Biology Schedule - Photosynthesis Unit

Wednesday Oct. 27-1: The Chemistry of Autumn Colors -

A reading and Study Guide2. Why Study Photosynthesis?-

Assignment- Answer the following questions while reading the article1. What is Photosynthesis?2. Why is photosynthesis important in food production, energy production, as fiber andother materials and the environment?3. Why study photosynthesis?4. What is the role of photosynthesis in agriculture, energy production, the environment,electronics and medicine.- Due Thursday, Oct. 28

Friday -Oct. 29 - Notes on Photosynthesis /Photosynthesis video

Monday November 1 The Worldng Ce!l: Energy From Sunlight Internet Activity inLibrary

Tuesday- November 2- Paper Chromatography Lab (Due Wednesday, Nov. 3)

Wednesday - November 3- Leaf diagram / photosynthesis drawings

Monday Nov 8- Electron Movement Lab Demonstration / prepare for leaf stomata lab

Tuesday - Nov. 9 -Leaf Stomata lab Due Thursday, Nov. 11

Wednesday - Nov. 10 Review

Thursday - Nov. 11 Test Photosynthesis Unit

Biology Study Guide - PhotosynthesisTest DateText Chapter 8Online textbook activities and multiple choice questions

Labs Paper Chrom,atographyLeaf Stomata

Worksheets-Reading the Chemistry of Autumn Colors and Why Study Photosynthesis?Video on PhotosynthesisThe Worldng Cell: Energy From SunlightInternet activityleaf diagramPhotosynthesis readingLab demonstrations on electron movementLab demonstration: Energy Flow: Photosynthesis

1. Write out the simple chemical reaction for photosynthesis.

2. What are the reactants of the light dependent reaction? The products?

3, What are the reactants of the Calvin Cycle? The products?

4. What is the other name for the Calvin Cycle?

5. What is the role of NADPH in photosynthesis?

6. What is the role of ATP in photosynthesis?

7. Describe a photosystem.

8. Draw and label a chloroplast.

9. What happens in the thylakoids?

10. What happens in the stroma?

11. What happens when water splits?

12. Describe how a stomata works in a leaf.

14. Be able to label a leaf diagram.

15. Be able to calculate an Rf value.

16. What does paper chromatography do and why is this process useIul.

¯ Ternls:

¯ chloroplast

¯ chlorophyll

¯ stroma

¯ thylakoid

¯ light reactions

THE " - _HEM!b OF AUTUMN COLORSEvery autumn across the Northern Hemisphere: diminishing daylight hours and fallingtemperatures induce trees to prepare for winter. In these preparations, they shed billions of tons ofleaves. In certain regions, such as our own, the shedding of leaves is preceded by a spectacularcolor show. Formerly green leaves turn to brilliant shades of yellow, orange, and red. These colorchanges are the result of transformations in leaf pigments.

The green pigment in leaves is chlorophyll. Chlorophyll absorbs rdd and bluelight from thesunlight that falls on leaves. Therefore. the light reflected by the leaves is diminished in red andblue and appears green. The molecules of chlorophyll are large (C55H70MgN406). They are notsoluble in the aqueous s’)lution that fills plant cells. Instead, they are attached to the membranes ofdisc-like structures, called chloroplasts, inside the cells. Chloroplasts are the site ofphotosynthesis, the process in which light energy is converted to chemical energy. In chloroplasts,the light absorbed by chlorophyll supplies the energy ’used by plants to transform carbon dioxideand water into oxygen and carbohydrates, which have a general formula of Cx(H20)y.

Eight

x CO2 +), H20 x Oa + rchlorophyll

In this endothennic transformation, the energy of the light absorbed by chlorophyll is convertedinto chemical energy stored ir~ carbohydrates (sugars and starches). This chemical energy drivesthe biochemical reactions that cause plants to grow, flower, and produce seed.

Chlorophyll is ~6t a very stable compound; bright sunlight causes it to decompose. To maintainthe amount of chlorophyll in their leaves, plants continuously synthesize it. The synthesis ofchlorophyll in plants requires sunlight and warm temperatures. Therefore, during summerchlorophyll is continuously broken down and regenerated in the leaves of trees.

