sx05_NCGR8_ch02CNEW.fm Page 58 Wednesday, June 8, 2005 4:08 PM
3
Section
3
Water on Earth
Water on Earth
Reading Preview
Objectives
Key Concepts
After this lesson, students will be able to
H.2.1.1 State how people and other living
things use water.
H.2.1.2 Describe how Earth’s water is
distributed.
H.2.1.3 Explain how Earth’s water moves
through the water cycle.
• How do people and other living
things use water?
• How is Earth’s water distributed?
• How does Earth’s water move
through the water cycle?
Key Terms
• photosynthesis • habitat
• groundwater • water cycle
• transpiration • precipitation
Target Reading Skill
Identifying Main Ideas Explain that
identifying main ideas and details helps
students sort the facts from the information
into groups. Each group can have a main
topic, subtopics, and details
Answers
Possible answers:
Detail: Earth’s oceans in the form of salt
water, in which 97 percent of Earth’s water
is found
Detail: Ice in the form of icebergs near the
North and South Poles
Detail: Rivers and lakes, which contain the
smallest amount of fresh water on Earth
Detail: Water below the surface, which fills
cracks and spaces in underground soil and
rock layers
Target Reading Skill
Identifying Main Ideas As you
read the Distribution of Earth’s
Water section, write the main idea
in a graphic organizer like the one
below. Then write four supporting
details that further explain the
main idea.
Main Idea
Earth’s water is distributed
among . . .
Detail
Detail
Detail
Detail
Where Does the Water Come From?
1. Fill a glass with ice cubes and water, taking care not to spill
any water. Set the glass aside for 5 minutes.
2. Observe the outside of the glass. Pick up the glass and
examine the surface it was sitting on.
Think It Over
Inferring Where did the water on the outside of the glass come
from? How do you think it got there?
In a galaxy called the Milky Way, nine planets orbit a star
known simply as the sun. Some of the planets have spectacular
rings. Others have volcanoes that are larger than continents or
storms that last for centuries. But only one of the planets,
Earth, has a surface covered mainly by water. In fact, oceans
cover about 70 percent of our planet’s surface. That’s why
Earth is often called the “blue planet.”
Earth differs from the other planets in another important
way. It is the only place known thus far where you, your classmates, your pets, your plants, and every other living thing can
survive. The wide variety of life on Earth could not exist
without water.
All living things
need water.
Teaching Resources
• Transparency H4
Preteach
Build Background
Knowledge
L1
Why We Need Water
Ask students to estimate how much water or
other liquid they have consumed today. Ask:
Why does your body need water? (To replace
liquid that is lost.) Ask: What other living
things need water? (Possible response: All of
them, including plants and animals. Some
students may mention that some organisms
live in water.) Accept all answers at this time.
Explain that students will learn how water is
important to life.
58
58 ◆
L1
Skills Focus Inferring
Materials ice, water, pitcher, clear
drinking glass
Time 10 minutes
Tips Add enough ice to the pitcher to
make the water very cold, causing droplets
to form quickly on the outer surface of the
glass. Advise students to avoid spilling the
water on the outside of the glass.
Think It Over Most students will
correctly infer that the water droplets
come from water vapor in the air
condensing on the cold surface of the
glass. Some students, however, may
propose that the water somehow came
from inside the glass.
sx05_NCGR8_ch02CNEW.fm Page 59 Wednesday, June 8, 2005 4:08 PM
Instruct
All Living Things
Need Water
Teach Key Concepts
All Living Things Need Water
Here’s a riddle for you: What do you and an apple have
in common? You both consist mostly of water! Water is a
large part of every living thing. Water makes up nearly
two thirds of your body’s mass. That water is necessary
to keep your body functioning. All living things need
water in order to carry out their body processes. In
addition, many living things use water for shelter.
Body Processes All organisms need water to carry
out their body processes. Water allows organisms to
obtain chemicals from their surroundings, break down
food, grow, reproduce, and move substances within their
bodies. Humans and other animals drink water or obtain
it indirectly by eating foods that contain water. Many animals can live several weeks without food. But they cannot
survive more than a few days without water.
Plants and other organisms that make their own
food also need water in order to carry out their foodmaking processes. Photosynthesis (foh toh SIN thuh
sis) is the process by which plants use water, along with
carbon dioxide and energy from the sun, to make their
own food. Animals and other organisms depend on the
food made by plants during photosynthesis. Animals may
eat the plants or eat organisms that eat the plants.
