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MSP:MiddleSchoolPortal/What Goes Around Comes Around: Water Cycle

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What Goes Around Comes Around: The Water Cycle - Introduction

Water cycle lg.jpg
This is the second publication in our series called What Goes Around Comes Around. The first publication covers the topic of the carbon cycle and the third, nitrogen cycle.


When it’s raining, waters always draining,
Flowing down into the woodland stream.
Girls: Some will come directly down.
Boys: Some will come in from the ground.
Girls: All around.
Boys: From the ground.
Ohh...
—from Land and Water, sung to the tune of Alouette.

A children's song conveys the water cycle to elementary students—a series of steps involving changing states of matter through the processes of evaporation, transpiration, condensation, and precipitation. In middle school, students can begin to investigate the chemical and physical properties of water that enable it to behave in ways necessary for the water cycle to happen.

As we did in The Carbon Cycle, we will assume students have been exposed to the water cycle but lack understanding of the more abstract properties of water. Thus, some of the resources here will facilitate student investigation and understanding of the properties of water and its role in and out of living things. An understanding of the nature of H2O combined with previous knowledge of the water cycle will enable students to explore real-world issues of water pollution; water conservation; water purification; water management; and the impacts of road, bridge, dam, parking lot, and other construction.

We all know water is essential for life, but do we ever ask why? Exactly what does water do for living things that's so important? The first resource in Background Information for Teachers addresses this question in a general and comprehensible way. Water, being essential to life, is highly valued in most cultures and care should be taken with its management. But if it’s a renewable resource and if it cycles as we are taught it does, how can there be such a thing as a water shortage?

The resources here will provide you with content information as well as lessons and activities to guide your students to deeper understandings of the nature of water, the need for and intricacies of its management, and why water management issues can be difficult and emotional.

Background Information for Teachers

Developing middle school students’ knowledge of water’s chemical properties, including its molecular structure, is not the main focus of this publication. However, middle school students can be introduced to the properties of water with the expectation that they may not master the related concepts until high school chemistry. Referring to atoms and molecules, the National Science Education Standards says:

use of such terminology is premature for these students and can distract from the understanding that can be gained from focusing
the observation and description of macroscopic features of substances and of physical and chemical reactions. At this level, elements
and compounds can be defined operationally from their chemical characteristics, but few students can comprehend the idea of atomic
and molecular particles.

With that in mind, the following simulation of the water molecule polarity can be conducted without using the terms "atom" or "molecule." After participating in the simulation, students should gain these understandings: there are two hydrogens for every one oxygen; these three are bonded to each other and constitute a "unit" (water molecule); these units align themselves in a specific pattern; and these units are not actually bonded to each other the way the Hs are to the O.

For the activity, give two-thirds of your students hang tags labeled "H, slightly +", and one-third hang tags labeled "O, slightly –". If the number of students is not evenly divisible by three, include yourself or an aide, or make an extra student your assistant and observer. Instruct students to form "units" of three students. All students have to be in a group, and no group can consist solely of all Hs or all Os. Have the Hs flank the single O in each group. Ask them to link arms (to model the atomic bonds between the atoms holding the molecule together). Finally, instruct the "units" to come close to each other, paying attention to the positive and negative signs on their hang tags.

Ask the students what happens when like charges come near each other, similar to the north ends of two bar magnets? Here, the Os need to consider their slightly negative charge and the Hs need to consider their slightly positive charge. They should end up aligning backs of student Os to a student H of another unit by standing near each other, but not actually connected or bonded to each other. Voila! You have a life-sized model depicting the polarity of water, the covalent bonds of H and O, and hydrogen bonding. You can have your students draw a picture on the board of what each unit consists of and how the units align with each other.

For eighth graders, or students cognitively prepared, you may want to now introduce the terms "atom," "molecule" and "bond" by connecting them to the simulation. You can extend the model by asking students to model the three states of matter. Students will stand fairly still to model the solid state, move moderately while compacting a bit to model the liquid phase (recall, water expands in the frozen state, due to H bonding), and increase their kinetic energy while increasing the distance between water molecules to model the gas state.

