Title: Sinks for Atmospheric Carbon Dioxide

Overview & Outcomes:

This lesson helps learners:

• explain the concept of a sink as it pertains to the accumulation and removal of carbon dioxide from the atmosphere.
• identify the two principal sinks for excess atmospheric carbon dioxide.
• describe the process underlying the terrestrial (land-based) sink as well as natural and human influences on the capacity of the terrestrial sink.

The concept map shows model relationships among concepts this lesson seeks to develop. Concepts introduced in this lesson are bolded on that concept map and concepts from other lessons are in plain text (not bolded).

Background Notes for the Teacher:

In this lesson, the specific greenhouse gas we will focus on is carbon dioxide, the principal sinks are terrestrial (land-based) green plants and the oceans, and the comprehensive biogeochemical cycle is the global carbon cycle (see Figure 1 below). The ocean is the largest sink, containing by far more carbon than the terrestrial ecosystem or the atmosphere. However, the processes that govern the oceans' uptake of CO2 from the atmosphere are very detailed. On the other hand, students likely already have some prior knowledge of the terrestrial CO2 sink processes on which to build. Additionally, the terrestrial sink is something students can influence directly (as will become apparent). Therefore, the principal focus of this lesson is on the terrestrial sink. However, brief coverage is provided at the end of this background section on the ocean CO2 sink processes and the teacher is given the option of expanding this lesson accordingly.

As is indicated by Figure 1, two other atmospheric gases, CH4 (methane) and CO (carbon monoxide), are also a part of the global carbon cycle, but will not be considered in this or the next lesson. One comment on the sources of CH4 as illustrated by the diagram. It may seem incorrect that a combustible gas (CH4) could be produced from biomass burning. However, the burning of plant material in tropical and subtropical areas, whether it be to clear forests or burn residue from crops (e.g., the latter is a common practice after harvesting sugarcane), is a significant source of atmospheric CH4. The background section of this lesson will comment on various aspects of Figure 1.

Figure 1. Illustration of the Global Carbon Cycle. Adapted from: Trabalka, J (Ed) (1985). Atmospheric carbon dioxide and the global carbon cycle, DOE/ER-0239 (pg. 178). Washington, D.C.: United States Department of Energy.

The global carbon cycle, and the carbon dioxide source-sink relationship, is very complex and uncertainties exist. One uncertainty is the missing carbon, depicted in Figure 2 below. Note that the (average annual) sum of atmospheric accumulation plus the estimated ocean uptake of carbon (5.4 Gt) equal an amount less than the carbon dioxide emitted (7.0 Gt). Therefore, other sink processes must be operating. This idea of missing carbon (shown to be 1.6 Gt) is more understandable if we refer to this missing carbon as the missing carbon sink. In other words, there must be a sink somewhere for this 1.6 Gt of missing carbon, or it would have accumulated in the atmosphere. Put another way, the amount of carbon dioxide now present in the atmosphere should be greater than what currently is there, based on what scientists know about the amount of CO2 emitted into the air and the capacity of the sinks to take it out of the atmosphere. Capacity here refers to the amount of CO2 that can be taken up and stored for some time. Figure 2 does not show any amount of carbon taken up by terrestrial green plants, and this probably accounts for much of where the missing carbon is going. In other words, terrestrial green plants are likely the missing carbon sink. Scientists hypothesize that this missing carbon sink is due especially to the processes of carbon dioxide fertilization and forest regrowth in the Northern Hemisphere. We will elaborate on these two processes under terrestrial sink, which follows.

*Gt refers to gigatons, which is billions of tons of carbon.

Figure 2. Estimated amounts of carbon emitted to, accumulated in, and removed from the atmosphere, 1980-1989. Adapted from: Houghton, J., Jenkins, G., and Ephraums, J. (1990). Climate change. The IPCC Scientific Assessment. New York: Cambridge University Press.