Another pigment found in the leaves of many plants iscarotene. Carotene absorbs blue-green and blue light. Thelight reflected from carotene appears yellow. Carotene is alsoa large molecule (C40H36) contained in the chloroplasts ofmany plants. When carotene and chlorophyll occur in thesame leaf, together they remove red, blue-green, and bluelight from sunlight that falls on the leaf. The light reflected bythe leaf appears green. Carotene functions as an accessory

http://scifun.chem.wisc.eduichemweek/fallcolr/fallcolr.html I 1/16/04

absorber. The energy, of the light absorbed by carotene istransferred to chlorophyll, which uses the energy inphotosynthesis. Carotene is a much morn stable compoundthan chlorophyll. Carotene persists in leaves even whenchlorophyll has disappeared. When chlorophyll disappearsfrom a leaf, the remaining carotene causes the leaf to appearyellow.

A third pigment, or class of pigments, that occur in leaves arethe anthocyanins. Anthoeyanins absorb blue, blue-green, andgreen light. Therefore, the light reflected by leaves containinganthocyanins appears red. Unlike chlorophyll and carotene.anthocyanins are not attached to cell membranes, but aredissolved in the cell sap. The color produced by thesepigments is sensitive to the pH of the cell sap. lfthe sap isquite acidic, the pigments impart a bright red color, if the sapis less acidic, its color is more purple. Anthoeyanin pigmentsare responsible for the red skin of ripe apples and the purpleof ripe grapes. Anthocyanins are formed by a reactionbetween sugars and certain proteins in cell sap. This reactiondoes not occur until the concentration of sugar in the sap isquite high. The reaction also requires light. This is whyapples often appear red on one side and green on the other:the red side was in the sun and the gt?een side was in shade.

Paper birch

During summer, the leaves of trees are factoriesproducing sugar from carbon~tioxide and water bythe action of light on chlorophyll. Chlorophyll causesthe leaves to appear green. (.The leaves of some trees.such a~ birches and cottonwoods, also containcarotene: these leaves appear brighter ~reen. becausecarotene ~bsorbs blue-green light.) Wa~er andnutrients flow from the roots, through the branches.and into the leaves. The sugars produced byphotosynthesis flow from the leaves to other parts ofthe tree. where some of the chemical energy is usedfor growth and some is stored: The shortening daysand cool nights of autumn trigger changes in the tree.One of these changes is the growth of a corkymembrane between the branch and the leaf stem. This

membrane interferes with the" flow of nutriants into the leaf. Because the nutrient flow isinterrupted, the production of chlorophyll in the leaf declines, and the green color of the leaf fades.If the leaf contaifis carotene, as do the leaves of birch and hickory, it will change from green tobright yellow as the chlorophyll disappears. In some trees, as the concentration of sugar in the leaf’increases, the sugar reacts to form anthoeyanins. These pigments cagse the yellowing leaves toturn red. Red maples, red oaks, and sumac produce anthocyanins in abandanee and display thebrightest reds and purples in the autumn landscape.

Red Maple .

The range and intensity of autumn colors is greatlyinfluenced by the weather. Low temperatures destroychlorophyll, and if they stay above freezing, promotethe formation of anthocyanins. Bright sunshine alsodestroys ehlorophylI and enhances anthocyaninproduction. Dry weather, by increasing sugarconcentration in sap, also increases ~e amount of

anthocyanin. So the brightest autumn colors areproduced when dry, sunny days are followed by cool,dry niahts.

11116/04

THE CHEMISTRY OF AUTUMN COLORS

1. Name two environmental factors that stimulate trees to prepare for winter.

2. Explain why chlorophyll appears green.

3.What conditions cause chlorophyll to decompose? What type of temperatures promote thesynthesis of chlorophyll?

What is carotene AND what colors does it reflect? Are carotenes present all the time?

5. What function does carotene perform AND what happens to carotene when chlorophyll breaks do~?

6. What are anthocyanins AND what colors do they reflect?

7. Where are anthocyanins found in the cell AND what happens to them if the pH is raised (less acidic)?

8. Name two factors that affect the formation of amhoyanins.

9. What forms between the branch and the leaf stem (petiole)?

10. Describe three ways that this corky, membrane influences events in the leaf.

1 I. Explain how temperature, sunshine, and moisture levels SPECIFICALLY affect autumn leaf colors.

12. What conditions are best for the brightest autumn colors.

WHY STUDY PHOTOSYNTHESIS?By Devens Gust, Ph:D:

Pro fessor of Chemistry,:,and BiochemistryCenter for the Study of Early Events in Photosynthesis

What is photosynthesis?

