Lesson 1.2 Recycling Matter

Lesson 1.2 Recycling Matter Lesson Objectives Define biogeochemical cycles. Describe the water cycle and its processes. Give an overview of the carbon cycle. Outline the steps of the nitrogen cycle. Lesson Vocabulary DIRECTIONS: Please read the words below. Decide how well you know each of the words and indicate your knowledge level by marking the appropriate column. Word 3 Can Define/ Use It 2 Heard It/ Seen It 1 Don t Know It Definition Biogeochemical cycle Exchange pool Reservoir Water cycle Evaporation Sublimation Transpiration Condensation Precipitation Infiltration 21

Word 3 Can Define/ Use It 2 Heard It/ Seen It 1 Don t Know It Definition Groundwater Aquifer Runoff Carbon cycle Nitrogen cycle Nitrogen fixation Lesson Introduction In the last section you learned about how ecosystems are constantly receiving an initial input of energy, mostly from the sun. That energy is captured first by autotrophs and then passed up trophic levels from heterotroph to heterotroph along the food chain. As each organism uses some of that energy for its own life processes and transfers some of the energy to the atmosphere as heat, about 90% of the available energy is lost every time it moves up a trophic level. Food chains not only show the movement of energy, however, they also follow the movement of matter. Unlike energy, matter is not lost as it passes through an ecosystem. Instead, matter is recycled. 22

Before Reading: Think Aloud Have you ever considered the idea that a drop of water from a cup that you drink could have molecules of the very same water that existed in the tissues of a dinosaur? Water, like other matter used by organisms, is constantly recycled. In fact, YOU are part of the water cycle too. How does water cycle through you? Answer the following questions: 1. A) What are different ways that water enters your body? B) How did water get to those sources? 2. A) What are different ways that water can leave your body? B) Where does the water go from there? Biogeochemical Cycles The chemical elements and water that are needed by organisms continuously recycle in ecosystems. They pass through biotic and abiotic components of the biosphere. That s why their cycles are called biogeochemical cycles. For example, a chemical might move from organisms (bio) to the atmosphere or ocean (geo) and back to organisms again. Elements or water may be held for various periods of time in different parts of a cycle. Part of a cycle that holds an element or water for a short period of time is called an exchange pool. For example, the atmosphere is an exchange pool for water. It usually holds water (in the form of water vapor) for just a few days. Part of a cycle that holds an element or water for a long period of time is called a reservoir. The ocean is a reservoir for water. The deep ocean may hold water for thousands of years. 23

The rest of this lesson describes three biogeochemical cycles: the water cycle, carbon cycle, and nitrogen cycle. Water Cycle Water on Earth is billions of years old. However, individual water molecules keep moving through the water cycle. The water cycle is a global cycle. It takes place on, above, and below Earth s surface, as shown in Figure 1.9. Figure 1.9: Like other biogeochemical cycles, there is no beginning or end to the water cycle. It just keeps repeating. During the water cycle, water occurs in three different states: gas (water vapor), liquid (water), and solid (ice). Many processes are involved as water changes state in the water cycle. Evaporation, Sublimation, and Transpiration Water changes to a gas by three different processes: Evaporation occurs when water on the surface changes to water vapor. The sun heats the water and gives water molecules enough energy to escape into the atmosphere. Sublimation occurs when ice and snow change directly to water vapor. This also happens because of heat from the sun. Transpiration occurs when plants release water vapor through leaf pores called stomata (see Figure 1.10). Some of the water is a product of photosynthesis. 24

Figure 1.10: Plant leaves have many tiny stomata. They release water vapor into the air. Condensation and Precipitation Rising air currents carry water vapor from all these sources into the atmosphere. As the water vapor rises in the atmosphere, it cools and condenses. Condensation is the process in which water vapor changes to tiny droplets of liquid water. The water droplets may form clouds. If the droplets get big enough, they fall as precipitation rain, snow, sleet, hail, or freezing rain. Most precipitation falls into the ocean. Eventually, this water evaporates again and repeats the water cycle. Some frozen precipitation becomes part of ice caps and glaciers. These masses of ice can store frozen water for hundreds of years. Groundwater and Runoff Precipitation that falls on land as rain may flow over the surface of the ground. This water is called runoff. It may eventually flow into a body of water. Some precipitation that falls on land may soak into the ground, becoming groundwater. Groundwater may seep out of the ground at a spring or into a body of water such as the ocean. Some groundwater may be taken up by plant roots. Some may flow deeper underground to an aquifer. This is an underground layer of rock that stores water, sometimes for thousands of years. 25

