ENERGY FLOW

Teacher's Guide

The programs are broadcast by TVOntario, thetelevision service of The Ontario EducationalCommunications Authority. For broadcast dates consultthe TVOntario schedule in School Broadcasts, which ispublished in September and distributed to all teachers inOntario. The programs are available on videotape.Ordering information for videotapes and this publicationappears on page 22.

Canadian Cataloguing in Publication Data

Galbraith, Donald I., 1936-Energy flow. Teacher's guide

To be used with the television program, Energy flow.Bibliography: p.ISBN 0-88944-051-4

1. Energy flow (Television program)2. Bioenergetics. I. TVOntario II. Title.

OH510.G3 1984 5.74.19'121 84-093016-X

©Copyright 1984 by The Ontario EducationalCommunications Authority.

All rights reserved.

Printed in Canada. 1300/84

Produced by TVOntario in cooperation with theOntario Ministry of Energy.

Note to Teachers

This six-part series explores the concept of energy flowthroughout the world of living organisms. The firstprogram introduces the concept by presenting thestudents with a problem. Program 2 examines the basicenergy-trapping process, photosynthesis, which takesplace in all green plants. Program 3 deals with themovement of energy within food chains and food webs,thus at the level of the organisms. Energy flow is nextstudied in Program 4 at the cellular level. Here, the cellis likened to a microecosystem. In Program 5, the inter-

vention of humans in the energy flow is explored withspecific reference to energy flow in an agriculturalsystem. The series concludes with a look at energy flowon a grander scale, at the biosphere level. In this finalprogram, some time is devoted to the global energy-related problem of carbon dioxide in our atmosphere.

Although the concepts of energy and energy flowpermeate the entire biology curriculum, rarely is thetopic addressed in any consolidated manner. The intentof this series is to examine these concepts in a logicalfashion. The programs can be viewed individually andincorporated into a variety of topic areas, but it is hopedthat you will find the time to view the series with yourstudents.as a series of interrelated programs.This guide provides program descriptions, describeslearning activities to reinforce and complement eachprogram, and suggests other materials for furtherreading.

The Series

Producer/Director: David ChamberlainWriter: Alan RitchieNarrator: James MoriartyConsultant: Don Galbraith, Faculty of Education,

University of TorontoAnimation: Northey Productions Ltd.

The Guide

Project Leader: David ChamberlainWriter: Don GalbraithEditor: Elaine AboudDesigner: Judith Hancock

ContentsProgram 1: THE CONCEPT OF ENERGY FLOW ... 1Program 2: PHOTOSYNTHESIS 4Program 3: ENERGY FLOW IN AN ECOSYSTEM . . 9Program 4: ENERGY FLOW AT THE

CELLULAR LEVEL .............. 11Program 5: ENERGY FLOW IN AGRICULTURE ... 15Program 6: ENERGY FLOW IN THE BIOSPHERE . . 19Ordering Information ..................... 22

The Concept of Energy Flow

1. Name three forms in which energy can exist.2. Describe the relationship between entropy and free energy within a

closed system.3. Cite examples to show that some energy is no longer available to a

system when energy is converted from one form to another.4. Solve the problem regarding the order in which chickens or corn

should be eaten in order to gain as much energy as possible fromthe system.

Program DescriptionThe program examines a problem pertaining to the most efficient useof available energy: Does it matter in which order food is consumed?

Before dealing with the question further, the program develops somebackground information regarding energy. Energy can be described asthe ability to perform work. The burning of wood serves as a simpleexample of the tendency for organic matter to move from a state ofhigh molecular organization to one of more random molecularorganization. The products of the burning of wood can be thought ofas less organized than the original wood. Not only is it impossible toremake wood out of the products, but there is also the irretrievabletransfer of heat energy. There is a tendency for the system to movetoward a state of decreasing free energy, where free energy isdefined as that portion of total energy of the system that is available todo work. Thus, the free energy of the wood (the chemical potentialenergy) is greater than the free energy of all of the products. As freeenergy decreases, the randomness or entropy of the systemincreases. In order to create order out of disorder, energy must be putthe quantities in water overnight.

into the system. Although energy can be converted from one form intoanother, it cannot be created or destroyed.

The program concludes with a re-examination of the original problemconcerning the astronaut, the hens, and the corn.

Before ViewingThe students should discuss their presently held concepts of energyto establish a basis from which to proceed, and then do Activity 1. Thiswill serve as a basis for establishing that heat energy is lost (i.e., nolonger available) even in the most elaborate systems. Activity 2, whichdeals with the heat generated by germinating peas, could also becarried out before viewing.

After ViewingThe teacher should review all of the concepts introduced in theprogram, specifically: energy, forms in which energy can exist,entropy, free energy, and energy flow. A discussion of whether or notthe products of the burning of wood could, indeed, be reordered insome manner by adding energy to the products (ashes, etc.) couldprove fruitful. It should become evident that a number of conditionsmust be met in order that a chemical reaction(s) can take place. It isi nsufficient to simply add energy to the products in order to obtain theoriginal object, in this case, the wood. The students should beencouraged to cite other examples in the living world where systemsrun down because of insufficient energy input. The simplest of allexamples is that of a green plant, which, when denied light energy foran extended period of time, will eventually die. (Needless to say,consideration of any such example would necessitate the creation ofexperimental controls.) The students could now perform Activity 3, adry lab activity that deals with a number of concepts introduced in theprogram.

ObjectivesStudents should be able to:

1

Activities Method: Discussion:

Activity 1: What Happens toEnergy When It Is Transferredfrom One System to Another?Apparatus:

thermometer

graduated cylinder

two 100 mL beakers

Bunsen burner

retort stand

ring clamp

gauze pad

l arge Styrofoam cup, with cover with a hole inthe centre for the thermometer

1. Record your observations in Table 1-1 .2. Measure 50 mL of water into a beaker and

heat over a Bunsen burner.3. Measure 100 mL of cold water with the

graduated cylinder, pour into the Styrofoamcup, and record the temperature.

4. When the 50 mL of hot water is near theboiling point, remove from the heat, measureand record the temperature, and quickly pouri nto the Styrofoam cup containing the coldwater.

5. With the cover on the cup, using thethermometer, stir the water and record thefinal temperature.

6. Calculate the change in temperature for boththe hot and the cold water.

7. Calculate the heat lost by the hot water andthe heat gained by the cold water by usina the

* I n proper SI usage, these values should be expressed inkilojoules per kilogram per degrees Celsius.

1. How does the heat lost by the hot watercompare with the heat gained by the coldwater?

2. Account for any discrepancy between theheat "lost" and the heat "gained."

3. Explain the results of this activity in terms ofavailable energy and entropy.

Activity 2: A Study of EnergyRelationships in Germinating PeasMaterials:

two large thermos flasks

one-holed rubber stoppers to fit flasks

two thermometers

peas or beans

Method:

1. Measure two equal amounts of peas,approximately 20 to 25 g, and soak one ofthe quantities in water over night.

2. Place the dry peas in one flask, stopper theflask, and put a thermometer through thestopper. Record the temperature.

3. Place the wet peas in the second flask on awet pad of absorbent cotton. With thethermometer in place, record the temperaturefor this flask.