Caution students that water is unique in its ability to expand when changing state from liquid to solid, that is, when freezing. For most compounds it's the opposite; volume decreases when changing state from liquid to solid. You may consider a demonstration involving the melting of chocolate as an example. The solid volume can be expressed in cubic cm, for example, 10cc, and the liquid volume for that same solid 10cc sample in ml. Since 1ml = 1cc, an easy conversion and comparison is made. It may take a considerable volume of chocolate to be able to observe a measurable difference in the two volumes between the two states.

When students are ready to delve deeper into the water cycle and all its implications, by all means jump in! If you would like some guidance on sequencing lessons, use NSDL Strand Map Service. These maps illustrate connections between concepts and across grade levels. For example, The Water Cycle is a major theme in the Weather and Climate Strand Map. But perhaps more importantly, the water cycle cuts across all the Common Themes identified by AAAS Project 2061; Systems, Models, Constancy, Patterns of Change, and Scale. An image of the middle grades (6-8) only part of the Systems map appears below. Clicking on a concept within the maps will show NSDL resources relevant to the concept, as well as information about related AAAS Project 2061 Benchmarks and National Science Education Standards. Move the pink box in the lower right hand corner of the page to see the grades 6-8 learning goals. Boxes that appear to be floating unconnected are connected to concepts in the bands above or below the middle grades. These connections are visible on the K-12 Constancy Map

Our World of Water: Living Things Depend on Water Briefly describes how and why living things use water. Provides an experiment one can do to illustrate the ratio of water to solids in a living thing.

Water: Properties and Behavior This module provides an introduction to the chemical properties of water. The dipole across the molecule, hydrogen bonding, surface tension, and solvation are all introduced.

Understanding the Unusual Properties of Water This downloadable article raises some interesting questions regarding water and living things and may give you additional insights and perspective as you begin your unit on the water cycle. Having found no clear reason why water should be the only liquid in which life could form and survive, scientists continue to search for the reason. Here we follow the first steps along the challenging path to this answer, trying to understand (i) what is unusual about water; (ii) why water has anomalies; (iii) which are the full implications of these unusual properties; and (iv) if these anomalies are exclusive properties of water. Since the change of local liquid structure could be relevant in biological processes, the possibility of a wide class of liquids with this property could help in understanding if water is essential for life.

Structure, Dynamics and Function of Aquaporins Aquaporins are membrane channels that control the flow of water across a cell membrane. Water's polarity is a problem when one needs water to pass through a nonpolar lipid bilayer, and yet all cells require water to survive! This Nobel Prize in Chemistry award-winning animation clearly illustrates the process. Sharing this with your students will build a bridge from water's universal chemical and physical properties to living things and how these properties are accommodated by and manifested in cells—a major cog in the larger water cycle on earth. Click on Download a detailed movie of water permeation.

LEARN: Atmospheric Science Explorers LEARN was created to increase middle school teachers’ knowledge of and interest in the atmospheric sciences. The module was created by teachers. The seven sections include introductions to the atmosphere, climate, ozone, stratospheric ozone and tropospheric ozone, the greenhouse effect, and global climate change. Each section provides background information, general learning concepts, and a list of classroom activities. Choose Introduction to the Atmosphere, and scroll down to Activity 4, The Water Cycle, at the bottom of the page.

USGS Water Management The U. S. Geological Survey provides maps, reports, and information to help others meet their needs to manage, develop, and protect America's water, energy, mineral, and land resources. Some of the 17 topics included here are flood forecasting, reservoir management, water allocation and bioremediation. Perusing this site will give you insight into how this country conceives of and executes water management programs. You might decide to have your students use one or two topics for their own research and information.

The Science Educator’s Guide to Selecting High-Quality Instructional Materials This guide presents a method for judging the quality of K-12 teaching materials, both in print and online. It is based on AAAS Project 2061’s curriculum-materials analysis procedure which was developed over several years with funding from the National Science Foundation and in consultation with K–12 teachers, materials developers, scientists, teacher educators, and cognitive researchers nationwide. The guide is designed to help science educators determine how well an instructional material supports students in learning important science ideas such as those described in national benchmarks and standards. With its step-by-step procedure for taking a critical look at instructional materials, the guide can help science educators take a more informed approach to a number of essential tasks. The online version of the guide includes examples from textbooks that have received high and low ratings when previously evaluated using the Project 2061 procedure, interactive tutorials, files that can be used as templates for recording evaluation judgments, and links to useful online resources.