FIGURE 13
Essential for Life
As part of their daily routine, these
women in Pakistan must walk to a well to
get the water they need.
Interpreting Photographs What can you
infer about the availability of fresh water
in the region where these women live?
L1
The Importance of Water
Focus Have students recall that water is the
universal solvent.
Teach Explain that water acts as a solvent
for nutrients and other materials, such as
sodium chloride, that our bodies need.
Water also helps in chemical reactions in
living things. Ask: In animals, what
processes require water? (Obtaining
chemicals from their surroundings, breaking
down food, growth, reproduction, and moving
substances in the body) Why do plants need
water? (They use water, carbon dioxide, and
energy to make their food.) How is water
important to the habitats of many
organisms? (Many organisms live in water
and get what they need to survive from water.)
Apply Ask: What is one reason that a plant
dies if it does not get enough water? (The
plant cannot carry out photosynthesis without
water, and so cannot make food for itself.)
learning modality: logical/mathematical
Independent Practice
L2
Teaching Resources
• Guided Reading and Study Worksheet:
Water on Earth
Shelter Bodies of water provide habitats for many
living things. An organism’s habitat is the place where it
lives and obtains all the things it needs to survive. You are
probably familiar with large water-dwelling organisms
such as sharks. But most water-dwelling organisms are
microscopic, such as amoebas. In fact, aquatic, or water,
habitats contain more organisms than land habitats.
Student Edition on Audio CD
What is a habitat?
Chapter 2
◆ 59
Differentiated Instruction
Less Proficient Readers
Analyzing Word Parts Explain that
photo means “light” and synthesis means
“to put together.” Ask how these two
meanings relate to the process of
photosynthesis. (Plants use light, water,
and carbon dioxide to make food.)
learning modality: verbal
L1
L3
Gifted and Talented
The Role of Water in Removing
Carbon Dioxide Ask students to find out
what chemical reaction takes place between
water and carbon dioxide to allow carbon
dioxide to be moved through the
bloodstream. (Water and carbon dioxide
combine to form carbonic acid, which is
highly soluble: CO2 + H2O → H2CO3.)
learning modality: logical/mathematical
Monitor Progress
L2
Oral Presentation Ask students to describe
why water is essential for all living things.
Answers
Figure 6 Fresh water is very scarce.
A place where an organism
lives and obtains the things
it needs to survive
59
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Distribution of Earth’s Water
Distribution of
Earth’s Water
L1
Oceans To explore Earth’s waters, take an imaginary boat
trip around the world. Starting in Florida, you head southeast
across the Atlantic Ocean toward Africa. Swinging around
the continent’s southern tip, you enter the smaller but deeper
Indian Ocean. Next, you travel east across the Pacific Ocean.
This vast ocean covers an area greater than all the land
on Earth combined. Pacific, Atlantic, Indian—these are the
names used for the different parts of the ocean. But the waters
are really all interconnected, making up one big ocean.
FIGURE 14
Earth’s oceans are all connected,
enabling a ship to sail all the way
around the world. This map also
shows some of the world’s major
rivers and lakes.
Interpreting Maps Which
continents touch the Pacific
Ocean? The Atlantic Ocean?
Where is most fresh water located?
Earth's
Earth‘s Major
Major Waterways
Waterways
ARCTIC OCEAN
NORTH
AMERICA
EUROPE
St. Lawrence River
Great
Lakes
ASIA
D IT
E RR
A
SEA NEAN
ATLANTIC
OCEAN
AFRICA
PACIFIC
OCEAN
modality: logical/mathematical
A m a zon
r
Riv e
C A S P I A N S EA
Yan
R iv er
Nile River
ME
Equator
Lake
Baikal
B L A C K S EA
i
gz
Where Water Is Found
Focus Refer students to Figure 8. Remind
them that most of Earth’s surface is water.
Teach Ask: Where is most water on Earth
found? (In the oceans) Explain that salt water
cannot be used for drinking and water crops.
The technology for converting salt water to
fresh water is expensive and impractical.
Only a small percentage of water on Earth
is readily available for human use. Have
students examine each of the other
categories featured in Figure 8. Ask: Where
are icebergs? (At the poles) Explain that
icebergs are fresh water, but this water is not
available for people to use. What freshwater
sources are available to people? (Rivers and
lakes, and water beneath Earth’s surface) Ask
students to examine Figure 8 and determine
the percentage of available fresh water.
(Approximately 23 percent) Ask: Where is the
greatest percentage of fresh water found?
(In icebergs; they contain 76 percent of fresh
water on Earth.)
