Biology Name: _______________________Food Webs, Biomass & Energy Date: ____________ Hour: _______

Part A: Constructing a Food Web

Producers are also known as autotrophs, and consumers are known as heterotrophs. It is important to note that not all organisms fit into a single group. Some organisms may gain matter and energy from consuming organisms in more than one trophic level. For example, bears may consume a primary consumer, such as a deer, as well as consume nuts and berries (producers). In this case, an organism that consumes both producers and consumers is called an omnivore. It is also important to note that some ecosystems are more complex, and can have additional trophic levels.

Food chains and food webs can be used as visual tools of organisms’ feeding patterns within an ecosystem. A food chain represents a single “chain” of organisms that consume each other, from producer to the primary consumer to the secondary consumer and to the tertiary consumer. A food web is much more complex, and shows all of the interactions between producers and consumers within an ecosystem. In any food chain or food web, arrows represent the movement of energy and matter from one organism to another. A food chainand a food web for organisms in a forest biome are represented below.

Scenario: In this activity you will construct a food web consisting of organisms from the chaparral or rainforest biome. Each organism in the food web contains information about its population, biomass, and energy contribution within a specific ecosystem. The chaparral biome population data was collected from San Diego, CA. The rainforest biome population data was collected from the Peruvian Amazon basin in South America. After the food web has been built, use the provided information to calculate and create a pyramid of numbers,biomass pyramid, and energy pyramid for the ecosystem.

1. Obtain a biome template, scissors, tape, and 2 sheets of scrap paper. Cut out the organism cards on the organism sheet on the dotted lines.

2. Tape the two sheets of scrap paper together to create one long sheet, and write “Rainforest Food Web” or “Chaparral Food Web” at the top of the paper depending on which organisms you have.

3. On the scrap paper, arrange the organism cards into a food web. Leave some space between each card. Your food web should consist of four levels. Producers should be at the bottom of the food web, followed by primary consumers, then secondary consumers, then tertiary consumers at the top of the food web.

4. If you are uncertain about what an organism’s food source may be, look on the back of the card for more information.

5. Once you are confident in the arrangement of your food web, place a piece of tape AT THE TOP edge of the card to hold it in place. You will need to be able to flip the card over to obtain the population, biomass, and energy information on the back for Part B.

6. Draw arrows representing the transfer of energy between organisms. The arrow should point toward the organism that will be CONSUMING it.

7. When complete, have your instructor check your food web for accuracy. It is okay if your food web looks slightly different than other students’ food webs.

8. Now highlight the outside of the different organisms accordingly.a. Green: Herbivoresb. Blue: Omnivoresc. Pink: Carnivored.

Biology Name: _______________________Food Webs, Biomass & Energy Date: ____________ Hour: _______

Part B: Modeling Energy Flow

Organisms within an ecosystem interact with one another and the environment to acquire matter and energy. One of the primary ways in which organisms interact is consuming one another. Organisms within an ecosystem are separated into groups, called trophic levels, depending on how they obtain food. These organisms may be different depending on the type of biome and ecosystem in which they live. The following chart summarizes these trophic levels, and provides an example of organisms within each level for a forest biome.

Matter and Energy Within a Food Chain and Food WebPlants or algae form the lowest level of the food web. At each link upward in a food web, only a small fraction of the matter consumed at the lower level is transferred upward, to produce growth and release of energy in cellular respiration at the higher level. Given this inefficiency, there are generally fewer organisms at higher levels of a food web. Some matter reacts to release energy for life functions, some matter is stored in newly made structures, and much is discarded. The chemical elements that make up the molecules of organisms pass through food webs and into and out of the atmosphere and soil, and they are combined and recombined in different ways. At each link in an ecosystem, some amount of matter and energy are conserved.

It is important to remember that energy cannot be created or destroyed—it only moves between one place and another place, between objects and/or fields, or between systems. When a consumer eats another organism, some of the energy is used or stored, but most of the energy is transformed into heat energy and returns to the atmosphere. For this reason, the amount of energy available is highest in producers, and least in consumers at the top of the food chain. The continuous loss of heat energy requires an outside energy source (the sun) to maintain a flow of energy into an ecosystem.

