Ecosystems and the Biosphere PDF

Ecosystems and the Biosphere: Energy Flow Through the Ecosystem and the Recycling of Matter Teacher Lecture Notes Overview: An ecosystem is all the living organisms in a given area as well as the abiotic factors with which they interact. All of the organisms living on Earth need...

Ecosystems and the Biosphere: Energy Flow Through the Ecosystem and the Recycling of Matter Teacher Lecture Notes Overview: An ecosystem is all the living organisms in a given area as well as the abiotic factors with which they interact. All of the organisms living on Earth need energy to carry out life processes such as growth, movement, and reproduction. In an ecosystem, the ultimate source of energy is the sun. The sun’s energy is converted from one form to another and passed through the various levels of the ecosystem. The flow of energy through an ecosystem is crucial to the ecosystem’s ability to sustain life. I. Energy Flow Through the Ecosystem A. Sunlight is the main energy source for life on Earth. 1. Without this energy from the sun, life on Earth could not exist. 2. Of all the sun’s energy that reaches the earth, less than 1% is actually used by living organisms. 3. This 1% is used by the organisms that are capable of photosynthesis. Photosynthesis is the process by which green plants (and a few other organisms) use the light energy from the sun to convert water and carbon dioxide into glucose and oxygen. 4. The organisms on Earth that cannot carry out photosynthesis rely on the energy that has been stored in the organic compound glucose (a type of sugar) as their source of energy. 5. Not only does photosynthesis provide food in the form of sugars and starches for many of the organisms on Earth, but it also removes carbon dioxide from the atmosphere and releases oxygen into the atmosphere. B. Autotrophs 1. Autotrophs are organisms that have the ability to use energy from the sun to convert simple inorganic substances into complex organic substances. 2. Autotrophs convert carbon dioxide and water into carbohydrates (glucose). 3. The only organisms that are autotrophs are the green plants, the algae, a few species of bacteria and a few protists. 4. On land, the green plants are the main autotrophs. In aquatic ecosystems, algae are the main autotrophs. Photosynthetic bacteria (cyanobacteria) are also important oxygen producers. 5. Autotrophs are also called “producers”. 6. The autotrophs are essential to the flow of energy through the ecosystem. 7. Our very life is dependent on these autotrophs. Without them, we would not have food to eat or oxygen to breathe. 8. A few autotrophs can produce food in the absence of light. Through a process called chemosynthesis, these autotrophs use the energy contained in the chemical bonds of inorganic molecules such as hydrogen sulfide to produce food. Chemosynthesis is a process that is carried out by several types of bacteria. C. Heterotrophs 1. Many organisms cannot directly use the energy from the sun as the autotrophs do. 2. These organisms acquire their energy from other organisms. 3. Heterotrophs are organisms that cannot make their own food. They rely on other organisms for their energy and food supply. Copyright ã Amy Brown Science 1  4. Heterotrophs are also called “consumers”. 5. There are many types of heterotrophs: a) Herbivores obtain energy by eating only plants. b) Carnivores obtain energy by eating other animals. c) Omnivores obtain energy by eating both plants and animals. d) Detritivores feed on plant and animal remains, animal wastes and other dead matter. Examples of detritivores are vultures, mites, earthworms, snails, and crabs. e) Decomposers are a class of detritivores that cause decay by breaking down organic compounds. Decomposers include bacteria and fungi. Some of the molecules released during decay are consumed by the decomposer, and some of these molecules are returned to the soil or water. The action of the decomposers makes the nutrients contained in the dead bodies and wastes of organisms available to autotrophs. The process of decomposition recycles chemical nutrients. f) What would happen if there was no decomposition? All life on Earth would cease as detritus (dead organic matter) piled up and the supply of chemical elements needed to build new organisms was exhausted. Chemical elements such as carbon, nitrogen, and phosphorus must be recycled to be used again in new organisms. D. In summary, energy enters the ecosystem in the form of sunlight. It is converted to chemical energy by autotrophs and passed to heterotrophs in the form of organic compounds (molecules of glucose). II. Feeding Relationships A. What happens to energy in an ecosystem as one organism eats another? The energy flows in a one-way path through the ecosystem. Energy enters the ecosystem in the form of sunlight. Photosynthetic organisms convert the sun’s energy into molecules of glucose. This energy is then passed on to the animals that eat the plants and to the animals that eat other animals. B. Energy flows through an ecosystem in one direction, from the sun to autotrophs and then to various heterotrophs. C. Food Chains 1. The energy stored by producers in the form of glucose molecules can be passed through an ecosystem along a food chain. 