Chapter Two: Cycles of Matter (pages 32-65) 2.2 Biogeochemical Cycles (pages 42 52) In order to survive and grow, organisms must obtain nutrients that serve as sources of energy or chemical building blocks, or both. The cycling of matter through the biotic and abiotic components of the biosphere allows all organisms to obtain nutrients. All biogeochemical cycles involve some substances that are temporarily stored in nutrient reservoirs for various amounts of time, while some substances are moving through the environment between reservoirs. The substances that are involved in biogeochemical cycles are: water carbon oxygen sulfur nitrogen phosphorus Each substance can be considered to be part of its own cycle, while all of the cycles are said to be interconnected. Substances may be part of a rapid cycle or part of a slow cycle depending on the amount of time spent in a reservoir. Nutrient reservoir: A nutrient reservoir is a component in the biosphere in which nutrients temporarily accumulate. Examples include: soil, water and organisms The four nutrient reservoirs are categorized with respect to whether they involve biotic or abiotic components of the ecosystem and whether the nutrients they contain are directly available to living things. Nutrients that are directly available to living things are said to be part of a rapid cycle. Nutrients that are not available to living things are said to be part of a slow cycle. 1
What to do: read the information on pages 42-43 of the text. Summarize the information in the table below. Definition: Substances cycle between nutrient reservoirs relatively quickly. Rapid Cycle Examples: Carbon moves from producer to consumer to decomposer, and back into the atmosphere through rapid cycling. how substances move into and out of nutrient reservoir photosynthesis, cellular respiration, decomposition, excretion Definition: Substances accumulate and are unavailable to organisms. It can take millions of years for these substances to again become available to organisms. Slow Cycle Examples: Organic carbon in the matter of living organisms is fossilized. The burning of fossil fuels millions of years later puts the carbon into the atmosphere. how substances move into nutrient reservoir fossilization, formation of sediments how substances move out of reservoir erosion, burning of fossil fuels, weathering The Carbon and Oxygen Cycles (pages 43 46) Rapid Cycling of Carbon Plants and animals play an important role in the rapid cycling of oxygen and carbon dioxide. Plants consume much greater amounts of carbon in the process of photosynthesis than plants and animals release in the process of cellular respiration. Much of the carbon in forest reservoirs is released back into the atmosphere as carbon dioxide from forest fires and the breakdown of organic matter by decomposers. Rapid Cycling of Oxygen Plants, animals, and decomposers also play an important role in the cycling or oxygen. Photosynthesis produces oxygen gas, which is needed for cellular respiration. 2
The Carbon and Oxygen Cycle The Slow Cycling of Carbon Living organisms also play an important role in the slow cycling of carbon. Organic carbon that is stored in the dead bodies of organisms may enter into a slow cycle if the carbon is not made immediately available by decomposers. Over millions of years, organic material that is not broken down by decomposers may become incorporated into rocks or contribute to petroleum (fossil fuel) deposits. Human activities influence the slow cycling of carbon in a number of ways. The combustion of petroleum deposits quickly releases carbon back into the atmosphere. Since the industrial revolution, levels of carbon dioxide in the atmosphere has increased by about 30%. Question 1. Using the diagram to the right, list the major carbon sinks (reservoirs) on the Earth. Major carbon sinks include: ocean, forests, petroleum deposits, limestone (CaCo 3 ) * note that the slow cycling of carbon is shown in bold against a darker background. 3
The Sulfur Cycle (pages 46 48) The sulfur cycle is a biogeochemical cycle that shows how sulfur is converted into different forms as it is transported through the air, water, and soil. All organisms require sulfur as an important component of proteins and vitamins What to do: Read the information of the sulfur cycle on pages 46 48 of the text. Summarize the information in the table below and answer the questions that follow. Component of the Biosphere Sulfur in the Air Sulfur in the Water Sulfur in the Soil Summary of information: The decomposition of organic matter, volcanic offgassing, and human activities all release sulfur into the atmosphere. Rain and snow soon return sulfur to Earth s surface via acid deposition. Plants and algae take up sulfur in the water-soluble 2 form of sulfate (SO 4 ). Decomposers quickly return sulfur to the soil or air as hydrogen sulfide (H 2 S). Soil bacteria use sulfur compounds in photosynthesis or cellular respiration, thus playing an essential role as they convert one form of sulfur to another. Some sulfur is taken out of rapid cycling when bacteria convert sulfur to forms that are layered down as sediments, eventually becoming part of rocks. 4
The Nitrogen Cycle (pages 48 49) The nitrogen cycle is a biogeochemical cycle that shows how nitrogen is converted into different forms as it is transported through the air, water, and soil. All organisms require nitrogen to make proteins and genetic material (DNA). What to do: Read the information of the nitrogen cycle on pages 48 49 of the text. Summarize the information in the table below and answer the questions that follow. Component of the Biosphere Nitrogen in the Air Nitrogen in the Water Nitrogen in the Soil Summary of information: Nitrogen gas (N 2 ) makes up 78.1 percent of Earth s atmosphere by volume. Most organisms, however, cannot use atmospheric nitrogen. Nitrogen gas is removed from the atmosphere via nitrogenfixing cyanobacteria, which convert it into a form plants can use ammonium (NH + 4 ). Some types of aquatic bacteria then convert the ammonium into nitrate (NO 3 ), which plants can also use. Other bacteria convert nitrate back into nitrogen gas via denitrification. Nitrogen-fixing soil bacteria live in close association with plants. They convert nitrogen gas into ammonium. Decomposers also break down organic matter to produce ammonium. Soil bacteria then convert the ammonium into nitrite (NO 2 ) and then nitrate. Denitrifying bacteria then convert these compounds back into nitrogen gas. 5
The Phosphorus Cycle (pages 49 50) The phosphorus cycle is a biogeochemical cycle that shows how phosphorus is converted into different forms as it is transported through the water and soil. All organisms require phosphorus as a part of cellular DNA and ATP (the energy carrier essential to all cells). What to do: Read the information of the phosphorus cycle on pages 49 50 of the text. Summarize the information in the table below and answer the questions that follow. Component of the Biosphere Phosphorus in the Air Phosphorus in the Water Phosphorus in the Soil Summary of information: Unlike carbon, nitrogen, and sulfur, phosphorus does not cycle through the atmosphere. The growth of algae in aquatic ecosystems is limited by the amount of available nutrients. Because it is scarce in the environment, excess phosphorus in aquatic ecosystems can result in algal overgrowth, known as an algal bloom. Weathering gradually releases phosphorus trapped in rocks and makes it available to organisms. Plants and algae can only use phosphorus in the form of phosphate (PO 4 3 ). Phosphorus is scarce in the environment. This keeps the growth of producers in balance, but it can also limit the growth of crops. 6
Question 2. Human activities can greatly affect many of the biogeochemical cycles. The increase in phosphates due to agricultural run-off can be a major problem for near-by aquatic environments. Use the phrases below and re-order to show how an increase in the amount of phosphorus in the environment can cause ecosystem damage. Algal bloom and overgrowth occurs Decomposer population grows quickly, depleting oxygen Excess phosphorus enters the aquatic system Fish and other organisms requiring oxygen die Plants below the surface can no longer photosynthesize and die Sunlight cannot penetrate below the surface 7