Apply Ask: Why can’t people directly
use water from the oceans for drinking?
Prompt students to think about what
happens when they eat salty foods. (The
human body cannot use salt water because the
salt causes the body’s cells to dry out. A person
who drinks only salt water will die.) learning
M is
s is s i p p i
R iv
er
Teach Key Concepts
Look at Figure 15. It shows how water is distributed among
saltwater and freshwater sources on Earth. Most of Earth’s
water—roughly 97 percent—is salt water found in oceans.
Only 3 percent is fresh water.
Of that 3 percent, about three quarters is frozen in huge
masses of ice near the North and South poles. Almost a quarter of the fresh water is underground. A tiny fraction of Earth’s
fresh water occurs in lakes and rivers. An even tinier fraction is
found in the atmosphere, most of it in the form of invisible
water vapor, the gaseous form of water.
PACIFIC
OCEAN
Equator
Lake Victoria
Indonesia
Lake Tanganyika
SOUTH
AMERICA
INDIAN
OCEAN
AUSTRALIA
ANTARCTICA
60 ◆
Skills Focus calculating
L2
Materials water, 1-liter clear plastic
bottle, large bowl, 5 plastic cups, graduated
cylinder, calculator, dropper
Time 30 minutes
Tips Point out that the water remaining in
the bottle represents only 3 percent of the
60
total (3 mL). This 3 percent represents
100 percent of the fresh water on Earth.
Expected Outcome Ice: 76 percent of
30 mL (about 22 mL); Shallow
groundwater: 12 percent of 30 mL
(3.6 mL); Deep groundwater: 11 percent
of 30 mL (3.3 mL); Lakes and rivers:
0.34 percent of 30 mL (about 0.1 mL); and
Water vapor: 0.03 percent of 30 mL (about
0.01 mL). Water from lakes and rivers and
shallow groundwater is available for human
use, or a little more than 1 percent of the
original one liter (about 3.6 mL).
Extend Ask students to repeat steps 3 and
4 with a full bottle of water that represents
Earth’s total amount of fresh water.
learning modality: kinesthetic
sx05_NCGR8_ch02CNEW.fm Page 61 Wednesday, June 8, 2005 4:08 PM
Use Visuals: Figure 8
Distribution of Earth’s Water
Ice 76%
Shallow groundwater 12%
Fre
sh
3%
er
at
w
Salt water in oceans
and salt lakes
97%
Deep groundwater 11%
Lakes and rivers 0.34%
Water vapor 0.037%
FIGURE 15
Only 3 percent of Earth’s water is fresh water. Of
that fresh water, only a tiny fraction is available
for human use. (Percentages in the art have
been rounded off.)
Calculating
This activity shows how
Earth’s water is distributed.
Ice How can you get back to Florida? You could sail all the
way around South America. But watch out for icebergs! These
floating chunks of ice are made of fresh water. Icebergs in the
southern Pacific and southern Atlantic oceans have broken off
from massive sheets of ice that cover most of Antarctica. If you
traveled around the North Pole, you would also find icebergs
in the Arctic Ocean and in the North Atlantic.
Rivers and Lakes To see fresh water in rivers and lakes, you’ll
have to make a side trip inland. Sail north past Nova Scotia,
Canada, to the beginning of the St. Lawrence Seaway. Navigate
through the series of locks along the St. Lawrence River. Suddenly the river widens and you enter Lake Ontario, one of North
America’s five Great Lakes. The Great Lakes contain nearly
20 percent of all the water in the world’s freshwater lakes.
Groundwater Some of the fresh water on Earth can’t be
seen from a sailboat. To find it, you would have to go underground. When it rains or snows, some water soaks into the
ground. This water trickles down through spaces between particles of soil and rock. Eventually the water reaches a layer of
rock that it cannot move through. Water that fills the cracks
and spaces in underground soil and rock layers is called
groundwater. Far more fresh water is located underground
than in all of Earth’s rivers and lakes. You’ll learn more about
groundwater in Section 6.
1. Fill a 1-liter plastic bottle
with water to represent
the total water on Earth.
2. Measure 97 percent, or
970 milliliters (mL), of the
water and pour it into a
large bowl to represent
salt water on Earth.
3. Label five cups to represent Earth’s freshwater
sources. Figure 15 shows
the percentage of water in
each freshwater source.
Using this graph, calculate
how much of the remaining 30 mL of water should
be poured into each cup.
