MATERIALS AND NUTRIENT CYCLES The energy that flows into an ecosystem cannot be recycled. Once the energy is used, it is lost. But it much be constantly repeatedly replenished if the ecosystem is to continuously function. The important chemical nutrients, however, are used repeatedly. They are cycled between the living and nonliving components of the ecosystem. Generally, they begin in the abiotic part of the ecosystem (water, land, and air). Then, they enter to the bodies of plants and animals and return into the abiotic environment. The movement of these materials and nutrients between the living and nonliving environment clearly shows the interrelatedness of the abiotic and biotic components in an ecosystem. Among these recycled materials and nutrients are carbon, oxygen, water, nitrogen, and phosphorus. After studying this chapter, you should be able to 1. Identify different nutrients that can be recycled. 2. Explain the water, carbon and oxygen, nitrogen, and phosphorus cycles. 3. Discuss the importance of each of these cycles. 4. Discuss how people affect these cycles. 5. Differentiate micronutrients from macronutrients 2.1. IMPORTANCE OF THE NUTRIENT CYCLES The energy from the sun flows to the plant goes to the herbivore that eats the plant, to the carnivore, and to the last consumer until the energy is lost into the ecosystem. The energy does not go back to the source. It cannot be used over and over again. In contrast, when the bodies of dead plants and animals decompose, they are changed into nutrients through the action of bacteria and fungi. The nutrients are stored in the abiotic environment like the soil. The nutrients can be used again by the plants. The plants are eaten by the animals and when the animals die, they decompose into nutrients. These nutrients can be used over and over again. In this way, a cycle of nutrients is formed. The cycle of nutrients is an important process that takes place in the ecosystem. Through the cycle of nutrients, the organic compounds found in the bodies of organisms are converted into inorganic compounds which serve as nutrients to the other organisms. In both processes of energy flow and nutrient cycles, the plants provide the link by which the biotic and abiotic components interact with one another. Insightfulness Energy cannot be recycled. When using, it is lost into the ecosystem. The nutrients in an ecosystem can be used over and over again. They are cycled beginning from the nonliving environment: air, water, and soil. Then, these substances are taken in by the producers and are passed on through several consumers. They are returned to the nonliving environment by decomposers. Nutrients may be classified into two types, namely, the macronutrients and the micronutrients. The macronutrients are those that are required by the organisms in large quantities. Examples are carbon, hydrogen, oxygen, and nitrogen. Sulfur, phosphorus, and potassium are also macronutrients but are needed by organisms in smaller quantities. The micronutrients are needed in very small amounts. They are also essential to life. Examples are copper, zinc, iron, and boron. The macronutrients are the major components of fats and carbohydrates. They make-up the cell structures of plants and animals. The cell walls of plants, for example, are made up of a very rigid substance called the cellulose. Cellulose is made up of these three elements with a ratio of 7.2 carbons, 1 hydrogen and 8 oxygen. This substance makes the cell walls very firm and rigid. It adds strength to the plant. Nitrogen, carbon, hydrogen, and oxygen are the building blocks of proteins. Phosphorus makes up many nucleic acids and is also essential for the transformation of energy in the cells. The micronutrients are as important as the macronutrients. Magnesium, for example, is necessary in the production of chlorophyll. Guide questions 1. What happens to the energy from the sun when it enters to an ecosystem? 2. What happens to the dead bodies of plants and animals in an ecosystem? 3. Define macronutrients and micronutrients. 4. Make a listing of micronutrients and macronutrients, and give their functions? 5. What are the components of cellulose? 2.2 THE WATER CYCLE As with any cycle, the water cycle has neither beginning nor end. However, it is useful to choose a starting point. Let us begin with water vapor in the atmosphere. a) b) Figure 2.1: The water cycle When water in the atmosphere reaches saturation (the highest amount of moisture that the air can hold), it falls as rain. This falls directly to the land and bodies of water like the oceans and seas. Some runs off the surface of the land into rivers. The rain that falls on the land is absorbed by plants through the roots and drank by animals. Some penetrates the soil and becomes part of the underground water, which eventually empties into the oceans. The processes of condensation and precipitation are responsible for the return of water from the atmosphere into the land and other bodies of water. The water from the land and other bodies of water returns to the atmosphere through the process of evaporation. Plants return the water by the process known as transpiration, while animals do this through respiration. Water accumulates again in the atmosphere as clouds and falls as rain. Guide questions 1. What is saturation? 