2.7
The Water and Carbon Cycles
Time
45–60 min
Key Ideas
Matter cycles within
ecosystems.
Skills and Processes
Observing
Measuring and Reporting
Scientific Problem Solving
Hypothesizing
Lesson Materials
per student
• 2 baggies
• 2 elastics or twist ties
Program Resources
SM 2.7 The Water and
Carbon Cycles
BLM 0.0-9 Chapter Key Ideas
Nelson Science Probe 7
Web site
www.science.nelson.com
Page 52
PRESCRIBED LEARNING OUTCOMES
• analyze the roles of organisms as part of interconnected food webs,
populations, communities, and ecosystems
• assess survival needs and interactions between organisms and the
environment
KNOWLEDGE
• ecosystems are entire systems formed by interactions among the
different living and non-living parts of the environment (e.g., forests,
deserts)
• organisms interact with each other and use and recycle chemicals from
the environment
ICT OUTCOMES
• work cooperatively using information technology tools
• use a variety of information technology tools to create, modify, explore,
and present electronic documents that express ideas or concepts
• create and present multimedia documents for intended audiences
• apply the principles of good design when developing electronic
documents
• develop interactive hypertext documents for presentations
• produce multimedia presentations
SCIENCE BACKGROUND
• In the atmosphere, there is an
overall movement of water from the
oceans to the land. Water falls on
land, then flows back to the oceans.
• Carbon is everywhere in the
environment. It goes from the
atmosphere into organisms, and
back again into the atmosphere. The
carbon cycle is discussed in a unit on
ecosystems because human
activities and land use are thought to
be altering the atmosphere. We are
burning more and more fossil fuels
and releasing more carbon into the
atmosphere. At the same time, we
are cutting down trees, which
absorb carbon for their growth
process. In combination, these
factors are thought to be creating an
imbalance in the amount of carbon in
the environment. The carbon dioxide
acts as a blanket above Earth,
holding in heat that would normally
be radiated into space. This is called
the greenhouse effect. The
greenhouse effect is thought to be
the cause of accelerated global
warming, as is documented in
ScienceWorks in Chapter 3.
TEACHING NOTES
1 Getting Started
• Check for Misconceptions
– Identify: Students may think that once water goes down the drain,
it disappears from the Earth. They may not realize that water
evaporates from these larger bodies.
74
Unit A: Ecosystems
NEL
– Clarify: Explain that water is constantly being recycled; water we
use has been in the air, underground, and on mountains as snow as
in the water cycle diagram (Figure 1). Review the diagram.
– Ask What They Think Now: Ask students what happens to the
water that people put on their lawns.
• Display a calendar to show the cycle of the days of the week and/or
the cycle of the phases of the Moon.
• Ask students how many examples of water they can think of.
Student responses may include snow, hail, sleet, rain, ocean, or ice.
• Refer to the chapter introduction question, “Why do ecosystems not
run out of materials and energy?” A description of the water cycle
will illustrate the answer with respect to water. Tell students that the
carbon cycle will help to answer this question as well.
• Use the Reading and Thinking Strategies to guide students’ review
of the water cycle diagram (Figure 1).
2 Guide the Learning
• Read the Learning Tips. Have students study and follow the diagram of
the water cycle while you read aloud the paragraph describing it. Have
students work in pairs to explain the carbon cycle using the diagram.
• For a very thorough practice session with the water cycle, have
students take the roles of the various parts in the water cycle and act
it out. Include the loss of water from leaves.
• Briefly review the process of photosynthesis to see where carbon
dioxide is used and help students understand the carbon cycle.
• Ask students, How do you think the carbon cycle is affected when
people burn fossil fuels? (More carbon dioxide is released into the
atmosphere.) What would be the effect of clearing the forests? (The
forest plants would no longer be there to use carbon dioxide, so
there would be additional carbon dioxide in the atmosphere.)
• For students who need additional support with the reading in this
section, use SM 2.7 The Water and Carbon Cycles.
• Introduce the paragraph on the carbon cycle by briefly reviewing the
process of photosynthesis. Explain that this is one way that carbon
(dioxide) is used. Follow the same procedure using the water cycle
Learning Tips, as a review process to help students understand the
carbon cycle paragraph and diagram.
• Assign the Try This activity.
NEL
Chapter 2
At Home
Have students think about
where their water comes
from. How reliable is the
supply? Have they ever
had to moderate the
amount of water they
use? Have they ever had
to boil their water to make
it safe to drink? What
things do they do at home
that add carbon dioxide to
the environment?
Energy flows and matter cycles in ecosystems.
75
Technology Connections
Students could create an
animated presentation on
the water or carbon cycle
using a multimedia or
hypercard computer
program. The presentation
could show how either the
water or carbon is carried
through the environment
in a perpetual cycle.
(e.g., rain—ground water
runoff—river—lake—
evaporation—
condensation—rain)
Math Connections
Scientists are able to date
fossils and artifacts by
using radiocarbon dating.