4. Record any changes in temperatures overseveral days.

2

results measured in joules.This will produceformula

Table 1-1

Cold Water Hot WaterMass of water 1 00 g * 50 gInitial temp. ° C ° CFinal temp. (of mixture) ° C ° CChange in temp. °C ° C(M x A T) x 4.2 j oules joules

Discussion:1. Account for any differences in temperature

that occurred during this activity.2. Design a simple experiment to determine

whether or not carbon dioxide or oxygen gasi s produced by the peas during this activity.

Activity 3

Examine Figure 1-3 and answer the questionsrelated to it.

1. If the vial suspended in the bottle ofgerminating seeds contained potassiumhydroxide, what would you expect to takeplace in the glass tubing suspended in thebeaker of water? Explain your answer.

2. Account for the fact that there would be achange in temperature if the apparatus wereallowed to stand for a couple of days.

Activity 4: Review Questions1 . Describe the relationship that exists between

free energy and entropy.2. Cite two specific examples where energy is

no longer available to a system when energyis converted from one form to another.

3. Explain why it is advantageous to eat thechickens before eating the corn.

4. What happens to the energy that is lost byliving organisms? Why is it so difficult torecover?

Further ReadingBaker, J., and Allen G. Matter, Energy, and Life.

4th ed. Reading, Mass.: Addison-Wesley,1981.

Postlethwait, S.N. Energy in Life. Toronto:W. B. Saunders, 1976.

Wallace, R.A., et al. Biology - The Science ofLife. Glenview, Illinois: Scott, Foresman andCo., 1981.

Wright, H. Molecules at Work - The Energy ofChemistry. Toronto: John Wiley and Sons,1977.

3

Objectives Before ViewingStudents should be able to:

1. Describe the relationship between free energy and entropy.2. Describe the role played by chlorophyll in the process of

photosynthesis.3. Describe, in simple terms, the light reactions of photosynthesis,

i ncluding any significant products.4. Describe, in simple terms, the dark reactions of photosynthesis,

i ncluding the end products.5. Write an equation summarizing the light and dark reactions of

photosynthesis.

Although this program could be used as a means of introducing thetopic of photosynthesis, it can also serve as a review of this topic.There is a tendency to lose sight of the key ideas in any of thesecomplex metabolic processes, and, for this reason, it is useful to havea teaching aid that simply concentrates on some of the main ideas,serving as a means of summarizing the topic or as a primitive "roadmap."

If the program is to be used as a means of reviewing the topic,consider the following concepts before viewing. To put things intoperspective, use a simple chalkboard or acetate outline such as Figure2-1. The students will already be familiar with the two processes,

Program DescriptionThis program begins by explaining the need to work toward reducingthe effects of entropy. This, of course, requires a constant input ofenergy to replace the energy that is lost, mainly in the form of heat.The role of chlorophyll as an energy-trapping molecule is developed.Chlorophyll is singled out for special consideration because of itsunique role in photosynthesis.

The next section of the program looks at the structure of achloroplast, and goes on to develop the stages of the light reactionsthat occur within it. Avoiding the detailed biochemistry of the process,the essential feature is that ATP and NADPH are made available for thedark reactions of photosynthesis. The point is also made that the darkreactions occur in the stroma, outside of the grana. The programconcludes with a summary of the relationship between the light anddark reactions of photosynthesis and the other major metabolicprocess, respiration.

Photosynthesis4

photosynthesis and respiration, from earlier studies. The emphasis atthis level should not be on the factors that are involved inphotosynthesis but rather on such things as quantitative activitiescentred around the changes in the rates of reactions when one of thevariables (such as temperature) is altered. In addition, some attentionshould be paid to the chemistry of the process without undueemphasis on the fine details.

It would be advisable to perform Activity 1 prior to showing theprogram. The chlorophyll extract, when subjected to a strong lightsource, appears blood red in color. You might wish to expand uponthis idea as illustrated in Figure 2-2, but at this point it will probablysuffice to say that chlorophyll absorbs some frequencies of light andre-emits this energy at a different frequency. It should be stressed thatlight behaves differently in an extracted state than it does within theconfines of a chloroplast in the extracted state it has nowhere to passthe energy, but within a chloroplast there are adjacent chemicals.

The foregoing can lead logically into the structure and function of thechloroplast, but before doing this you might wish to have the studentsperform Activities 2 and 3, which deal further with the properties ofchlorophyll.

At this stage in their biological education, students will be familiarwith the factors that must be present in order that photosynthesis takeplace. Take time, now, to perform Activity 4, which deals with the rateof photosynthesis. When doing this activity, always work with fresh,actively growing plant tissue. There are numerous labs that can beperformed in this section of the course. For further sources ofi nformation, see Further Reading, page 8.

After ViewingNow that the students have seen the program and have a generaloverview of the chemistry involved, it would be in order to consider thedetails of the light reactions and the dark reactions. Again, theessential nnints to stress are the products of each of the two parts of

5

NADPI-12.dthe process. In the light reactions the products are ATP anThe actual production of ATP is still rather poorly understood but do besure to refer to the chemiosmotic model in this regard. For anexcellent description of this model, refer to the text by Wallace (seeFurther Reading, page 8). Figure 2-3 might be of some use in trying toshow where the stages of the light reaction are taking place. In thisfigure the boxes belowphotosystem I respectively. The CFI particles are tiny swellings on thethalakoid membranes of the grana where ATP is thought to beproduced.

represent photosystem II and

Figure 2-4

Traditional Equation

Dark Reactions

A schematic photochemical unit.P680 and Ptoo refer to wavelengths of light used in thephotosynthesis process.

After both the light and dark reactions have been considered,summarize the various reactions involved as shown in Figure 2-4.

' You will note that in this representation of the traditional equation, water appears asboth a reactant and a resultant. This is a more acceptable way of writing this reactionalthough the water is frequently cancelled out on the resultant side of the equation.

ActivitiesActivity 1: The Effect of Light on aChlorophyll ExtractMaterials:

spinach leaves (or leaves of virtually any greenplant)

green food coloring

mortar and pestle

three small, square or flat-sided bottles withstoppers

strong white light source (e.g., 35mm slideprojector)

Caution: When using acetone or any otherorganic solvent, always ensure adequateventilation. Use a fume hood.

Method:

1. With the aid of a mortar and pestle, extractchlorophyll from leaves using an organicsolvent such as acetone.

2. If necessary, filter the extract to remove anysolid matter and thin the extract with a littleacetone. Place this in a small, square or flat-sided bottle.

