Science 1206
Unit 1- Topic 3
Cycling of Materials in Ecosystems
Organic and Inorganic Materials

Organic Materials
– Made up of Carbon and Hydrogen. Usually
contains Oxygen and Nitrogen as well.
– Living things are composed of organic
compounds.
– Eg. Sugar

Inorganic Materials
– Don’t contain Carbon AND Hydrogen
– Eg. Carbon dioxide
Cycling of Matter



Many, if not all, of the carbon and other
molecules in our bodies once belonged to other
organisms.
Carbon, Nitrogen, and Phosphorus are just a few
of the compounds that are cycled through the
environment.
Eg. Caplin and seaweed were used as fertilzer
for nfld gardens. Nutrients in the caplin and
seaweed passed to the potatoes and then to
humans.
The role of Decomposers

Decomposers, such as bacteria, turn
organic molecules in waste (feces, dead
organisms) into inorganic molecules which
can then be used by plants again.
Carbon-Oxygen Cycle

The Carbon-Oxygen Cycle is
interconnected and involves three major
processes and one minor process:
– Photosynthesis
– Respiration
– Combustion
– Decomposition

See http://www.slideshare.net/melissamercer/carbonoxygen-cycle
Photosynthesis

Green plants take in carbon dioxide and
water; using the chlorophyll in their leaves
and energy from the sun they release
oxygen, sugar and water vapour.
 6CO2 + 6H2O + Light Energy  C6H12O6 + 6O2

Carbon Dioxide + Water + Light Energy  Glucose + Oxygen
Respiration
Animals take in simple sugars and oxygen
then release carbon dioxide, water and
energy
 C6H12O6 + 6O2  6H2O +6CO2


Glucose + Oxygen  Water + Carbon Dioxide
Complementary Processes

Because the products of photosynthesis
become the reactants of respiration AND
IN TURN the products of respiration
become the reactants of photosynthesis,
photosynthesis and respiration are known
as complementary processes.
Combustion


This is the process of burning. When combustion
occurs CO2 is released into the atmosphere.
Natural combustion includes volcanic eruptions,
however most pollution problems occur because
cars and factories release CO2 by their burning
fossil fuels.
Combustion with pure Oxygen:
– Fuel + Oxygen  Heat + Water + Carbon Dioxide

Combustion in Air:
– Fuel + Air  Heat + Water + Carbon Dioxide +Nitrogen
Decomposition
When a plant or animal dies, all the
carbon, oxygen, nitrogen, water, etc.
return to the soil and the air during
decomposition. Certain insects, fungi, and
bacteria (called decomposers) aid in the
decomposition process.
 The decomposers turn the organic waste
into inorganic compounds.

Reserves of Carbon

Carbon is constantly being cycled
throughout the environment through the
carbon-oxygen cycle. However, that
process takes time and therefore carbon is
stored in various places and forms during
that cycle, delaying the cycle.
Reservoirs of Inorganic Carbon
Atmosphere – Carbon Dioxide
 Oceans

– Dissolved carbon dioxide
– Carbonate ions
– Bicarbonate ions
– Calcium Carbonate

Earth’s Crust
– Carbonates eg Limestone
Reservoirs of Organic Carbon
Bodies of living things.
 Peat Deposits ( eg in Bogs)
 Fossil Fuels

Nitrogen
Nitrogen is used for the production of
protein and DNA in living things.
 79% of the atmosphere is composed of
nitrogen (N2) but living things cannot use
nitrogen in that form.
 Nitrogen must be supplied to organisms in
the form of nitrates (NO3-).
 A lawn with a rich green colour has plenty
of nitrates.

The Nitrogen Cycle
Like Carbon, Nitrogen is also constantly
cycled through the environment.
 The nitrogen cycle is actually very
complex and we will study just a simplified
model.
 Several processes are required for the
cycling of nitrogen.

Nitrogen Fixation


Nitrogen fixation is the process of combining
Nitrogen (N2) and Oxygen(O2) into nitrates (NO3).
Nitrogen fixation can take place in a number of
ways:
– 1. Lightning – the energy from the lightning causes
nitrogen to react with oxygen in the air producing
nitrates. A very small amount of nitrates are produced
this way.
– 2. Nitrogen Fixing Bacteria – These bacteria,
found mostly in soil, produce the vast
majority of nitrates. These bacteria are also
found in clumps (called nodules) on the
roots of legumes. There is a symbiotic
relationship between the bacteria and the
plant. The plant gets the nitrates it needs to
survive from the bacteria and the bacteria
gets the sugar it needs from the plant.
– 3. Decomposers – all organisms produce
waste and die. The resulting organic waste is
broken down by decomposers into inorganic
compounds. Some of the bacteria that
decompose the waste produce ammonia
(NH3). Then others take the ammonia and
turn it into nitrites(NO2) and others take the
nitrites and produce nitrates (NO3-).
Nitrogen Cycle Diagram
Denitrification
The process where by denitrifying bacteria
change Nitrates (NO3-) to nitrites (NO2-)
and then nitrites back into nitrogen gas
(N2) .
 Denitrifying bacteria do not require
oxygen, so aerating lawns helps to stop
the denitrifying process which keeps the
soil rich in nitrates.

Fertilizer


Fertilizers are materials used to restore nutrients
and increase production from land.
When crops are harvested from a field or when
grass is raked up and taken away from your
lawn. The nutrients that were in those plants
are also removed from that area. Farmers and
landscapers use fertilizers to replenish the
nutrients that have been removed.
Fertilizer and Soil Acidity (pH)
Bacteria convert the nitrogen in fertilizers
into nitrates, but too much fertilizer may
result in high levels of nitric acid which
affects the organisms living in the soil.
 For most crops favour a neutral pH
(pH=7). Some sensitive crops will not
grow if the pH is below 6 and very few
commercial crops will grow in soil with a
pH less than 5

Fertilizer and Ecosystems

Runoff from farms and golf courses,
where fertilizers are used, carries access
nutrients into ponds and streams. The
extra nutrients cause algae to grow
quickly (known as an algal bloom). When
the extra algae die, the decomposers use
up a lot of the oxygen to digest the waste
materials. This leaves the water with too
little oxygen to support the larger
consumers such as fish.
More Fertilizers and Ecosystems

Raised nitrate levels cause another
problem. You should recall that
denitrifying bacteria change nitrates to
nitrites. Nitrites are dangerous to animals
because it attaches to hemoglobin in the
blood and reduces its ability to carry
oxygen.