Radioactive carbon atoms
(carbon-14) break down
over time in a predictable
pattern.
Half of a sample of C-14
decays in 5568 (30)
years. Half of the
remaining sample decays
in another 5568 years, and
so on. After 10 "half-lives,"
there is a very small
amount of radioactive
carbon remaining in a
sample. At about 50 000 to
60 000 years, then, the
limit of the technique is
reached. (Beyond this time,
other radiometric
techniques must be used
for dating.) By measuring
the amount of carbon
remaining in a fossil or
artifact, scientists are able
to determine, with an
accuracy of /50 years,
how old an object is.
TRY THIS: OBSERVE WATER LOSS FROM LEAVES
Purpose
• Students will observe the difference in water loss from two different types of
plant leaves and write an appropriate hypothesis.
Notes
• Have students reread the Skills Handbook section called Thinking as a Scientist,
starting with Predicting.
Suggested Answers
• The larger leaves will produce more water in the bag, as a larger leaf has a
greater surface area than a needle.
• Possible hypothesis: If a plant has large leaves, then it will lose more water over
the same time period than a plant with small leaves.
3 Consolidate and Extend
• Consider the importance of caring for water resources, since other
living things eventually end up using the same water again.
• The issue of global warming, an imbalance in the amount of carbon
in the atmosphere, is discussed in ScienceWorks in Chapter 3.
• In the diagram of the carbon cycle, students may need to be told
that oil, gas, and coal, which formed underground (fossil fuels), are
part of the carbon cycle. However, the process is very, very slow.
• Refer to the chapter introduction questions to see which ones have
been answered in this section. (Where do the materials that make up
its [the orca’s] body come from? Where do they go if the orca dies of
disease or old age? Why do ecosystems not run out of materials and
energy?)
• Refer back to the chapter introduction photo, noting that the orca
lives in the ocean, which has a significant role in the water cycle. Ask
students, Is there is an example of carbon in this photo? (Yes, the orca)
• Have students add details to BLM 0.0-9 Chapter Key Ideas.
• Assign the Check Your Understanding questions.
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. Rain and snow come from clouds carrying water that has evaporated from
Earth’s surface.
76
Music Connections
2. Answers may vary. Anything living (or now dead) is a source of carbon.
A song about the water
cycle can be found at
Nelson Science Probe 7
Web site
www.science.nelson.com.
3. If there were no decomposers, the carbon cycle would cease, since the
decomposers return carbon to the air, water, and soil.
Unit A: Ecosystems
NEL
2.7
The Water and Carbon Cycles
Plants constantly trap new energy from the Sun. This new energy
replaces the energy that was lost as heat in every level of the food
chain. In this way, energy is constantly being added to ecosystems.
Although new energy continues to arrive from the Sun, no new
water arrives. The water that is on Earth now is the same water that
was here when the dinosaurs lived. It has been reused and recycled
many, many times.
The Water Cycle
Anything that happens over and over again, like the seasons of
the year or the phases of the moon, is called a cycle. Water moves
through a cycle (Figure 1).
LEARNING TIP
Condensation
Follow the arrows on the
diagram as you read about
the water cycle. Check your
understanding by using the
diagram to explain the
water cycle to a partner.
Precipitation
(rain and snow)
ice and
snow
Evaporation
Precipitation
Evaporation
Ocean
Runoff
Water table
Reading and Thinking Strategies: Interpret
Visuals and Graphics
• Analyzing illustrations and photographs is similar to
looking at diagrams. Have students begin by developing
a holistic impression. Ask students, What does this
show? Then have them look at each element, starting
with the largest and most pronounced (often in
foreground), then considering the details. One strategy
is to begin by simply listing everything in the illustration
or photograph.
• Students also can consider the purpose of each
illustration, photograph, or other graphic element. Ask
students, Why have the writers included this? Why is it
important here?
Figure 1
The water cycle
52
Unit A
Ecosystems
NEL
Meeting Individual Needs
ESL
• Point out to students that the order of a cycle in some situations
cannot be changed or the information they are providing will be
inaccurate. If resource support is available, have students write from
their graphics to learn how text is developed from cycles with its focus
on a series of actions/events.
Extra Support
• For students who need additional support with the reading in this
section, use SM 2.7 The Water and Carbon Cycles.
Extra Challenge
• Refer to the chapter introduction question, “Why do ecosystems not
run out of materials and energy?” Research why some ecosystems
experience drought.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Suggestions for Teaching Students Who Are Having Difficulty
Evidence that students can
• describe how matter recycles within
ecosystems (e.g., water cycle)
• explain the role of decomposers (plants
and animals, including humans) in the
carbon cycle
• use technical language correctly
(cycle)
Review the water cycle diagram (Figure 1), in conjunction with performing the Try
This activity. Provide a sentence frame for writing the Try This hypothesis.
NEL
Chapter 2
Energy flows and matter cycles in ecosystems.
77