3. Place a couple of drops of green foodcoloring in a second bottle containing water.

4. A third bottle containing water only should alsobe used.

5. Project a strong white light source througheach bottle, in turn, making note of allobservations.

Discussion:

Account for any differences that you observedwith respect to the colors of the solutions whenlight was played on each of the bottles.

Figure 2-3

Light Reaction

Activity 2: What Part of theChlorophyll Extract is Activated bythe Light?Materials:

acetone

petroleum ether

methyl alcohol

ethyl ether

potassium hydroxide

separatory funnels

Method:

This is an activity that should be set up as ateacher demonstration because of the poten-tially hazardous chemicals involved. The follow-i ng recipe can be used, but do note the largequantities of the chemicals required.

It can be performed on a much simpler level byusing smaller quantities of the chemicals andperforming the activity in a large test tube. Thevarious layers of chlorophyll a and b and thecaretenoids will be readily visible. Having donethis, again pass the white light source through thedifferent extract fractions and note any colorchanges that occur.

Questions:

1. After step 6 in the flow chart, which pigmentsare present in the upper petroleum ethersolution? (Ans: chlorophyll a and carotene.)

2. After step 6 in the flow chart, which pigmentsare present in the lower methyl alcoholsolution? (Ans: chlorophyll b and xanthophyll.)

3. Describe the appearance of the pigmentextracts when a strong white light source ispassed through each of the two test tubes.Which of the pigments fluoresce?

7

(1) Ground spinach40 mL of 80% acetone

(2) Colored solutionFilter

(3) Colored filtrate(Add to separatory funnel.)

50 mL of petroleum etherAgitate gently.

(4) Colored solution( Add distilled water to almost fill funnel; rotategently.)

(5) Allow layers to separate.Draw off lower layer and discard.

(6) Repeat steps (4) and (5).50 mL of methyl alcohol

Flow Chart

Activity 3: Separation ofPhotosynthetic Pigments UsingPaper ChromatographyMethod:

This activity is commonly used to separate thepigments present in a leaf extract. Again, thepigments can be extracted either by alcohol, oncea leaf has been boiled and the burner turned off,or, the mortar and pestle/acetone method can beemployed. With either method, caution shouldbe exercised to avoid inhaling the vapors. Usea fume hood.

Figure 2-5

Activity 4: Paper Chromatography- Recognizing ExperimentalVariablesThis is an activity which appears in the BSCSI nquiry Slides series, produced by the BSCS

organization in conjunction with Harcourt BraceJovanovich and World Publishers. This is but oneof many excellent "dry" labs which involveobserving data displayed on 35 mm slides andformulating hypotheses, drawing conclusions,etc., from the data.

Activity 5: Investigating theFactors Affecting the Rate ofPhotosynthesis

MaterialsChlorella

manometer (see Figure 2-6)

one percent sodium bicarbonate solution

Method:

This activity involves placing a rich culture ofChlorella, an alga, or Elodea, if available, into amanometer and determining the effects of alteringthe following factors: light, temperature, andavailability of carbon dioxide (using a one percentsodium bicarbonate solution as a source). Theapparatus exhibits many fine features, not thel east of which are its portability and ease of

storage. This activity is described in detail inExperimental Biology Manual, page 174, byBrown and Creedy, as well as in the Lab Manual- Biological Science, page 62, by Galbraith (seeFurther Reading).

Activity 6: Review Questions1 . Describe the relationship between entropy

and free energy.2. Account for the fact that chlorophyll appears

blood red when subjected to a strong whitelight source but appears green when presenti n a leaf.

3. Describe the role played by chlorophyll in thelight reactions of photosynthesis.

4. Name the two important products producedby the light reactions of photosynthesis andpassed on to the dark reactions.

5. What is the primary function of the darkreactions of photosynthesis?

Further ReadingBrown, G., and Creedy, J. Experimental Biology

Manual. London: Heinemann EducationalBooks Ltd., 1970.

BSCS. Inquiry Slides. New York: Harcourt BraceJovanovich and World, 1969.

Galbraith, D. I. Lab Manual - Biological Sciences,Principles and Patterns of Life. Toronto: Holt,Rinehart, and Winston, 1976.

Kimball, J. Biology. 5th ed. Reading, Mass:Addison Wesley, 1983.

Postlethwait, S.N. Energy in Life. Toronto:W.B. Saunders, 1976.

Purves, W., and Orians, G. Life, the Science ofBiology. Sunderland, Mass: Sinauer Pub.,1983.

Wallace, R.A., et al. Biology - The Science ofLife. Glenview, Illinois: Scott, Foresman andCo., 1981.

8

Energy Flow in an Ecosystem

ObjectivesStudents should be able to:

1. Define the terms ecosystem, biotic, abiotic, individual, population,and community.

2. Develop an energy model of an ecosystem.3. Develop the concepts of a food chain and a food web within an

ecosystem.4. I n photosynthesis, list the products of the light reactions that are

passed on to the dark reactions.5. Use the concept of trophic levels to develop a pyramid of biomass,

indicating the significance of the amount of biomass at each trophiclevel.

Program DescriptionThis program deals with energy flow at the organismal level. It beginswith a review of the concepts of entropy, the trend towardrandomness and disorder, and proceeds to review photosynthesis, thesingularly most important process that traps energy for virtually all lifeforms here on earth.

An aquarium and the life within it are used to develop the vocabularyassociated with energy flow within an ecosystem. The termsdeveloped include biotic, abiotic, individual, population, andcommunity. This leads to a recapping of the food chain concept, firsti ntroduced in Program 1. The related vocabulary (producer,consumer, herbivore, carnivore, scavenger, and decomposer) isdeveloped, using specific examples of organisms.

The foregoing is necessary as a background for the consideration ofthe concept of trophic levels and the energy pyramids associated withthem. The point is made that at each successive trophic level, there issubstantially less energy available to be passed on to the next trophicl evel. Expressed in another way, a substantial amount of energy isdissipated back to the environment as one moves up from theproducers to the various levels of consumers. Virtually all of the energyavailable to all of the organisms at the different trophic levels originates

from the sun. Much of the subsequent decrease arises from the factthat much of the energy potentially available at any trophic level iseither not consumed or is used up by the organism in the process ofcarrying out the organisms' own metabolic processes. Using generalfigures only, approximately 10 percent of the available energy ispassed on from one trophic level to the next.

The program concludes with the sober observation that if we couldcut out just one trophic level in the beef cattle operation, specificallyconfining ourselves to eating range-raised animals rather than those fedgrains, there would be a remarkable energy saving.

Before ViewingThe topic of ecosystems and the related vocabulary is one with whichthe students might have some degree of familiarity from previouscourses. To determine this, give the students some form of a pre-test.Chances are, even though they might have touched on the topic in anearlier program, they will not have retained much of the detail. Thisprogram is designed to highlight some of the key ideas pertaining toecosystems, and to tie it into their knowledge of photosynthesis. If atall possible, incorporate some fieldwork into this topic. Much of thevocabulary can be built into the course as the needs arise.