Photosynthesis is arguably the most important biological process on earth. By liberating oxygen andconsuming carbon dioxide, it has transformed the world into the hospitable environment we know today.Directly or indirectly, photosynthesis fills all of our food requirements and many of our needs for fiber andbuilding materials. The energy stored in petroleum, natural gas and coal all came from the sun viaphotosynthesis, as does the energy in firewood, which is a major fuel in many parts of the world, This beingthe case, scientific research into photosynthesis is vitally important. If we can understand and control theintricacies of the photosynthetic process, we can learn how to increase crop yields of food, fiber, wood,and fuel, and how to better use our lands. The energy-harvesting secrets of plants can be adapted toman-made systems which, provide new, efficient ways t’o collect and use solar energy. These same natural’"technologies" can help point the way to the design of new, faster, and more compact computers~ andeven to new medicql breakthroughs. Because photosynthesis helps control the makeup of ouratmosphere, understanding photosynthesis is crucial to understanding how carbon dioxide and other"greenhouse gases" affect the global climate. In this document, we Will briefly explore each of the areasmentioned above, and illustrate how photosynthesis research is critical to maintaining and improving ourquality of life.

Photosynthesis and food. All of our biological energy needs are met by the plant kingdom, either directly orthrough herbivorous animals. Plants in turn obtain the energy to synthesize foods’tufts via photosynthesis.Although plants draw necessary materials fromthe soil and water and carbon dioxide from the air, theenergy needs of the plant are filled by sunlight. Sunlight is pure energy. However, sunlight itself is not a veryuseful form of energy; it cannot be eaten, it cannot turn dynamos, and it cannot be stored. To bebeneficial, the energy in sunlight must be converted to other forms. This is what photosynthesis is all about.If is the process by which plants change the energy in sunlight to kinds of energy that can be stored forlater use. Plants cam/out this process in photosynthetic reaction centers. These tiny units are found inleaves, and convert light energy to chemical energy, which is the form used by all living organisms. One ofthe major energy-harvesting processes in plants involves usiog the energy of sunlight to convert carbondioxide from the air into sugars, starches, and other high-energy carbohydrates. Oxygen is released in theprocess. Later, when the plant needs food, it draws upon the energy stored in these carbohydrates. We dothe same. When we eat a plate of spaghetti, our bodies oxidize or "burn" the starch by allowing if tocombine with oxygen from the air. This produces carbon dioxide, which we exhale, and the energy weneed to survive. Thus, if there is no photosynthesis, there is no food. Indeed, one widely accepted theoryexplaining the extinction of the dinosaurs suggests that a comet, meteor, or volcano ejected so muchmaterial into the atmosphere that the amount of sunlight reaching the earth was severely reduced. This in .turn caused the death of many plants and the creatures that depended upon them for energy.

Photosynthesis and energy. One of the Carbohydrates resul;ring from photosynthesis is cellulose, which

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~(~,~ d n other lant matenal When w bum wood, we cony t IImakes up the bulk of drywoo a d p " . e eft he ce uloseback to carbon dioxide and release the stored energy as heat. Burning fuel is basically the same oxidationprocess that occurs in our bodies; it liberates the energy of "stored sunlight" in a useful form, and returnscarbon dioxide to the atmosphere. Energy from bumir~g "biomass" is important in many parts of the world.in developing countries, firewood continues to be critical to survival EthanoF{grain alcohol) producedfrom sugars and starches by fermentation is a major automobile fuel in Brazil, and is added to gasoline insome parts of the United States to help reduce emissions of harmful pollutants. Ethanol is also readilyconverted to ethylene, which serves as a feedstock fo a large part of the petrochemical industry. If ispossible fo convert cellulose to sugar, and then into ethanol; various microorganisms carry out this process.It could be commercially important one day.

Our major sources of energy, of course, are coal, oil and natural gas. These materials are all derived fromancient plants and animals, and the energy stored within them is chemical energy that originally camefrom sunlight through photosynthesis. Thus, most of the energy we use today was originally solar energy!