2. A food chain is a series of steps in which organisms transfer energy from one organism to another by eating and by being eaten. 3. All food chains begin with an autotroph. 4. Examples: a) grass à mouse à snake à hawk b) marine algae à zooplankton à small minnow à squid à whale Copyright ã Amy Brown Science 2  D. Food Webs 1. In an ecosystem, the feeding relationships between organisms are much too complex to be shown in a single food chain. 2. Many consumers eat more than one type of food. More than one species may feed on the same organism. 3. There are many complex interactions between many different food chains. 4. Food web: The network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem. 5. A food web links all the food chains in an ecosystem together. E. Trophic Levels 1. Each step in a food chain is called a trophic level. The trophic level indicates the organism’s position in the sequence of energy transfers. 2. The first trophic level in a food chain is always made up of producers. These organisms are referred to as primary producers. 3. The second trophic level is occupied by the herbivores that feed on the producers. These organisms are referred to as primary consumers. 4. Predators of herbivores belong to the third level. These organisms are referred to as secondary consumers. 5. A tertiary consumer eats the secondary consumer. 6. Each consumer depends on the trophic level below it for energy. 7. Most ecosystems contain only three or four trophic levels. III. Productivity of the Ecosystem A. The productivity of the ecosystem can be measured in two ways: 1. Gross primary productivity 2. Net primary productivity B. Gross primary productivity: 1. Gross primary productivity is the rate at which the producers (autotrophs) in an ecosystem capture energy. 2. Gross primary productivity is the amount of light energy that is converted to chemical energy by photosynthesis per unit time. 3. The photosynthetic organisms in the ecosystem capture the energy from the sun and store it in molecules of glucose. C. What does the plant do with the glucose it produces? 1. About half of the glucose is used immediately in cellular respiration. Respiration is the conversion of glucose into molecules of ATP, the energy source for a cell. 2. Some of the glucose molecules are used as raw materials (building blocks) for the building of other organic compounds within the cell. 3. Much of the glucose is stored by the plant for future use. D. Biomass is a term that is used to describe the amount of organic material in an ecosystem. Producers add biomass to an ecosystem by making organic compounds. Copyright ã Amy Brown Science 3 E. Net primary productivity 1. The energy stored as biomass is available to other organisms in the ecosystem. 2. Net primary productivity is equal to gross primary productivity minus the amount of energy used by the producers for respiration. 3. Remember: Gross primary productivity is the total amount of glucose produced by photosynthesis. Some of this glucose is used immediately by the plant in cellular respiration. The remaining glucose is stored and is available to consumers. 4. Net primary productivity is the most important measurement because it represents the amount of chemical energy (glucose) that will be available to consumers in the ecosystem. 5. Net primary productivity varies greatly from one ecosystem to another. For example, net primary productivity in a tropical rain forest is about 25 times greater than the net primary productivity in a desert of the same size. 6. Rain forests account for 5% of the Earth’s surface, but account for 30% of the world’s net primary productivity. 7. In terrestrial ecosystems, three factors determine the net primary productivity: a) light b) temperature c) amount of rainfall An increase in these three factors generally leads to an increase in the amount of photosynthesis taking place, and therefore, an increase in productivity. 8. In aquatic ecosystems, productivity is limited by two factors: a) light b) the availability of nutrients. F. Energy Transfer Between Trophic Levels 1. The amount of energy or matter in an ecosystem can be represented by an ecological pyramid. 