After ViewingOnce the students have a good overview of the topic as presented inthe program, proceed to consider one or more of the suggestedactivities. This topic is well served by a number of excellent films.These include "Nature's Food Chain" and "The Arctic Islands - AMatter of Time" from the National Film Board, and "Life in a VacantWood Lot" from Encyclopaedia Britannica Films. Although films shouldnot be substituted for actual fieldwork, they frequently present dataand situations that the average teacher could not duplicate on a schoolouting. Aim at establishing the energy flow concepts rather than simplyhaving the students learn a considerable amount of vocabulary.

9

1 0

ActivitiesThis topic does not lend itself to activitiesconfined to the classroom. Rather, the conceptsof food chains, webs, and trophic levels shouldbe carried out by means of field studies. In thisregard, the excellent Contours: Studies of theEnvironment series, edited and largely written byW.A. Andrews and published by Prentice-Hall,begs comparison as a source of field activities.Canadian-written, such titles as "TerrestrialEcology" and "Soil Ecology" contain all of thedetail, lists of equipment, etc., necessary to carryout virtually any field activities suitable forstudents at this level. The following activities aresuggested only as second-best options if you areunable to carry out any fieldwork.

Activity 1: A Computer Simulation- PollutionThis public domain computer simulation isavailable through the Ontario Educational SoftwareProject, supported by Commodore BusinessMachines. Designed to run on PETs and C64s,this simulation deals with five variables andgraphically shows what effects each one has on afish population. It is particularly useful to illustrateexperimental design. (See this page for orderinginformation.)

Activity 2: "Pollution Game"This is another dry-lab activity that involves theuse of the commercially available game"Pollution." The game can be purchased fromCarolina Biological. Like the computer simulationin Activity 1, it shows the students that thefactors within an environment are constantlyi nteracting. (See this page for orderingi nformation.)

Activity 3: "Predator: The FoodChain Game"Another commercial product from CarolinaBiological, this one uses a deck of cards andi nvolves a number of variations on the game ofrummy. The object of the activity is to getstudents to learn the various food chain inter-relationships, as well as the associatedvocabulary.

Activity 4: Review Questions1 . With the aid of examples, distinguish clearly

between the terms individual, population, andcommunity.

2. Cite a simple example of a food chain and, byusing one organism within this chain, relatethis to a food web.

3. Energy is first trapped by plants in theprocess called photosynthesis. Name the twosignificant chemicals produced in the lightreactions of the process that are passed on tothe dark reactions.

4. Assume that an aquatic food chain consists ofalgae, water fleas, minnows, and bass, listedi n order from the producer to the finalconsumer. Describe what would happen tothis food chain if the population of minnowswas decimated by disease.

5. Explain why a pyramid of biomass is indeedpyramid shaped. Specifically, what happens tothe energy as you move from the base of thepyramid to the top?

As another potential source of classroom drylabs, refer to the book Environmental Biology,written by S.N. Postlethwait and published byW.B. Saunders. Originally written as ani ndependent study program for first-year collegestudents in the U.S., it has a number of fine

activities suitable for use with this program. Again,the Contours series has, at the back of eachbook, a number of case studies. Here thestudents are asked to examine data and toanswer a number of questions based upon thedata.

Further ReadingAndrews, W.A. Environmental Pollution. Toronto:

Prentice-Hall Pub., 1972.

. Terrestrial Ecology. Toronto: Prentice-Hall Pub., 1974.

Miller, G.T. Living in the Environment. Belmont,California: Wadsworth Publishing, 1982_

Nebel, B.J. Environmental Science - The Waythe World Works. Englewood Cliffs, N.J.:Prentice-Hall Pub., 1981.

Purdom, P.W., and Anderson, S. EnvironmentalScience. 2nd ed. Columbus, Ohio: Bell andHowell Ltd., 1983.

Games and ComputerProgramsCarolina Biological Supply Co., 2700 York Road,

Burlington, North Carolina, U.S.A. 2715.(Source of the "Pollution Game," "Predator,The Food Chain Game," "Cell Game," and"Game of Metabolism.")

Ontario Educational Software Project, c/o WindsorSoftshare, Windsor Separate School Board,1 485 Janette Avenue, Windsor, Ont. (Asource of the computer program "Pollution,"as well as a catalogue listing other scienceprograms.)

Energy Flow at the Cellular Level

ObjectivesStudents should be able to:

1. Explain why there is a limit to which a cell can grow, taking intoaccount the relationship between cell volume and cell surface area.

2. Explain the analogy between the limit to cell size and the size of afactory.

3. Relate the structure of the mitochondrion to the role it plays incontrolling the release of energy from molecules such as glucose.

4. Describe, in general terms, the function of the Krebs cycle.5. Describe, in general terms, the role of the electron transport

system in the mitochondrion of a cell.6. Describe how ATP is thought to be formed within a mitochondrion.7. With respect to energy, describe the relationships that exist

between the following cell organelles: mitochondrion, chloroplast,nucleus, ribosome, and cell membrane.

Program DescriptionThis program opens with a review of the trophic level concept fromProgram 3 and then examines the energy flow concept at the cellularl evel. The cell is viewed as a "micro" ecosystem, with energy flowfrom one cell organelle to another. As in all ecosystems, death wouldultimately ensue were it not for a steady inflow of energy. In the caseof the cell, this energy frequently is stored in nutrients such ascarbohydrates, amino acids, etc. To develop the idea that there is alimit to which a cell can. grow before it must divide, the cell iscompared with a factory. Like a factory, there is a constant movementof raw materials and products into and out of the cell. The function ofthe mitochondrion with respect to the gradual, controlled release ofuseable energy is considered. Relationships between structure andfunction are stressed.

The essential points of glycolysis and Krebs cycle are developed,showing, in each case, the significant end products. The electrontransport system is likened to a stairway where the electrons on thetop steps possess more energy than the electrons at the bottom. Theformation of ATP using the chemiosmotic model is also included. Themain function of photosynthesis is also reviewed.

The program concludes with a series of animated diagrams that showhow various organelles are related to each other in terms of the flow ofenergy.

Before ViewingIt is assumed that the students are reasonably knowledgeable aboutcell structures. If necessary or desirable, the teacher may wish toconduct a review of cell structures at this time. Present the studentswith a stylized cell and raise the following questions:

a. How do all of the organelles within a cell interact?b. What energy transfers take place within a cell?c. How are the materials that enter and leave a cell controlled?

Another review technique that could be used is the "Cell Game," listedas Activity 1.

