutritionists plan food programs and supervise food preparation for hospitals, nursing homes, and clinics. They help prevent and treat illness by suggesting changes in diet and by encouraging healthful eating habits. Many states require nutritionists to be licensed.

Energy Pyramids

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Food chains and food webs show how energy moves in an ecosystem. However, they do not show how the amount of energy in an ecosystem changes. Scientists use a model called an energy pyramid to show the amount of energy available in each step of a food chain, as shown in Figure 7. The steps of an energy pyramid are also called trophic (TROH fihk) levels.

Producers, such as plants, make up the trophic level at the bottom of the pyramid. Consumers that eat producers, such as squirrels, make up the next trophic level. Consumers such as hawks that eat other consumers make up the highest trophic level. Notice that less energy is available for consumers at each higher trophic level. As you read earlier, organisms use some of the energy they get from food for life processes. During life processes, some energy is changed to thermal energy and is transferred to the environment. Only about 10 percent of the energy available at one trophic level transfers on to the next trophic level.

Figure 7 An energy pyramid shows the amount of energy available at each trophic level.

Visual Check How does the amount of available energy change at each trophic level?

The amount of available energy decreases at each trophic level.

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Modeling Energy Flow Through Living Systems

Once students have responded to all three items for this activity, use the following question to assess their understanding of energy pyramids.
Ask: How did you know which organism to place into each trophic level in question 3? The trophic level at the bottom of an energy pyramid is always made up of producers, which would be the clover grass. The next trophic level is made up of consumers that eat producers, which would be the whistling swans. The highest trophic level is made up of consumers that eat other consumers—the American alligators.

In-Class Activity: Modeling Energy Flow Through Living Systems

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Some of the feeding relationships among organisms that live on the Gulf Coast of Texas are described below.
• Clover grass and algae are producers.
• Muskrats, whistling swans, hermit crabs, sea urchins, and Gulf pipefish eat clover grass.
• Muskrats, hermit crabs, sea urchins, and Gulf pipefish eat algae.
• Raccoons, bald eagles, and American alligators eat muskrats and whistling swans.
• Blue crabs and snowy egrets eat hermit crabs and sea urchins.
• Loggerhead sea turtles and catfish eat Gulf pipefish.
• Snowy egrets eat blue crabs, loggerhead sea turtles, and catfish.
• Bald eagles and American alligators eat raccoons, whistling swans, loggerhead sea turtles, and catfish.

1. Diagram five food chains in the Gulf Coast ecosystem. Remember that each food chain should begin with a producer.

All food chains should begin with either clover grass or algae. Sample food chain:
clover grass → hermit crab → blue crab → snowy egret

2. Use the food chains from question 1 to create a food web of the Gulf Coast ecosystem.

The food web should incorporate all the organisms in the five food chains. Check that the feeding relationships are correct based on the information above.

3. Create an energy pyramid using the following organisms: American alligators, clover grass, whistling swans.

The energy pyramid should have clover grass at the lowest trophic level, whistling swans at the next trophic level, and American alligators at the highest tropic level.

Math Skills: Use Percentages

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Use Percentages
The first trophic level—producers—obtains energy from the Sun. They use 90 percent of the energy for their own life processes. Only 10 percent of the energy remains to flow through the second trophic level—herbivores. Assume that each trophic level uses 90 percent of the energy it receives. Use the following steps to calculate how much energy remains to flow through the next trophic level.

First trophic level gets 100 units of energy.

First trophic level uses 90 percent = 90 units

Energy remaining for second trophic level = 10 units

Second trophic level uses 90 percent = 9 units

Energy remaining for third trophic level = 1 unit

1. Practice
If the first trophic level receives 10,000 units of energy from the Sun, how much energy is available to flow through the second trophic level?

The answer is 1,000 units.

Lesson Review

Visual Summary

Energy flows in ecosystems from producers to consumers.

Producers make their own food through the processes of photosynthesis or chemosynthesis.

Food chains and food webs model how energy moves in ecosystems.

What do you think NOW?

You first read the statements below at the beginning of the lesson.

