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Matter in Ecosystems
Science 1206
Cycling of Matter in Ecosystems
• Organic substances –
– Contain atoms of Carbon and Hydrogen
– Are broken down into simpler forms in living things
– Ex. Sugar, carbohydrates, proteins, amino acids
• Inorganic substances –
– Does not contain combination of carbon and
– Ex. Water (H2O), ammonia (NH3), Carbon dioxide
Matter: Recycled
• The atoms and molecules available to make
up organisms on earth is limited
• All the atoms MUST be recycled in order
for new organisms to form.
– It is very likely that at least one
of the carbon atoms in your body
was also in a a 70 million year old
The Matter Cycle
1. Dead plants and animals are broken
down by decomposers – their atoms /
molecules are released into the system to
be re-used
Atoms, molecules accumulate in the soil
3. Nutrients are taken up by grasses
4. Cows eat the grass – nutrients and atoms
are passed on to the cow
5. Person eats cow – nutrients and atoms
are passed on to person
6. Each of these things can die, the atoms
are broken down by decomposers and
recycled for the next living things
The Oxygen Cycle
Respiration from plants
and animals
Photosynthesis by
green plants
Carbon Dioxide
Respiration from
Note: The complementary processes of
photosynthesis and respiration ensure that not
only oxygen, but also carbon and hydrogen
are repeatedly cycled.
6 CO2 + 6 H2O + light ------> C6H12O6 + 6O2
C6H12O6 + 6O2 ------> 6CO2 + 6H2O + energy
The Carbon Cycle
• In the carbon cycle we use CO2 from both biotic and
abiotic sources:
• 1. Biotic: aerobic respiration (in the presence of
CO2), and decomposition.
• Note: Here, the organic reservoirs (storage areas)
for carbon are the bodies of living things.
• 2. Abiotic: combustion and geological activity
• Note: Here, the inorganic reservoirs for carbon are
the atmosphere, the oceans, and the Earth’s crust.
• See page 62, figure 1.
CO2 in the atmosphere
Photosynthesis carbon is stored in
the biomass
Conversion to fossil fuels
in water
Fossil fuels
The Nitrogen Cycle
• The movement of nitrogen through the ecosystems,
the soil, and the atmosphere is called the nitrogen
• Nitrogen gas composes 79% of the Earth’s
atmosphere, but in this inorganic form it can not be
used by animals. In order for nitrogen to be useful to
organisms, it must be converted to a nitrate ion
(NO3-) by the process of nitrogen fixation, or
nitrification, either by lightning or by bacteria in
the soil.
• Nitrogen is required to make proteins and DNA
which is the genetic material found in every cell.
Plant protein
Atmospheric nitrogen (N2)
Animal protein
Death and decomposition
Ammonification (NH3)
Nitrification to nitrites (NO2-)
Nitrification to nitrates (NO3-)
Denitrifying bacteria
Pests and Pesticides
4 Types of Pesticides
• Herbicides : kills plants
• Insecticides : kills insects
• Fungicides : kills fungi
• Bactericides : kills bacteria
First-Generation Pesticides
• metals such as arsenic, lead and
• These were found to be toxic to
humans, polluted water and soil
and were not biodegradable (not
able to break down naturally).
Second-Generation Pesticides
• 20th century pesticides were generally man
made organic chemicals in a lab designed to
be less toxic to humans and were capable of
breaking down within the ecosystem.
• However, it was found that some of these
chemicals were fat soluble and became
stored within animal tissues. This created a
problem known as bioaccumulation.
Bioaccumulation & Bioamplification
• Bioaccumulation – An increase in
the concentration levels of a
pesticide within the body of an
organism over time.
• Bioamplification – Where a species
at a higher trophic level feeds on
more that one organism below it,
pesticide concentrations tend to
increase rapidly the higher up the
food chain you look.
Figure 4 on page 54 in your book
For Bioamplification to occur…
• Long-lived Present for a long time in the system
• Mobile Easily passed up the food chain
• Soluble in fats Dissolves in, and is stored in fatty tissue
• Biologically active –
Affects biological body tissue
Pesticides - Past and Present
• Past Chemical Pesticides:
–Stored in fat tissue
–Not soluble in water
• Modern Chemical Pesticides:
–Not stored in fat tissue
–Soluble in water
Pesticide Resistance:
• Over time some species of
‘pest’ become resistant to the
pesticide. Meaning the
pesticide no longer effects
• The survivors then have
offspring which are mostly
• These individuals survive the
next spraying. If a similar
pesticide is often used, resistant
pests will soon make up most of
the population.
• See fig. 5 pg. 55
Dichloro, Diphenyl Trichloroethane
• Pesticide that is suitable for bioamplification
• Has a half-life of 15 years
– That is, every 15 years the amount left in the system
will be reduced by one half.
– If you use 100 kg of DDT, after 15 years it will be
reduced to 50 kg, and after another 15 years it will
be 25 kg, and so on..
Effects of DDT in Birds
Shell thinning
1. Carnivorous birds such as ospreys and bald
eagles eat other birds, dead animals and fish
which contain a build-up of DDT
2. DDT causes the shells to become too thin to
allow the large females to sit on the eggs
without them breaking
3. Since eggs are being broken, the over-all
population of these birds is declining
• After DDT was banned in the US and
Canada in the early 1970’s the bird
populations of began to recovered.
• DDT bioaccumulates in humans the same as
it would other animals
• Male birds have also become more feminine
as the DDT mimics female sex hormones
1. Not all countries, like Mexico for
example, have banned the use of DDT.
Since birds migrate from winter to summer
from one country another, do you think the
birds are 100% safe from the presence and the
effects of DDT? Why?
2. How do you think a pesticide like DDT
would affect the over all biodiversity in an