Before considering the energy relationships between cell organelleswithin a cell, carry out Activities 2 and 3. Activity 2 deals with therelationship between the volume of a cell and the surface area. Itestablishes the need to divide the cell in order to maintain a size thatenables materials to enter and leave the cell, which, in turn, ensuresthe well-being of the cell. Activity 3 can serve to motivate the studentsto study the energy relationships of a typical cell. Because of potentialdanger, this activity should be performed as a demonstration. Duringthis activity, stress the need for a gradual, controlled release of theenergy stored in the sugar. (You might to do this activity after viewingthe program, to stress the idea of a need for a controlled release ofenergy.)

1 1

1 2

Since ATP plays such a pivotal role in all biological energy consider-ations, do at least one activity involving ATP. Activity 4 is one suchexercise. The chemicals are expensive but the lab is well worthperforming.

At this time, depending on your teaching sequence, you might wishto carry out a detailed consideration of the chemistry of respiration. Inthis regard, Activity 5 can be used as a novel way of teaching some ofthe details of the process. It is a game called "Metabolism," marketedby Carolina Biological.

After ViewingTake time to review the stages of respiration. Stress that glycolysis issimply setting the stage for the subsequent events of the Krebs cycle.The major energy payoff in respiration takes place in the hydrogenelectron transport system. Here, the basis is that electrons andhydrogen ions, split away from the original sugar molecule, are finallybrought together with the oxygen that we breathe in, to producewater. The combination of hydrogen and oxygen is very exothermic,but this energy is trapped in ATP molecules rather than being permittedto go off as waste heat energy.

The chemiosmotic model, described briefly in the program, is nicelydepicted on page 166 of Kimball's text, Biology (see Program 2,Further Reading). The model was originally put forward by PeterMitchell in 1961, but only recently has it gained reasonably generalacceptance. The following is a brief summary of this model:a. Hydrogen ions tend to build up on one side of a membrane of an

organelle.b. Similarly, hydroxyl ions build up on the other side of the membrane.c. This results in a pH differential and a difference in the net electrical

charge across the membrane. This concentration difference canalso be viewed as potential free energy in a system.

d. It takes work to build up and maintain this hydrogen and hydroxylion differential. It is a matter of taking this potential energy andusing it to produce ATP.

e. I n chloroplasts, the electron transport system carriers areimbedded in the thylakoid membranes, and the system useschemical energy to pump electrons across the membrane in onedirection, and hydrogen ions across the membrane in the oppositedirection. The net difference is the movement of hydrogen ions intothe cavity of the discs during the intense light period. This results inan acid medium inside the discs and a basic medium outside.

f. The hydrogen ions exit from the discs at specific points called CF1particles, and this energy differential is used to couple ADP toinorganic phosphate to produce ATP.It appears that it takes three hydrogen ions exiting from the disc toproduce one molecule of ATP.

h. The chemiosmotic system in the mitochondrion is similar, but is thereverse of that in the chloroplast. In the mitochondrion, thehydrogen ions are pumped outside of the central stroma to thespace between the two membranes.

9.

The final concept that should be considered at this time is that of theorganelle interrelationships based on the idea of energy flow. Forexample, it could be pointed out that:a. The nucleus controls and directs the formation of enzymes in the

ribosomes.b. The enzyme could become part of a chloroplast that traps light

energy.c. The energy-rich products from the chloroplast can be used to

produce more useful ATP units.d. Some of the ATP will be used to pump ions across membranes.e. Some of the products of photosynthesis, in one form or another,

will probably find their way into the Golgi apparatus and ultimatelyout of the cell by way of the secretory vesicle.

The above could be expanded in many ways to include other cellorganelles and other concepts. For example, much more could bemade of the concept of active transport.

ActivitiesActivity 1: The "Cell Game"The "Cell Game," manufactured by CarolinaBiological, is one way of reviewing cell structuresand functions (for ordering information, seeProgram 3, page 10). There are four gameboards included in the package, and it is intendedthat a maximum of four players play at a time. Theconcepts present in the game include synthesis,autolysis, respiration and photosynthesis, as wellas the structures and functions of the organelles.Although it is not suited for class use (because ofthe large number of games that would berequired), nevertheless, it would serve as adifferent type of review for a small group ofi nterested students.

Activity 2: The RelationshipBetween Cell Surface Area andCell VolumeMaterials:

household gelatin

phenolphthalein indicator

large, flat tray or glass baking dish

dilute sodium hydroxide solution

Method:

1 . Dissolve packets of household gelatin in hotwater. To ensure that it sets firmly, increasethe manufacturer's recommended amount by50 percent (i.e., if the recipe calls for twopackets of gelatin, use three packets).

2. Pour the warm gelatin into a shallow pan orbaking dish. The maximum depth need only befour centimetres.

3. Add a few millilitres of phenolphthaleini ndicator to the gelatin and stir before it sets.Place in a refrigerator to speed up the settingprocess. Allow to stand overnight.

4. From the large pan of gelatin, carefully cut outfive cubes with the following dimensions: 0.5,1.0, 2.0, 3.0, and 4.0 per side.

5. Place simultaneously all five cubes into a weaksolution of sodium hydroxide.

6. Precisely one minute later, remove the cubes,pat them dry with paper towelling, and cuteach cube in half. Be sure to wipe yourscalpel clean between cuts to avoid smearingthe color.

7. For each cut cube, measure the width of theuncolored part of your "cell" and approximatethe percentage of the "cell" that is colored.Record your results in Table 4-1.

8. Plot the following three graphs:1. cube size (x-axis) vs.

°lo colored (y-axis)2. cube size (x-axis vs.

total volume (y-axis)3. cube size (x-axis) vs.

total surface area (y-axis)

Discussion:

1 . As the size of the "cell" (cube) graduallyi ncreases, how does the volume of the "cell"change?

2. As the size of the "cell" increases, how doesthe surface area of the "cell" change?

3. Which increases faster, the volume of the"cell" or the surface area?

4. How does the percent of the colored part ofthe "cell" change with size?

Table 4-1

e.g. b

Approx. % Simplestof Cube Ratio

that is Colored (surface area/vol.)

(where "b" is the length of one of the sides)

13

Surface AreaCube Size(length of

side in cm)

Total Volume

1 4

Activity 3: The Energy in SucroseCaution: Due to the sudden release of asubstantial amount of heat and light energy,this activity should be performed as a teacherdemonstration.

Materials:

sucrose

potassium

chlorate

concentrated sulphuric acid

30 cm length of glass tubing, firepolished atboth ends

spatula

fireproof surface or container

safety goggles and, if available, a safety shield

Method:1 . Measure out approximately five grams of

sucrose and grind to fine powder with amortar and pestle.

2. To the sugar, add an equal amount ofpotassium chlorate, and mix gently.

3. With the two chemicals, form a small cone ona fireproof surface. Make a small depressionin the tip of the cone.

4. While wearing safety goggles, with the aid ofa l ength of glass tubing place a couple ofdrops of concentrated sulphuric acid into thedepression in the cone. Have students recordall observations.