Lessons and Activities about the Properties of Water

In this section, the goal is to introduce students to properties of water. However, you may choose to skip it if you feel your students are not cognitively ready. Due to the abstract nature of the water molecule and bonding, students will need a great deal of scaffolding to come to a conceptual understanding of the water molecule and its properties.

Approaches to support students in their learning may include exposing them to several different representations, from 2-D schematic drawings and animations to 3-D physical models and the human simulation described in Background Information for Teachers. Students should then be able to construct an understanding of the properties of the water molecule, which you can assess in a number of ways. For example, you could have students create their own drawings or build their own 3-D models alone or collaboratively with labels and explanations. The resources in this section focus on the 2-D images and animations.

Hydrogen Bonds Animation This color animation of water molecules interacting and forming hydrogen bonds is a hybrid between a PowerPoint slide show and an animation. Students can replay portions or click next if they do not need to replay a segment.

Water Properties A simple description of the chemical and physical properties of water produced by the U.S. Geological Survey.

Lessons and Activities Reviewing the Water Cycle

This section is rather brief, as it is assumed students have been exposed to the water cycle in the past. The goal of this section is to provide a review for students, to activate their prior knowledge and prepare them to augment their existing knowledge of the water cycle with the resources found in Lessons and Activities Investigating Human Activities Impacting the Water Cycle.

Observe a Raindrop Traveling Through Various Paths of the Water Cycle In this interactive resource, students move a raindrop through different parts of the water cycle. By clicking on an arrow, students can select where the raindrop in a cloud will fall as precipitation and continue to transfer the drop through different paths in the cycle. When students place their cursor over an arrow, two text boxes appear—one contains the name of the process and another supplies a short definition of it. Precipitation, sublimation, transpiration, infiltration, runoff, and melting are among the processes represented.

The Water Cycle This interactive diagram of the water cycle invites students to click on a part of the cycle to get information about streamflow, surface runoff, freshwater storage, ground-water discharge, ground-water storage, infiltration, precipitation, snowmelt, runoff to streams, springs, condensation, evaporation, evapotranspiration, water in the atmosphere, ice and snow, and oceans. A summary of the water cycle on a single web page is also available as text with pictures in about 50 languages, text only in 13 languages, or diagram only.

The Water Cycle This web site, developed by the Environmental Protection Agency, is divided into four interactive, animated graphic sections: rain, water storage, vapor, and clouds. Students can discover the forms of precipitation and why it occurs, the development of aquifers, transpiration, and condensation. This is a great web site for young students to grasp the connections between different forms of water.

Lessons and Activities Investigating Human Impacts

If your students understand the principles of the water cycle, they are ready to investigate environmental issues involving the relationships between and among human needs, technological innovations, and the forces of nature.

One issue is the growing human population worldwide and the increased demand for clean, fresh water that comes along with it. Some say there is enough water, it's just not potable. The infrastructure required to purify and move water to where it needs to be is extremely costly. From the perspective of a for-profit business, there is not much profit to be gained in doing so. Rather, for-profit businesses thrive on building and development, which means deforestation and increased incidence of flooding, which contributes to water pollution and exacerbates the clean water issue.

Drought Causes Conservation In this interdisciplinary, multiday lesson, students will use their knowledge of the importance of water to learn about the hydrosphere. A drought will be explored through graphs and a personal plan for water conservation.

Rain: Friend or Foe? In this lesson students will use their knowledge of rainfall, vegetation, and the slope angles of hillsides to make decisions, predict outcomes, and analyze the effects of certain events or practices (e.g., overgrazing, forest fires, and clear-cutting woodlands). This lesson will help students appreciate the complex relationships between physical processes and the features they help create and understand the physical processes affecting the surface of the earth.