Photosynthesis, fiber, and materials. Wood, of course, is not only burned, but is an important material forbuilding and many other purposes. Paper, for example, is nearly pure photosynthetically producedcellulose, as is cotton and many other natural fibers. Even wool production depends onphotosynthetically-derived energy. In fact, all plant and animal products including many medicines anddrugs require energy to produce, and that energy comes ultimately from sunlight via photosynthesis. Manyof our other materials needs are filled by plastics and synthetic fibers which are produced from petroleum,and 6re thus also photosynthetic in origin. Even much of our metal refining depends ultimately on coal orother photosynthetic products. Indeed, it is difficult fo name an economically important mafedal orsubstance whose existence and usefulness is not in some way tied to photosynthesis,

Photosynthesis and the environment. Currently, there is a lot of discussion concerning the possible effects ofcarbon dioxide and other "greenhouse gases" on the environment. As mentioned above, photosynthesisconverts carbon dioxide from the air to carbohydrates and other kinds of "fixed" carbon and releasesoxygen to the atmosphere. When we.burn firewood, ethanol, or coal, oil and other fossil fuels, oxygen isconsumed, and carbon dioxide is released back to the atmosphere. Thus, carbon dioxide which wasremoved from the atmosphere over millions of years is being replaced very quickly through ourconsumption of these fuels. The increase in carbon dioxide and related gases is bound to affect ouratmosphere. Will this change be large or small, and will it be harmful or beneficial? These questions arebeing actively studied by many scientists today. The answers will depend strongly on the effect ofphotosynthesis carried out by land and sea organisms. As photosynthesis consumes carbon dioxide andreleases oxygen, it helps counteract the effect of combustion of fossil fuels. The burning of fossil fuelsreleases not only carbon dioxide, but also hydrocarbons, nitrogen oxides, and other trace materials thatpollute the atmosphere and contribute to long-term health and environmental problems. These problemsare a consequence of the fact that nature has chosen to implement photosynthesis through conversion ofcarbon dioxide to energy-rich materials such as carbohydrates. Can the principles of photosynthetic solarenergy harvesting be used in some way to produce non-polluting fuels or energy sources? The answer, aswe shall see, is yes.

Why study photosynthesis?

Because our quality of life, and indeed our very existence, depends on photosynthesis, it is essential thatwe understand it. Through understanding, we can avoid adversely affecting the process and precipitatingenvironmental or ecological disasters. Through understanding, we can also learn to control photosynthesis,and thus enhance production of food, fiber and energy. Understanding the natural process, which hasbeen developed by plants over several billion years, will also allow us to use the basi~; chemistry andphysics of photosynthesis for other purposes, such as solar energy conversion, the design of electroniccircuits, and the development of medicines and drugs. Some examples follow.

Photosynthesis and agriculture. Although photosynthesis has interested mankind for eons, rapid progress inunderstanding the process has come in-the last few years. One of the things we have learned is that

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overall, photosynthesis is relatively inefficient. For example, based on the amount of carbon fixed by a fieldof cam during a typical growing season, only about ] - 2% of the solar energy falling on the field isrecovered as new photosynthetic products. The efficiency of uncultivated plant life is only about 0.2%. Insugar cane, which is one of the most efficient plants, about 8% of the light absorbed by the plant spreserved as chemical energy. Many plants, especially those that originate in the temperate zones suchas most of the Unffed States, undergo a process called photorespirafion. This is a kind of "short circuit" ofphotosynthesis that wastes much of the plants’ photosynthetic energy. The phenomenon ofphoforespirafion including its function, if any, is only one of many riddles facing the photosynthesisresearcher.

If we can fully understand processes like photorespiration, we will have the ability to alter them. Thus, moreefficient plants can be designed. Although new varieties of plants have been developed for centuriesthrough selective breeding, the techniques of modern molecular biology have speeded up the processtremendously. Photosynthesis research can show us how to produce new crop strains that will make muchbetter use of the sunlight they absorb. Research along these lines is critical, as recent studies show thatagricultural production is leveling off at a time when demand for food and other agricultural products isincreasing rapidly.

Because plants depend upon photosynthesis for their survival, interfering with photosynthesis can kill theplant. This is the basis of several important herbicides, which act by preventing certain important steps ofphotosynthesis. Understanding the details of photosynthesis can lead to the design of new, extremelyselective herbicides and plant growth regulators that have the potential of being environmentally safe(especially to animal life, which does not carry out photosynthesis). Indeed, it is possible to develop newcrop plants that are immune to specific herbicides, and to thus achieve weed control specific to one cropspecies.

