Energy and Ecosystems

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Food Chains and Food Webs 5.1

  • Producers: Photosynthetic organisms that manafacture organic substances using light energy, water and carbon dioxide   6CO2 + 6H2O ---->  C6H12O6  +  6O2
  • Cosumers: Organisms that obtain their energy by feeding on other organisms e.g. animals. Those that directly eat producers are called primary consumers, and those that eat primary consumers are called secondary consumers and so on. Secondary and tertiary consumers are often predators but can be parasites/scavengers.
  • Decomposers: Organisms that break down complex materials of dead producers/consumers into simple components. This release valuble minerals and elements in a form that can be absorbed by plants. Examples are fungi and bacteria.

Food Chains: Describes a feeding relationship between the producers and consumers (primary, secondary, tertiary). Each stage in this chain is referred to as a trophic level. Arrows on food chain diagrams represent the direction of energy flow.

Food Webs: Illustrates how diifferent food chains are linked together. Their complexity means that they can be very hard to chart as thousands of organisms are often linked together and these links change depending on the time of year, age and popualtion size.

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Energy Transfer between Trophic Levels 5.2

  • Energy loses in food chains: Most of the sun's energy is not converted to organic matter by photosynthesis because 1.Reflected back into space 2.Not all wavelengths can be absorbed and used for photosynthesis 3. Light may not fall on a chlorophyll molecule 4. Limiting factors e.g CO2 levels may affect the rate of photosynthesis
  • Gross production: Total quantity of energy that the plants in a community convert to organic matter
  • Net production: The rate at which a plant stores energy, Net production= gross production- respiratory loses
  • The low percentage of energy transferred at each stage (e.g. between the primary and secondary consumer) is a result of 1.The whole organism isn't eaten 2.Some parts cannot be digested so is lost in faeces 3.Lost in urine 4.Lost as heat from respiration (movement, maintaining body temperature)
  • The loss of energy explains why 1.Most food chains only have 4 or 5 trophic levels 2.The biomass of organisms is less at higher trophic levels 3.The total amount of energy stored is less at each level
  • Energy transfer= (energy after transfer/ energy before transfer) x100
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Ecological Pyramids 5.3

  • Pyramids of number: Bars are drawn with lengths proportional to the number of organisms present at each level. Disadvantages 1.No account is take of size of organism 2.Cannot accurately represent large numbers
  • Pyramids of biomass: The biomass at each trophic level is measured. Biomass is measured in gm-2 (area) or gm-3 (volume). Disadvantages 1.Organism must be dead= small sample size
    2.Doesn't illustrate seasonal differences (in early spring the biomass of zooplankton in greater than phytoplankton
  • Pyramids of energy: Measures the energy stored in organisms, (measured in KJ m-2 year-1). The most accurate representation of energy flow because it takes into account that two organisms with the same bimass may have differrent amounts of energy stored dye to fact storing more energy than carbohydrates. Disadvantages 1.difficult and complex (data must be collected in the area over a year)
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Agricultural Ecosystems 5.4

  • Agricultural Ecosystem: Made up of domesticated animals and plants, used to produce food for mankind. Tries to ensure that as much of the available energy from the sun as possible is transferred to humans. This increases the productivity of the human food chain.
  • Productivity: The rate at which something is produced. Net productivity is important in agricultural ecosystems and is affected by two factors 1.The efficiency a crop carries out photosynthesis 2.Ground covered by leaves of the crop

Natural vs Agricultural Ecosystems:

  • Energy input: Natural ecosystems use only solar energy whereas in agriculture additional energy is put in in order to remove unwanted species and to maximise growth, this done through food and fossil fuels (ploughing, harvesting ect.)
  • Productivity: In natural ecosystems productivity is low, productivity in agriculture is increased by removing competition, using fertilisers and using pesticides.
  • Natural ecosystems have a higher species diversity and a higher genetic diversity within species
  • Natural ecosystems reach a climax communtity whereas is agriculture this is prevented
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Chemical and Biological Control of Agricultural Pe

  • Pests and Pesticides: A pest is an organism that competes with humans for food or space, a pesticid is a poisonous chemical that kill pests. They are names after the pests they kill e.g. herbicides kill plants. An effective pesiticide should be specific, biodegradable, cost effective and non accumulative.
  • Biological Control: It is possible to control pests by using organisms that are either predators or parasites of the pest organism. The aim is to control the pest but not to eradicate it so that there is still an available food source for the predator/parasite. Disadvantages: 1.There is an interval of time before they control the pest 2.The control organism may become the pest
  • Biological vs chemical:-Biological is specific and the control orgnisms reproduces itself  -Pests do not become resistant to biological control
  • Integrated pest-control systems: Aims to integrate all forms of pest control rather than being reliant on one type. The emphasis is on deciding the acceptable of the pest rather than eradicating it.
  • How controlling pests affects productivity: Pests reduce productivity in agriculture as they act as competition with plants are cause disease in animals. The demand for cheap food must be balanced with the conservation of natural resources.
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Intensive Rearing of Domestic Livestock 5.6

Intensive rearing and energy conversion:
Intensive rearing is about converting the smallest possible amount of food energy into the greatest quantity of animal mass. Energy conversion can be made more efficient by ensuring that as much energy from respiration goes into growth rather than other activities. This achieved by:

  • Restricting movement
  • Maintaining a warm environment
  • Controlling feeding
  • Exclusion of predators
  • Selectively breeding animeals that are more efficient at converting food into body mass
  • Using hormones to increase growth rates
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Intensive rearing of domestic livestock 5.6

Economic and environmental issues with intensive rearing:

  • Finding a balance between cheap food and conserving the environment
  • Diminshes the variety of habitats within ecosystems which has led to a reduction in biodiversity e.g. the removal of hedgerows and wood land and the creation of monoculture
  • The introduction of fertilisers and pesticides
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