Earth Exploration Toolbook Chapter: Investigating the Precipitation-Streamflow Relationship This activity can enrich a study of the water cycle. It prepares you to launch an investigation of the relationship between precipitation and streamflow for a local watershed. Following the step-by-step instructions in a case study, students can locate and graph one year of web-based data for these two variables. The graph provides a context for launching a discussion of the balance between surface runoff and infiltration during and after a rain event, soil porosity, soil saturation level, the influence of impervious surfaces such as concrete parking lots and roads in a basin, the impact of slope, wind and air temperature on watershed hydrology, and the influence of high or low vegetation. You should allow at least four 45-minute class sessions for the entire activity.

Development and Flooding: Hurricane Floyd Lesson Plan In this lesson, students will take their knowledge about the hydrosphere and apply it to the issue of population growth and development. In particular, students will learn how increasing development in eastern North Carolina may have worsened the effects of flooding from Hurricane Floyd, due to lack of soil and tree absorption of runoff. In small groups, students will create their own development plans for North Carolina and explain how their plan will benefit the state’s water resources and environment.

A River Runs Through It In this online activity, students research the ecological impacts of developing a community along a river that has been dammed for some time. Once they have completed the research (in teams), the students prepare a presentation for a town meeting. Activity pages, resource pages, evaluation criteria, and teacher pages are included.

Three Gorges: The Biggest Damn in the World Though this lesson focuses heavily on engineering, you can use it as a segue to discussion of human activities as they relate to the water cycle. The Three Gorges Dam in China is a sensational example of the benefits and problems of damming major rivers, but you can probably find smaller scale, analogous projects in your own area to discuss with students.

Down the Drain: How Much Water Do You Use? This Internet-based collaborative project will allow students to share information about water usage with other students from around the country and the world. Based on data collected by their household members and their classmates, students will determine the average amount of water used by one person in a day. They will compare this to the average amount of water used per person per day in other parts of the world. Students can publish reports, photos, or other work directly to the site. A teacher’s guide with information on how to implement lessons in the classroom is included.

Latest Science News from the New York Times

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SMARTR: Virtual Learning Experiences for Students

Visit our student site SMARTR to find related science-focused virtual learning experiences for your students! The SMARTR learning experiences were designed both for and by middle school aged students. Students from around the country participated in every stage of SMARTR’s development and each of the learning experiences includes multimedia content including videos, simulations, games and virtual activities.

Careers

The FunWorks Visit the FunWorks STEM career website to learn more about a variety of science-related careers (click on the Science link at the bottom of the home page).

National Science Education Standards

All of the middle school content standards in the National Science Education Standards are linked in some way to the lessons and activities in this publication; however, content standards C, D and F are most directly linked.

Science as Inquiry: Content Standard A

As a result of activities in grades 5-8, all students should develop:

  • Abilities necessary to do scientific inquiry
  • Understandings about scientific inquiry

Physical Science: Content Standard B

As a result of their activities in grades 5-8, all students should develop an understanding of:

Properties and changes of properties in matter

  • A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.
  • Substances react chemically in characteristic ways with other substances to form new substances (compounds) with different characteristic properties. In chemical reactions, the total mass is conserved. Substances often are placed in categories or groups if they react in similar ways; metals is an example of such a group.

Transfer of energy

  • Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways.
  • The sun is a major source of energy for changes on the earth's surface. The sun loses energy by emitting light. A tiny fraction of that light reaches the earth, transferring energy from the sun to the earth. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation.

Life Science: Content Standard C

As a result of their activities in grades 5-8, all students should develop understanding of:

Structure and function of living things

  • Cells carry on the many functions needed to sustain life. They grow and divide, thereby producing more cells. This requires that they take in nutrients, which they use to provide energy for the work that cells do and to make the materials that a cell or an organism needs.

Regulation and behavior

  • All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.

Populations and ecosystems

  • For ecosystems, the major source of energy is sunlight. Energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis. That energy then passes from organism to organism in food webs.
  • The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem.