Photosynthesis and energy production. As described above, most of our current energy needs are met byphotosynthesis, ancient or modem, increasing the efficiency of natural photosynthesis can also increaseproduction of ethanol an’d of her fuels derived from agriculture. However, knowledge gained fromphotosynthesis research can also be used to enhance energy production in a much more direct way.Although the overall photosynthesis process is relatively wasteful, the early steps in the conversion ofsunlight to chemical energy are quite efficient. Why not learn to understand the basic chemistry andphysics of photosynthesis, and use these same principles to build man-made solar energy harvestingdevices? This has been a dream of chemists for years, but is now close to becoming a reality. In thelaboratory, scientists can now synthesize artificial photosynthetic reaction centers which rival the naturalones in terms of the amount of sunlight stored as chemical or electrical energy. More research will lead tothe development of new, efficient solar energy harvesting technologies based on the natural process.

The role of photosynthesis in control of the environment. How does photosynthesis in temperate andtropical forests and in the sea affect the quantity of greenhouse gases in the atmosphere? This is animportant and controversial issue today. As mentioned above, photosynthesis by plants removes carbondioxide from the atmosphere and replaces it with oxygen. Thus, if would tend to ameliorate the effects ofcarbon dioxide relec~;ed by the burning of fossil fuels. However, the question is complicated by the factthat plants themselves react fo the amount of carbon dioxide in the atmosphere. Some plants, appear togrow more rapidly in an atmosphere rich in carbon dioxide, but this may not be true of all species.Understanding the effect of greenhouse gases requires a much better knowledge of the interaction of theplant kingdom with carbon dioxide than we have today. Burning plants and plant products such aspetroleum releases carbon dioxide and other byproducts such as hydrocarbons and nitrogen oxides.However, the pollution caused by such materials is not a necessary product of solar energy utilization. Theartificial photosynthetic reaction centers discussed above produce energy without releasing anybyproducts other than heat. They hold the promise of producing clean energy in the form of electricity orhydrogen fuel without pollution. Implementation of such solar energy harvesting devices would preventpollution at the source, which is certainly the most efficient approach to control.

Photosynthesis and electronics. At first glance, photosynthesis would seem to hage no association with th~design of computers and other electronic devices. However, there is potentially a very strong connectic

electronics research is to make transistors and other circuit cam anentA"goal of modem p s as small as ..possible. Small devices and short connections between them make computers faster and more compact.The smallest possible unit at a material is a molecule (made up cxf Otoms of various types). Thus, the smallestconceivable transistor is a single molecule (or atom). Many researchers today are investigating theintriguing possibility of making electronic components from single molecules or small groups of molecules.Another very active area at research is computers that use light, rather than electrons, as the medium forcarrying information. In principle, light-based computers have several advantages over traditional designs,and indeed many of our telephone transmission and switching networks already operate through fiberoptics. What does this have to do with photosynthesis? It turns out that photosynthetic reaction centers arenatural photochemical switches of molecular dimensions. Learning how plants absorb light, control themovement of the resulting energy to reaction centers, and convert the light energy to electrical, andfinally chemical energy can help us understand how to ma~e molecular-scale computers. In fact, severalmolecular electronic logic elements based on artificial photosynthetic reaction centers have alreadybeen reported in the scientific literature.

Phofosynthesis and medicine. Light has a very high energy content, and when it is absorbed by asubstance this energy is converted to other forms. When the energy ends up in the wrong place, it cancause serious damage to living organisms. Aging of the skin and skin cancer are only two of manydeleterious effects of light on humans and animals. Because plants and other photosynthetic species havebeen dealing with light for eons, they have had to develop photoprotective mechanisms to limit lightdamage. Learning about the causes of light- induced tissue damage and the details of the naturalphoto’protective mechanisms can help us can find ways to adapt these processes for the benefit ofhumanity in areas far removed from photosynthesis itself. For example, the mechanism by which sunlightabsorbed by photosynthetic chlorophyll causes tissue damage in plants has been harnessed for medicalpurposes. Substances related to chlorophyll localize naturally in cancerous tumor tissue, illumination of thetumors with light then leads to photochemical damage which can kill the tumor while leaving surroundingtissue unharmed. Another medical application involves using similar chlorophyll relatives to localize intumor tissue, and thus act as dyes which clearly delineate the boundary between cancerous and healthytissue. This diagnostic aid ~does not cause photochemical damage to normal tissue because the principlesof photosynthesis have been used to endow it with protective agents that harmlessly convert theabsorbed light to heat.

