Natural Ecosystems

• In a natural ecosystem there is close interaction between the plants and animals
• The green plants are the producers
• The animals are the consumers
• There are several levels of consumers
• Primary consumers-these eat plants directly
• They are also known as herbivores
• Secondary and tertiary consumers eat other animals
• The relationship and links between these producers is shown by a food chain
• Each food chain relies on energy from the sun
• Each link level is also known as a trophic level
• Trophic level-is a feeding level in the food chain
• Energy is transferred from one trophic level to another as each level is used by another level
• As organisms die they are broken down by decomposers
• The nutrients trapped in the living organisms are released back into the soil for use by plants
• Decomposers such as bacteria are not typically included in the food chain diagrams
• There are many different food chains around us
• There are links between food chains
• These links join food chains to form food webs
• A food web is made up of plants and animals which are closely linked by their feeding relationships
• For example there may be four consumers feeding on the same type of plant each consumer with its own chain
• The more organisms are in a food web the more stable it is
• This is because if one organism dies out, there are other organisms that can carry out a similar role in the food web
• While energy is transferred from one trophic level to another in a food chain there is a limit to the number of consumers in a food chain because energy is lost at each level
• At each trophic level the organism uses some of the energy for itself
• More energy is lost to the environment as heat
• Some energy may also be lost as sweat, excretion or feces
• There is only one source of energy input in the cycle i.e the sun
• There is one way flow of energy along and out of the food chain
• Because energy is lost at each trophic level the number of organisms at each level is restricted
• As a result there are usually not more than four levels of consumers in a food chain
• The amount of organisms decrease as one goes up the food chain to the upper trophic levels
• The amount of living material is known as a biomass
• The relationship between organisms can be shown in a pyramid of biomass
• When organisms in a food chain die they are processed by decomposers
• Some of the energy that is trapped in their bodies is used by the decomposers
• Decomposers include fungi and bacteria
• These decomposers recycle components or nutrients in the soil
• Two mineral elements that are part of all living organisms are nitrogen and carbon
• All organic components contain carbon in the form of organic components
• I is the main essential element in carbohydrates, fats and proteins
• Nitrogen is essential for protein manufacture and growth in plants and animals
• These two elements are constantly being recycled in the ecosystem

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