Reading Check: 1. An aquifer would be an example of a(n): (circle one) exchange pool reservoir 2. A full grown tree can lose hundreds of gallons of water on a hot day through this process: A) evaporation B) sublimation C) transpiration 3. Explain how evaporation and condensation are opposite processes. 4. What is the difference between evaporation and sublimation? 5. Describe three different paths water can take after it becomes groundwater. 6. If water is abundant and constantly going through a cycle, why do you think we often hear about a shortage of water? 26

Graphic Organizer: Water Cycle DIRECTIONS: In the blank boxes below, write the name of each process shown. Gas Surface Water Ice/Snow Plants Precipitation Carbon Cycle Molecules are considered organic molecules if they contain the element carbon. Carbon is important to the structure of living organisms because it is used to create all the biomolecules: carbohydrates, lipids, proteins, and nucleic acids. The carbon cycle, shown in Figure 1.1, moves carbon back and forth between the environment and the living organisms. In other words, the carbon cycle is the movement of carbon through the abiotic and biotic factors of the ecosystem. 27

Figure 1.1: Carbon moves from one reservoir to another in the carbon cycle. What role do organisms play in this cycle? The Carbon Cycle Autotrophs remove carbon from the atmosphere to make organic molecules. The atmosphere stores carbon as carbon dioxide. Organisms release carbon from cellular respiration and decomposition into the atmosphere. Runoff, rivers, and streams dissolve carbon in rocks and carry it to the ocean. Cold ocean water dissolves carbon from the h Sediments from dead organisms form fossil fuels or carbon-containing rocks that store carbon for millions Subduction pulls rocks containing carbon down into the magma. Human actions such as burning fossil fuels and making cement release carbon into the t h Warm ocean water releases carbon into the h Volcanic eruptions release carbon from magma into the atmosphere. Carbon cycles quickly between organisms and the atmosphere. Photosynthesis removes carbon dioxide from the atmosphere and uses it to make food. Have you heard the saying you are what you eat? The food made helps the producer grow by contributing to the structure of its cells. When a producer is consumed, the carbon moves into the consumer and again the carbon can be used for the growth of the consumer. The matter in the food you consume is literally used as the building blocks for creating you! For all organisms, producers and consumers, food also provides the organism with energy. As organisms convert food into energy they can use through the process of cellular respiration, carbon is released back into the atmosphere as carbon dioxide. When organisms die, decomposition releases the carbon within the organism back into the atmosphere. Carbon cycles far more slowly through geological processes such as sedimentation. Carbon may be stored in sedimentary rock for millions of years. Flowing water can slowly dissolve carbon in sedimentary rock. Most of this carbon ends up in the ocean. The deep ocean can store 28

carbon for thousands of years. Sedimentary rock and the ocean are major reservoirs of stored carbon. Another reservoir of stored carbon is fossil fuel deposits. If dead organisms are covered before they can decompose and are not exposed to oxygen, over millions of years they can form fossil fuels. When we burn fossil fuels such as coal and oil, we release carbon back into the atmosphere. Reading Check: 1. Name three processes that release carbon back into the atmosphere. 2. What is the only process that moves carbon from an abiotic factor to a biotic factor? 3. A) What are some reservoirs of carbon? B) What part of the carbon cycle serves as an exchange pool? 4. Explain why the burning of trees also releases carbon dioxide. 5. Application Question: When you lose weight, where does that weight go? 29

