Part I: Water s Trip Around the World Fundamental Question: How does water cycle through living systems? What is the Water Cycle? Three of the key processes in the water cycle are evaporation, condensation, and precipitation. In the water cycle, water moves from the land to the air though the process of evaporation. In order for water to change phase from a liquid on the land to a gas in the atmosphere, heat energy must be added to the water molecule. The Sun is the usual source of heat in the water cycle. Another way to think about evaporation is that it s one of the processes that allows the living part of Earth where biological organisms exist (BIOSPHERE), to the solid Earth (LITHOSPHERE), to the gaseous portion around planet Earth (ATMOSPHERE), to the water on the planet (HYDROSPHERE). Some of the water that enters the atmosphere comes from plants through a process known as TRANSPIRATION, see diagram of a plant. Earth s water is not evenly distributed throughout the water cycle. Instead there are parts of the cycle that serve as large water reservoirs, locations where water is stored for long periods of time before transferring to other locations. By far the largest reservoir in the water cycle is the ocean which contains about 97% of all Earth s water. Other reservoirs are the frozen water in glaciers and the groundwater found in Earth s crustal rocks. Water molecules can be stored for millions of years in one of these reservoirs before they are transferred to another sphere through the water cycle. Start a Cycles Travel Journal by reading the postcard that your teacher gives you from Water. In the postcard, Water will tell you about its journey around the world. Then tape the postcard in the space provided and answer the questions in your Student Journal. 1
7.5B: Cycling of Matter Part II: Nitrogen s Trip Around the World Fundamental Question: How does the essential element nitrogen cycle through living systems? You may find it interesting that most of Earth s atmosphere is actually composed of nitrogen. In fact, over 78% of our atmosphere is made of nitrogen! Is there evidence that nitrogen cycles to the other spheres as well? It is required by all organisms for the basic processes of life to make proteins, to grow, and to reproduce, but most organisms cannot use the nitrogen directly from the air. One family of plants, called legumes, are especially important for taking nitrogen from the atmosphere and making it available to all living organisms. Legumes connect the inorganic atmospheric nitrogen to the organic nitrogen chemicals that plants and animals can use. Peas, beans, lentils, peanuts, alfalfa, soybeans, and clover are all classified as legumes. A form of nitrogen that plants and animals can use are called nitrates. Nitrates are returned to the soil in the form of animal feces (waste) and decaying plant and animal matter. The decaying process is the action of bacteria and fungi that decompose the plant and animal waste, forming a nitrogen-rich layer of organic matter in the soil called humus. Over time other bacteria continue to break down the nitrogen-rich molecules into simpler forms, this releasing nitrogen back into the atmosphere, thereby completing the cycle. One place that this process can be observed is in a compost bin. 2
Part II: Nitrogen s Trip Around the World, continued 1. Continue your Cycles Travel Journal with the adventures of nitrogen. 2. This time you write the postcard as if you where the element nitrogen. Refer to the postcard that your teacher gave you from Water to use as a postcard example. 3. Since you are Nitrogen, use the Nitrogen Cycle Diagram to help describe your travels around the world. Nitrogen s journey will be very different from Water s journey. 4. Your teacher will give you an index card that you will use to write your postcard. 5. Be creative about your travels as Nitrogen yet accurate with regard to how and where you traveled. Your postcard must include at least five separate places that you visited in your journey. 6. Exchange your postcard with your partner. Discuss any differences in your journeys. 7. Then tape your postcard in place and answer the questions about the nitrogen cycle in your Student Journal. Nitrogen Cycle Diagram 3
Part III: Carbon s Trip Around the World Fundamental Questions: How does the essential element carbon cycle through living systems? The element carbon is one of the most important elements on our planet. All living organisms contain carbon, making it an essential component of all life on planet Earth. In fact, the element carbon makes up close to half of the dry weight of all living things! So where does all of this carbon come from, and how does it move around? Carbon is freely cycled between the biosphere, the hydrosphere, the lithosphere, and the atmosphere. Carbon is found in our atmosphere in forms such as carbon dioxide. Carbon is found in rocks such as limestone and volcanic materials. Carbon is found in all living organisms. When organisms die, it is returned to the soil through the process of decay. Carbon is also found in fossil fuels such as natural gas and oil, and when these fuels are burned, carbon is returned to the atmosphere. Forrest Fires Atmosphere Volcanoes Terrestrial Biosphere Water and Oceans Human Caused 1. Continue your Cycles Travel Journal with the adventures of Carbon. 2. Complete another postcard, this time as if you were Carbon. 3. Be creative about your travels as Carbon yet accurate with regard to how and where you traveled. Your postcard must include at least five separate places that you visited in your journey. 4. Exchange your postcard with your partner. Discuss any differences in your journeys. 5. Then tape your postcard in place and answer the questions about the carbon cycle in your Student Journal. Fossil Fuels 4
Part IV: The Compost Bin: Linking the Nitrogen Cycle, Water Cycle, and Carbon Cycle Together Fundamental Questions: What processes are involved in cycling of matter within living systems? What organisms found in the soil aid in the cycling of matter? In order to understand how water, carbon, and nitrogen all play a major role in some important biological processes, such as decomposition, you need to focus on the bacteria. Composting is one such example. Although composting sets up conditions similar to those in humus-rich soils found in forest floors, composting is a process that we use to speed up the natural rate of decomposition of organic material. Bacteria play a major role in the decomposition process. Therefore, it is not an exaggeration to say that whatever is good for bacteria is good for the compost bin! How to Nurture Your Pet Bacteria in Your Class Compost Columns Bacteria, like all other organisms need food, water, and shelter. Too much or too little of these three variables will affect the bacterial activity in the soil or in the compost bin. To provide the best environment for bacteria to grow and reproduce, it is important to control the moisture content, temperature, oxygen, carbon, and nitrogen in the compost. Water: Bacteria need water to survive so if the compost is too dry, bacterial activity will be very slow. On the opposite end of the scale, too much water will limit the amount of oxygen moving through the small pore spaces of the soil. Bacteria need oxygen for respiration. Oxygen: Many types of bacteria need oxygen for respiration. If there is not enough oxygen present, the only types of bacteria that can grow are the types that produce unpleasant odors, making the compost bin offensive. Water Nitrogen 5
Part IV: The Compost Bin: Linking the Nitrogen Cycle, Water Cycle, and Carbon Cycle Together, continued Temperature: The best composting temperatures are in the range of 120 o F and 150 o F. This warm environment stimulates rapid growth of heat-loving bacteria that promote decomposition of organic matter. Nutrition: Like all living things, bacteria need carbon and nitrogen to grow and reproduce. Most bacteria need a food source that contains about 25 times as much carbon as nitrogen. If there is too much nitrogen compared to the amount of carbon, the extra nitrogen will be released into the air in the form of ammonia. Monitor the compost columns that you created for several weeks and watch for signs that provide evidence of how water, carbon, and nitrogen cycle through this manmade system. Now tie all that you have learned together, by answering Reflections and Conclusions questions in your Student Journal. 6