Conclusions

The above examples illustrate the importance of photosynthesis as a natural process and the impact that ithas on all of our lives. Research into the nature of photosynthesis is crucial because only by understandingphotosynthesis can we control it, and harness its principles for the betterment of mankind. Science has onlyrecently developed the basic tools and techniques needed to investigate the intricate details ofphotosynthesis. It is now time to apply these tools and techniques to the problem, and to begin to reap thebenefits of this research.

--Written by and C0py~’ight (C) 1996 Devens Gust, Professor of Chemistry and Biochemistry, Arizona StateUniversity

Professor Devens Gust’s Home Pa£e

Read another article by Dr. Gust, Research Trends: Emulating Photosynthesis

Visit the ASU Photosynthesis Center

revised Friday, Avgust 14, 1998

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InnerThylakoid

Space

ThylakoidMembrane

Stroma

[] Photosystem !i ,

4 + 02

f [] Electron~ransport Chain

[] HydrogenIon Movement

Chloroplast

ATP synthase

ADP2 NADP+

Photosystem I ATP Formation

Summary of the Light dependent reaction in photosynthesis

1. Pigments in photosystem II absorb light.

2. Energy from that light is absorbed by electrons increasing their energy level.

3. So now these electrons are high energy and can be (they are) passed onto the electrontransport chain.

4. There are enzymes on the irmer surface of the thylakoid that break up two watermolecules into 2 H+ ions, 1 oxygen atom and 2 electrons

H O H+H +O

5. The oxygen is released as a gas and the H+ ions are released inside the thylakoidmemebrane.

6. So now high energy electrons move from Photosystem II to Phootsystem I. Theenergy is used by the molecules in the electron transport chain to transport H+ ions fromthe stroma into the inner thylakoid.

7. Pigments in Photosystem I use light energy to reenergize the electron.

NADP+ picks up these eiectrons plus a H+ ion ---) NADPH

8. Now the inside of the thylakoid membrane is positively charged. (Which is a result oftH+ ion released during water splitting and electron transport. The outside becomesnegatively charged.This difference in charges across the membrane provides the energy to make ATP.

9. ATP synthase is a protein in the membrane that allows H+ ions to pass through.

Class

Flowchart

The tCollowing.flowchart represents th~ reactions qf photosynthesis. Fill in themis~ing information u~ing the formulas listed below.

NADP÷ ATP ADP + PH20 C02 NADPH

Light-DependentReactions

Light

CalvinCycle

Teaching Resources / Chapter

Biology Intemet Assigrunent on Photosynthesis-

When light hits the P680 molecule of PS II, electrons are

Log on to the intemetgo to google.com type in biology I Interactive animationsGo to the section on Photosynthesis and PlantsChoose the last entry which is Photosynthesis Forest Biology Virginia TechFirst a leaf will appear and then you will see a close up of a leaf, label the diagramin this packet from the diagrampush the CONTINUE BUTTONDraw a picture of the cell labeling the cell wall, vacuole, nucleus, chloroplasts andcytoplasmpush the CONTINUE BUTTONDraw a picture of the enlarged chloroplast labeling: the outer and innermembranes, thylakoids, stromapush the CONTINUE BUTTONYou will see 5 points of interest on the inner membrane space.Push number 1 - which is at PS 11 (photosystem II) Listen and watch the clip andfill in the blanks below.

and become

New electrons are reduced by splitting water which produces and

~ Go back to the main menu and choose the second point ofinterest~Point #2 - When electrons are passed from PSI1 to PS~ what happens to the hydrogenions?

Go back to the main menu and choose the third point of interest.Point #3 - More light strikes the PS 700 molecule of PSI and eiectrons are

and become

Go back to the main menu and choose the fourth point of interest.Point #4 - Electrons pass to an electron acceptor to NADP+ which isbecomes NADPH which is

and

Go back to the main menu and choose the fifth point of interest.Pointe #5 - When the H+ ions concentrated on the inside diffuse through ATPase what is.produced.