2. Ecological pyramid: A diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or a food web. 3. Roughly 10% of the total energy consumed in one trophic level is passed to the organisms in the next trophic level. 4. The pyramid shape of the diagram below represents the low percentage of energy transfer from one trophic level to the next. Label each section of the ecological or energy pyramid. Copyright ã Amy Brown Science 4  5. Why is the transfer of energy to the next trophic level so low? a) Not all of the energy possessed by the organisms at one trophic level will be passed up to the next trophic level. Organisms use much of the energy they consume for their own life processes such as respiration, movement, or reproduction. b) Many organisms at one trophic level will escape being eaten by the predators at the next level. The energy of these “escapees” will not be passed to the organisms at the higher level. c) Even if the organism is eaten by a predator, some of the molecules in its body will be in a form that the consumer cannot break down and use. An example might be the antlers and hooves of an antelope eaten by a lion. d) Any energy consumed from cellular respiration cannot be passed up to the next trophic level. e) Finally, no energy transformation is 100% efficient. At each trophic level some energy will be lost to the environment in the form of heat. 6. Because each trophic level receives only 10% of the energy from the trophic level below, it can support only about one tenth the amount of living tissue. 7. Label each section of the energy pyramid seen below: 0.5 calories Quaternary Consumer per m2 Tertiary Consumers 5 calories per m2 Secondary Consumers 50 calories per m2 Primary Consumers 500 calories per m2 5,000 calories per m2 Producers If the energy content of the grass is approximately 5,000 calories per square meter of land surface, calculate the amount of energy that will be passed up to each trophic level. Copyright ã Amy Brown Science 5  8. The low rate of energy transfer between trophic levels explains why food chains rarely contain more than a few trophic levels. Organisms occupying the lower trophic levels are usually much more abundant than organisms belonging to the highest level. There are many more grasses, shrubs, and trees than there are herbivores. There are many herbivores (deer, antelope, gazelles) for each carnivore (lion). 9. Higher trophic levels contain less energy, and therefore, they can support fewer individuals. IV. Ecosystem Recycling A. Energy is crucial to an ecosystem, but the organisms need more than energy to survive. The organisms in the ecosystem also need water, minerals and other compounds. For most organisms, more than 95% of the body is made up of only four elements: Carbon, hydrogen, oxygen, and nitrogen. There is an abundant supply of these elements on earth, but they must be in a form that living cells can take up. B. Recycling in the Biosphere 1. Energy and matter move through an ecosystem in very different ways. 2. Energy moves through an ecosystem in a one-way path. Energy enters an ecosystem in the form of sunlight and exits the ecosystem in the form of heat. This energy cannot be recycled. 3. Matter, however, is recycled within and between ecosystems. 4. Elements and compounds are recycled in biogeochemical cycles. A biogeochemical cycle connects the biological, the geological, and the chemical aspects of the biosphere. 5. Biogeochemical cycle: A process in which elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another. C. Types of biogeochemical cycles include: 1. The water cycle 2. The carbon cycle 3. The nitrogen cycle 4. The phosphorus cycle V. The Water Cycle A. Everyone knows that water is crucial to life. Living cells are 70 to 80% water. Water provides the environment in which most of the chemical reactions of the cell occur. B. At any given time, the water of earth can be found in the following places: 1. Bodies of water such as the oceans, lakes, and rivers. 2. Stored in the bodies of living organisms. 3. In the atmosphere as clouds and water vapor. 4. Stored in underground formations as ground water. 5. Oceans contain 97% of the water on earth. 2% is found in the glaciers on earth. Only 1% of the water on earth is found in lakes, rivers, and in groundwater. Copyright ã Amy Brown Science 6 C. The movement of water between these various reservoirs is known as the water cycle. D. Four processes account for the movement of water molecules through the ecosystem: 1. Evaporation 2. Precipitation 3. Transpiration 4. Condensation E. Steps to the Water Cycle Have students begin by labeling each numbered section of the diagram to the right: 1 – Evaporation 2 – Condensation 3 – Transpiration 4 – Precipitation 5 – Runoff 6 – Percolation 7 – Groundwater 1. In the process of evaporation, water molecules are added to the atmosphere in the form of water vapor. Heat causes water molecules to evaporate from bodies of water and from the bodies of living organisms. 