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Timing
Teacher's Notes
Biosphere
Cycles
Energy flow and
Nutrient Cycles
Grades: 7-10
Duration: 23 mins
Cycles and Energy Flow
1:14
The Carbon-Oxygen Cycle
Nutrients and soil
The Phosphorus cycle
Putting in what we take out
The Nitrogen Cycle
Nutrient Cycling
Summary
Credits
4:16
7:05
9:02
10:34
17:03
18:39
20:30
22:44
About this Video.
This video explores the Earth’s biosphere by
examining the pathways and cycles that maintain
it. As we are part of the biosphere our actions must
always be moderated by our position. The video
also explores how our knowledge can be applied to
sustainable farming. We investigate these cycles
and find out how they are applied to farming
practice. In managing a farm as an ecosystem,
knowledge of the ways matter is recycled allows
the owner to maintain the growth of crops on a
sustainable basis. But the cycles are not just
localized events. They operate worldwide. And this
has very important implications for all of us. Our
daily actions influence the operation of these cycles
and therefore of the ecosystems they maintain.
Teachers Notes.
Farmers and others involved in sustainable
agriculture have as their goal the production of
food on a sustainable basis through the
maintenance of soil quality. Regenerative
agriculture attempts to repair the damage caused
by the destructive practices of the past. Both value
soil as a precious item which is not easily replaced.
Building soil is a very slow process. Under ideal
conditions it accumulates at an annual rate of
about 10 tons per hectare, a layer of 1mm in depth.
Under poor conditions such growth in soil takes
thousands of years. Without a constant supply of
healthy soil, life on land would not be possible. To
understand this requires an understanding of the
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interactions and interdependence of all living
organisms on the earth and their relationship
to the environment in which they live. The area
of study is ecology and the domain is the
Earth’s biosphere.
Cycles and Energy Flow.
Viewed from space the Earth appears as a
smooth sphere, covered by water, land and thin
wisps of white cloud. The biosphere is that
region where life exists and flourishes. The
habitable zone is very thin, like a layer of paint
on the globe, extending about 6 km above the
oceans and about 10 km below it. The
biosphere operates as a closed system that
contains only a finite amount of matter
available for life. Thus the materials are
recycled over and over again. To drive the
recycling, energy from the sun is used and is
the only input to the system that sustains life.
The flow and fixation of energy is at the core.
Food chains and food webs begin with plants
fixing sunlight in high energy organic molecules
and other structures that become the food for
animals. For a brief moment these molecules
are assembled into living organisms. They are
decomposed on their death to form less
complex molecules that then re-enter the cycle.
Such recycling and the flow and fixation of
energy from the sun is the basis of all
ecosystems.
In a simple food chain the flow of energy is
conveniently shown as in the following diagram
in the video and the various members grouped
into their distinct trophic levels.
Each energy transfer is about 10% efficient, the
other 90% is used by organisms at that level in
respiration and in the building and maintenance
of body tissue. It is to be remembered that of
all the energy received by the Earth, less than
1% is ever fixed by the plants as dry matter
and in the end all energy received is returned
to space as radiation. There is no net gain of
solar radiation from the sun. Instead it is
stored in various systems for a period of time
which may be hours to years in plants, years in
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leaf litter and humus, years in animals, thousands
of years in ocean systems, millions of years in
natural gas, oil and coal.
The Carbon-Oxygen Cycle.
The first person to seriously try and figure out
how trees grew was Jean-Baptiste van Helmont.
He experimented by growing a willow cutting in a
pot containing 90.6 kg of soil. He found that even
though the cutting grew into a tree, the mass of
soil in the pot was hardly affected. While the plant
grew into a tree of some 77 kg over 5 years, only
a very small amount of soil, less that 0.1 g had
disappeared from the pot. So where did the
material in the tree come from? Van Helmont was
partly correct when he suggested that the tree
was built from the water he gave it. What he
didn’t know was that trees also take in large
amounts of carbon dioxide from the air. Indeed, it
is the carbon - oxygen cycle that forms the basis
of a tree’s growth.
The carbon-oxygen cycle is divided into two parts:
photosynthesis and cell respiration.
Through photosynthesis, plants use some of the
sun’s energy to combine water and carbon
dioxide into high energy compounds as sugars or
simple carbohydrates.
The overall reaction is given as:
6 CO2 + 6 H2O + light Energy —> C 6H12O6 + 6 O 2
The reaction is much more complex than this. The
essential chemical is chlorophyll. In fact it is a
series of redox reactions where water is split and
electrons along with hydrogen ions are
transferred from the water to the carbon dioxide,
reducing it to sugar. Water is oxidized and carbon
dioxide is reduced. The electrons increase their
potential energy in forming new bonds, and this
energy comes from sunlight. The bi-product of the
reactions is oxygen. In a further series of
reactions in non-photosynthetic cells, sugar
provides the raw material for cell respiration and
for the production of proteins, lipids and other
materials for new cell growth. A considerable
amount of the sugar in the form of glucose is
linked together to form cellulose to build cell walls
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and is the most abundant organic compound in
plants. Plants produce an excess of organic
materials that are stored as starch, oils and
proteins in leaves, tubers, roots and fruit. Some
conversions require other elements such as
nitrogen and phosphorus. All require energy and
this comes from cell respiration.