Terrestrial Sink. The terrestrial sink for CO2 also includes the soil, because when plants die, they contribute dead organic (carbon containing) matter to the soil. Additionally, animals eat the plants and their feces contribute to this dead organic matter. However, the terrestrial sink begins with green plants through the process of photosynthesis and this will be our focus. Photosynthesis is the process through which (green) plants take up carbon dioxide from the atmosphere and make sugar. (As indicated in the diagram, photosynthesis also occurs in the ocean and this will be discussed under Ocean Sink.) The term and its meaning is rather easy to remember when broken down: Photo implies light and synthesis means to make. Accordingly, photosynthesis is to make (food) from light. Of course this definition is incomplete. A better one is-The process by which plants harness the energy contained in electromagnetic energy from the sun (specifically the visible light component of the spectrum) to make sugar (a simple carbohydrate) from water and carbon dioxide. Indeed, photosynthesis is the reverse of respiration. Green plants are called producers (as opposed to consumers, which comprise the animal kingdom) because of this photosynthetic ability. The diagram also shows that plants undergo respiration, which is a source of carbon dioxide to the atmosphere. Plants do need to burn up some of the food they make in order to live and grow. However, they do take up more carbon dioxide through photosynthesis than they contribute through respiration. Yet, when they are burned (as is often the case in tropical areas) in the process of deforestation, they become a source of as opposed to a sink for atmospheric CO2. The latter is illustrated plainly by Figure 2.

The terms photosynthesis, producers, and primary production (which refers to production of biomass via photosynthesis) appear frequently in discussions of the biological aspects of global climate change. A process related to this is carbon dioxide fertilization. This process speaks to the idea that excess carbon dioxide will stimulate plant growth: As plant growth is stimulated, more carbon dioxide is taken out of the atmosphere and this helps to slow the accumulation of CO2 in the atmosphere. In other words, carbon dioxide fertilization has the potential to contribute a negative feedback to global warming. Earlier, the missing carbon was discussed. Some experts believe that this process of carbon dioxide fertilization, along with the regrowth of deforested areas in the Northern Hemisphere, account for much of this missing carbon. However, there are uncertainties about carbon dioxide fertilization. For example, plants need nutrients besides carbon to grow, such as nitrogen, phosphorus, and water. Will these nutrients be available in sufficient supply? Will a warmer climate foster the growth of weeds and pests that reduce plant growth? Will a warmer climate upset the relationship between plants and the insects (e.g. bees) that pollinate them? No one can be certain of the extent to which carbon dioxide fertilization will occur or provide a negative feedback to global warming.

Today, approximately 1/3 of the Earth's land surface is forested. A few centuries ago, the terrestrial ecosystem had a greater sink capacity than it does today for atmospheric carbon dioxide because of the much greater number of trees. Over the last couple of centuries, land use practices by humans has decreased this sink capacity. For example, the United States has lost about 25% of its forests since settlement began. Deforestation results from the fulfillment of many economic and social needs and is magnified by insufficient reforestation efforts. A rapidly expanding human population plays no small role in this problem. Trees provide timber for many purposes, e.g., construction, fuel, and paper manufacturing. Land is cleared for agriculture and urban development and to provide dams for hydroelectric power. Oftentimes, tropical forests are burned to provide land for agriculture, including the raising of cattle. Forests store anywhere from 20 to 100 times as much carbon as an equivalent land area devoted to agriculture. Deforestation reduces greatly the ability of our terrestrial ecosystem to sink carbon dioxide. And, as is obvious from previous investigations lessons, the burning of forests enhances the greenhouse effect in two ways: Carbon dioxide is added to the atmosphere and future sinks for atmospheric carbon dioxide are reduced.

Careless humans who have started forest fires, and governments which have allowed the latter to burn uncontrolled, have added to this problem. For example, in the Great Hinggan Forest, located in the northern Chinese province of Heilongjiang that borders Russia, a forest fire started by a careless smoker in 1987 demolished the World's greatest stand (3 million acres) of virgin pine. This was an area equal in size from (length) Detroit, MI to Portland, ME and (width) New York City to Washington D.C.! The forest fire was known as The Great Black Dragon Fire, and on the Russian side, where the former Soviet Union government allowed the fire to burn on, it is estimated that as much as 30 million more acres were demolished! What Smokey the Bear stands for is becoming increasingly important in the face of global warming.

Deforestation is proceeding at a more rapid rate in the tropics than anywhere else. Geographic areas where substantial amounts of tropical forest are being lost include, but are not limited to, Brazil (State of Rondonia), Mexico (State of Chiapas), Guatemala, and Burma. In Burma, the forests are a source of expensive teak wood. The lumbering and sale of teak provides the government with a substantial income, which is used to help support military efforts for defense against border attacks. A very close example of tropical deforestation is the island of Haiti (see Cobb under references at end of section). It once was almost completely forested, but now hardly any forest remains! It has been estimated (with some uncertainty!) that every year an amount of tropical rain forest that would cover the state of Pennsylvania is removed! This is extremely unfortunate because tropical forests (which are mostly rain forests') contain about ½ of the total carbon stored collectively by all terrestrial plants.

