Name____________________________________________________
Cycles in an
Ecosystem
Chapter 6.2
Period____
Earth
Earth is a __________ system.
It is like a large _______________.
There is a set amount of _______, _______, _______, and other ________.
This means that there will never be __________ or __________.
The three major cycles are:
1) ____________________
2) ____________________
3) ____________________
Water Cycle
Water plays many different roles on the Earth. Some is at the poles in ice caps, and some is in the
snow and glaciers at the tops of high mountains. Some is in lakes and streams, and some is
underground. Some is vapor in the atmosphere. But most of the water on Earth is in the oceans.
Water is always on the move! The Sun’s energy causes water to evaporate from oceans and lakes
into the atmosphere. Plants and animals also release water vapor into the atmosphere as they
breathe. When the atmosphere cools, water vapor condenses; making clouds that might produce
rain or snow. Water has been recycled in its different forms as ice, liquid, or vapor –for more
than 3.5 billion years.
Vocab:
 Evaporation
 Condensation
 Precipitation
 Run-off
 Percolation
 Absorption
 Transpiration
Water Cycle Diagram
Draw a diagram of the water cycle that includes the following parts:
Evaporation, Condensation, Precipitation, Run-Off, Transpiration, Percolation, Absorption
Carbon Cycle
All living things are made of carbon. Carbon is also a part of the ocean, air, and even rocks.
Because the Earth is a dynamic place, carbon does not stay still. It is on the move!
In the atmosphere, carbon is attached to some oxygen in a gas called carbon dioxide.
Plants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes
part of the plant. Plants that die and are buried may turn into fossil fuels made of carbon like coal
and oil over millions of years. When humans burn fossil fuels, most of the carbon quickly enters
the atmosphere as carbon dioxide.
Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it and other
greenhouse gases, Earth would be a frozen world.
Vocab:
 Carbon
 Photosynthesis
 Respiration
 Decomposition
 Fossil Fuels
 Emissions
Carbon Cycle Diagram
Draw a diagram of the carbon cycle that includes the following parts:
CO2, Photosynthesis, Respiration, Decomposition, Fossils, Fossil Fuels, Emissions
Nitrogen Cycle
Take a deep breath. Most of what you just inhaled is nitrogen. In fact, 80% of the air in our
atmosphere is made of nitrogen. Your body does not use the nitrogen that you inhale with each
breath. But, like all living things, your body needs nitrogen. Your body gets the nitrogen it needs
to grow from food.
Nitrogen is used by lifeforms to carry out many of the functions of life. This element is especially
important to plant life. Yet, nitrogen in its gaseous form is almost entirely unusable to lifeforms.
It must first be converted or ‘fixed’ into a more usable form. The process of converting nitrogen
is called fixation.
There are specialized bacteria whose function it is to fix nitrogen, converting it, so that it can be
used by plants. There are still other bacteria that do the reverse. That is, they return nitrogen to
its gaseous form through a process called denitrification.
After nitrogen is fixed, it can be absorbed and used by plants, and subsequently by animals.
The process of nitrogen being fixed, used by plants and animals, and later returned to the
atmosphere is referred to as the nitrogen cycle.
Vocab:
 Nitrogen
 Nitrate
 Proteins
 Nitrogen Fixation
 Denitrification
Nitrogen Cycle Diagram
Label the following parts of the nitrogen cycle in the boxes above:






Plants use nitrates to make proteins
Nitrogen enters the soil
Animals eat plants
Decomposers release nitrogen into the air
Free atmospheric nitrogen
Bacteria change nitrogen into nitrates
Industrialization and the Carbon Cycle
1. What was the average global temperature in 1900? ______°C
2. What was the average global temperature in 2000? ______°C
3. How much did the average global temperature increase between 1900 and 2000? ______°C
4. Based on the graph, what do you predict the average global temperature to be in 2020? ______°C
1. What is the story that this graph tells?
2. Based on the graph above, describe the relationship between temperature and CO2 in the atmosphere.
3. What are two main reasons why the atmospheric CO2 concentration is rising? (hint: Page 167 in your textbook)


4. What do you think society should do about this issue?
Nitrogen Fertilizer … A Blessing or Disaster?
By Eric Sideman, PH.D.
Since humans began to cultivate food, nitrogen has been the most common limit to crop yields. Modern
agriculture has answered this limit with synthetic production of nitrogen fertilizers, which has greatly increased
global food production and has supported an astonishing growth in the world’s population. However, the
environmental problems are just being realized and are not yet being seriously dealt with.
Nitrogen, being a part of DNA, proteins and chlorophyll, is crucial for all life. Nitrogen cycles through living
organisms, through the soil and water, and eventually returns to its largest reservoir, the atmosphere. It is the
most common component of the atmosphere, making up almost 80%, yet, it is unavailable to plants or animals
because of its peculiar chemistry. It exists in the atmosphere in a very stable form (N2) and enters the cycle
through living systems only by the initial fixation by bacteria (either free living or symbiotic with such higher
plants as legumes). The N2 nitrogen is converted by the bacteria to chemical forms that plants can absorb. The
ecosystem is balanced by the stability of nitrogen in the atmosphere that naturally allows only a puny fraction of
the reservoir to be fixed at any one time.
