Transcript Change and Sustainability

Cycles of Life
Chapter 2
Key Concepts
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How carbon, oxygen, and nitrogen are cycled
through an ecosystem
How the composition of soil affects an
ecosystem
How human activities affect natural cycles
What is the meaning of sustainability
Life and Death
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Leaves fall, decay, and new plant matter reappears
the next spring-decomposers break down dead
leaves and plant matter
Every organism is made up of chemical elements
such as carbon, oxygen, hydrogen, and nitrogen
Nutrients are chemicals used by organisms to build,
grow, and maintain their bodies
These nutrients are obtained from the surrounding
environment e.g. soil, air, water, other organisms.
Nutrients cycle through the environment
Life and Death
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Planet Earth is a closed system in which there is
little if any input of new materials from outside the
system
Life is sustained by recycling these nutrients
Life requires energy and nutrients
As nutrients cycle, sometimes they are in the biotic
(living) environment and at other times the
abiotic(non-living) part.
Nutrients are input into organisms, then throughput
as they are processed, and then output back to the
environment
The Carbon Cycle
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Plants produce carbohydrates through
photosynthesis which can be summarized by
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6CO2 + 6H2O + energy → C6H12O6 + 6O2
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Where do the reactants come from?
Photosynthesis, Cellular
Respiration, and the Atmosphere
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Photosynthesis involves the capture of sunlight by
green plants and the fixation of atmospheric carbon
into carbohydrate molecules i.e chemical energy
The carbon is present in CO2
When consumers eat plants, the carbohydrates are
broken down and recombined to build animal
tissues. It must be returned to the atmosphere.
This is accomplished through cellular respiration
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6O2 + C6H12O6 → 6CO2 + 6H2O + energy
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Photosynthesis and cellular respiration go
together
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Photosynthesis uses carbon dioxide and produces
oxygen whereas cellular respiration uses oxygen
and produces carbon dioxide.
In this way, carbon is cycled between living things
and their environment
Note that only producers carry out photosynthesis
but all organisms carry out cellular respiration
When organisms die, the remaining carbon in their
bodies is released when bacteria and fungi carry out
cellular respiration
Disrupting the Carbon Cycle
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Recall from “An Inconvenient Truth” that CO2 levels remained
fairly constant for a long time
How has the Carbon Cycle been disrupted?
Much of the carbon cycle takes place in the oceans and lakes i.e
50X as much carbon dioxide is held in the oceans and lakes as
in the atmosphere.
Carbon dioxide dissolves in water to form carbonic acid which
aquatic plants use as their source of carbon. It has been
estimated at 100 billion tonnes. Carbon is an ingredient in the
calcium carbonate shells of organisms with shells. In this way,
some carbon is removed from the cycle. See graphic p. 50.
The Nitrogen Cycle
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When we want our lawns and gardens to grow and
maintain good health, we fertilize them.
Nitrogen, phosphorus, and potassium are three
elements needed for growth and are found in most
fertilizers.
Most plants are not fertilized so they must draw their
nitrogen from other sources.
Where would you think they could access a ready
supply of nitrogen?
Nitrogen Cycle
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Atmospheric nitrogen is easily accessible but
not usable in this gaseous form. It must be
fixed into compounds usable by plants.
Nitrogen fixation refers to the process of
taking nitrogen atoms and bonding them
chemically to other elements to form
compounds. Two common polyatomic ions
usable by plants are ammonium NH4+ and
nitrate NO3-
Nitrogen Cycle
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Nitrogen-fixing bacteria such as Rhizobia (found in
nodules of roots of legumes such as peas, beans,
alfalfa, and clover) perform the task of nitrogen
fixation
Once nitrogen fixation has taken place, it enters the
soil and water for uptake and movement through the
food chain..
Nitrogen returns to the soil through dead organisms
and waste material
Nitrogen can also cycle in an aquatic ecosystem.
See graphic.
Nitrogen Cycle
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Animals can only obtain nitrogen by eating plant
material or other animals.
Refer to the graphic
Denitrifying bacteria carry out denitrification in which
gaseous nitrogen is removed from nitrates and
ammonia and is returned to the atmosphere.
Decomposers break down waste and dead
materials often releasing ammonia- a strong
smelling gas found in chicken coops, outhouses,
commercial cleaners etc.
Altering the balance
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As elements move through a nutrient cycle,
they move through the abiotic environment,
through living organisms and through waste
products or dead matter.
The rate at which the nutrient cycles is
balanced at each step. If additional nutrients
are added at any step, the balance is altered
and subsequent stages are impacted.
Human Impacts on Nitrogen
Cycle
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In the early 20th Century artificial fertilizers
were added to crops resulting in a dramatic
increase in food production. Increasing the
amount of nitrates for plants greatly
increased the growth of the plants.
Combined with the increased combustion of
fossil fuels, and other human activities, there
is approximately 140 million tonnes of extra
nitrogen in the environment. This is nitrogen
overload!
Effects on the Soil and the
Atmosphere
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Soil
Plant growth limited by scarcity of
resources such as phosphorus,
calcium, water
Ecosystem saturation leads to
run-off into streams and ground
water
Tree roots damaged
Growth stunted
Needles on conifers turn yellow
and fall
Soil acidity increases
Reactions with metals in soil
further damage roots and
organisms
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Nitrogen oxides lead to acid
precipitation
Fish, birds, amphibians, other
organisms killed by acid precip
Sugar maple trees in Ontario and
Quebec killed by acid precip
Effects on Fresh Water and
Marine Ecosystems
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In 1970’s many lakes & streams
became choked by rapid growth of
algae and weeds.
Increased growth was due to
nitrates and phosphates which
washed into waterways.
Nitrogen-containing wastes in
sewage lead to a buildup of
nutrients in aquatic ecosystems.
This is called eutrophication.
In rural areas, nitrates in the
drinking water supply lead to
reduction in the ability of blood to
carry oxygen producing a form of
anemia
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Increased nitrogen levels find their
way to ocean ecosystems.
Added nitrates lead to algal
blooms which result from a
population explosion of algae in
the warmer surface waters.
Algae are broken down by
bacteria. They decompose using
up more oxygen in the deeper
colder seawater. This depletes the
oxygen level and further impacts
food chains.
End result is significant fish and
shellfish kills
Effects on Biodiversity
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Biodiversity measures the variety of species
on Earth.
What conditions would favour high
biodiversity? Low biodiversity?
Biodiversity is lowered by very high level of
nutrients as only a few species would benefit
and the less dominant ones would be
eliminated or significantly reduced
Sustainability
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Ecosystems are sustainable i.e. they can perpetuate themselves
indefinitely requiring little or no additional materials each year. The
key to this is recycling.
Human activities deplete non-renewable resources and produce
polluting wastes which enter nutrient cycles and damage the
productivity of ecosystems.
We need to implement the concept of sustainable development in
which development meets present needs without compromising the
ability of future generations to meet their own needs.
Decisions needed for
Sustainable Development
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More efficient and effective use of scarce resources
Reducing, re-using, recycling, recovering materials in
manufacturing products as well as waste products
created
Restoring and reclaiming damaged environments
Conserving and developing substitutes for scarce
resources
Changing political and social structures to reduce human
impact on the environment
Reducing consumption