Discussion:

Activity 4: Fireflies and theEnergy of ATPSeveral manufacturers produce a kit that containsall of the ingredients necessary to demonstratethe action of ATP. One such Canadian distributori s Boreal Laboratories Ltd., Mississauga. The kitsusually contain powdered firefly lanterns,powdered ATP, and a sodium arsenate buffersolution. It is one of the very few examples of ATPaction available for classroom use, and althoughexpensive, it is worth the effort.

Activity 5: The "Game ofMetabolism"Another commercial product worthy of yourconsideration is the "Game of Metabolism." Iti nvolves the use of a large playing board depictingthe various stages of respiration. The playingpieces include oxygen molecules, carbon tokens,

Activity 6: Review Questions1 . Explain why there is a limit to which a cell can

grow, taking into account the relationshipbetween cell volume and cell surface area.

2. Explain the analogy between the limit to cellsize and the size of a factory.

3. Relate the structure of the mitochondrion tothe role it plays in controlling the release ofenergy from molecules such as glucose.

4. Describe, in general terms, the function of theKrebs cycle.

5. Describe, in general terms, the role of theelectron transport system in the mitochondrionof a cell.

6. With respect to energy, describe the relation-ships that exist between the following cellorganelles: mitochondrion, chloroplast,nucleus, ribosome, and cell membrane.

Further ReadingGalbraith, D. I. Lab Manual - Biological Science,

Principles and Patterns of Life. Toronto: Holt,Rinehart and Winston, 1976.

Postlethwait, S. N. Energy in Life. Toronto: W. B.Saunders, 1976.

Shakhashiri, B.Z. Chemical Demonstrations - AHandbook for Teachers of Chemistry.Madison, Wis.: University of Wisconsin Press,1983.

Wallace, R.A., et al. Biology - The Science ofLife. Glenview, Illinois: Scott, Foresman andCo., 1981.

1. Account for the sudden release of energyof the sugar/acid/potassium chlorate mix.

2. How does this differ from the release of foodenergy in our bodies?

components of the real process. This game isavailable through Carolina Biological Co. (forordering information, see Program 3, page 10).

etc. - all of the variousATP,

Energy Flow in AgricultureObjectivesStudents should be able to:

1 . Explain why, up until the beginning of the agricultural revolution, thepopulation of humans in the world was very small.

2. List five significant processes that have enabled humans toi ncrease crop yields substantially.

3. Describe the role played by the cycling of materials in a modernagricultural operation.

4. Explain the statement that farmers of the Western world areproducing large yields by drawing on energy reserves from thepast.

5. Distinguish between a range cattle operation and a feed lotoperation with respect to the efficient use of energy.

6. Explain why nitrogen, an important nutrient in crop production,poses a unique problem.

Program DescriptionThis program opens with a review of the previous programs, with aspecific emphasis on the central role of photosynthesis. The primitiveexistence of humans prior to the agricultural revolution is described,stating why the population was limited by a number of factors. Theadvent of the agricultural revolution and the beginning of the cycling ofmaterials necessary for plant growth is discussed briefly. Componentsthat led to the considerable increase in crop yields (e.g., plantbreeding, mechanization, recycling of nutrients, and irrigation) are alsoi ntroduced. More recent developments, including the marked increasei n the use of chemical fertilizers and pest controls, have led to furtheri ncreases in crop yields, but at a price. Since much of the chemicalfertilizer industry depends on an abundant supply of fossil fuels toproduce their products, there will be a limit as to how long the worldwill be able to produce large quantities of food using these materials.

I n terms of actual energy efficiency (i.e., the number of food energyunits required to grow, harvest, and distribute the crop), manycountries of the world are more efficient than the Western nations. It

must be stressed, of course, that North American farmers produceincredible crop yields but this is accompanied by massive doses ofchemical fertilizers. The point is made that in North America, theenergy required to produce food is going up much faster than percapita food consumption.

The program concludes with a brief consideration of the natural andartificial fixation of nitrogen. Again, chemical fertilizers are called uponto subsidize the process to once more enable the yields obtained byour farmers.

Before ViewingThis program deals with the heart of one of our serious energyproblems, that of the amount of energy required to plant, harvest, anddistribute the crops that our farmers grow. Before introducing theprogram, hold a discussion or a debate, as in Activity 1, to establishthe extent of the class's knowledge about our agricultural practices.Since Activity 2 can span several weeks, you might wish to have somestudents set it up prior to the time at which you wish to consider thistopic. The Ministry of Agriculture and Food is an excellent source ofdata for information regarding energy use on Ontario farms. You will besurprised to learn that much of the energy used in the agriculturebusiness is not energy used on the farm, but rather for transporting,processing, and storing the products. In Ontario in 1979, for example,approximately 12 percent of all the energy consumed within theprovince was used by agrobusiness. Note how this 12 percent isactually broken down:

Food production (the actual farm end of things) ....... 3%Processing and packaging ......... 4%Transportation and distribution ................. 2%Food preparation (including cooking food at home) . . . . 3%

Expressed in another way, fully 75 percent of the energy consumedby agriculture-related activities is spent after the food leaves the farmgate.

1 5

1 6

After ViewingIt would now be in order to carry out Activities 3, 4, and 5, each ofwhich deals with something that was raised or discussed in theprogram. Stress the fact that in order to obtain a certain amount ofenergy from our crops, we must put energy into the ground. As such,we are really subsidizing our farming practices with energy, the energy

of fossil fuels, energy that in the final analysis was originally trapped,through photosynthesis, by plants. In no way is this meant to slight ourvery capable farmers. It does mean, however, that there is nothingmagic in growing the bumper crops so common in our fields. It simplyrequires a great deal of energy.

ActivitiesActivity 1This activity might serve to generate somei nterest in the topic of energy use within ouragricultural system. It can be carried out in theform of a debate, with the following resolution:

Be it resolved that Canadian farmers are moreenergy-efficient that farmers in ... (WesternEurope, India, etc.)

Select three class members to present the case"for" the resolution and three students torepresent the "against" position. Obtain as muchinformation as you can from such places as theMinistry of Agriculture and Food. Use standarddebating rules. Be sure to count the remainingclass members who favor the resolution andthose against, before you conduct the debate,and again after the debate. The side that"swings" the most votes as a result of the debatewill be declared the winner.

