INTEGRATING
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CHEMISTRY
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Cycles of Matter
DISCOVER
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Are You Par' 01 a Cyde?
1.
mHold a small mirror
a few
IL:J centimeters from your
mouth.
2. Exhale onto the mirror.
Think It Over
Inferring What is the
substance that forms on the
mirror? Where did this
substance come from?
3. Observe the surface of the mirror.
pile of crumpled cars is ready for 10a<1inginto a giant
compactor. Junkyard workers have already removed many
of the cars' parts. The aluminum and copper pieces were
removed so that they could be recycled, or used again. Now a recycling plant will reclaim the steel in the bodies of the cars. Earth
has a limited supply of aluminum, copper, and the iron needed to
make steel. Recycling old cars is one way to provide a new supply
of these materials.
A
• WJ'lat three major processes
make up the water cycle?
• How is carbon dioxide used
by producers?
Reading Tip As you read, use
the section headings to make
an outline of the section.
Recycling Matter
The way matter is recycled in ecosystems is similar to the way the
metal in old cars is recycled. Like the supply of metal for building
cars, the supply of matter in an ecosystem is limited. If matter
could not be recycled, ecosystems would quickly run out of the
raw materials necessary for life.
Energy, on the other hand, is not recycled.You must constantly
supply a car with energy in the form of gasoline. Ecosystems must
also be constantly supplied with ~nergy,usually in the form of sunlight. Gasoline and the sun's energy cannot be recycled-they
must be constantly supplied.
As you read in Section 1, energy enters an ecosystem
and moves from the producers to the consumers to the
decomposers. In contrast, matter cycles through an
ecosystem over and over. Matter in an ecosystem includes water, oxygen, carbon,
nitrogen, and many other substances.
To understand how these substances
cycle through an ecosystem, you need
to know a few basic terms that describe
the structure of matter. Matter is made
Cars awaiting recycling
at a Utah plant T
Figure 8 In the water cycle,
water moves continuously
from Earth's surface to the
atmosphere and back.
Interpreting Diagrams
In which step of the water
cycle does water return to
Earth's surface?
up of tiny particles called atoms. Combinations of two or more
atoms chemically bonded together are called molecules. For
example, a molecule of w~ter consists of two hydrogen atoms
bonded to one oxygen atom. In this section, you will learn about
some of the most important cycles of matter: the water cycle,the
carbon and oxygen cycles, and the nitrogen cycle.
harpen your
Developing Hypotheses
You're having
.-"-"'~''--",
cocoa at aA.~"
friend's house
.
on a cold, rainy day. As your
friend boils some water, you
notice that a window next to
the stove is covered with water
droplets. Your friend thinks the
window is leaking. Using what
you know about the water
cycle, can you propose another
explanation for the water
droplets on the window?
52. E
The Water Cycle
How could you determine whether life has ever existed on another
planet in the solar system? One piece of evidence scientists look for
is the presence of water. This is because water is the most common
compound in all living cells on Earth. Water is necessary for life as
we know" it. .
Water is recycled through the water cycle. The water cycle is
the continuous process by which water moves from Earth's surface
to the atmosphere and back. The processes of evaporation, condensation, and precipitation make up the water cycle. As you
read about these processes, follow the cycle in Figure 8.
Evaporation The process by which molecules of liquid water
absorb energy and change to the gas state is called evaporation.
In the water cycle liquid water evaporates from Earth's surface
and forms water vapor, a gas, in the atmosphere. Most water
evaporates from the surfaces of oceans and lakes. The energy for
evaporation comes from the sun.
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-- --...~
Some water is also given off by living things. For example, plants
take in water through their roots and release water vapor from their
leaves.Youtake in water when you drink and eat. Yourelease liquid
water in your wastes and water vapor when you exhale.
Condensation What happens next to the water vapor in the
( atmosphere? As the water vapor rises higher in the atmosphere, it
cools down. When it cools to a certain temperature the vapor turns
back into tiny drops of liquid water. The process by which a gas
changes to a liquid is called condensation. The water droplets collect around particles of dust in the air, eventually forming clouds
like those in Figure 8.
Precipitation As more water vapor condenses, the drops of
water in the cloud grow larger and heavier. El,rentuallythe heavy
drops fall back to Earth as a form of precipitation-rain,
snow,
sleet, or hail. Most precipitation falls back into oceans or lakes'.
The precipitation that falls on land may soak into the soil and
become groundwater. Or the precipitation may run off the land,
ultimately flowing into a river or ocean once again.
M'~
What change of state occurs when water from the
surface of the ocean enters the atmosphere as water vapor?