4. Use a graduated cylinder
to measure the amount of
water for each cup. Use a
plastic dropper for
amounts that are too small
to measure accurately.
Which cups contain water
that is easily available to
humans? How do these
amounts compare to the
amount in Step 1?
Chapter 2
◆ 61
L2
Distribution of Earth’s Water
Focus Remind students that circle graphs
show parts of a whole.
Teach Focus attention on the circle graph.
Ask: What significant fact does this circle
graph tell you? (Salt water on Earth makes up
almost all of the water on Earth.) How is the
lower graph related to the upper graph? (It
represents all of the water in the wedges of the
upper graph.) Explain that the freshwater
sources represent those percentages of the
3 percent represented by the wedges, not the
100 percent represented by the entire circle.
Apply Show students how to calculate the
percentage of Earth’s total water that is made
up of ice: 76 × 0.03 = 2.28 percent. Ask them
to calculate the same for groundwater
(23 × 0.03 = 0.69 percent) and lakes and
rivers. (0.34 × 0.03 = 0.01 percent) learning
modality: logical/mathematical
L3
Interpreting Maps
Materials map of your state or county
Time 10 minutes
Focus Survey students to determine which
of them can identify the source of their
family’s drinking water.
Teach Give each student an outline map of
your state or county. Have students identify
rivers and lakes and note the proximity of
these sources to towns and cities. Ask
students to infer which sources might be
used for their town’s drinking water.
Apply Ask students to confirm the source of
their drinking water (if it is not from a
private well) and locate the source on the
map. They can consult a phone directory,
or contact the local or state Environmental
Protection Agency. learning modality:
visual
Differentiated Instruction
L1
Less Proficient Readers
For
each
Understanding Main Ideas
blue heading in this passage, have students
write a sentence in their own words that
describes the main idea for that paragraph.
Then have each student use his or her
sentence and the graphics on these two
pages to compose a brief paragraph
supporting this statement: Fresh water is a
scarce resource. learning modality: verbal
L1
Special Needs
Provide
Identifying Water Sources
pictures from magazines or encyclopedias
of the different sources of water discussed
in the text. Ask students to identify and
explain the relative availability of each type
of source, or point out this information to
them. learning modality: visual
Monitor Progress
L2
Skills Check Have each student make a
circle graph of the water available for human
use. Students may use Figure 8 as a reference.
Answer
Figure 7 Asia, Australia, North America,
South America
In huge masses of ice around
the North and South poles
61
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Bringing Up Groundwater
The Water Cycle
Suppose you live far from a city, town, or body of fresh water.
How could you reach groundwater to use it for your daily
needs? You may be in luck: the water table in your area might
be only a few meters underground. In fact, in some places the
water table actually meets the surface. Springs can form as
groundwater bubbles or flows out of cracks in the rock. A short
distance away, the water table may be deep underground.
For: Water Cycle activity
Visit: PHSchool.com
Web Code: cfp-4024
Aquifers Any underground layer of rock or sediment that
holds water is called an aquifer. Aquifers can range in size from a
small underground patch of permeable material to an area the
size of several states. The huge Ogallala aquifer lies beneath the
plains of the Midwest, from South Dakota to Texas. Millions
of people obtain drinking water from this underground storehouse. The aquifer also provides water for crops and livestock.
Do you picture groundwater as a large, still pool beneath
Earth’s surface? In fact, the water is moving, seeping through
layers of rock. The rate of movement depends largely on the
slope of the aquifer and the permeability of the rocks. Groundwater in some aquifers moves only a few centimeters a day. At
that rate, the water moves about 10 meters a year. Groundwater may travel hundreds of kilometers and stay in an aquifer for
thousands of years before coming to the surface again.
Students can interact with the art of
the water cycle online.
Teach Key Concepts
L1
How Water Moves
Focus Ask students to give examples of
cycles. (Possible answers: Seasons and the
rock cycle)
Teach Explain that a cycle has no beginning
or end. Ask: How does water move in a
cycle? (Water moves from Earth’s surface to
the atmosphere and back to the surface.) Refer
students to Figure 9. Ask: What are the three
steps in the water cycle? (Evaporation,
condensation, and precipitation) What are
sources of water that evaporate? (Bodies of
water, such as oceans and lakes, and plants) In
which state is evaporated water? (Gaseous)
How does water form clouds? (Water vapor
in the atmosphere condenses.) How does
water return to Earth’s surface? (It falls as
precipitation when the water droplets in clouds
become larger and heavy enough to fall.)
