2.  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.

3.  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.

4.  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.

5.  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.

6. A familiar Example

7.  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.

8.  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.

9.  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!

10.  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.

12.  All living things need carbon. It forms the
basis of all organic material- carbohydrates,
fats, proteins and nucleic acids.

13.  Carbon cycles through the organic
compounds of living things and their non-
living surrounds in a number of ways.

15.  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.

17.  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.

19.  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.

20.  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.

21.  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.

22.  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.

27.  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.

30.  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.

31.  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.

32.  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.