The Carbon and Oxygen Cycles
Two other chemicals necessary for life are carbon and oxygen. The
processes by which they are recycled are linked together, as shown
in Figure 9. Carbon is the building block for the matter that makes
up the bodies of living things. It is present in the atmosphere in
the gas carbon dioxide. ~~ers
take in carbon dioxide from
Figure 9 This scene shows how
the carbon and oxygen cycles are
linked together. Producers use
carbon dioxide to carry out
photosynthesis.
In this process,
carbon is used to create sugar
molecules such as those found in
apples. The producers release
oxygen, which is then used by other
organisms. These organisms take in
carbon in food and release it in the
form of carbon dioxide again.
the atmosphere during photosynthesis. In this process, the producers use carbon from the carbon dioxide to produce other
carbon-containing molecules. These molecules include sugars
and starches. To obtain energy from these molecules, consumers
break them down into simpler molecules. Consumers release
water and carbon dioxide as waste products.
At the same time, oxygen is also cycling through the ecosystem. Producers release oxygen as a result of photosynthesis.
Other organisms take in oxygen from the atmosphere and use it
in their life processes.
wf e~
How is oxygen returned to the environment?
The Nitrogen Cycle
Figure 10 In the nitrogen cycle,
nitrogen moves from the air to the
soil, into living things, and back
into the air.
Interpreting Diagrams How do
consumers obtain nitrogen?
·1
Bacteria releCf",se
some free nitrogen
back to air
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Like carbon, nitrogen is a necessary building block in the
matter that makes up living things. Since the air around you is
about 78 percent nitrogen gas, you might think that it would be
easy for living things to obtain nitrogen. However, most organisms cannot use the nitrogen gas in the air. Nitrogen gas is
called "free" nitrogen, meaning it is not combined with other
kinds of atoms. Most organisms can use nitrogen only once it
has been "fixed," or combined with other elements to form
nitrogen -containing compounds. You can follow this process in
Figure 10 below.
~
Decomposers break down
wastes and the re[l1ains
of organisms and return
nitrogen compounds to soil
Free nitrogen in air
Bacteria in root nodules
fix free nitrogen
into compounds
.r
Nitrogen Fixation The process of changing free nitrogen gas
into a usable form of nitrogen is called nitrogen fixation. Most
nitrogen fixation is performed by certain kinds of bacteria. Some
of these bacteria live in bumps called ~
(NAHJ oolz) on the
roots of certain plants. These plants, known as legumes, include
clover, beans, peas, alfalfa, and peanuts.
The relationship between the bacteria and the legumes is an
example of mutualism. As you recall from Chapter 1, a symbiotic
relationship in which both species benefit is called mutualism.
Both the bacteria and the plant benefit from this relationship:
The bacteria feed on the plant's sugars, and the plant is supplied
with nitrogen in a usable form .
..Jt!.!.f&f!lA.fH\J.~
Many farfIl.elfs make use of the nitrogen= •..J
TECHNOLOGY
fixing bacteria in legumes to enrich their
fields. Every few years, a farmer may plant a legume such as
alfalfa in a field. The bacteria in the alfalfa.roots build up a new
supply of nitrogen compounds in the soil. The following year,
the new crops planted in the field benefit from the improved soil.
Return of Nitrogen to the Environment Once the nitrogen has been fixed into chemical compounds, it can be used by
organisms to build proteins and other complex substances.
} Decomposers break down these complex compounds in animal
wastes and in the bodies of dead organisms. This returns simple ')
nitrogen compounds to the soil. Nitrogen can cycle from the soil
to producers and consumers many times. At som~ point, however, bacteria break down the nitrogen compounds completely.
These bacteria release free nitrogen back into the air. Then the
cycle starts again.
'~"~'''''''''''''''~''5!!S''"''''''''C''''''''''~'''''.'N~''
\,Section
·'C'··"',"''''
2 Review
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1. Name and define the three major processes that
occur during the water cycle.
2. Explain the role of plants in the carbon cycle.
3. How is nitrogen fixation a necessary part of the
nitrogen cycle?
4. Where do nitrogen-fixing bacteria live?
5. Thinking Critically Comparing and
Contrasting Explain how the movement of
matter through an ecosystem is different than
the movement of energy through an ecosystem.
.
(~, \/1
Figure 11 Lump nOQul~jJ,are
clearly visible on t~f
this
clover plant. Bacteria inside the
nodules carry out nitrogen fixation.
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f
Chefk Your Progress
: Once your teacher has
f approved your plan, place the
: waste into your compost chambers.
: Record your hypothesis about the effect
: of the variable you are investigating.
: Observe the two containers daily. (Hint: If
: there are no signs of decomposition after
: several days, you may wish to stir the
f contents of each chamber. Stirring allows
: more oxygen to enter the mixture.)
Chapter 2
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