Ecological Pyramids

Researchers use population, biomass, and energy pyramids to track the flow of energy and cycling of matter through an ecosystem. The pyramid of numbers (see A) tracks population sizes of organisms within an ecosystem. The pyramid of numbers accounts for the total population of organisms within a specific ecosystem at each trophic level. Biomass is the total mass of organisms within each trophic level. Biomass is calculated by weighing organisms and subtracting the mass of water that makes up the organism. A biomass pyramid (see B) compares the amount of biomass in organisms at each trophic level and is represented as grams per meter2 (g/m2). An energy pyramid (see C) is used to illustrate the flow of energy between each trophic level.

Approximately 90% of energy is lost at each trophic level. Energy is represented as kilocalories produced per meter2

per year (kcal/m2/yr). Ecological pyramids are useful for characterizing the structure of an ecosystem. The pyramids for each ecosystem are slightly different. In addition, changes in the structure of an ecosystem’s ecological pyramids over time can provide information about the relative stability.

Scenario: Energy flow between organisms in a food chain is difficult to visualize. We can feel energy being released as body heat, but it is not visible. In this activity you will have the opportunity to simulate the flow of energy, represented by water, between organisms in a food chain.

1. Producers perform photosynthesis, and therefore store the solar energy directly from the sun in the form of chemical energy. No organisms in the food chain will contain more energy than producers. As consumers eat producers and other consumers, energy is lost. This means that consumers at the top of the food chain obtain the least energy.

2. Form a group of 6-7 students. Obtain 1 cup without a hole in the bottom, 4 cups with holes in the bottom, 5 beakers (500 ml), and a sheet of labels.

3. Each label represents a different organism in a food chain – producer, primary consumer, secondary consumer, tertiary consumer, and a quaternary consumer.

4. Place the producer label on the cup without a hole, and the consumer labels on the cups with holes.5. Five group members each need a cup and beaker. The 6th group member will measure the amount of

water in each beaker. The 7th group member will be the recorder (Table 1), and should have a pen or pencil.

a. What will represent energy in this activity?

b. What do the cups represent?

c. What does each marker or line represent?

d. Hypothesize what will happen to the energy (water) as it moves through the food chain in this activity. (If… then…)

6. Your instructor will have an area set up for the activity. Take your supplies to the “start line.”7. Read through steps 8 - 28 BEFORE starting this activity!8. Notice that there are 5 markers or lines spread out in the area, and a water source has also been

provided. The water will represent energy and each line represents an energy level. The amount of energy contained in each organism after it consumes the organism before it will be measured at each of these lines.

9. Measure out 500 ml of water using a beaker, and place it in the producer cup. The individual with the producer cup will be stationed at the start line.

10. Recorder: Record the amount of water in the producer cup in Table 1, Trial 1 for the producer.11. The primary consumer will stand at the start line next to the producer. The secondary consumer will

stand at the next line closest to the start line. The tertiary consumer will stand at the next line, and the quaternary consumer at the next.

12. When the recorder says “go,” the producer will pour all of the water (energy) from the first cup into the primary consumer cup.

13. As soon as all of the water has been poured, the primary consumer will WALK as fast as possible to the next line where the secondary consumer is located. Try to spill as little water from the top of the cup as possible, and do not cover the hole in the bottom of the cup.

14. Once the primary consumer reaches the line, he or she will pour the entire contents of the cup into his or her 500 ml beaker. (You should not have let the cup drip into the beaker on the walk.)

15. The measurer and recorder will follow. Measure the amount of water left in the 500 ml beaker. Record this amount in Table 1, Trial 1 for the primary consumer.

16. When the recorder says “go,” the primary consumer will pour all of the water (energy) from the beaker into the secondary consumer cup.

17. As soon as all of the water has been poured, the secondary consumer will WALK as fast as possible to the next line where the tertiary consumer is located. Try to spill as little water from the top of the cup as possible, and do not cover the hole in the bottom of the cup.

18. Once the secondary consumer reaches the line, he or she will pour the entire contents of the cup into his or her beaker. (You should not have let the cup drip into the beaker on the walk.)

19. The measurer and recorder will follow. Measure the amount of water left in the 500 ml beaker. Record this amount in Table 1, Trial 1 for the secondary consumer.

20. When the recorder says “go,” the secondary consumer will pour all of the water (energy) from the beaker into the tertiary consumer cup.

21. As soon as all of the water has been poured, the tertiary consumer will WALK as fast as possible to the next line where the quaternary consumer is located. Try to spill as little water from the top of the cup as possible, and do not cover the hole in the bottom of the cup.

