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Energy, ecosystems and nutrient cycles GapFill
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Producers convert sunlight into chemical energy using from their surroundings. The sugars produced are mainly used as respiratory substrates, but the remainder make up biological molecules to form biomass. The amount of biomass in a sample can be estimated using calorimetry.
feed on other organisms, and food chains can be used to describe these feeding relationships, with each stage representing a different , and arrows representing the direction of energy flow.
The total chemical energy in plant biomass in a given area or volume is referred to as (or as NPP when respiratory losses are taken into account). Biomass transfer is generally inefficient, with less energy available at each successive stage of a food chain, so productivity, measured in , is generally quite low. In order to maximise the biomass for human consumption, it is important to simplify by eliminating weeds (which compete for resources) and insect pests (that compete directly with people).
As well as biomass, nutrients are cycled along food chains in ecosystems before being released into the soil. Nitrogen is important for synthesising proteins and nucleic acids, but most organisms cannot make use of gaseous nitrogen. Nitrogen fixation is the process by which mutualistic bacteria living in nodules on plant roots convert nitrogen gas to , and then to amino acids, gaining carbohydrates in return. This process can also occur industrially or via lightning strikes.
Three other processes are essential in cycling nitrogen:
is another nutrient which must be recycled in an ecosystem. Organisms need it to make ATP, phospholipids and nucleic acids, but as it does not exist in a gaseous form, it is mostly obtained from sedimentary rocks. recycle this element when organisms die, as some of it remains as bones or shells and can be transported by water back into oceans to form rocks.
can replace minerals lost when crops are removed during farming. They can be organic, i.e. composed of decaying material and waste, or inorganic. It is generally best to use a mixture of both of these to get appropriate quantities of different minerals while releasing them slowly over time. Care must be taken, however, to avoid them leaching into water and causing , which can lead to algal blooms, which limit the growth of fish and aquatic insects.