The net productivity, or net rate of carbon fixation
varies from one type of vegetation to another. In
forests and cultivated fields between 0.2 and 0.4
kg of C are fixed each year per square metre,
while in tropical rainforests this figure increases to
1-2 kilograms per square metre per year but such
areas are relatively small. The estimates for the
total land area is 20 to 30 billion tons of carbon
per year. The forests also represent the main
reservoir of fixed carbon except for fossil fuels
where the carbon has been mainly removed from
the carbon cycle. It is estimated that there is
about 400 to 500 billion tons of C in the Earth’s
forests or about 70% of that present in the
atmosphere (700 billion tons). The phytoplankton
in the oceans fix a further 40 billion tons of C per
year.
The carbohydrates (and oxygen) produced are
used in the cell respiration of all living things.
Plants, soil organisms and animals all respire. In
cell respiration the redox reactions are reversed,
carbon dioxide and water are produced and
energy is liberated. The energy liberated is used
for all the organism’s activities: to maintain and
run cell processes, construct new proteins and
cells in growth and repair, and movement. The
carbon dioxide is returned to the air.
Nutrients and soil.
In order to grow, plants need more than just the
carbon-oxygen cycle. As well as carbon dioxide
and water, plants need several other chemicals,
termed nutrients, which they get from the soil.
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The nutrients in soil come from various
sources. One of the most important source is
from the breakdown of dead animal and plant
matter by soil organisms, including detritus
feeders, micro-organisms including bacteria
and protists, and fungi. They are the
decomposers. When plants and animals die,
detritus feeders, bacteria and fungi use the
dead matter as food. Decomposition releases
nutrients into the soil and gases into the air.
It’s amazing how soon after an animal’s
death, these processes get to work and how
quickly they release key elements back to the
soil. The time-lapse video shows the active
process well.
A healthy home compost heap is a perfect
place for fungal and bacterial activity. It’s a
most magnificent recycling factory. Microscopic
organisms play a crucial role in producing
organic and nutrient rich humus and returning
the elements to the soil in a form that is easily
used by plants. And as they go to work, they
release the key elements of life back into the
soil. One of these is phosphorus.
The Phosphorus cycle.
Phosphorus is an essential element in
proteins in all cells especially DNA, RNA,
molecules that convert and transport energy
(ATP and ADP) and the fats of cell membranes.
Phosphorus is also a building block of certain
parts of animals, such as bones and teeth.
It enters the environment and soils through
the weathering of rocks or deposits laid down
as oceanic sediments millions of years ago.
Terrestrial sedimentary rock, and thus the
soils on them, are generally deficient in
phosphorus, so it is often the limiting factor
for plant growth. Thus fertilizers containing
phosphates have been applied to farmland for
the past 150 years sometimes in
disproportional amounts. It is also the limiting
factor in rivers and the ocean, and when it
enters such systems, algal blooms often
result.
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When plants and animals die, decomposers go
to work almost immediately, to release
phosphorous into the soil. The phosphorous is
again taken up by plants, which pass it on to
animals. Unlike nitrogen, phosphorous occurs in
only one significant inorganic, or non-living form,
the orthophosphate ion (H 2PO4-1). It is also one
of the elements not cycled through the
atmosphere.
Some phosphorous leaches into waterways and
some is carried away in streams and rivers.
The first part of the phosphorous cycle is
relatively rapid, taking place over weeks and
months as humus and soil particles bind
phosphate and so its cycling tends to be local.
In contrast, the second part of the cycle occurs
over millions of years. The phosphates that
leach out from the soil enter waterways. On
reaching the ocean they precipitate out, settle
and slowly form into new rock over millions of
years. Geological processes will eventually lift
the sediments above the ocean into mountain
chains. Rain and other weathering processes
then leach the phosphorous from rocks and
return it to the soil.
Putting in what we take out.
As rich as the soils are around Mt. Warning,
agriculture has an effect on the key nutrient
cycles.
Cattle can be thought of as a meat-growing
machines. The cows grow because they get
energy and nutrients from grass, They also give
birth to young and raise them on milk - which
has also been made from the grass. The energy
and nutrients in the grass have come from the
sun, from water and from elements such as
carbon from the air, and phosphorus from the
soil.
Some of the elements are returned to the soil
through the cows waste, but most will end up
hundreds, even thousands of kilometres away
when the animal is sold as meat at
supermarkets.
