Ecosystems
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An ecosystem is a community of living organisms and their abiotic (non-living) environment. Ecosystems can be small, such as the tide pools found near the rocky shores of many oceans, or large, such as those found in the tropical rainforest of the Amazon in Brazil. All organisms in an ecosystem are connected. One connection is through feeding relationships. Food chains and food webs are way to map how organisms are connected through their feeding relationships.
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A (a) tidal pool ecosystem in Matinicus Island, Maine, is a small ecosystem, while the (b) Amazon rainforest in Brazil is a large ecosystem. (credit a: modification of work by Jim Kuhn; credit b: modification of work by Ivan Mlinaric)
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Studying an ecosystem means looking at the interactions between the living organisms and between the living organisms and the non-living factors in the environment. Organisms interact with with other by feeding off each other and competing for resources. Organisms interact with the environment because they need to get matter from the environment to grow and for shelter. Other, non-living, factors in the environment also affect their health such as the amount of water, the temperature, and the amount of sunlight.
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Moving Matter and Energy through an Ecosystem
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Ecosystems are made of many organisms that interact with each other and the environment to get energy or molecules.
Energy enters the ecosystem as light energy from the sun. Plants then use the light energy to make chemical energy, in the form of glucose. When the plants need to use the energy they perform cellular respiration. On the other hand, if an organisms eats the plant the organism is able to get the chemical energy from the molecules in the plant. If the plant dies then decomposers are able to get the chemical energy from the plant. Molecules move through the ecosystem as plants perform photosynthesis. During photosynthesis, carbon dioxide and water enter the plant. These molecules are converted into glucose, which is stored in the plant, and oxygen, which leaves the plant. The other process that moves molecules through the ecosystem is cellular respiration. During cellular respiration glucose in the plant/animal is converted into water and carbon dioxide. The water and carbon dioxide then leave the organism, going back into the environment. |
Food Chains and Food Webs
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A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another; the levels in the food chain are producers, primary consumers, higher-level consumers, and finally decomposers. These levels are used to describe ecosystem structure and dynamics. There is a single path through a food chain. Each organism in a food chain occupies a specific trophic level (energy level), its position in the food chain or food web.
In many ecosystems, the base, or foundation, of the food chain consists of photosynthetic organisms (plants or phytoplankton), which are called producers. The organisms that consume the producers are herbivores: the primary consumers. Secondary consumers are usually carnivores that eat the primary consumers. Tertiary consumers are carnivores that eat other carnivores. Higher-level consumers feed on the next lower trophic levels, and so on, up to the organisms at the top of the food chain: the apex consumers. In the Lake Ontario food chain, shown to the right, the Chinook salmon is the apex consumer at the top of this food chain. One major factor that limits the number of steps in a food chain is energy. Energy is lost at each trophic level and between trophic levels as heat and in the transfer to decomposers. Thus, after a limited number of trophic energy transfers, the amount of energy remaining in the food chain may not be great enough to support viable populations at yet a higher trophic level. |
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There is are problems when using food chains to describe most ecosystems. Even when all organisms are grouped into appropriate trophic levels, some of these organisms can feed on more than one trophic level. Also, species feed on and are eaten by more than one species. As the food chain only shows one interaction at each level it is too simple to really explain the flow of matter and energy through the ecosystem.
A more complete model—which includes all the interactions between different species and their complex interconnected relationships is a food web. A food web show all the organisms that eat or are eaten by other organisms in the ecosystem. In a food web, the several trophic connections between each species and the other species that interact with it may cross multiple trophic levels. The matter and energy movements of virtually all ecosystems are more accurately described by food webs.
A more complete model—which includes all the interactions between different species and their complex interconnected relationships is a food web. A food web show all the organisms that eat or are eaten by other organisms in the ecosystem. In a food web, the several trophic connections between each species and the other species that interact with it may cross multiple trophic levels. The matter and energy movements of virtually all ecosystems are more accurately described by food webs.
This text is adapted under a Creative Commons 4.0 license. You can find the original source here.
Summary: Organisms in an ecosystem acquire energy in a variety of ways, which is transferred between trophic levels as the energy flows from the base to the top of the food web, with energy being lost at each transfer. There is energy lost at each trophic level, so the lengths of food chains are limited because there is a point where not enough energy remains to support a population of consumers. Food webs show all the connections between organisms. This makes food webs better at showing the movement of matter and energy through an ecosystem.