It is important to recognize that the governments of countries that contain tropical forests may be concerned about the long-term ramifications of deforestation. However, they often have current pressing problems (e.g., war, rapidly expanding populations, and large debts owed to developed countries) that overshadow this concern. Indeed, the forests are often a victim of such problems and the exploitation of this resource provides part of an immediate solution. Deforestation in tropical countries is an international problem and developed countries will have to aid tropical countries in various ways to contain this problem. Some tropical countries recently have taken positive steps toward the deforestation problem and mounted reforestation efforts. Recent reforestation efforts of land in the temperate latitudes in the Northern Hemisphere also are helping to counter the problem and increase the sink power of the terrestrial ecosystem.

Ocean Sink. (Various of the terms and processes alluded to below are illustrated in Figure 1.) The surface layers of the ocean, which cover about 70% of the Earth's surface, take up (via diffusion) carbon dioxide from the atmosphere until equilibrium between the ocean and atmosphere is reached. At any point in time, most of the carbon present in sea water is dissolved in the form of the bicarbonate ion (HCO3). The latter is formed as a result of a sequence of reactions initiated by the reaction of carbon dioxide with sea water, forming carbonic acid (H2CO3).

In order for the surface water to take up any more carbon dioxide from the atmosphere, other processes must come into play to lower the carbon content of this surface water. These other processes are described below:

(a) Phytoplankton are mostly algae. Although phyto does refer to plant, algae technically are not classified as plants. However, like green plants, they perform photosynthesis. Phytoplankton, residing near the surface of the ocean, take up CO2 from the ocean to perform photosynthesis. Phytoplankton are the base of the oceanic food chain and are consumed by zooplankton (zoo referring to animal) and larger animals. Fecal pellets (containing carbon) from the animals that eat the phytoplankton sink to the bottom of the ocean. Here, they become an ingredient in the ocean floor sediment, and eventually undergo decomposition.

(b) Foraminifera, microscopic animals that are a type of zooplankton, and coral also take up carbon from the surface ocean waters and use it to synthesize their shells or outer body covering. The latter are composed of calcium carbonate (CaCO3). Foraminifera also serve as food for other animals, and accordingly, contribute to feces that are deposited on the ocean floor. Foraminifera that are not consumed also sink to the ocean floor when they die and become an ingredient in the ocean floor sediment. The processes whereby the carbon in phytoplankton and foraminifera is transported from the surface waters to the ocean floor is called biological pumping.

(c) As the surface waters of the ocean flow toward the poles, they are cooled, and accordingly, become more dense and sink. This is a part of a more comprehensive process, the conveyer belt model, that drives the circulation of the ocean waters.

Additional Teacher Resources.

1. Benarde, M. (1992). Global warning...global warming. New York: John Wiley & Sons.

2. Cobb, C. (1987). Haiti: Against all odds. National Geographic, 172, 645-671.

3. Houghton, J.T., Callander, B.A., & Varney, S. (Eds.) (1992). Climate change 1992. The supplementary report to the IPCC Scientific Assessment. New York: Cambridge University Press.

4. Houghton, J.T., Jenkins, G., & Ephraums, J. (Eds.) (1990). Climate change: The IPCC Scientific Assessment. New York: Press Syndicate of the University of Cambridge.

5. Meszaros, E. (1993). Global and regional changes in atmospheric composition. Ann Arbor, MI: Lewis Publishers

6. Panel on Policy Implications of Greenhouse Warming. (1992). Policy implications of greenhouse warming: mitigation, adaptation, and the science base. Washington D.C.: National Academy of Sciences

7. Post, W., Peng, T., Emanuel, W. King, A., Dale, V., & DeAngelis, D. (1990). The global carbon cycle. American Scientist, 78, 310-326

8. Scientific American (1989), Volume 261 (3). This September issue is devoted to global climate change.

9. Trabalka, J. (1985) Atmospheric carbon dioxide and the global carbon cycle. Technical Report DOE/ER-0239. Washington, D.C.: United States Dept. of Energy.

Materials:

For class

1. 1 map of the world (Ideally, visible to all students from seats).

2. 2" utility size sponges [dimensions 6" (152mm) x 3.6" (91mm) x .9" (22mm)]. One sponge should be blue, representing the ocean, and the other green, representing terrestrial green plants. Sponges do not have to be exactly of the previous dimensions, but they need to be large enough to soak up, upon saturation, at least 120 mls (blue sponge) and 80 mls (green sponge): See section on Preparation, below.

