Explain how matter cycles between the living and nonliving components of an ecosystem. Be able to outline the biogeochemical cycles of water, carbon, oxygen and nitrogen as examples of how matter cycles though an ecosystem. Explain how toxins become more concentrated along food chains.
So far we have looked at how energy flows through an ecosystem As energy travels though an ecosystem it is lost an cannot be reused. All energy eventually leaves the ecosystem in a form that cannot be used. Luckily this energy is continually being replaced by the sun. Energy inputs equal energy outputs and balance is maintained.
Matter cannot be created or destroyed. The matter that currently exists on Earth will never leave it nor will new matter be created. Matter will simply cycle between the living and non-living components of any ecosystem recycled over and over again. In this way, ecosystems stays balanced and inputs equal outputs.
Decomposers play a vital role in recycling matter. They take the matter lost in waste products and dead tissue and turn into into simple compounds ready to be used by producers and returned to the food chain. These simple compounds (organic matter) in the soil are known as humus. Detritivores consume dead matter and in turn become a food source returning the matter to the food chain.
A more familiar example of the cycling of matter is the exchange of oxygen and carbon dioxide between plants and animals. We know that plants consume carbon dioxide and produce oxygen in the process of photosynthesis. Oxygen is a plants waste product while carbon dioxide is like a nutrient.
Animals on the other hand require oxygen for cellular processes (in particular respiration) and produce carbon dioxide as a waste product. Plants produce oxygen which is taken in by consumers and used for respiration. Consumers produce carbon dioxide when then they respire and this in turn is taken up by plants and used during photosynthesis.
If you think about the individual atoms of matter one particular atom can be found in a producer at one time, a consumer at another time and in the soil in another instance. It is possible that one of the atoms within your body was once an atom that belonged to the body of Leonardo Di Vinci or Charles Darwin!
We need to recognise that certain compounds are required for the survival of living things. For organisms to grow, reproduce and maintain life they need a supply of elements (atoms) of which their tissues are made. Nutrient cycles describe how particular elements cycle through a system. They have two parts: a biological component showing how the element cycles through living organisms and a geochemical component showing how the element cycles through non-living components such as soil, rocks, water and the atmosphere. Nutrient cycles are also known as biogeochemical cycles.
All living things need carbon. It forms the basis of all organic material- carbohydrates, fats, proteins and nucleic acids.
Carbon cycles through the organic compounds of living things and their non- living surrounds in a number of ways.
Carbon is unique in that it can cycle without the aid of decomposers. Sometimes dead material does not decay because it exists in an anaerobic (no oxygen) or highly acidic environment. In such situations the organic material may accumulate to form fossil fuels such as peat, coal, oil and gases. The amount of carbon in the atmosphere is maintained largely by a balance between photosynthesis, which withdraws carbon dioxide from the atmosphere, and respiration and combustion, which add carbon dioxide to the atmosphere.
Oxygen is a waste product of photosynthesis but is required as in input in cellular respiration. In this way, oxygen cycles from plants, to the atmosphere, and then to animals. In a balanced system the amount of oxygen required for cellular respiration equals the amount produced by photosynthetic organisms.
Nitrogen, just like carbon and oxygen, is an essential element needed by living organisms. Proteins are involved in cell control and the growth of new cells. Nitrogen (N2) makes up about 80% of the atmosphere but plants are unable to take in nitrogen from the atmosphere. Most plants can only absorb nitrogen in the form of nitrates from the soil. Animals rely on plants for their source of nitrogen. The nitrogen cycle is more complicated than the carbon and oxygen cycle and relies on three types of bacteria: the fixers, the nitrifiers and the denitrifiers. Nitrogen can only be removed from the atmosphere in two ways: by lightening or by nitrogen fixation.
In order for nitrogen to be usable by plants it needs to be “fixed”- free nitrogen is combined with hydrogen or oxygen to form ammonium (NH4) or nitrate (NO3). The process of nitrogen fixation is carried out by certain types of bacteria in the soil. The bacteria absorb nitrogen gas from air spaces within the soil. Some bacteria enter the roots of plants such as casuarinas, acacias and legumes (clover, peas, beans) causing the plant to form swellings called nodules. It is in these nodules that the bacteria fix nitrogen.
Ammonia (NH3) is released in urine and decay of faeces, dead plants and animals. Nitrifying bacteria in the soil convert this ammonia to nitrites (NO2-). Other bacteria then convert the nitrites to nitrates (NO3-) which can be taken up by plants. Animals obtain nitrogen by eating plants.
Converting nitrates back to nitrites releases oxygen. This the reverse of the nitrification needed by plants to be able to absorb nitrogen. Bacteria in waterlogged soils denitrify nitrates to produce much needed oxygen. While the oxygen is used by the bacteria, the nitrites are released back into the atmosphere and the nitrogen cycle starts again.
Water is essential for the proper functioning of cells. The water cycle describes how water circulates through an ecosystem. The water cycle is driven by two energy sources: solar energy and gravity. This cycle involves the processes precipitation, infiltration, percolation, evaporation, transpiration, and condensation.
Some materials are not biodegradable- decomposers cannot break them down. Such materials include pesticides and heavy metals such as mercury. These materials can be taken up by producers in small, insignificant amounts. However as these materials get passed from one organism to the next in a food chain and biomass declines they accumulate and become more concentrated. This process of concentration is referred to as biological magnification or bioaccumulation. It can affect top consumers to the point their vital organs do not work properly, they do not reproduce and death rates rise.
Dichloro-diphenyl-trichloroethane (DDT) was introduced in 1943. It was used commonly as a spray to control insect pests, especially mosquitoes. DDT molecules break down only slowly (they are non-biodegradable) and are not excreted. They accumulate in the body fat of fishes and birds. Because the biomass is less at each level along the food chain, the molecules become concentrated in the tissues of the consumers.
In the 1950s, some doctors became concerned when organochlorine compounds such as DDT were detected in cow’s milk, after the animals fed on food that had been sprayed with insecticides. DDT has been found to interfere with the formation of egg shells. Birds’ eggs become fragile, and they break before young can hatch. A dose of DDT that may not kill an adult can be lethal to offspring. The peregrine falcon in Australia was greatly affected in this way. The use of DDT was banned in Australia in 1987.