Activity 2: Investigating a Plant'sNutrient RequirementsAt some point in every student's biology program,there should be an opportunity to study theeffects of mineral deficiencies on the growth of aplant. This activity does require a large number ofchemicals, all of which are relatively common. You

can purchase a kit from a company such asWard's or Carolina Biological or you can prepareyour own solutions. Germinate tomato or beanseedlings on a soilless, nutrient-free medium. Youwill require 21 seedlings of approximately thesame size, three for each of the seven nutrientcontainers. The one container is for the control(Table 5-1) while the other six are described inTable 5-2. Prepare the nutrient solutionscommencing with the complete control solution,which can be made up of the following:

These chemicals should be added to one litre ofdistilled water. Prepare the nutrient-deficientsolutions according to the following schedule (in

Table 5-1

each case, the deficient nutrient appears in theleft-hand column):

Table 5-2

Potassium replaceCalcium replace

I ron omitNitrogen replacePhosphorus replaceSulphur replace

Figure 5-1 Activity 3: The Action of aHerbicide on SeedlingsMaterials:

ten Petri dishes with covers

two packages of lettuce, mung bean, radish,or watercress seeds

ten millitres graduated cylinder

commercial 2,4-D (available from your localhardware or garden centre)

paper towelling

Method:

1. Place ten seeds in each of the ten Petridishes, using discs of paper towelling bothabove and under the seeds. Number thedishes one to ten.

2.

3.

4.

The seedlings, along with the various nutrients,should be placed in jars that have been sterilizedalong with the corks used to support the youngplants. The setup is shown in Figure 5-1. Toreduce root damage, consider wrapping thei ndividual seeds in a small quantity of sterilecotton and inserting each into one of the holes inthe cork. Float the cork in a pan of distilled waterand after a period of ten days to two weeks,depending on the seeds used, transfer them tothe nutrient containers. The steps describedabove would be used in lieu of germinating theseedlings in a nutrient-free, sterile medium. Havethe students record any changes that they note inthe leaves, stems, and roots of the seedlings.

Table 5-3

Concentrationof 2,4-D

Discussion:

The above activity could lead to a gooddiscussion of the amount of herbicide chemicalsused and necessary to use to achieve the desired

No. of seedsgerminated

Average length of Otherroots after 72 h observations

end. Large amounts of herbicides are used fornon-agricultural purposes, such as lawns, golfcourses, etc.

5.

6.

7.

Prepare the concentration of 2,4-D, asrecommended by the manufacturer, andmeasure out ten millilitres in a graduatedcylinder.Pour nine millilitres of the 2,4-D into the firstPetri dish, making certain that all of the seedsare wet.Add nine millilitres of water to the remainingone millilitre in the cylinder. Mix with a glassstirring rod.Pour nine millilitres of this solution into Petridish number two.Repeat the above steps so that you have asequence of serial dilutions, each one one-tenth as concentrated as the previous one. Doso up to and including Petri dish number nine.Place nine millilitres of water in Petri dish ten.Record your observations after three days, inTable 5-3.

1 7

1 8

Activity 4: Examination of theRoots of LegumesA simple but effective way of demonstrating howsome plants obtain fixed nitrogen is to have thestudents examine the roots of any of the commonleguminous plants such as clover or alfalfa.Associated with the roots of these plants you willfind a number of small nodules or bumps. These,in turn, contain nitrogen-fixing bacteria. Thebacteria make use of the nitrogen gas present inthe soil to combine it into nitrates, which theplants can then use. The actual nodule itself isproduced by the host plant.

Activity 5: Review Questions1 . Explain why, up until the beginning of the

agricultural revolution some 10 000 yearsago, the population of humans on Earth wasvery small.

2. List five significant processes that haveenabled humans to increase crop yieldssubstantially.

3. Explain the statement that farmers of theWestern nations are producing large cropyields by drawing on the plant energyreserves from the past.

4. Distinguish between a range cattle operationand a feed lot operation with respect to theefficient use of energy.

5. It seems contradictory to say that while therei s an abundance of nitrogen in theatmosphere, many plants have a nitrogenproblem. Why is this so?

Further ReadingBarrett, B., and Stratton, J. From Nature to Man.

Toronto: John Wiley and Sons, 1976.

Brown G., and Creedy, J. Experimental BiologyManual. London: Heinemann EducationalBooks, 1970.

Current 4, no. 4 (October 1983). (A magazinepublished for Ontario Hydro as a componentof its Energy Education Program. This issue isdevoted to energy and agriculture.)

Miller, G.T. Living in the Environment. Belmont,California: Wadsworth Publishing, 1982.

Morholt, E., et al. A Sourcebook for the BiologicalSciences. New York: Harcourt, Brace,Jovanovich and World, 1966.

Nebel, B.J. Environmental Science - The Waythe World Works. Englewood Cliffs, N.J.:Prentice-Hall Pub., 1981.

Purdom, P.W., and Anderson, S. Environmental

Science. 2nd ed. Columbus, Ohio: Bell andHowell Ltd, 1983.

ObjectivesStudents should be able to:

1. Explain why nitrogen, an important nutrient in crop production,poses a unique problem to plants.

2. Name the part of the incoming solar radiation that is useful to plantsfor photosynthesis.

3. Indicate the consequences of nuclear war with respect to thegrowth of plants.

4. Explain the "greenhouse effect" as it relates to the burning of fossilfuels and the build-up of carbon dioxide in the atmosphere.

5. Describe the role of tropical forests with respect to the possibleeffects of the increase of carbon dioxide in the atmosphere.

6. Explain the role of the oceans as receptors of carbon dioxide fromthe atmosphere.

Program DescriptionThis program deals with energy flow at the level of the biosphere,energy flow on a global scale. It begins by describing the need for abalanced intake of nutrients by plants and includes in this list theenergy of sunlight, so necessary for photosynthesis. It also drawsparticular attention to the role of nitrogen and the need to fix the freenitrogen before it is available to plants.

Although a substantial amount of energy strikes the surface of theearth, only a small part of the visible spectrum is available to plants forphotosynthesis. The point is made that a nuclear holocaust would leadto a further reduction of the available light and, as a consequence,would drastically reduce the amount of food available for the feworganisms still living.

The concept of the greenhouse effect is then developed. Closelyrelated to this is the idea of carbon sinks or reservoirs, places where

carbon dioxide can be withdrawn from the atmosphere and, in time, bemade available again. One of the most significant carbon reservoirs, ona global scale, would be the tropical forests of the world, specifically,the rain forests of the Amazon region of South America. With thecutting down of these forests, there is a further reduction in the abilityto remove excess carbon dioxide from the atmosphere. Not only is theability to remove carbon dioxide from the atmosphere reduced, butalso the cutting down of the forests speeds up the breakdown of thehumus and organic matter present in the soil on the forest floor. Thisdecomposition adds further to the carbon dioxide in the atmosphere.

Although the oceans of the world hold, by far, the largest amount ofcarbon dioxide, it has been estimated that the largest amount of netphotosynthesis takes place on land and not in the oceanic waters, ashad previously been assumed. Vast amounts of carbon dioxide aredissolved in the surface waters of the world's oceans, but the rate ofexchange between the atmosphere and the oceans, as a whole, isvery slow. Current estimates suggest that more carbon dioxide isentering the atmosphere than is being removed by the oceans and thetotal of all photosynthesizing organisms in the world. [The Woodwellarticle entitled "The Carbon Dioxide Question" is very readable and a,'must" to include in any resource list for this topic (see FurtherReading). It is now available in Scientific American offprint format (alongwith all other Scientific American articles.]