3. 1 clear container, such as a beaker or beverage bottle (latter with the top cut off), with capacity to hold about 2 liters. (Note: Sponges must be able to fit, with little squeezing up, into container)

4. 1 volumetric measuring container (to measure water added to and removed from the clear container)

For each group of 4 students.

1. Bean plants (2 containers per 4 students), grown in advance (as directed under preparation prior to day of lesson below)
2. Bean seeds (green or yellow beans, but all students should use same kind of beans; 2 seeds per container; use a fresh lot of seeds to help insure germination)
3. Potting soil (2 cups per container)
4. Plant containers to hold potting soil (2 per 4 students)
5. Ruler
6. Scale to weigh bean seeds and plant seedlings (scale may be shared between students).

For each student.

1. BEAN SEEDLING EXPERIMENT worksheet.
2. Safety goggles (and lab aprons if desired)

Preparation:

Day of lesson.

1. Set up apparatus for sink demonstration using sponges, clear container of water, and volumetric measuring container.

Prior to day of lesson.

1. About 2 ½ to 3 weeks before this lesson, the teacher and each group of 4 students (as assigned by teacher) should start bean plants following the procedures listed below. The teacher should prepare a few extra plants, in the event that some of the students' seeds do not germinate:
   • Reproduce and distribute BEAN SEEDLING worksheet. Each group should obtain 4 seeds, weigh each seed, and record weight of each seed on the worksheet. Students should decide which two seeds will go into the dark and light growing conditions container and label as such on worksheet.

   • Each group should obtain 2 empty containers and place 2 level cups of potting soil in each container. Tap containers just a bit to settle the soil.

   • Follow directions on package of bean seeds for planting seeds to required depth -students should measure depth of hole where each seed will go with a ruler. Plant two seeds to each container and separate the two seeds by an inch. Label the outside of each container as to the location of each seed: Seed 1 and 2 for plants grown under light conditions and seed 3 and 4 for dark conditions.

   • Water seeds. The teacher should determine the amount each container should receive at the first watering and students should measure and water accordingly. Subsequently, students should water as needed (i.e., so surface remains a bit damp). The teacher should caution students to not over water and that the plants placed in the dark location will not need as much watering. All amounts of water added should be measured and recorded on the BEAN SEEDLING worksheet.

   • Students should label each container (dark or light conditions, and group identification) and set in the designated dark (e.g., closet) and light (e.g., by sunnyside window or under fluorescent lights) location. Do not place in cool location, as this will retard germination. Ideally, temperatures between dark and light locations will be the same, but this likely will not be possible if the light conditions plants are set right close to windows. If the teacher desires, temperature differences can be monitored (and recorded on worksheet by students) by placing thermometer in each location, and later taken into consideration by students when they analyze the results of this experiment.

   • Over the next 2 ½ weeks, students should observe daily their bean plants, and record observations on their worksheet. Students will need to remove temporarily their dark conditions containers from their location in order to make the observations. These observations can include linear measurements of the height of each seedling, taken daily after each seedling breaks the surface. Students must be very gentle so as not to break the seedlings.

2. At least one day before this lesson, procure the two sponges (blue and green) listed under materials needed and determine what amount of water they soak up, upon saturation: Immerse sponge and let excess water drain off. A utility size sponge, at saturation, will hold between 120 mls (4 fl oz) and 165 ms (5 ½ fl oz). Cut sponges down (as necessary) to soak up, at saturation, the approximate amounts of water (blue-120ml; green-80 ml) referred to under the materials needed section.

Instructional Procedures: (2 Days, 40 minutes each)

Day 1. (40 minutes)

1. Externalizing Students' Existing Thoughts/Ideas.

   To find out what students currently know/believe about where carbon dioxide, given off by anthropogenic sources, goes and to bridge the gap between previous lessons and this lesson, have students hypothesize answers to the following question:

   What happens to the carbon dioxide that is given off by the sources that we have investigated in previous lessons?

   Encourage students to think a bit and not stop at simple answers such as it goes into the air. Utilize the think, pair, share instructional strategy, described as follows:

   • Give students about three minutes to think and write down answers individually to the above question. Tell students that they can draw (e.g., rough pictures or diagrams) their thoughts if they like.

   • Pair students and have them share and compare answers.

   • Solicit answers from class and put on board. Do not correct at this point: Save for referral and modification at the end of this lesson.

2. Demonstrating the Sink Concept Using a Familiar Phenomenon.

   In this sequence of steps (a-c), the teacher explores with the students the concept of sink using a familiar phenomenon: a sponge soaking up water. This serves as an advance organizer in that it helps students connect and anchor content in the remainder of this lesson to concepts and phenomena which they already hold in memory.