Apply Emphasize that transpiration by
plants releases water vapor, a gas, into the air,
not liquid water. Ask: How else is water
vapor released from your body besides
evaporation from your skin? (When you
breathe out, water vapor is present in your
breath.) learning modality: logical/
mathematical
Teaching Resources
Water Use in the United States
Uses of Water
The graph shows water use in the United
States. Each category of water use is
represented by a different color. Use the graph
to answer the questions below.
9.1%
Households and
10.4%
Businesses
Agriculture
41.8%
1. Reading Graphs How many categories of
water use are shown on the graph?
2. Interpreting Data The two largest categories
of water use combine to make up about
what percentage of the total water used in
the United States?
3. Interpreting Data Which of the categories of
water use shown in the graph represents the
largest use of water in the United States?
Which represents the smallest?
4. Predicting How would an increase in the
number of farms affect this graph?
• Transparency H5
62 ◆
62
Industries
and Mining
Power
Plants
38.7%
5. Calculating If the total daily usage of water
in the United States is 1,280 billion liters,
about how many liters are used each day by
power plants?
sx05_NCGR8_ch02CNEW.fm Page 63 Wednesday, June 8, 2005 4:08 PM
Condensation Forms Clouds What happens after a water
molecule evaporates? Warm air carries the water molecule
upward. At higher altitudes, air tends to become much colder.
Cold air cannot hold as much water vapor as warm air can.
As a result, some of the water vapor cools and condenses into
liquid water. Condensed droplets of water clump together
around tiny dust particles in the air, forming clouds.
Monitor Progress
L2
Answers
Figure 9 Precipitation
Any three: Oceans, lakes,
puddles, soil, groundwater,
surface runoff, plants, animals
Water Falls As Precipitation As more water vapor con-
denses, the water droplets in a cloud grow larger and larger.
Eventually, they become so heavy that they fall back to Earth.
Water that falls to Earth as rain, snow, hail, or sleet is called
precipitation.
Most precipitation falls directly into the ocean. The precipitation that falls on land may evaporate immediately or run off the
surface into rivers and lakes. From there, it may evaporate or flow
back into the ocean. In addition, some water may trickle down
into the ground. After a long time, this groundwater may reach a
river, lake, or ocean and continue the cycle by evaporating again.
Precipitation is the source of all fresh water on and below
Earth’s surface. The water cycle renews the usable supply of fresh
water on Earth. For millions of years, the total amount of water
on Earth has remained fairly constant—rates of evaporation and
precipitation are balanced.
Assess
Reviewing Key Concepts
FIGURE 17
Precipitation
Precipitation is part of the water
cycle. But you might not want it
falling on your head!
List three sources from which water evaporates.
3
Section 2 Assessment
Target Reading Skill Identifying Main Ideas
Use your graphic organizer to help you answer
Question 2 below.
Reviewing Key Concepts
1. a. Describing What are two reasons that living
things need water?
b. Applying Concepts Why can’t animals
survive more than a few days without water?
c. Developing Hypotheses Some desert animals
live for many days without drinking water.
How do you think these animals survive?
2. a. Listing What are the four main sources of
water on Earth?
b. Classifying Which of the four main water
sources contain salt water? Which contain
fresh water?
c. Making Judgments Which freshwater source
is most important to people? Use facts to defend
your answer.
3. a. Identifying What three major steps make up
the water cycle?
b. Sequencing Starting with a puddle on a sunny
day, describe how water might move through
the water cycle and eventually fall back as rain.
Product Label Create a product label for
bottled drinking water, explaining to
consumers why water is a precious resource.
1. a. All living things need water to carry
out body processes. Many living things use
water for shelter. b. Animals need water in
order to obtain chemicals from their
surroundings, break down food, grow,
reproduce, and move substances within their
bodies. c. Some animals may require less
water for body processes. Animals in hot
deserts may be active during cooler parts of
the day or at night.
2. a. Oceans, ice, rivers and lakes, and
groundwater b. Oceans and some lakes
contain salt water. Rivers, icebergs, most
lakes, and groundwater contain fresh water.
c. Possible answer: Groundwater, because it
contains the greatest percentage of usable
fresh water
3. a. Evaporation, condensation, and
precipitation b. Liquid water evaporates
from the puddle to become water vapor.
Clouds form as water vapor rises and cools.
Water droplets condense and then fall
back to Earth as precipitation. That water
eventually evaporates again, continuing
the process.
Reteach
L1
Use the figures to summarize the
distribution of Earth’s water and how water
moves through the water cycle.