2. Transpiration also adds molecules of water to the atmosphere. Transpiration is the loss of water from the leaves of plants. Water enters plants through the roots, and travels to the leaves of the plant. The leaves contain pores called stomata that open to take in the carbon dioxide that is needed for photosynthesis. When the stomata are open, molecules of water evaporate from the leaf and enter the atmosphere. 3. The water vapor in the atmosphere condenses to form the clouds. This is known as condensation. 4. Animals also contribute water molecules to the water cycle, but in a much less significant way than plants. Animals lose water when they breathe, sweat, or excrete. 5. Water leaves the atmosphere and returns to Earth through the process of precipitation. The atmosphere can only hold so much water vapor. The amount of water vapor in the atmosphere is dependent upon temperature and air pressure. Once the atmosphere becomes saturated with water vapor, it returns to the Earth in the form of rain, snow, sleet, hail or fog. Copyright ã Amy Brown Science 7 VI. The Carbon Cycle A. Carbon is the key element of all organic compounds. All of the carbohydrates, lipids, proteins and nucleic acids that compose all living things contain atoms of carbon. In order to build new organic compounds for living cells, there must be a constant and steady supply of available carbon. B. Photosynthesis and respiration form the basis of the carbon cycle. Carbon dioxide is taken in by plants and used to build molecules of glucose (carbohydrates). Both autotrophs and heterotrophs carry out cellular respiration in which the molecules of glucose are broken down into carbon dioxide and water. Photosynthesis removes carbon from the atmosphere in the form of carbon dioxide. Respiration returns carbon dioxide back to the atmosphere. C. Many types of processes move carbon through the ecosystem: 1. Photosynthesis removes carbon dioxide from the atmosphere. 2. Cellular respiration and decomposition release carbon dioxide. 3. Geochemical processes, such as erosion and volcanic activity, release carbon dioxide to the atmosphere and oceans. 4. Biogeochemical processes cause dead organisms to decay. Under pressure, their bodies are converted into coal and petroleum (fossil fuels). This stores carbon underground. 5. Human activities, such as mining, cutting and burning forests, and burning fossil fuels, release carbon dioxide into the atmosphere. D. Steps in the Carbon Cycle Students should label the diagram of the carbon cycle as the steps below are covered. Copyright ã Amy Brown Science 8  1. In the atmosphere, carbon is present in the form of carbon dioxide. 2. This carbon dioxide is released to the atmosphere by cellular respiration, volcanic activity, the burning of fossil fuels and by the decomposition of organic matter. 3. Plants (autotrophs) take in the carbon dioxide and use it during photosynthesis to build molecules of glucose. 4. The glucose molecules and other carbohydrates are passed up the food chain to animals and other consumers. 5. The ocean also serves as a storage area for carbon. Many marine organisms combine carbon, calcium and oxygen to form calcium carbonate. This calcium carbonate accumulates in marine sediments and in the bones and shells of many marine organisms. Eventually these compounds break down and the carbon returns to the atmosphere. E. The Human Impact on the Carbon Cycle 1. In the last 150 years, the concentration of carbon dioxide in the atmosphere has risen dramatically. Most of this increase has occurred in the last 40 years. The activities of humans are responsible for this huge increase in atmospheric carbon dioxide. 2. Our industrial society depends on the energy that comes from the burning of the fossil fuels such as oil, coal and natural gas. But the burning of these fossil fuels increases the amount of carbon dioxide entering the atmosphere. 3. Life on Earth depends on the “greenhouse effect”. Carbon dioxide, water vapor and other gases trap the heat from the sun in our atmosphere. This warms the Earth and insulates it from the deep cold of space. 