   • Tell students: Just as there are sources for atmospheric CO2, there must also be sinks for atmospheric CO2. This is true for the other greenhouse gases too, but we will focus mainly on CO2 in this lesson. We will describe a sink as someplace for the atmospheric CO2 to go, in order to help prevent it from building up in the atmosphere. So, a sink removes CO2 from the atmosphere. In this lesson, we want to learn about the sinks for CO2.

   • Ask students: What is the function of a sponge? Explain that we can also think of soaking up as sinking in. Sponges will be used to demonstrate the concept of a sink for atmospheric carbon dioxide.

   • Demonstrate sink concept and identify the two sinks. [Note: The amounts of water , representing atmospheric CO2, added to and removed from the clear container in steps #2-5 below are based on what we know about the increase (approximately 25%) in atmospheric carbon dioxide levels since industrialization (and the amounts of carbon emitted to and removed from the atmosphere over the last decade. For example, in step # 2 below, the 200 mls to be added is 25% of the pre-industrial atmospheric CO2 (represented by the 800 mls of water in step # 1). Thus 200 mls represents the proportional accumulation of CO2 in the atmosphere, pre-industrial to present. The amounts of water added and removed to illustrate the sink processes in steps #3-5 are not meant to reflect the exact proportional changes in atmospheric CO2 nor exact proportional amounts taken up by the ocean and terrestrial green plants sinks. The intent of the lesson is teach students the concept and sources of sink(s) and not facts that quantify proportional changes in atmospheric carbon dioxide that result from how well the sink processes work.]

   

   1. Place 800 mls (26 2/3 fl oz) of water in clear coontainer. You will need to "mark off" with a dry mark or grease pencil the level to which you fill it. Write "past" beside the makr. To make water visible to students, add red or orange food coloring. Announce to students that this water level represents the past "preindustrial" amount of atmospheric CO2, as learned in investigation lesson #7.

      

   2. Add an amount of water to increase the total by 25%, e.g., if the natural amount is 800 mls then the amount added should be 200 mls (about 6 2/3 fl ox), bring the total to 1000 mls (about 33 1/3 fl ox). Tell the students this extra CO2 represents the amount that has accumulated in the atmosphere over the last couple of centuries due to "industrialization." Remind students that most of this accumulation has happened over the last 50 years or so and that we are continuing to add "too much" CO2 to the atmosphere. Mark this level off: Write "now" beside it.

      

   3. Tell students that the now level (in step #2) would be even higher if mechanisms to remove CO2 back out of the atmosphere were operating poorly. Add another 200 mls, bringing level to 1200 mls (40 fl oz) and mark this off: Write a yikes beside it. Tell students that this (yikes) level represents an additional amount of CO2 that might have accumulated in the atmosphere by today if the mechanisms operating to take some of the CO2 back out of the atmosphere were working poorly. Tell students that these mechanisms are referred to as sinks and help to slow the build-up or accumulation of atmospheric carbon dioxide.

      

   4. Explain to students that the ocean is thought by scientists to be the main sink for atmospheric carbon dioxide. Take the larger of the two sponges (the blue sponge) to illustrate (by analogy) the sink process: Immerse the sponge in to soak up and remove about 120 mls (4 fl oz) of water. The water level should now be visibly between the yikes and now levels. Tell students that the oceans take up and dissolve CO2 from the air, but they can only take up so much at a time. In other words, the oceans have a limited capacity to take up carbon dioxide, just like the sponge has a limited capacity to take up the water.

      

   5. Tell students there is another sink: Hold up the smaller (green) sponge and ask them what they think this sink might be. This sink represents green plants (especially trees) on land. Immerse this sponge to soak up the remaining 80 mls (2 2/3 fl oz) of water. [Note: We do not advise, and this lesson does not attempt, to teach students that this terrestrial green plant sink is thought to be the missing carbon sink, as discussed in the teacher background section. It will be sufficient for students to learn that green plants, as photosynthetic producer organisms, are an important sink. The remainder of this lesson focuses on these concepts/phenomena of photosynthesis and producer.]

   6. Ask students to speculate about three different questions:

      

      • Why have these two sinks (ocean and green plants) not kept CO2 at the past (pre-industrial) level? Discussion should bring out again the concept of capacity, i.e., that the sinks can only remove so much at a time and that we are putting CO2 into the atmosphere much faster than the sinks can take it out. Therefore, the CO2 accumulates in the atmosphere.