Performance Assessment
Chapter 2
Keep Students on Track Check that
students have kept a daily record of water use
and have listed the different uses of water in
the home. Advise them to calculate the total
amount of water used over one week by
recording readings on a water meter or by
estimating usage based on estimates for
common household activities.
◆ 63
Writing Skill Description
Scoring Rubric
4 Exceeds criteria by showing creativity and
including extra details, such as art
3 Meets criteria
2 Explanation lacks imagination or is
incomplete
1 Is incorrect and incomplete
L2
Writing Encourage students to think about
the types of precipitation and sources of
water in the area where they live. Then have
each student write a detailed description of
the water cycle.
Teaching Resources
• Section Summary: Water on Earth
• Review and Reinforce: Water on Earth
• Enrich: Water on Earth
63
sx05_NCGR8_ch02CNEW.fm Page 64 Wednesday, June 8, 2005 4:08 PM
Water From Trees
L2
Prepare for Inquiry
Skills Objectives
Students will be able to
• observe the product of transpiration in
leaves
• calculate the mass of the water transpired
by leaves after 24 hours
• infer the important role that plants play in
the water cycle
Class Time 20 minutes for setup;
20 minutes the next day
Teaching Resources
• Lab Worksheet: Water From Trees
Safety
Caution students to avoid plants such
as poison ivy and poison oak. Show
pictures of these plants so that students will
recognize them. Instruct students to carry
out the activity in secure, familiar places.
Review the safety guidelines in Appendix A.
Guide Inquiry
Troubleshooting the Experiment
• The bigger the leaf, the greater the
difference in mass after 24 hours. Point
students toward plants with large leaves.
• Advise students to twist the ties tightly so
that the bags will be as airtight as possible.
Expected Outcome
After 24 hours, the bags should contain
liquid water from transpiration. The water
vapor given off by the leaves will have
condensed because of the cooler overnight
temperatures. Therefore, the bags will have
more mass than before.
Analyze and Conclude
1. The difference in mass is a result of
the water that collected in the bags over
24 hours.
Water From Trees
Problem
How much water do the leaves on a tree give off
in a 24-hour period?
Skills Focus
observing, inferring, calculating
Materials
• 3 plastic sandwich bags • balance
• 3 small pebbles • 3 twist ties
Procedure
1. Copy the data table into your notebook.
2. Place the sandwich bags, twist ties, and pebbles on a balance. Determine their total mass
to the nearest tenth of a gram.
3. Select an outdoor tree or shrub with leaves
that are within your reach.
4. Put one pebble into a sandwich bag. Place the
bag over one of the tree’s leaves as shown.
Fasten a twist tie around the bag, forming a
tight seal around the stem of the leaf.
5. Repeat Step 4 on two more leaves, using the
remaining plastic bags. Leave the bags in
place for 24 hours.
6. The following day, examine the bags and
record your observations in your notebook.
7. Carefully remove the bags from the leaves
and refasten each twist tie around its bag so
that the bag is closed tightly.
Data Table
Starting mass of bags,
ties, and pebbles
Mass of bags, ties, and
pebbles after 24 hours
Difference in mass
9. Subtract the original mass of the bags, ties,
and pebbles that you found in Step 2 from
the mass you found in Step 8.
Analyze and Conclude
1. Observing Use the observations you made in
Step 6 to account for the difference in mass
you found in Step 9.
2. Inferring What is the name of the process
that caused the results you observed? Explain
the role of that process in the water cycle.
3. Calculating A single birch tree may give off
as much as 260 liters of water in a day. How
much water would a grove of 1,000 birch
trees return to the atmosphere in a year?
4. Communicating Based on what you learned
from this lab, write a paragraph explaining
why some people are concerned about the
destruction of forests around the world.
Design an Experiment
Write a hypothesis about what would happen if
you repeated this activity with a different type of
tree. Design a plan to test your hypothesis.
Obtain your teacher’s permission before carrying
out your investigation.
64 ◆
2. Transpiration; plants absorb water from
the ground and release water that evaporates
into the atmosphere.
3. 260 L/day × 1,000 trees × 365 days =
94,900,000 L
4. Possible response: Trees are part of the
global water cycle. If forests are destroyed,
the water cycle may be affected because trees
increase the amount of water vapor in the
atmosphere.
64
8. Place the three bags, including pebbles and
twist ties, on the balance. Determine their
total mass to the nearest tenth of a gram.
Extend Inquiry
Design an Experiment Students may
record different results with different types
of trees.