Earth and Space Science: Content Standard D

As a result of their activities in grades 5-8, all students should develop an understanding of:

Structure of the earth system

  • Land forms are the result of a combination of constructive and destructive forces. Constructive forces include crustal deformation, volcanic eruption, and deposition of sediment, while destructive forces include weathering and erosion.
  • Water, which covers the majority of the earth's surface, circulates through the crust, oceans, and atmosphere in what is known as the "water cycle." Water evaporates from the earth's surface, rises and cools as it moves to higher elevations, condenses as rain or snow, and falls to the surface where it collects in lakes, oceans, soil, and in rocks underground.
  • Water is a solvent. As it passes through the water cycle it dissolves minerals and gases and carries them to the oceans.
  • The atmosphere is a mixture of nitrogen, oxygen, and trace gases that include water vapor. The atmosphere has different properties at different elevations.
  • Clouds, formed by the condensation of water vapor, affect weather and climate.
  • Living organisms have played many roles in the earth system, including affecting the composition of the atmosphere, producing some types of rocks, and contributing to the weathering of rocks.

Science and Technology: Content Standard E

As a result of their activities in grades 5-8, all students should develop:

Understandings about science and technology

  • Science and technology are reciprocal. Science helps drive technology, as it addresses questions that demand more sophisticated instruments and provides principles for better instrumentation and technique. Technology is essential to science, because it provides instruments and techniques that enable observations of objects and phenomena that are otherwise unobservable due to factors such as quantity, distance, location, size, and speed. Technology also provides tools for investigations, inquiry, and analysis.
  • Perfectly designed solutions do not exist. All technological solutions have trade-offs, such as safety, cost, efficiency, and appearance. Engineers often build in back-up systems to provide safety. Risk is part of living in a highly technological world. Reducing risk often results in new technology.
  • Technological solutions have intended benefits and unintended consequences. Some consequences can be predicted, others cannot.

Science in Personal and Social Perspectives: Content Standard F

As a result of activities in grades 5-8, all students should develop understanding of:

Populations, resources, and environments

  • When an area becomes overpopulated, the environment will become degraded due to the increased use of resources.
  • Causes of environmental degradation and resource depletion vary from region to region and from country to country.

Natural hazards

  • Internal and external processes of the earth system cause natural hazards, events that change or destroy human and wildlife habitats, damage property, and harm or kill humans. Natural hazards include earthquakes, landslides, wildfires, volcanic eruptions, floods, storms, and even possible impacts of asteroids. (See Content Standard D (grades 5-8))
  • Human activities also can induce hazards through resource acquisition, urban growth, land-use decisions, and waste disposal. Such activities can accelerate many natural changes.
  • Natural hazards can present personal and societal challenges because misidentifying the change or incorrectly estimating the rate and scale of change may result in either too little attention and significant human costs or too much cost for unneeded preventive measures.

Risks and benefits

  • Risk analysis considers the type of hazard and estimates the number of people that might be exposed and the number likely to suffer consequences. The results are used to determine the options for reducing or eliminating risks.
  • Students should understand the risks associated with natural hazards (fires, floods, tornadoes, hurricanes, earthquakes, and volcanic eruptions), with chemical hazards (pollutants in air, water, soil, and food), with biological hazards (pollen, viruses, bacterial, and parasites), social hazards (occupational safety and transportation), and with personal hazards (smoking, dieting, and drinking).

Science and technology in society

  • Technology influences society through its products and processes. Technology influences the quality of life and the ways people act and interact. Technological changes are often accompanied by social, political, and economic changes that can be beneficial or detrimental to individuals and to society. Social needs, attitudes, and values influence the direction of technological development.
  • Science and technology have advanced through contributions of many different people, in different cultures, at different times in history. Science and technology have contributed enormously to economic growth and productivity among societies and groups within societies.
  • Science cannot answer all questions and technology cannot solve all human problems or meet all human needs. Students should understand the difference between scientific and other questions. They should appreciate what science and technology can reasonably contribute to society and what they cannot do. For example, new technologies often will decrease some risks and increase others.

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.

Author and Copyright

Mary LeFever is a resource specialist for the Middle School Portal 2: Math & Science Pathways project, a doctoral candidate in science education at Ohio State University, and presently teaches high school biology. She has taught middle school science, as well as biology and natural sciences at Columbus State Community College.

Please email any comments to msp@msteacher.org.

Connect with colleagues at our social network for middle school math and science teachers at http://msteacher2.org.

Copyright July 2007 - The Ohio State University. Last updated September 19, 2010. This material is based upon work supported by the National Science Foundation under Grant No. 0424671 and since September 1, 2009 Grant No. 0840824. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.