ENERGY FLOW THROUGH THE ECOSYSTEM
A food chain is a diagram that is drawn up to show the feeding relationship in a community, with arrows to show the energy flow.
Plants are at the bottom of the food chain. They contain the highest amount of energy which they obtain from sunlight. Other food chains are supported by bacteria that can trap chemical energy.
Food webs give a more accurate picture of what happens in an ecosystem, since they show how an organism can be in different trophic levels of the different food chains that make up a food web.
80-95% of the energy is lost as heat or used for maintenance by the plant. Energy is lost as heat as it moves from producer to the rest of the consumers. Therefore, most energy in an ecosystem is lost through metabolic heat.
Fact:
Plants produce glucose during photosynthesis. Plants also breakdown the glucose molecules (respiration) and use the energy released for maintenance activities, such as growth, repair, and reproduction. Some of the energy is lost through excretion and it is transferred to decomposers.
Pyramids of energy – graphical model of energy flow through trophic levels in a community. The width of the block indicates how much energy it contains.
Usually, only 10% of the energy from one trophic level is transferred to the next level. However, energy flow is affected by other factors so this percentage may vary between 5-10%.
Gross primary production (GPP) – amount of organic matter synthesized by producers. It refers to the total productivity including energy used for respiration by the producers.
Net primary production (NPP) – amount of organic matter stored by producers. It is the productivity of the producer excluding the energy used for respiration.
Pyramids of energy:
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They show how much energy is left at each trophic level.
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Each row represents a trophic level: eg, producers, primary consumers etc.
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Only 10% of energy flows from one level to the next in an ideal situation.
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Actual transfers depend on many factors and vary between 5% and 20%.
Where is the energy lost?
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Some is lost through metabolic heat and net system loss (i.e. heat, respiration, and maintenance.)
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Some is transferred to ‘organic wastes and remains’ which eventually reaches the decomposers.
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Eventually all of the energy that flows through the ecosystem is lost as metabolic heat.
Where does the initial energy come from?
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The sun provides the initial energy which is used by producers to manufacture their nutrients.
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The producers only absorb about 1.2% of the energy from the sun, the rest is lost.