Pyramids of Biomass and Energy
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Another way to visualize ecosystem structure is with pyramids of biomass. This pyramid measures the amount of energy converted into organic tissue at the different trophic levels. You should assume that all pyramids of biomass are upright. Biomass is all the organic matter in the organism or trophic level. To measure the biomass you can dry out the organisms and they weigh them. As water is not organic, it is not included in biomass.
Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels. Pyramids of energy are always upright. An ecosystem without enough energy in the producers will not be able to support the next trophic level of organisms. Energy is always lost from one trophic level to the next to there can never be more energy at the top of the pyramid than the bottom. Energy is lost because not all the energy can be transferred up the food chain. Some of the energy that goes into an organism is used for movement, reproduction, etc. That energy cannot be transferred when the organism is eaten as it has been used up. Only about 10% of the energy from one trophic level can be passed to the next level. Pyramids of biomass and pyramids of energy are linked. Energy within the organisms is stored in the biomass of the organism. Therefore, if you have more biomass you will have more energy. This is because the molecules that store energy (the organic molecules with high energy C-C or C-H bonds) are the same molecules that are biomass molecules. |
Pyramids of energy -
In pyramids of biomass or energy you should include all the organisms at at trophic level. If there are 5 different species of producer you would include all of them in the bottom level.
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Carbon Cycle
Carbon is the second most common element in living organisms. Carbon is present in all organic molecules. Since the 1800s, the number of countries using massive amounts of fossil fuels has increased. Since the beginning of the Industrial Revolution, global demand for the Earth’s limited fossil fuel supplies has risen; therefore, the amount of carbon dioxide in our atmosphere has increased. This increase in carbon dioxide has been linked to climate change, and other disturbances of the Earth’s ecosystems, and is a major environmental concern worldwide. Thus, the “carbon footprint” is based on how much carbon dioxide is produced and how much fossil fuel countries consume.
The carbon cycle is most easily studied as two sub-cycles. Rapid carbon exchange occurs among living organisms. Long-term cycling of carbon occurs through geologic processes.
Carbon dioxide is the basic building block that autotrophs (plants) use to build glucose. The energy harnessed from the sun is used by these organisms to form the bonds that link carbon atoms together. These chemical bonds thereby store this energy for later use in the process of respiration. Most terrestrial autotrophs obtain their carbon dioxide directly from the atmosphere, while marine autotrophs acquire it in the dissolved form.
Heterotrophs get the high-energy carbon compounds from the autotrophs by eating them, and breaking them down by cellular respiration to obtain cellular energy, such as ATP. The most efficient type of respiration, aerobic respiration, requires oxygen obtained from the atmosphere or dissolved in water. Thus, there is a constant exchange of oxygen and carbon dioxide between the autotrophs (which need the carbon) and the heterotrophs (which need the oxygen). But don't forget, plants do cellular respiration as well, so they also need oxygen.
The movement of carbon through the land, water, and air is complex, and in many cases, it occurs much more slowly geologically than as seen between living organisms. Carbon is stored for long periods in what are known as carbon pools, which include the atmosphere, bodies of liquid water (mostly oceans), ocean sediment, soil, land sediments (including fossil fuels), and the Earth’s interior. The atmosphere is the main reservoir of carbon in the form of carbon dioxide and is essential to the process of photosynthesis.
Carbon dioxide is the basic building block that autotrophs (plants) use to build glucose. The energy harnessed from the sun is used by these organisms to form the bonds that link carbon atoms together. These chemical bonds thereby store this energy for later use in the process of respiration. Most terrestrial autotrophs obtain their carbon dioxide directly from the atmosphere, while marine autotrophs acquire it in the dissolved form.
Heterotrophs get the high-energy carbon compounds from the autotrophs by eating them, and breaking them down by cellular respiration to obtain cellular energy, such as ATP. The most efficient type of respiration, aerobic respiration, requires oxygen obtained from the atmosphere or dissolved in water. Thus, there is a constant exchange of oxygen and carbon dioxide between the autotrophs (which need the carbon) and the heterotrophs (which need the oxygen). But don't forget, plants do cellular respiration as well, so they also need oxygen.
The movement of carbon through the land, water, and air is complex, and in many cases, it occurs much more slowly geologically than as seen between living organisms. Carbon is stored for long periods in what are known as carbon pools, which include the atmosphere, bodies of liquid water (mostly oceans), ocean sediment, soil, land sediments (including fossil fuels), and the Earth’s interior. The atmosphere is the main reservoir of carbon in the form of carbon dioxide and is essential to the process of photosynthesis.