Nitrogen Cycle Nitrogen makes up 78 percent of Earth s atmosphere. It s also an important part of living things. Nitrogen is found in proteins, nucleic acids, and chlorophyll. The nitrogen cycle moves nitrogen through the abiotic and biotic parts of ecosystems. Figure 1.12 shows how nitrogen cycles through a terrestrial ecosystem. Nitrogen passes through a similar cycle in aquatic ecosystems. Figure 1.12: Nitrogen cycles between the atmosphere and living things. Nitrogen Cycle in a Terrestrial Ecosystem Although nitrogen gas is abundant in the atmosphere, plants cannot use nitrogen gas from the air to make organic compounds for themselves and other organisms. The nitrogen gas (N 2 ) must be changed to a form called nitrates (NO 3 ), which plants can absorb through their roots. The process of changing nitrogen gas to nitrates is called nitrogen fixation, which is carried out by nitrogen-fixing bacteria. The bacteria live in soil and roots of legumes such as peas or beans. The nitrates can then be used by plants to create proteins, nucleic acids, and chlorophyll. When consumers eat these plants the nitrogen gets reused to make new proteins. When plants and other organisms die, decomposers break down their remains. In the process, they release nitrogen in the form of ammonium ions (NH 4 + ). Nitrifying bacteria change the ammonium ions into nitrates. Some of the nitrates are used by plants. Some nitrates are changed back to nitrogen gas by denitrifying bacteria. 30

Reading Check: 1. Explain why bacteria are critical to the nitrogen cycle. 2. A) What form of nitrogen can be used by plants? B) What are two ways nitrogen can be converted intoits usable form? 3. What are some ways that the nitrogen cycle is similar to the carbon cycle? Graphic Organizer: The Role of Bacteria in the Nitrogen Cycle DIRECTIONS: Explain the role each type of bacteria plays in the nitrogen cycle in the box to the right. Nitrogen-fixing bacteria Decomposers Nitrifying bacteria Denitrifying bacteria 31

Lesson Summary Chemical elements and water are recycled through biogeochemical cycles. The cycles include both biotic and abiotic parts of ecosystems. The water cycle takes place on, above, and below Earth s surface. In the cycle, water occurs as water vapor, liquid water, and ice. Many processes are involved as water changes state in the cycle. The atmosphere is an exchange pool for water. Ice masses, aquifers, and the deep ocean are water reservoirs. In the carbon cycle, carbon passes among sedimentary rocks, fossil fuel deposits, the ocean, the atmosphere, and living things. Carbon cycles quickly between organisms and the atmosphere. It cycles far more slowly through geological processes. The nitrogen cycle moves nitrogen back and forth between the atmosphere and organisms. Bacteria change nitrogen gas from the atmosphere to nitrogen compounds that plants can absorb. Other bacteria change nitrogen compounds back to nitrogen gas, which re-enters the atmosphere. Lesson Review Questions Recall 1. What is a biogeochemical cycle? Name an example. 2. Identify and define two processes by which water naturally changes from a solid or liquid to a gas. 3. Define exchange pool and reservoir, and identify an example of each in the water cycle. 4. State three ways that carbon dioxide enters Earth s atmosphere. 5. List all the ways that a single tree may be involved in the carbon cycle. Apply Concepts 6. Assume you are a molecule of water. Describe one way you could go through the water cycle, starting as water vapor in the atmosphere. 7. Read the following passage. Then apply information from the lesson to explain why the farmer plants peas. A farmer has three fields in which she grows corn for market. Every year, she plants one of the fields with peas, even though she cannot make as much money selling peas as she can selling corn. She rotates the fields she plants with peas so that each field is planted with peas every 3 years. Think Critically 8. Compare and contrast biological and geological pathways of the carbon cycle. 9. Explain why bacteria are essential parts of the nitrogen cycle. 32

Points to Consider In this lesson, you read how matter is recycled through ecosystems. Ecosystems vary in the amount of matter they can recycle. For example, rainforests can recycle more matter than deserts. Consider the abiotic and biotic factors of a rainforest and desert. How are they different? Why do you think a rainforest can recycle more matter than a desert? Multimedia Links To learn about how what s happening to the water cycle today, watch the following video from NASA. http://www.youtube.com/watch?v=a_y8mrngxa4 Have you ever wondered about where your water supply comes from? The following video link discusses California s water supply and water cycle: http://www.teachersdomain.org/asset/kqed07_vid_calwater/ For an overview of the carbon cycle watch the video at the link below: http://www.youtube.com/watch?v=0vwa6qteih8 An interactive animation on the carbon cycle and human impact on the carbon cycle can be found at the following link: http://epa.gov/climatechange/kids/carbon_cycle_version2.html You can learn more about the nitrogen cycle in the interactive animation at the following link: http://www.teachersdomain.org/asset/lsps07_int_nitrogen/ 33