1. The Sun is the source for all energy used by living things on Earth.

2. All living things get their energy from eating other living things.

Did you change your mind about whether you agree or disagree with the statements? Rewrite any false statements to make them true.

Lesson Assessment

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Use Vocabulary

1. Scientists use a(n) __________ to show how energy moves in an ecosystem.

food chain or food web

2. Distinguish between photosynthesis and chemosynthesis.

During photosynthesis, producers use sunlight and make food. During chemosynthesis, producers use chemical energy in matter to make food.

Understand Key Concepts

3. Which organism is a producer?

A.cow

B.dog

C.grass

D.human

4. Construct a food chain with four links to show the flow of energy through a living system.

Answers will vary. Sample answer: algae → insect → frog → snake

Study the energy pyramid shown here.

5. Which organism might you expect to find at trophic level I?

A.fox

B.frog

C.grass

D.grasshopper

6. Which best represents the flow of energy through a food chain?

A.Sun → rabbit → fox → grass

B.Sun → grass → rabbit → fox

C.fox → grass → rabbit → Sun

D.grass → rabbit → fox → Sun

7. A person who ate a salad made of lettuce, tomatoes, cheese, and ham is a(n)

A.carnivore.

B.detritivore.

C.herbivore.

D.omnivore.

Interpret Graphics

8. Assess Which trophic level has the most energy available to flow through living things?

Trophic level 1

Critical Thinking

9. Recommend A friend wants to show how energy flows in ecosystems. Which model would you recommend? Explain.

Answers will vary. Students may select either a food chain or a food web; a food web is more complete as it shows more feeding relationships.

10. Role-Play Working in a group, perform a skit about organisms living near a hydrothermal vent. Be sure to include information about how the organisms obtain energy.

Responses will vary. Accept any reasonable response.

11. Assess the usefulness of models as tools for studying ecosystems.

Models are useful for studying ecosystems because you cannot see the actual transfer of energy between organisms.

12. Study the flow of energy through the food web below. Classify each organism according to what it eats.

Herbivores: fish (small), shrimp; Carnivores: fish (medium), raccoons; Omnivores: ducks, humans

13. Diagram Algae is floating in a pond ecosystem. Stoneflies and minnows eat the algae. Sunfish and bats eat the stoneflies. Walleye eat the sunfish and minnows. Great blue heron eat the sunfish and minnows. Diagram a food web showing the flow of energy through the living systems in this ecosystem.

Algae are at the base of the food web. Arrows flow from the algae to minnows and stoneflies. Arrows flow from the minnows to walleye and great blue heron. Arrows flow from the stoneflies to sunfish and bats. Arrows flow from the sunfish to walleye and great blue heron.

Writing in Science

14. Write an argument for or against the following statement. The energy humans use in cars originally came from the Sun.

Answers should indicate that fossil fuels are derived from remains of animals that either consumed or ate animals that consumed plant material. This plant material received its energy from the Sun.

Math Skills

Use Percentages

15. The plants in level 1 of an energy pyramid obtain 30,000 units of energy from the Sun. How much energy is available to flow through the organisms in level 2? Level 3?

The plants use 90 percent of the 30,000 units, leaving 3,000 units for the organisms in level 2. These organisms use 90 percent of the 3,000 units, leaving 300 units of energy for the organisms in level 3.

Use the information below to answer questions 16 and 17.

A group of plankton, algae, and other ocean plants absorb 150,000 units of energy.

16. How much energy is available to flow through the third trophic level?

The producers use 90 percent of the 150,000 units of energy, leaving 15,000 for the second energy level. The second trophic level uses 90 percent of the 15,000, leaving 1,500 units for the third trophic level.

17. How much energy would remain to flow through a fourth trophic level?

If the third trophic level uses 90 percent of the 1,500 units of energy, there would be 150 units left for a fourth trophic level.

18. Some organisms, such as humans, are omnivores. They eat both producers and consumers. How much more energy would an omnivore get from eating the same mass of food at the first trophic level than at the second trophic level?

An omnivore would get 10 times as much energy eating the same mass of producers than organisms in the second trophic level.

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Decomposing Rabbit

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