Before there were large cities, when the cow
died she would have either rotted away or
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been eaten by other animals or humans who lived
close by. The nutrients locked away in the cow’s
body would have been returned to the soil,
somewhere nearby.
Environmentally aware farmers like Andrew Ford
recognize that humans cannot keep taking from
the soil without putting back. For the system to
continue it must be kept in balance. This is done
by applying fertilizers in a way that promotes the
long term health of the soil. Inorganic fertilizers
are popular and easy to use. But they do little to
maintain soil quality and can result in unwanted
build-up of nutrients in streams. Organic fertilizers,
such as manure, provide soil nutrients, and they
help to maintain the structure and health of the
soil by adding micro-organisms and other soil
components. But organic materials can’t always
supply all the nutrients needed by the soil. So
often the best approach is a combination of
organic and inorganic fertilizer.
Andrew says he is fortunate that farmers before
him have looked after the soils in his valley.
One way Andrew controls the amount of inorganic
fertilizers is by spraying them directly onto the
plant’s foliage. This provides a measured dose,
which can be quickly assimilated by the plants and
minimizes the risk of runoff. Another important
strategy is to apply just enough nutrient for the
plants’ needs. Andrew uses data loggers to
monitor the level of moisture and nutrients in his
soils. He also tests selected leaves to ensure that
the plants have absorbed the optimum mix of
nutrients.
Another part of Andrew's strategy for use of
organic fertilizer is the recycling of the organic
matter discarded during the processing of these
valuable coffee beans. The actual beans only
make up about 10 percent of the organic material
collected. All these leftovers are in fact locked
away energy and nutrients. By composting this
material, Andrew returns the energy and nutrients
to his plants, and boosts the quality of the soil at
the same time. Soils are further enhanced by
spreading organic fertilizers like chicken manure.
This encourages the growth of soil micro-
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organisms. Hungry coffee plants thrive on this
because the micro-organisms release a power
packed burst of usable nitrogen, one of the most important elements for plant growth.
The Nitrogen Cycle.
Although the Earth’s atmosphere is 78%
nitrogen, most plants cannot assimilate it in
this atmospheric form. It must first be fixed by
specialized organisms or by industrial
processes into ammonia or nitrate salts. In
fixing the nitrogen it is incorporated into a
compound that can be used by the plant.
Nitrogen is a basic component of proteins and
is a nutrient essential to all life
Most nitrogen enters the soil during the
decomposition of plant and animal matter by
soil decomposers such as bacteria and fungi.
The process releases Ammonia (NH3), but
ammonia cannot be absorbed directly by
plants. So special nitrifying bacteria turn the
ammonia into nitrites, then nitrates, the form
of nitrogen plants can absorb.
Some nitrates are turned back into
atmospheric nitrogen by denitrifying bacteria.
And some of this atmospheric nitrogen enters
the cycle when it is converted into ammonia,
again by nitrifying bacteria. Other bacteria in
the root nodules of plants called legumes
convert nitrogen from the atmosphere directly
into usable compounds. So there are several
pathways in recycling nitrogen, which is why
the nitrogen cycles are so complex.
The action of the bacteria in fixing nitrogen
and in returning the excess to the atmosphere
maintained a balance and no accumulation
occurred. This has changed over the past 150
years through the wide cultivation of nitrogen
fixing legumes and the large-scale
manufacture of synthetic fertilizers. Of all our
interventions in the natural cycles of matter,
the industrial fixation of nitrogen exceeds all
others. It now exceeds the amount that was
fixed by all terrestrial ecosystems before the
advent of modern agriculture, and totals
about 210 million metric tons per year. Natural
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processes contribute about 140 million metric
tons. In fact since 1984 one half of all the
commercial nitrogen fertilizer ever produced has
been applied to farmland. The problem is that
only half of this ever ends up being used by
terrestrial plants directly. The remaining half is
leached from the soils and washed away.
Andrew’s methods of applying fertilizer only to
meet the requirements of the plants, using
foliage sprays as his method of application and
monitoring the plant’s uptake is excellent
practice. It is also sustainable.
Nutrient Cycling.
Some natural systems are faster than others at
recycling nutrients and transferring energy.
Rainforests, especially tropical rainforests, are
rapid recyclers of detritus. As soon as a tree or
animal dies, it is quickly broken down by
decomposers and absorbed by the roots of fast
feeding trees. So while the forests appear rich
in life, the soils are actually very thin with very
little organic matter because it doesn’t have
time to accumulate. That’s why an activity like
slash and burn agriculture is so devastating in
these areas. Once the forest is cleared the soils
are only good for several crops until they
become depleted and produce poor yields.
