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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Link to image: click here
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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. |
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. |
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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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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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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