4. However, the increase of carbon dioxide also increases the greenhouse effect. Today, too much heat is being trapped by the atmosphere and this has led to the current period of global warming. VII. The Nitrogen Cycle A. All organisms must have nitrogen in order to build proteins and nucleic acids. B. Nitrogen gas makes up about 78% of Earth’s atmosphere. It would appear that nitrogen is readily available for use in manufacturing proteins and amino acids. However, most organisms do not have the ability to make use of atmospheric nitrogen. C. Nitrogen is also found in ammonia, the bodies of dead plants and animals, and in the wastes (both urine and feces) of living organisms. D. The nitrogen cycle is possible only because of several different types of soil-dwelling bacteria. Each type of bacteria plays a particular role in the recycling of nitrogen. Copyright ã Amy Brown Science 9 E. Nitrogen Fixation 1. A special group of soil-dwelling bacteria, known as nitrogen-fixing bacteria, are able to transform atmospheric nitrogen into a form that other living cells can use. 2. These bacteria take nitrogen from the air and convert it into nitrates (NO3-). 3. Nitrogen Fixation: The process of converting nitrogen gas to nitrates. 4. The nitrates are absorbed by the roots of plants. Plants use nitrates to build proteins and nucleic acids. 5. The nitrogen is then passed up the food chain. F. Steps of the Nitrogen Cycle Have students fill in the blanks on their diagram as you discuss the steps below The nitrogen cycle is a complex cycle with five important processes: 1. Nitrogen Fixation: The process of converting atmospheric nitrogen into ammonia and nitrates. 2. Ammonification a) Many animals excrete and eliminate nitrogen in urine and in feces. Soil bacteria convert these waste products into ammonia (NH3). In addition, these bacteria convert the nitrogen compounds in dead plants and animals to ammonia. b) Some of this ammonia is absorbed by plants and used to make proteins and nucleic acids. c) Ammonification is the production of ammonia by bacteria during the decay of nitrogen containing organic matter. Copyright ã Amy Brown Science 10  3. Nitrification a) Some of the ammonia in the soil is converted by several kinds of bacteria to nitrates, NO3-. b) These nitrates are absorbed from the soil by plants. c) Nitrification is the production of nitrates from ammonia. 4. Denitrification a) Another kind of bacteria acts on the remaining nitrate, converting it back into nitrogen gas. b) This nitrogen gas is released into the atmosphere. c) Denitrification is the conversion of nitrate to nitrogen gas. 5. Assimilation a) Ammonia and nitrates are picked up by plants. b) Plants use ammonia and nitrates to build proteins and nucleic acids. c) When animals eat the plants, they use the nitrogen to build their own proteins and nucleic acids. d) Nitrogen assimilation is the absorption and incorporation of nitrogen into plant and animal compounds. G. The nitrogen cycle requires 4 different types of bacteria. What is the role of each of the following groups of bacteria? 1. Nitrogen – fixing bacteria: They are able to take atmospheric nitrogen and convert it to ammonia. 2. Ammonifying bacteria: These are the decomposers. They break down dead, organic matter and convert it to ammonia. 3. Nitrifying Bacteria: These bacteria convert ammonia to nitrates. 4. Denitrifying bacteria: These bacteria consume nitrates and release elemental nitrogen back into the atmosphere. VIII. The Phosphorus Cycle A. Phosphorus is essential in all living organisms because it is needed to build molecules of ATP and the nucleotides that compose DNA and RNA. B. Although phosphorus is of great biological importance, it is not very common in the biosphere. C. Unlike the other essential elements that are recycled such as carbon, nitrogen, and oxygen, phosphorus does not enter the atmosphere. Copyright ã Amy Brown Science 11  D. Phosphates are usually present in rocks and soil as calcium phosphate. Calcium phosphate dissolves in water to form inorganic phosphate ions. As phosphates are released from soil and rocks, it washes into streams and rivers, eventually making its way to the oceans where it is used by marine organisms. E. Some phosphates remain on land and cycle between organisms and the soil. F. When plants absorb phosphate from the soil or from water, they bind the phosphate into organic compounds. The phosphate moves through the food web from producers to consumers. IX. Nutrient Limitation A. As we have already learned above, primary productivity is the rate at which organic compounds are created by producers during photosynthesis. A factor that determines the primary productivity of an ecosystem is the amount of nutrients available. B. Limiting nutrient: A limiting nutrient is a single nutrient (such as nitrogen or phosphorus) that either is scarce or cycles very slowly, limiting the growth of the organisms in the ecosystem. Created by Amy Brown Copyright © Amy Brown Science All rights reserved by author. This document is for your classroom use only. This document may not be electronically distributed or posted to a public web site, except for intended use by the author. http://www.teacherspayteachers.com/Store/Amy-Brown-Science Copyright ã Amy Brown Science 12