        

      • How much CO2 will be in the air when you (the students) are about at retirement age (i.e., 50 or so years from now)? Discussion should bring out the fact that it depends on how much we keep putting into the air as well as the CO2 sink capacity of the Earth. Even if we do not increase the amount of CO2 we are adding to the atmosphere each year (i.e., rate of addition remains the same as it is today), scientists estimate that the amount of CO2 in the atmosphere by the year 2050 will still increase by almost 1/3 over today's level! [Add 333 mls (11 fl oz) to the container to illustrate the magnitude of this increase. Mark off the level and label it Future 1.] If we increase by 2% per year the amount of CO2 we add to the atmosphere, the levels will increase 2/3 over what they are today! [Add another 333 mls, or 11 fl oz, to container, which will bring level up to 1666 mls, or almost 56 fl oz. Mark off this level and label it Future 2.]

      • How can we increase the capacity of the green plant sink? Discussion could bring out planting trees and figuring out ways to decrease deforestation.

        [Note: See optional sink capacity paper towel experiment at the end of the Instructional Procedures section for an experiment that could provide students with further exposure to the concept of sink capacity.]

3. Investigate more thoroughly the green plant sink. Important Note: This investigation was initiated 2 ½ to 3 weeks ago when students planted bean seeds and placed them under dark or light growing conditions, as detailed in the Preparation section for this lesson. Students should have considerable data recorded on the growing conditions and growth of these plants at this point, and will use this data in completing what follows.]

   • Each group of students should obtain their bean plants and get out their BEAN SEEDLING worksheets. A final measurement of the length of each seedling should be taken and recorded.

   • Each group of students should harvest (roots included) carefully their two seedlings from each container. Students should remove all of the soil from the roots (soil should go back into container) of the seedlings.

   • Students should weigh and record (appropriate place on worksheet) the weight of each seedling, and determine the difference in weight between each seedling and its respective seed.

   • Students should use their data to discuss briefly in their small groups the analysis questions on their worksheet. However, the writing up of the analysis, as well as conclusions, should be assigned (after step e below) as homework since class time will be insufficient.

   • The teacher should host a class discussion with the students, following the group discussion, which reveals scientifically acceptable answers to the analysis questions and includes the scientific explanations of the concepts of photosynthesis and producer. The discussion probably will reveal that some students had a common misconception prior to the experiment: The seeds placed under dark conditions will not germinate. It is important that students realize why these dark conditions seeds did grow (seeds contain a small amount of stored food that provides the energy needed for it to germinate and grow a bit) and why they eventually died or will die when kept in the dark (stored food was used up and seedlings were not able to photosynthesize any more, due to absence of light). The teacher should ask students to use these concepts (photosynthesis and producer) in their homework where they answer the analysis questions and write up the conclusions to the BEAN SEEDLING experiment.

   • The teacher should present students with some of the facts on the importance of green plants as sinks, as taken at the teacher's discretion from the teacher background section of this lesson. Ideally, this should include the importance of tropical forests as a CO2 sink and the locations (pointed out on world map) of tropical forest deforestation. The teacher should also explain the concept of CO2 fertilization. Reference should be made to the list of students pre-instructional conceptions placed on the board in step (1) of this lesson, and any alternative conceptions should be modified to reflect the current scientific conceptions.

Homework Assignment.

Optional:

Day 2. (40 minutes)

In cooperative groups, students perform an experiment where they hypothesize which of three different brands of paper towels (chosen by the teacher) will have the greatest sink capacity (i.e., ability to soak up liquid) and subsequently test to determine those sink capacities. Step-by-step procedures for conducting this experiment have not been provided. However, a general description is given below and the form Paper Towel Sink Experiment is included (end of lesson), providing space for hypothesizing, collecting the data, and writing up results. The teacher can add instructions to the form or just list them on the board.

Prior to conducting the experiment, the teacher should ask the students what kind of preliminary information might be helpful to them in order to formulate a hypothesis. Students may mention (a) manufacturer advertising claims about the towels, (b) surface texture or characteristics of the towels, or © measuring the thickness or weight of each of the brands of towels. (Note: Since the thickness of one towel will be difficult to measure, the average thickness can be estimated by measuring several towels together and calculating the average.) The teacher must decide how much preliminary information will be allowed, but the previous information could be used to help refine or formulate additional Problems/Questions (as well as the Hypothesis), listed as the first item on the Paper Towel Sink Capacity form. As examples: Does the brand that claims to have the greatest capacity to absorb also have the greatest sink capacity? Is the dry weight, thickness, or particular surface characteristics of the towel related to its sink capacity?