Before ViewingTake time to review the concepts of photosynthesis and energy flow inan agricultural system. This program carries on with these ideas anddeals specifically with the fixation of nitrogen. Time permitting, alsodiscuss the cycling of other nutrients associated with the growing offood plants.

1 9

Energy Flow in the Biosphere

20

After ViewingFollowing a general discussion of the program, carry out the activitiesas time permits. In addition, use any other sources of actual data (e.g.,Ministry of Agriculture and Food and Ministry of the Environment) togenerate more questions.

You might wish to make distinctions between ecosystems andbiomes. (The term biome was not introduced in the program because itwould, in turn, require further clarification.)

National Film Board films are available from a number of communityoutlets including many local libraries. Many school boards have theirown prints of the more popular films. (Some of these are listed inActivity 4.)

Since this is the final program in the series, consider having thestudents write an essay on some aspect of energy flow as it relates toliving organisms. This could serve to pull together many of the diverseaspects of the series.

ActivitiesThis topic area, which deals with the biosphere,does not lend itself to many in-class lab activities.Again, aspects of the topic can be considered bymeans of fieldwork, but even here the topic is farmore global in its very nature. Having said this,texts and magazines such as Scientific Americanare excellent sources of data that can be used asthe bases for dry-lab activities. The activities thatfollow fall into this category.

Activity 1: Examination of PrimaryProduction DataHave the students examine the data in Figure 6-1and answer the accompanying questions.Figure 6-1 depicts the primary production byplants in various world ecosystems. (Primaryproduction is the rate at which green plantsconvert solar energy, via photosynthesis, tochemical energy. The amount of energy used bythe plants themselves has been subtracted fromthe values that appear in Figure 6-1. In effect,then, the values are net primary production valuesand are expressed in energy units per squaremetre of surface area per year. To further clarifythe values in the figure, "less than 2.1 " wouldmean "less than 2.1 x 10 3 kj/m 2/a.")

1. Which class of ecosystems has the highestprimary production measured in kilojoules/square metrelannum? Can it be concludedthat this group makes the most significantglobal contribution to primary production in agiven year? Explain your answer.

2. From your knowledge of global ecosystems,which ecosystem actually accounts for the

3.

largest total amount of primary plant biomassproduction? What data, in addition to thatpresent in the figure, would you require inorder to support your choice?It has been suggested that the oceans of theworld play a major part in fixing much of thecarbon present in the atmosphere. Does

2 1

Figure 6-1 support or reject this point of view?Again, what additional data would you like inorder to answer this question?

4. "Desert ecosystems of the world account forone-half of the primary production of theoceans of the world in a given year." UsingFigure 6-1 and any other relevant data,support or refute this statement.

Activity 2: A Balance Sheet for theNitrogen CycleFigure 6-2 depicts nitrogen transfers, gains, andl osses on a global scale per annum. Answer thequestions that relate to the data.

1 . What are the two most important nitrogen-fixing processes in terms of the total amountof nitrogen fixed?

2. On a net basis per annum, is the world supplyof fixed nitrogen increasing or decreasing?Use data from Figure 6-2 to support youranswer.

3. What significant raw material is used in thei ndustrial fixation of nitrogen?

4. Assume that because of a shortage of rawmaterials, the industrial fixation of nitrogen hasto be reduced to one-half of the presentamount. Describe the effect that this mighthave on the total agricultural output in a givenyear. Describe the effect over a number ofyears.

Activity 3: The Carbon DioxideQuestionThe issue of whether or not the cutting andburning of tropical forests will have a deletonouseffect on life on Earth has been considered atlength in the popular press. Have the class carry

out a debate centred around the followingresolution:

Be it resolved that the cutting and burning oftropical forests will have an irreparable effecton the amount of carbon dioxide in ouratmosphere.

To do justice to the topic, gather as much data asyou can and also give the students sufficient timeto research the topic. Stress the need forstudents to support their opinions with data.

22

Activity 4: National Film BoardFilmsiIn lieu of actual fieldwork, a truly excellent sourceof films is that supplied by the National FilmBoard. The following are but a few of the filmsthat could serve as discussion points for thecontent of this program:

"The Biosphere" - An examination of theMackenzie and the Amazon valleys,making comparisons between the two andbuilding a case for the preservation ofthese important ecosystems. 56 min; Cat.no.: 106C 0 179 085.

"The Top Few Inches" - Deals with theimportance of the soil, touching on manyaspects of soil structure and fertility.18 min; Cat. no.: 106C 357.

"If You Love This Planet" - An anti-nuclearfilm that features Dr. Helen Caldicott. Theeffects of a nuclear holocaust, as referredto in the film, would be devastating.26 min; Cat. no.: 106C 0 182 098.

Activity 5: Review Questions1 . Explain why nitrogen, an important nutrient in

crop production, poses a unique problem toplants.

2. Explain the "greenhouse effect" as it relatesto the burning of fossil fuels and the build-upof carbon dioxide in the atmosphere.

3. Describe the role of tropical forests withrespect to the carbon dioxide question.

4. Explain the role of the oceans with respect tothe carbon dioxide question.

Further ReadingThe Biosphere. A collection of Scientific American

articles. San Francisco: W.H. Freeman, 1970.Gosz, J., et al. "The Flow of Energy in a Forest

Ecosystem." Scientific American, March1978, 92.

Miller, G.T. Living in the Environment. Belmont,California: Wadsworth Publishing, 1982.

National Film Board of Canada. A schoolcatalogue can be obtained from McIntyreEducational Media Ltd., 30 Kelfield Street,Rexdale, Ont. M9W 5A2

Nebel, B.M. Environmental Science - The Waythe World Works. Englewood Cliffs, N.J.:Prentice-Hall Pub., 1981.

Postlethwait,S.N. Energy in Life. Toronto:W.B. Saunders, 1976.

OrderingInformationTo order this publication or videotapes of the programsin the series Energy Flow, or for additional information,please contact one of the following:

TVOntario Sales and LicensingBox 200, Station QToronto, Ontario M4T 2T1(416) 484-2613

E-mail: ussales@tvo.org

Videotapes BPNProgram 1 : The Concept of Energy Flow 233701Program 2: Photosynthesis 233702Program 3: Energy Flow in an Ecosystem 233703Program 4: Energy Flow at the Cellular Level 233704Program 5: Energy Flow in Agriculture 233705Program 6: Energy Flow in the Biosphere 233706

Woodwell, G.M. 'The Carbon Dioxide Question.Scientific American, January 1978, 34.

United StatesTVOntario U.S. Sales Office901 Kildaire Farm Road, Building ACary, North Carolina 27511Phone: 800-331-9566Fax: 919-380-0961

Ontario