22. Once the tertiary consumer reaches the line, he or she will pour the entire contents of the cup into his or her 500 ml beaker. (You should not have let the cup drip into the beaker on the walk.)

23. The measurer and recorder will follow. Measure the amount of water left in the 500 ml beaker. Record this amount in Table 1, Trial 1 for the tertiary consumer.

24. When the recorder says “go,” the tertiary consumer will pour all of the water (energy) from the beaker into the quaternary consumer cup.

25. As soon as all of the water has been poured, the quaternary consumer will WALK as fast as possible to the end line. Try to spill as little water from the top of the cup as possible, and do not cover the hole in the bottom of the cup.

26. Once the quaternary consumer reaches the end line, he/she will pour the entire contents of the cup into the 500 ml beaker. (You should not have let the cup drip into the beaker on the walk.)

27. The measurer and recorder will follow. Measure the amount of water left in the 500 ml beaker. Record this amount in Table 1, Trial 1 for the quaternary consumer.

28. When finished, return everyone to the lines and repeat steps 10-27 recording for Trials 2-5.29. Return to the classroom, and return the supplies to the instructor. Everyone in the group should copy

the results from their recorder’s Table 1.30. Individually, each group member should average the amount of water (energy) remaining for each

organism from Trials 1-5. Record in Table 1.31. Using the averages, calculate the percent of

energy (water) remaining, and the percent of energy lost for each organism. (See formulas at right.) Record in Table 1.

Graph the average percent of energy remaining and percent of energy lost for this food chain exercise below. Don’t forget to label your x-axis, y-axis, and a title for your graph!

Discussion Questions1. What did the water represent?

2. How was the energy “lost” in this activity between each step of the food chain? In an actual ecosystem, how would this energy be “lost”?

3. At which level in the food chain was the most energy lost? The least energy lost?

4. What was the purpose of performing more than one trial?

5. Summarize this activity and how it represents the flow of energy through a food chain?

Biology Name: _______________________Food Webs, Biomass & Energy Date: ____________ Hour: _______

Part C: Population, Biomass, and Energy Pyramids1. Data collected by researchers on population size, biomass, and energy can be used to determine the

health and relative stability of an ecosystem. Data on population size, biomass, and energy availability at each trophic level can be analyzed and compared with future data to determine whether an ecosystem is stable or changing.

2. Using the organism card in the food web you created, determine which organisms are producers. Record the name of all the producers in Table 2, in the Producer column.

3. For each producer, look at the back of the card and record the population, biomass, and energy information for each organism in Table 2. Be sure to include the units!

4. Add all of the producer populations together to determine the total producer population for this ecosystem. Add all of the producer biomass together to determine the total producer biomass. Add all of the producer energy together to determine the total producer energy. Record these values as the “TOTAL” for each column in Table 2.

5. Repeat steps 2 - 4 for the primary consumers, secondary consumers, and tertiary consumers.6. Using the population, biomass, and energy totals for each trophic level, draw a pyramid of numbers,

biomass pyramid, and energy pyramid on the back of the food web.7. Use a ruler and create a scale on the paper to make the size of each step in the pyramids proportional

to one another. See the example pyramids at right and in the Background.8. For each pyramid: Title it; label each trophic level; include the totals; and use color.

Table 2. Populations, biomass and energy

Producers Primary Consumers

Organism Population Biomass Energy Organism Population Biomass Energy

Total Total

Table 2. Populations, biomass and energy

Secondary Consumers Tertiary Consumers

Organism Population Biomass Energy Organism Population Biomass Energy

Total Total

Discussion Questions

9. In the pyramid of numbers, at which trophic level is most of the population located? The least population?

10. Why do you think the population is distributed in this ecosystem in this manner?

11. In the biomass pyramid, at which trophic level is most of the biomass located? The least biomass?

12. Why do you think the biomass is distributed in this ecosystem in this manner?

13. In the energy pyramid, at which trophic level is most of the energy located? The least energy?

14. Why do you think the energy is distributed in this ecosystem in this manner?

15. Explain how energy would flow through the food web.

16. Explain how matter would cycle through the food web.

17. Describe one possible food chain that can be found in your food web.

18. Find a student with a different biome, and compare the pyramid of numbers, biomass pyramid, andenergy pyramid of your biome to that of the other biome. How are they similar and how are they different?