2. What is evaporation? 3. What is respiration? 4. Trace the pathway of the water cycle. 2.3. THE CARBON AND OXYGEN CYCLE Much of the carbon in the environment exists in the form of carbon dioxide. Plants absorb this gas though the leaves and use in the process of photosynthesis. Oxygen is given off during this process. Animals and other consumers obtain their food as well as their oxygen needs from plants. In the process of respiration, the food is broken down into CO 2 and water which are returned into the atmosphere. Figure 2.2: The carbon and oxygen cycles When the animals and plants die, their bodies and waters are broken down by the decomposers. In this process, CO 2 is produced and returned to the atmosphere. Sometimes dead organisms fail to decompose quickly. When this happens, the dead bodies change to coal, oil, and gas which become fossil fuels after a long time. When burned, fossil fuels release carbon dioxide into the atmosphere. Insightfulness Carbon dioxide is present in the atmosphere from wastes, dead bodies of organisms, and fossil fuels. Plants use CO 2 in the process of photosynthesis. Animals obtain their food from the plants and release CO 2 though the process of respiration. Decomposers and burning also release CO 2 into the environment. Erupting volcanoes emit carbon dioxide. The eruption of the volcano supplies fresh carbon to the atmosphere from the deeper part of the interior of the earth. Carbon dioxide combines with water and forms calcium carbonate (CaCO 3 ). This compound is used in the production of shells of animals like clams and oysters. When shelled organisms die, the calcium carbonate may dissolve or form part of carbonate rocks serve as an buffer environment and storing carbon for many years. During the process of weathering, carbon dioxide is again released into the environment. Guide questions 1. What are the sources of carbon dioxide? 2. What are the sources of oxygen? 3. How is carbon released from carbonate rocks into the atmosphere? 4. How are fossil fuels formed? 5. What two important processes are involved in the cycle of carbon and oxygen? Discuss these processes. 2.4. THE NITROGEN CYCLE Nitrogen is an element crucial to life. It is an important component of proteins and nucleic acids. The nitrogen gas constitutes about 78 percent of the air in the atmosphere. However, it cannot be used directly by plants and animals. Plants use it in the form of nitrates. You inhale large quantities of nitrogen but it remains in your body unchanged. Figure 2.3: The Nitrogen Cycle Nitrogen in the atmosphere is converted into nitrates in two ways: (1) by the action of lightning and (2) by action of specialized organisms. Electrical activity (lightning) during thunderstorms converts nitrogen into nitrates but only a small amount. The nitrates produced by this process fall to the earth with the rain. The organisms that convert nitrogen are bacteria, algae, and fungi, of which bacteria is the most important. Nitrogen-fixing bacteria directly convert nitrogen into nitrates though the process called nitrogen fixation. Examples of nitrogen-fixing bacteria are the Rhizobium, which live in the roots of legumes like beans, peas, and peanuts. The association between Rhizobium and legumes forms swollen areas within the roots called nodules. Nitrates are formed within the nodules. The compounds are then used by the plants to build proteins, or remain in the soil as fertilizers. Because of this, legumes are important crop rotation as they help maintain soil fertility. This explains why farmers plant legumes in soil before they plant new crops. Decomposers break down the protein in the bodies of plants, animals, and their wastes. In this process, ammonia is produced. Ammonia may be used directly by some plants but others cannot. They have to transform this into nitrates through the nitrogen-fixing bacteria. This process converting ammonia to nitrates is known as nitrification. The plants are then able to obtain nitrates to synthesize amino acids and proteins. The nitrates produced by the nitrogen-fixing bacteria are converted into nitrites by another group of bacteria called nitrite bacteria. Nitrites are converted into nitrogen by the denitrifying the bacteria in a process called denitration. Denitration completes the cycle of nitrogen. Insightfulness - The most complex of the nutrient cycles is the nitrogen cycle. It involves many microorganisms. - Nitrogen cannot be used directly by the plants. It has to be transformed into nitrates. - Lightning, nitrogen-fixing bacteria, and decomposers convert nitrogen into nitrates. - Denitrifying bacteria convert nitrites into nitrogen, thus completing the nitrogen cycle. - Plants use nitrogen for the synthesis of amino acids and proteins. What will happen if the nitrates are not absorbed by plants? Is this beneficial to the soil? If nitrates are not absorbed by plants, they are washed away by heavy rains. This process is called leaching. Leaching drains the soil of its nutrients which are ultimately lost into the rivers and shallow marine sediments. These nitrates enter the marine food chain and are returned to land by the droppings of seabirds. These droppings are known as guano, which were once a major world supply of fertilizer. Guide questions 1. What is the important of nitrogen? 