Humans have disrupted the natural cycling of nitrogen by burning fossil fuels, growing legumes, and by using
nitrogen rich fertilizers. The chief culprit identified by recent studies reported in Scientific American is the
industrial fixation of nitrogen gas to make fertilizer. More than half of the nitrogen fertilizer made before 1990
was used during the 1980s.
Traditional farmers provided nitrogen to their crops by enriching their fields with crop residues, animal wastes
and human wastes, and by raising legume crops to be plowed into the soil (green manures). A real breakthrough
in nitrogen fertilization occurred in the past century with the development of ammonia synthesis. Under high
heat and pressure, which of course uses a lot of energy, nitrogen gas and hydrogen gas can be combined to
produce ammonia gas. Modern nitrogen fertilizers, such as ammonium nitrate, anhydrous ammonia and urea,
are made using ammonia gas. The first ammonia factory was built in Germany in 1913. More recent technical
developments allowed cheaper production of ammonia, and the fertilizer industry zoomed ahead.
The ready availability of ammonia and of the nitrogen fertilizers derived from it has effectively eliminated a
fundamental restriction on food production. During the 20th century, humanity has almost quadrupled its
numbers, and this sudden growth is supported by the food production made possible by nitrogen fertilizer. The
fertilizer industry fixes about 80 million tons of nitrogen per year. This will have to increase to support the global
population as it zooms to 10 billion during the next century.
Obviously this vast fixation of atmospheric nitrogen leads to a change in the nitrogen cycle, with much more
nitrogen pulled out of the atmospheric reservoir. Nitrates from extensive fertilizer use end up in the soil and
contaminate ground water through leaching and runoff. Problems range from local health issues such as blue
baby disease to global changes. Fertilizer nitrogen that escapes to surface water promotes algal growth and
subsequent eutrophication. Nitrous oxide is released into the air. In the low atmosphere nitrous oxide promotes
the greenhouse effect, much more so than carbon dioxide does. It also contributes to smog. In the upper
atmosphere, reactions of nitrous oxide with excited oxygen contribute to destruction of ozone in the
stratosphere.
The Scientific American articles point out that these disturbances receive surprisingly little attention. Carbon
dioxide emissions are being reduced and research is supported to continue reduction. A transition away from the
use of fossil fuels must eventually happen anyway, because these resources are finite. But there is no way to
grow crops without nitrogen, and to grow crops at today’s expected yields per acre to feed the world’s exploding
population from a shrinking farm land base takes highly concentrated nitrogen fertilizers. The EPA recognizes the
damage caused by nitrous oxides from combustion and has introduced regulations to limit emissions.
Cooperative Extension has “Best Management Practices” that reduce fertilizer use and nitrogen leaching and
runoff; but not all farmers follow these and no controls exist on the amounts of fertilizers a farmer can use.
An early stabilization of the global population is the best solution to the problems raised by excessive nitrogen
fixation. Organic methods of crop production, including crop rotation, using legume green manures, soil
conservation, and the recycling of all organic wastes, are management techniques that are needed to reduce the
damage that has been done. In land-rich nations these practices can produce enough food to feed today’s
population. In land-poor areas nitrogen fertilizers are necessary to maximize production – which leads to
devastating environmental disruptions. This is a very strong argument for preserving farm land. Let’s control our
population, save our farmland, and farm organically.
Article Discussion Questions:
1) What is the major benefit of the use of modern nitrogen fertilizers?
2) What are some negative effects of nitrogen fertilizer use?
3) What is one solution suggested in the article?
4) What do you think society should do about this issue?
Cycles Review
Water Cycle
atmosphere
water cycle
precipitation
runs
vapor
soaks
condenses
evaporates
1. Water moves between Earth and the _______________________.
2. This movement of water is called the _______________________.
3. Heat from the sun causes water on Earth to change from liquid to a _____________ as it _____________, rising
from Earth’s oceans, lakes, and rivers.
4. Eventually, this water _____________, or forms drops and falls to Earth as _____________.
5. Much of the rain that falls _____________ into the ground.
6. The rest either _____________along the ground or evaporates and begins the process again.
Carbon Cycle
oxygen
volcanoes
1.
2.
3.
4.
5.
6.
7.
greenhouse
photosynthesis
decayed
respiration
fossil fuels
ocean
Plants use CO2 in the process of________________ to make sugars and_____________.
Animals use oxygen in the process of _____________ and make more CO2.
The _____________ is the main regulator of CO2 in the atmosphere because CO2 dissolves easily in it.
In the past, huge deposits of carbon were stored as dead plants and animals _____________.
Today, these deposits are burned as ________________, which release lots of CO2 into the air.
Another natural source for CO2 is _____________.
Too much CO2 in the atmosphere may be responsible for the _____________ effect.
Nitrogen Cycle
atmosphere
nitrates
1.
2.
3.
4.
waste
nitrogen-fixation
proteins
plants
denitrification
animals
Animals and plants cannot directly use all the nitrogen found in our ________________.
Specialized bacteria “fix” nitrogen so other organisms can benefit through a process called ____________________.
The process turns nitrogen into ___________ that other complex organisms can use to make their ____________.
Other bacteria in the soil can break down the ammonia into the gaseous form of nitrogen, which is not available for
use by plants or animals. This reverse process is called________________.
5. In another part of the cycle, animals eat ________________ containing nitrogen, which is again returned to the soil
by animal ________________ or decaying plants and ________________.