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CHAPTER 12
LESSON 2
Matter and Energy in the
Environment
Cycles of Matter
Essential Question
What do you think? Read the two statements below and decide
whether you agree or disagree with them. Place an A in the Before
column if you agree with the statement or a D if you disagree. After
you’ve read this lesson, reread the statements to see if you have
changed your mind.
Before
Statement
• How does matter move in
ecosystems?
After
Carbon, nitrogen, and other types of matter are
used by living things over and over again.
Clouds are made of water vapor.
Mark the Text
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How does matter move in ecosystems?
The water that you use to wash your hands might once have
traveled through the roots of a tree in Africa. It might also have
been part of a glacier in Alaska. How can this be? Water is used
over and over again in ecosystems. It never stops moving. The
same is true of carbon, oxygen, nitrogen, and other types of matter.
Elements that move through one matter cycle might play a role
in another cycle.
The Water Cycle
Science v. Common Use
element
Water covers about 70 percent of Earth’s surface. Water
surrounds all of Earth’s landmasses.
Most of Earth’s water is in the oceans. Water is in rivers,
streams, lakes, and underground. Water is also in the
atmosphere, in icy glaciers, and in living things.
Water is always moving from Earth to the atmosphere and
back again. This movement is called the water cycle. The water
moves by three processes: evaporation, condensation, and
precipitation.
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Science Use one of a class
of substances that cannot be
separated into simpler
substances by chemical
means
Common Use a part or
piece
Matter and Energy in the Environment 243
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Identify the Main Point
As you read, highlight
the main point of each
paragraph. Then use a
second color to highlight a
detail or example to help
explain the main point.
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1. Evaluate Why is
condensation the opposite
of evaporation?
Evaporation In the water cycle, as shown below, the Sun
supplies the energy. As the Sun heats water on the surface of
Earth, evaporation occurs. Evaporation (ih va puh RAY shun) is
the process during which liquid water changes into a gas called
water vapor. This water vapor rises into the atmosphere.
Temperature, humidity, and wind affect how quickly water
evaporates.
Water is also released from living things. Cellular respiration
occurs in many cells. Water is a by-product of cellular
respiration. This water leaves cells and enters the environment
and atmosphere as water vapor. Transpiration is the release of
water vapor from the leaves and stems of plants.
Condensation The higher in the atmosphere you are, the
cooler the temperature is. As water vapor rises in the
atmosphere, it cools. This cooling causes condensation.
Condensation (kahn den SAY shun) is the process during which
water vapor changes into liquid water.
Clouds form as a result of condensation. Clouds are made of
millions of tiny water droplets or ice crystals. These form when
water vapor condenses on particles of dust and other substances
in the atmosphere.
Precipitation
Evaporation
Transpiration and
Exhalation
Lake
Ocean
Transpiration and
Exhalation
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Condensation
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Precipitation Water that falls from clouds to Earth’s surface is
precipitation (prih sih puh TAY shun). This water enters bodies
of water or soaks into soil. Precipitation can be rain, snow, sleet,
or hail. Precipitation forms as water droplets or ice crystals join
together in clouds. The droplets or crystals get so large and
heavy that they fall to Earth as precipitation. Over time, living
things use this precipitation, and the water cycle continues.
The Nitrogen Cycle
You know that water is necessary for life on Earth. The
element nitrogen is also necessary for life. Nitrogen is part of
proteins, which all organisms need to stay alive. It also is part of
DNA, the molecule that contains genetic information. Like
water, nitrogen cycles between Earth and the atmosphere and
back again. The nitrogen cycle is shown below.
Bacteria in soil convert nitrogen
compounds into nitrogen gas,
which is released into the air.
Nitrogen gas in
atmosphere
Lightning changes nitrogen gas in the
atmosphere to nitrogen compounds. The
nitrogen compounds fall to the ground
when it rains.
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Animals
eat plants
Nitrogen-fixing bacteria on
plant roots convert unusable
nitrogen in soil to usable
nitrogen compounds.
Decaying organic
matter and animal
waste return nitrogen
compunds to the soil.
Plants take in
and use nitrogen
compounds
from the soil.
Nitrogen
compounds
in soil
From the Environment to Organisms
You learned earlier that the atmosphere is mostly nitrogen.
Plants and animals cannot use the form of nitrogen that is in the
atmosphere. How do organisms get nitrogen into their bodies? The
process that changes nitrogen in the atmosphere into nitrogen
compounds that living things can use is called nitrogen fixation (NI
truh jun • fihk SAY shun). Nitrogen from the atmosphere is
changed into a different form with the help of bacteria that live in
soil and water. These bacteria take in nitrogen from the atmosphere
and change it into nitrogen compounds that organisms can use.
Plants and some other organisms take in this changed
nitrogen from the soil and water. Then animals take in nitrogen
when they eat these plants and other organisms.
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2. Nitrogen fixation occurs
in some types of sugar cane,
a crop grown in Florida. How
does nitrogen fixation benefit
the sugar cane plant?
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From Organisms to the Environment
Make a half book from a
sheet of paper. Select a
cycle of matter and use your
book to organize information
about the biotic and abiotic
parts of that cycle.
Cycles
in
Nature
How does nitrogen from living things return to the
environment? Some types of bacteria can break down the
tissues of dead organisms. These bacteria help return the
nitrogen in the tissues of those organisms to the environment.