Where did the H+ ions come from (look back at your answers)

What are the final products that go onto the dark reaction of photosynthesis? there are 2.

ChloroplastPigment Analysis

EXPLORATION

~When you look at a leaf, the green pigment chlorophyll is usuallythe only pigment that appears to be present. Actually, chlorophyllis only one of many types of pigments present in the leaf and one ofseveral that are involved in the process of photosynthesis. Onceremoved from the leaf, the photosynthetic pigments can beseparated from one another and identified using a process calledchromatography.

Chromatography is a physical process in which severalcompounds are separated from a solution and from each other. Inthin layer chromatography, the solvent is absorbed by a thin layerof silica gel. As the solvent moves upward in the gel, it carries withit the compounds that have been placed on the gel. Thesecompounds each move upward at a specific rate in relation to themoving solvent and can be identified by the dlstances they move.

OBJECTIVES¯Extract a mixture of plant photosynthetic

pigments. "¯Separate pigments of spinach leaves by thin layer

chromatography.

¯Prepare and analyze a silica gel chromatogram.¯Calculate the R~ values for various photosynthetic

pigments.

baby food jar with lidspinach leaves, driedchromatography solventthin layer chromatography slide

funnelcheeseclothdark-colored bottle or vialgoggles

capillary tubemetric rulerpencilethyl alcohol

mortar and pestlelaboratory apron

PROCEDUREPart A. Preparing For Chromatography

2o

Obtain a small amount (approximately 5 mL) ofthe chromatography solvent from your teacher.Pour enough of this solvent into the baby-foodiar so that it just covers the bottom of the jar,but is less than 1 mm deep. Screw the cap ontothe jar and set aside for later use.Place a pea-sized amount of dried spinach in amortar. Using the pestle, grind up the spinachfor 2 minutes. Add 2 mL ot ethyl alcohol to theground spinach and continue to grind foranother 2 minutes as shown in Figure 1. Theproduct should be a deep green fluid. Filter thisfluid through a double layer of cheesecloth intoa dark-colored bottle or vial. Stopper the bottletightly until needed.

Part B. Making and Analyzing th~Chromatogram

I. Select a chromatog~’aphy slide¯ Handle it onlyby its edges. Make a small pencil dot 5 mmfrom the bottom of the slide. DO NOT use a pento make the dot.

2. Dip a capillary tube into the pigment-containingfluid in the dark bottle.

3, Lightly touch the filled end of the capillai~ tubeto the dot on the .coated slide as shown inFigure 2. Allow a small amount of the fluid to bedeposited on the slide, forming a spot I mm indiameter. Do not disturb the silica film abovethe spot. Allow the spot to dry l~about 30seconds).

4. Repeat step 3, applying leaf pigments to thesame spot four or five times, being sure toallow the spot to dry each time. This willproduce a concentrated spot of pigments.

5, Hold the slide along the outside of the jar toverify that the spot will not be below the levelof the solvent. If the solvent is too deep pour alittle of it out of the jar into a specially labeledcontainer. Place the slide into the baby food iaron a level surface as shown in Figure 3. Do notallow the spot to contact the solvent at anytime. Quickly screw the cap on the jar. Do notmove the jar once the slide is placed in thesolvent.

6. Watch the slide closely and note the movementof solvent up the film of silica gel. Remove theslide from the baby food jar when the solventfront nearly reaches the top of the slide.

7. Mark the top of the solvent front with a pencilas shown in Figure 4.

8. Make a drawing of your slide in the spaceprovided in Data and Observations. Be sure toindicate the position of the original spot ofpigments as well as the locations of pigmentsanywhere else on the slide. Indicate the relativeamounts of pigments in each spot by drawingthe spots the same size and darkness as thoseon your slide.

Carotenes, which are yellow or orange pigmentslusually appear near the top of the slide. Lutein is agray pigment iust below the carotenes. Chlorophylla will appear next as a blue-green pigment.Xanthbphylls are yellow pigments, and chlorophyll bis a yellow-green pigment. They are found togetherlust below chlorophyll a. Your chromatogram mayor may not have all of these pigments.

9. Measure with a metric ruler the distance in mmfrom the original spot to the solvent front youmarked in step 7. Record this measurement inTable I.