The teacher might also want to ask the students in advance what kind of quality control measures should be taken during the experiment in order to help insure that the results are accurate. Regardless of whether this is asked, the teacher does need to standardize procedures and this should include the following:

• A uniform method and time of exposure for immersing each towel.

• After extraction, allowing the excess water from the towel to drip off over the container in which it was immersed.

• Defining a time period between drips after which the towel immediately will be weighed. For example, when 3 seconds lapses between drips, the towel should be weighed.

• Weighing the towel in a vessel that will capture any water that comes off the towel, but calibrating the scale to "0" with the vessel on it before weighing each towel.

Prior to immersing the paper towel in water, students should measure and record (a) the volume of water in the container in which the towel will be immersed and (b) the dry weight of the towel. Subsequently the towel should be immersed for a given amount of time, allowed to drip off above the container (for the time decided upon), and weighed. The saturated weight of the towel and the volume of water left in the container after saturation each should be recorded.

At least three replicates of each brand should be performed and the average sink capacity of each paper towel calculated. Group reports should be given and results from each group recorded on the board. The teacher should calculate one set of results, averaging each group's results. The teacher should also discuss (a) ways in which the different groups' data varied and what might be responsible for this variance and (b) the relationship of this experiment to sinks for atmospheric CO2.

Optional: Ocean CO2 sink processes. The teacher may want to introduce some of the organisms/phenomena associated with the ocean CO2 sink process. You may want students to map in these new concepts on any concept map of this lesson that students have in progress. The demonstrations of the sponge as sink process employed earlier in this lesson also can be used to illustrate/help explain how phytoplankton, foraminifera, and coral play roles in the ocean sink for atmospheric CO2. Here, the container of water represents the CO2 in the ocean and the sponge extracts represent CO2 removal by phytoplankton, foraminifera, and coral. The demonstration is purely qualitative-no numbers are provided. The teacher may also want to bring in how human influence can affect negatively the ocean sink capacity. For example, water pollution can kill phytoplankton, zooplankton, and coral.

Assessment /Portfolio Items:

• BEAN SEEDLING experiment worksheet.

• SINK CAPACITY PAPER TOWEL experiment worksheet (if this optional instructional procedure is completed).

• Student produced concept map integrating the new and familiar concepts related to this lesson.

Sample quiz items:

True/False. In the space provided underneath each question (or on a separate sheet of paper), state whether each statement is true or false and explain why the statement is either true or false. Then, if you said the statement is true, rewrite the statement to make it false. If you said the statement is false, rewrite the statement to make it true.

1. The main purpose of a sink is to put carbon dioxide into the atmosphere. (Answer: False. Sample reason: A source puts carbon dioxide into the atmosphere and a sink removes it.)

2. Planting trees is a way to increase the capacity of a sink for atmospheric carbon dioxide. (Answer: True. Sample reason: Through photosynthesis, trees take carbon dioxide out of the atmosphere. Therefore, adding trees will increase the capacity of the green plant sink for atmospheric carbon dioxide. )

Multiple Choice. Each question gives 4 different choices as the answer. For each question, either 1 or none of the answers is correct. Read each question carefully, including all of the choices. If you decide that 1 of the choices given is correct, circle that choice. Then, explain why this choice is the correct one and why each of the other choices is incorrect. If you decide that none of the choices given is correct, write a choice that would be correct. Then, explain why your choice is correct and each of the other choices is incorrect. (Note to Teacher: If a correct answer is amongst the four choices, it is underscored. If no correct answer is amongst the four choices, a sample correct answer is listed after the four choices. Reasons for answers being right or wrong are not listed.)

1. Which of the following is the name of the process by which green plants use carbon dioxide to make sugar?

   a) Respiration
   b) Producer
   c) Sink capacity
   d) Electromagnetic energy
   (Correct answer: Photosynthesis)

2. Carbon dioxide fertilization is a process that causes which of the following?
   a) The death of trees
   b) An increase in the amount of atmospheric CO2
   c) An increase in the growth of green plants
   d) A decrease in the Earth's sink capacity for CO2

Name_________________________________ Date started_____________________

Questions:

What differences will we observe between the planted seeds kept under dark conditions and those kept under light conditions?

• What factors influence plant growth?

• What relationship is there between green plants and global warming?