You’ve seen these bacteria at work in a decaying log or a
rotten apple. Nitrogen also returns to the environment in the
waste products of organisms. Manure is a waste product of
organisms. Farmers often spread manure on their fields as a way
to provide nitrogen for crops.
The Oxygen Cycle
FL8_C12_010A_904411
3. Generalize Imagine that
there are no plants on Earth.
Would the planet have
oxygen in its atmosphere?
Why or why not?
You learned that organisms need water and nitrogen. Almost
all organisms also need oxygen for cellular processes that release
energy. Oxygen is also a part of carbon dioxide and water,
substances that are important to life.
Most of the oxygen in the atmosphere comes from
photosynthesis. Earth’s early atmosphere probably did not
contain oxygen gas. Certain bacteria evolved that made their
own food through photosynthesis. Oxygen gas is a byproduct of
photosynthesis. Over time, other photosynthetic organisms
evolved. The amount of oxygen in Earth’s atmosphere increased.
Photosynthesis is the main source of oxygen in Earth’s
atmosphere today.
The Carbon Cycle
All organisms contain carbon. Some organisms, including
humans, get carbon from food. Other organisms, such as plants,
get carbon from the atmosphere or bodies of water. Carbon
cycles through ecosystems like water, nitrogen, and oxygen do.
It is used over and over again.
NGSSS Check
4. How is matter transferred
in the carbon cycle? Does
the amount of carbon in the
carbon cycle ever change?
Explain why or why not.
Record your responses in
your Science Journal.
Carbon in Soil
All organisms return carbon to the environment, as shown
above. Like nitrogen, carbon can enter the environment when
organisms die and decompose. Decomposition is the breaking
down of dead plants and animals. This process returns carbon
compounds to the soil and releases carbon dioxide (CO2) into
the atmosphere. Other organisms then use carbon dioxide.
Carbon also is found in fossil fuels.
SC.8.L.18.3, SC.8.L.18.4
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Humans and many other living organisms take in oxygen
and release carbon dioxide during cellular processes. There are
many other relationships between different types of matter in
ecosystems.
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Carbon in Air
NGSSS Check
How do living things use the carbon dioxide that is in the
air? Plants and other organisms make their own food through
photosynthesis. They take in carbon dioxide and water to make
sugars. When other organisms eat plants, they get carbon and
energy. Carbon dioxide is a by-product of the cellular processes
that break down sugars to release energy. Carbon dioxide enters
the atmosphere to be used again, as shown in the diagram below.
Carbon compounds
in atmosphere
5. What roles do
photosynthesis and cellular
respiration play in the
carbon cycle? Write your
response in your Science
Journal. SC.8.L.18.1, SC.8.L.18.2
Combustion
Photosynthesis
Plants, certain protists,
and bacteria on land
Photosynthesis
Cellular
respiration
Cellular
respiration
Decomposition
Cellular
respiration
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Animals
Plants, certain protists,
and bacteria in water
Decomposition
Carbon compounds
in soil
Decomposition
Sediments
CO₂ in water
Fossil fuels
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The Greenhouse Effect
Carbon dioxide and other gases in the atmosphere absorb
thermal energy from the Sun. This energy keeps Earth warm.
This process is called the greenhouse effect.
Life on Earth could not exist without the greenhouse effect.
As you can see in the figure below, some of this energy is
reflected back into space, and some passes through Earth’s
atmosphere. Greenhouse gases in the atmosphere absorb
thermal energy that reflects off Earth’s surface. The greenhouse
effect helps keep Earth from becoming too hot or too cold.
4 Some heat is absorbed
1 The Sun gives
by greenhouse gases,
such as carbon dioxide,
in the atmosphere.
Sun
off solar radiation.
Atmopshere
2 Some solar radiation
is reflected by Earth’s
atmosphere.
3 Some of the radiation passes
through the atmosphere and
is absorbed by Earth’s surface.
Earth
the greenhouse effect
benefits Earth.
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6. Describe Explain how
While the greenhouse effect, shown above, is necessary for
life, a steady increase in greenhouse gases can harm ecosystems.
For example, carbon is stored in fossil fuels, such as coal, oil,
and natural gas. When people burn fossil fuels to heat homes, to
power cars, or to provide electricity, carbon dioxide gas is
released into the atmosphere. The amount of carbon dioxide in
the air has increased because of both natural and human
activities. The more greenhouse gases released, the greater the
gas layer becomes and the more heat is absorbed.
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Mini Glossary
condensation (kahn den SAY shun): the process
during which water vapor changes into liquid
water
evaporation (ih va puh RAY shun): the process
during which liquid water changes into a gas
called water vapor
nitrogen fixation (NI truh jun •
fihk SAY shun): the process that changes
atmospheric nitrogen into nitrogen compounds
that are usable to living things
precipitation (prih sih puh TAY shun): water that
falls from clouds to Earth’s surface
1. Review the terms and their definitions in the Mini Glossary. Choose a term and write at least two
sentences explaining how the term is linked to the nitrogen cycle.
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2. On the lines in the graphic below, identify the processes that make up the water cycle.
3. How did highlighting the main point of each paragraph, along with a detail or example to explain
that point, help you understand what you read?
What do you think
Reread the statements at the beginning of
the lesson. Fill in the After column with an A
if you agree with the statement or a D if you
disagree. Did you change your mind?
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