While rainforests are rapid recyclers, deserts
are one of the slowest. In the desert the lack of
water makes for a perilous existence for all but
the hardy. Living things are few and far
between. In between the extremes of deserts
and rainforests are ecosystems like savannah,
woodland, alpine, wetlands and open ocean,
Summary.
Whether it’s pasture for cattle, nutrients for
forests, or the ideal soil for growing coffee
beans, the right balance of nutrients is vital.
Healthy nutrient cycles allow plants to harness
the energy from the sun and continue with
healthy, balanced growth.
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In the past, nutrients were very slowly added to
biological systems through the weathering of
rocks, the decay of animals and plants, and the
creation of soils.
CREDITS
Produced by
Peter Beeh
Educational Consultant
John Willis
Camera
Peter Beeh
Editor
Phil Sheppard
Post Production Sound
Philip McGuire
Executive Producer
Corinna Klupiec
Teachers Notes
John Willis
But we have dramatically changed the way
nutrients pass through many of these systems.
Each time we wash our hands, do the dishes,
clean the car we are affecting our environment by
adding excess nutrients. Every sink-full of water
that goes down the drain is going to affect
biological cycles which have evolved over many
millions of years. When we use soaps and
detergents, or flush the toilet, we change the way
nutrients are distributed throughout our
waterways. The end result is an alarming
imbalance emerging in the complex cycles of life.
The better our understanding of the way these
cycles work, the more we can do to modify our
actions and work towards a sustainable future.
Farms such as Mountain Top are living proof that
this is not only possible, but can have some added
benefits for your next cup of coffee.
Key Words.
Biological cycle, farming system, sustainable
agriculture, biosphere, living world, non-living
world, ecology, ecosystem, sunlight, food, food
chain, food web, producers, consumers,
decomposers, transform, Jean-Baptiste van
Helmont, carbon dioxide, water, carbon-oxygen
cycle, photosynthesis, (cell) respiration, sugar,
fossil fuel, nutrient, detritus, humus, soil, microorganism, bacteria, fungi, compost, phosphorus
cycle, rain weathering, leaching, soil quality,
nutrient cycle, limiting nutrient, waste, faeces,
nutrient balance, organic, inorganic, intensive
farming, data logger, nitrogen cycle, nitrifying
bacteria, denitrifying bacteria, ammonia, biomes,
forest, grassland, deserts, savannah, woodland,
distribution of nutrients.
Copyright
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CLASSROOM VIDEO (2004)
Classroom Video
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QUESTIONS
1. Suggest a geographical area where there is a maximum growth of plants. Why do plants seem to grow so well
there? What measurements could be made to support your choice?
2. Why use the term “farming system” rather than just “farm”?
3. List some of the important factors used by farmers in maintaining sustainable farming systems. Suggest why these
factors are important. What might happen to the farm if the system does not work?
4. What is meant by the term “food”? Do plants have food? How is food related to nutrients?
5. There are six elements that are essential for life. List them and find out how they occur naturally. Why do some
lists of elements contain a further 24 or more elements? Is our original list of six elements wrong?
6. What is a food chain? How are food chains important in agriculture?
7. Find other names for “producers”, “consumers” and “decomposers”. Find the meaning of the phrase “trophic level”.
8. Carbon dioxide and water are transformed into sugar during photosynthesis. How is the term “transformed” used
here? Is it the best word to use? Find out more about photosynthesis. Is it true that we were part of a plant at some
time.
9. Is photosynthesis the only thing that plants do? How do they use the products of photosynthesis to grow? Do they
need other materials?
10. How are fossil fuels related to photosynthesis?
11. Where would you find examples of detritus? Describe detritus. What would happen if the detritus was not
decomposed by bacteria and fungi?
12. List some of the nutrients and other soil components that are released by decomposition.
13. How is composting related to the production of humus? What are some of the advantages of having a home
compost bin? Are there any disadvantages?
14. Where in the body of living things is phosphorus used? How much phosphorus do you have in your body? Why is
it important? Why must the phosphorus in living things be recycled?
15. Distinguish between “organic” and “inorganic” fertilizers. How did farmers produce crops before artificial fertilizers
became available? Find the name of an inorganic fertilizer and research how it is produced. What are the raw
materials required to produce the fertilizer? Why can’t these materials be applied to the soil for the plant to use?
16. Visit a garden shop and examine the variety of fertilizers that are available. Note how they are different and how
they are used.
17 Andrew Ford uses a data logger to monitor conditions in his soils. What measurements do you think he makes?
How does he respond to the changes in the soil?
18. Nitrogen is the fourth most common element in living matter, yet it can be in short supply in some soils. How can
this be? Trace the path of a nitrogen atom as it enters the soil from the air.
19. Distinguish between the roles of nitrifying bacteria and denitrifying bacteria. Why are they both essential?
20. How does a city affect the local ecosystem? Consider air pollution, waste disposal, power use.