2. What is the useful form of nitrogen? 3. How is nitrogen converted into nitrates? 4. What is nitrogen fixation? 5. Differentiate between nitrification and denitrification. 6. Explain leaching. What is its role in the nitrogen cycle? 2.5. THE PHOSPHORUS CYCLE Phosphorus is essential to life. It is a component of the cell membranes, nucleic acids, and adenosine triphosphate – the energy currency of the cell. Figure 2.4: The phosphorus cycle Phosphorus is found naturally in the environment in the form of phosphates. Phosphates in the soil come from phosphate rocks. Though the process of weathering, the phosphates are incorporated into the soil in soluble or insoluble forms. The plants absorb the phosphate and use it for protein synthesis. The animals obtain phosphate from the plants they eat. When the plants and animals die, decomposition brings back the phosphate into the soil. Phosphate in the soil may be washed away into shallow marine sediments by means of leaching. It may also reach the deep ocean sediments. From the shallow marine sediments, the phosphates are returned to the soil in the form of guano deposits of marine fish and sediments. Phosphates in the deep ocean sediments are recycled back to the soil by means of upwelling. If upwelling does not take place, the phosphate becomes incorporated into the phosphate rocks. Phosphate rocks are mined to be used in the manufacture of phosphate fertilizers. Though leaching, the phosphorus in these fertilizers is lost from the soil. Human therefore hasten the rate of loss of available phosphate. This can have serious effects on the supply of phosphorus for agriculture in the future. Insightfulness - Phosphorus presents in soil in the form of phosphates. Though weathering, phosphate rocks contribute to the amount of phosphate in the soil. - Phosphate is taken in by plants and passed on the food chain. When plants and animals die, the bacteria convert the dead bodies into phosphates and return them into the soil. - Guano deposits are good sources of phosphates. Human activities have altered the cycle of materials in the environment. When people cut down trees or destroy forest in one area, rainwater continues to flow until it finally reaches the sea instead of rising to the atmosphere and falling again on the forests. The massive destruction of the forests changes the environmental conditions, so that forests may never recover at all. Figure 2.5: Eutrophication Similarly, deforestation also affects the mount of nitrates in the soil though leaching. This loss of nitrogen limits the growth of plants and pollutes groundwater. The phosphorus cycle has also been disrupted by the activities of humans especially in the water ecosystem. People use a lot of agricultural fertilizers and detergents of which phosphates are major components. When the phosphates from fertilizers and detergents run off into lakes, they stimulate the rapid growth of algae and other aquatic plants causing algae bloom. This condition is known as eutrophication. As the plants age and die, decomposition takes place and use up so much oxygen causing the death of fish and other animals. Guide questions 1. What is the importance of phosphorus? 2. What processes are involved in the cycle of phosphorus? 3. In what ways have people altered the cycle of nutrients in the environments? 4. Define algae bloom. How does it lead to eutrophication? 5. What are the effects of eutrophication? VOCABULARY Algae bloom: Very rapid growth of algae in surface waters due to increase in inorganic nutrients, especially phosphorus and nitrogens. Conservation: Process of reducing the use of resources through recycling, decreased demand, and increased efficiency use. Denitrifying bacteria: Bacteria that convert nitrates into nitrogen gas. Denitrification: Process that convert nitrates into nitrogen gas. Eutrophication: Accumulation of nutrients in a lake or pond due to human intervention or nature causes. Evaporation: The process of the change in the state of a liquid or solid to a gas or vapor. Vanishing of the surface of a liquid to the atmosphere. Leaching: The process by which nutrient chemicals or contaminants are dissolved and carried away by water, or are moved into a lower layer of soil. Nitrate: Inorganic anion containing three oxygen atoms and one nitrogen atom. Nitrogen fixation: A process whereby nitrogen fixing bacteria living in mutualistic associations with plants convert atmospheric nitrogen to nitrogen compounds that plants can utilize directly. Bacteria: Group of single - celled organisms responsible for functions like that decay of organic materials and nutrient recycling. Nutrient: Substance taken by a cell from its environment and used in catabolic or anabolic reactions. . of plants and animals in an ecosystem? 3. Define macronutrients and micronutrients. 4. Make a listing of micronutrients and macronutrients, and give their. (water, land, and air). Then, they enter to the bodies of plants and animals and return into the abiotic environment. The movement of these materials and nutrients