• Others:

  _____________________________________________________________________________

  _____________________________________________________________________________

  _____________________________________________________________________________

Hypotheses:

Data: The chart on the last page of this handout provides a place for you to record the date you make observations of this experiment and what you observe on each of these dates. Take a look at this form now, as it tells you some of the things you will want to be sure and record. Your teacher may want you to record other things, such as the temperature and the amount of water you add to the containers. On the day you complete your experiment, you will uproot and record the harvest weight of any seedlings. Your teacher will give you specific instructions for doing this.

Analysis (Results and Interpretation):

1. Did all of the seeds germinate? How do you explain these results?

2. Of the seeds that did germinate into seedlings, what differences were there over the course of their growth. For any differences you describe below, also explain why these differences occurred. (a) Rate of growth (use actual growth measurements in describing any differences)

   (b) Color of seedlings

   (c) Overall health

   (d) Harvest weight

   (e) Other differences

Conclusions: Use a separate sheet of paper to write your conclusions and attach them to this form. In writing your conclusions, you should discuss what your answers are NOW to the questions posed at the beginning of this experiment. You also should discuss your hypothesis(es): Were your results the same or different than what you hypothesized (explain)? Additionally, discuss anything about the results of this experiment that were surprising to you.

It will help you to think about the following, when writing your conclusions:

1. What seeds need in order to germinate.
2. Any differences between the seedlings.
3. What the seedlings are made up of.
4. If the amount (specifically the dry weight) of the soil in any of the containers changed much during the experiment.

Instructions: Make sure to enter the date on each day that you make observations. Some things you should record:

1. the weight of the seed before planting;
2. if and when (date) each seed germinates;
3. the length, width, and color of any seedlings (be very gentle in taking measurements);
4. other observations about any seedlings, such as when leaves appear, direction of growth, how healthy the seedlings appear, and so on.
5. the harvest weight of each seedling, taken on the last day of the experiment (your teacher will provide specific instructions).

The space provided below is not sufficient to record all your observations, so use additional sheets of paper (draw in columns) as needed.

Date of Observation	Seeds Grown Under Light		Seeds Grown in Dark
	Seed 1	Seed 2	Seed 3	Seed 4

Name _________________________________________________

Questions/Problems: Which brand of paper towel has the greatest sink capacity?

_____________________________________________________________

Hypothesis:

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

Data: Follow your teachers directions in collecting and recording the data on the last page of this handout.

Analysis:

1. Based on the average towel weight difference before and after saturation, how would you rank the brands?

   1 - Largest sink 2 - Second largest sink 3 - Smallest sink

2. Does your answer to 1) above change if you rank the brands according to the average container volume difference before and after paper towel extraction of water? ________

   If your answer is "yes," explain why you believe you obtained these results:

   __________________________________________________________________

   __________________________________________________________________

3. For one brand of paper towel, compare the average towel weight difference to the difference you obtained in each of trials 1, 2, and 3. How much (gms) larger or smaller is each trial than the average?

   Trial 1 _____________ gms (circle one): larger smaller

   Trial 2 _____________ gms (circle one): larger smaller

   Trial 3 _____________ gms (circle one): larger smaller

   What brand is the above data for? ___________________________________________

   Repeat this for one more brand (list brand here __________________):

   Trial 1 _____________ gms (circle one): larger smaller

   Trial 2 _____________ gms (circle one): larger smaller

   Trial 3 _____________ gms (circle one): larger smaller

4. Explain how you might improve the way you did the above experiment:

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

5. If the paper towels represent trees and the water represents atmosphere carbon dioxide, explain what your results have to do with global warming.

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

   (Was your hypotheses correct? Explain why or why not.)

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

   Conclusions:

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

   ___________________________________________________________________________

Brand ______________			Brand ______________			Brand ______________
Description	Towel Weight (gms)	Volume H2O in Container (mls)	Description	Towel Weight (gms)	Volume H2O in Container (mls)	Description	Towel Weight (gms)	Volume H2O in Container (mls)
Trail #1			Trail #1			Trail #1
Pre:			Pre:			Pre:
Post:			Post:			Post:
Difference:			Difference:			Difference:
Trail #2			Trail #2			Trail #2
Pre:			Pre:			Pre:
Post:			Post:			Post:
Difference:			Difference:			Difference:
Trail #3			Trail #3			Trail #3
Pre:			Pre:			Pre:
Post:			Post:			Post:
Difference:			Difference:			Difference:
Average			Average			Average
Pre:			Pre:			Pre:
Post:			Post:			Post:
Difference:			Difference:			Difference:

Click Here to go to Investigations Lesson 12: Carbon Dioxide and Global Temperature Through Time