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Nitrogen Cycle
Getting nitrogen into the living world is difficult. All living things need nitrogen in order to make proteins and DNA. However, while the air is mostly nitrogen, plants and animals are not able to incorporate nitrogen from the atmosphere (which exists in its gaseous form: N2) directly into their bodies. Plants and animals require bacteria to convert the atmospheric nitrogen into a form that is accessible. Bacteria that convert nitrogen from the air are call nitrogen fixing bacteria. Cyanobacteria live in most aquatic ecosystems where sunlight is present; they play a key role in nitrogen fixation. Cyanobacteria are able to use inorganic sources of nitrogen to “fix” nitrogen. Rhizobium bacteria live symbiotically in the root nodules of legumes (such as peas, beans, and peanuts) and provide them with the organic nitrogen they need. Free-living bacteria, such as Azotobacter, are also important nitrogen fixers.
Nitrogen fixing bacteria convert atmospheric nitrogen (N2) into ammonia. Ammonia is then converted into Nitrite and Nitrate. Nitrate is absorbed by plants and incorporated into the proteins and DNA of the plant. Animals get nitrogen by eating plants.
Nitrogen fixing bacteria convert atmospheric nitrogen (N2) into ammonia. Ammonia is then converted into Nitrite and Nitrate. Nitrate is absorbed by plants and incorporated into the proteins and DNA of the plant. Animals get nitrogen by eating plants.
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Human activity can release nitrogen into the environment in two main ways: the combustion of fossil fuels, which releases different nitrogen oxides, and by the use of artificial fertilizers in agriculture, which are then washed into lakes, streams, and rivers by surface runoff. Atmospheric nitrogen is associated with several effects on Earth’s ecosystems including the production of acid rain (as nitric acid, HNO3) and greenhouse gas (as nitrous oxide, N2O) potentially causing climate change. A major effect from fertilizer runoff is saltwater and freshwater eutrophication, a process whereby nutrient runoff causes the excess growth of microorganisms, depleting dissolved oxygen levels and killing ecosystem fauna.
Water and Soil Ecosystems
Ecosystems can be large (we think of the earth as an ecosystem) or very small (a puddle can be an ecosystem). Soil is an ecosystem that contains many microorganisms that you might not be familiar with. The video below shows some of the organisms that can be found in most soils. At the beginning of the video the scientist uses a micropipette to collect a small amount of water that contains the microorganisms.
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Nematodes are the most numerous multicellular animals on earth. A handful of soil will contain thousands of the microscopic worms, many of them parasites of insects, plants or animals.
Protozoa are single-celled animals that feed primarily on bacteria, but also eat other protozoa, soluble organic matter, and sometimes fungi. They are several times larger than bacteria. Fungi are microscopic cells that usually grow as long threads or strands called hyphae, which push their way between soil particles, roots, and rocks. Hyphae are usually only several thousandths of an inch (a few micrometers) in diameter. A single hyphae can span in length from a few cells to many yards. A few fungi, such as yeast, are single cells. Because of its decomposition properties, soil mites love compost. You may find several different species of bin mites in compost, including predatory fast moving mites that are flat and light brown. Water can also be an ecosystem. Pond water contains protozoa, single celled organisms that feed on bacteria, as well as photosynthetic protozoa called algae. Algae is a plant-like protozoa that can perform photosynthesis. As algae is a protozoa we know it is a single celled organism.
Bacteria are commonly found in pond water. These bacteria are responsible for converting nitrogen for the aquatic plants and animals. Bacteria are also decomposers, helping to keep the water clean. Tardigrades are commonly found in pond water. These tiny creatures, which are slightly less than 1 millimeter in length, are also called “water bears,” as they bear a strong resemblance to the large mammals. |
Ecosystems are affected by biotic and abiotic factors. You can test some of these interactions in the virtual lab above.
This video shows some of the organisms you might find in pond water from Ronald Bog. These organisms live together in the water ecosystem.
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Using Microscopes
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The first video explains how to use a dissecting microscope. The second video is an explanation of the parts and usage of a compound microscope. We used the compound microscope to look at water and the dissecting scope to look at soil samples.
Remember, the most important thing about using either scope is to start by using the lowest magnification. |
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