4O

Figure 4.

I

10. Measure the dist~ce each pigr~ent traveledfrom the original spot to its final location.Record these data in Table 1.

11. Calculate the R~ value for each pigment spot.The Ph value is the ratio of the distance traveledby the pigmen~ to the distance traveled by thesolvent. By comparing Ph values of unknowncompounds with the P~ v~ues of known

compounds, an unknown substance ca~ beidentified.

distance pigment traveleddistance solvent traveled

12. Record your R, values in Table l.13. Clean your equipment and dispose of your

solvents in the designated container.

DATA AND OBSERVATIONSTable 1.

Chromatography Data

Substance Distance fromoriginal spot (mm)

Solvent front

Carotends

Lutein

Chlorophyll a

Xanthophylis

Chlorophyll bYour thin layer slide

ANALYSIS1. Which pigments were you able to identify?

2. Judging from the darkness of the pigment spots on your chromatogram, which pigment would you say is

most abundant in spinach leaves?

3. Which pigment appeared to travel the fastest? slowest?

4. Which pigment had the highest R, value?

5. How do R~ values compare with the rate of trave’, o! the pigment?

6. Why do the pigments travel in the solvent at different speeds? Remember that each pigment is a different

molecule with its own characteristic size and mass.

41

~ "L Do you think you would get simila~ result~ if.you used a diflerent k~nd of leaf?. Explaln.

8. Why do leaves appear green even though there are other pigments present? ,

9. Many leaves change color in the autumn. How is It possible for this color change to occur? Base youranswer on your new knowledge of pigments present In leaves. (HINT: Chlorophyll a and chlorophyll bare broken down in autumn when day length begins to shorten and temperatures decrease.)

FURTHER EXPLORATIONS1. Conduct this Exploration using several different plants with

differently colored leaves to see how their leaf pigments comparewith’those of spinach.

2. Separate pigments in spinach leaves by paper chromatography andcompare the results with those obtained by thin layer "chromatography.

42

Photosystem Model = hands on activity see page T165- Biology Exploring Life

Objective-To model the result of light striking a photosystem

Time 20 min

Skills Focus using models

Materials (per group of 6)Markerspaper(index cards)string for signsa flashligh4 tennis balls to represent electrons

Procedure1. Have students write "e-" on each of the tennis balls, then create signs with thefollowing labels:chlorophyli 1chlorophyll 2chlorophyll 3(reaction-center chlorophyll)Primary electron carrierwater moleculelight source

punch holes in cards and attach string so students can wear around their neck,

2. To act out the process, have students choose roles axad put the signs on. The threechlorophyll molecules sit down, each holding a tennis-ball electron. The PrimaryElectron Carrier and the Water Molecule stand near Chlorophyll 3 the water moleculehiding a tennis-ball electron behind its back.

3. The light Source shines the flashlight on the chlorophyll molecules. As the light shineson chlorophylll, chlorophyll 1 gets up "excited"-standing up quickly and waving itselectron then "wakes up " chlorophyll 2. Chlorophyll 2 stands up excitedly and wakesup Chlorophyll 3 while Chlorophyll 1 sinks back down, "exhausted". Chlorophyll 2 sitsdown next. Then Chlorophyll 3 gets up and waves its electron, the Primary ElectronAcceptor grabs it. Chlorophyll 3 then sits back down acting startled to have "lost " itselectron. The Water Molecule comes over, waves it electron, and hands it to chlorophyll3.

Follow-up

Have students draw diagrams representing the process they just modeled and addcaptions to explain each step

Investigation

26Learning Objectives

To determine the locations anddensity of stomata on a leaf.To describe the effect of an envi-ronmental change on stomata.

Process ObjectivesTo observe the effect of sail onstomata and guard cells.To hypothesize about the re-sponse of guard cells to astimulus.

¯ - To predict how a change in sto-mata influences photosynthesis.

MaterialsFor Group of 4

Distilled water in a small beakerwith a dropper5% NaCI solution in a smallbeaker with a dropper

For Each Student¯ 1-3 Microscope slide(s)¯ Leaves from a watered, nonwilted

plant exposed to lightRazor blade or pair of forceps1-3 Coverslip(s)

¯ Compound microscope¯ Paper towel

Leaf Stomata

Where are stomata located on a leaf,and how do they work?

IntroductionIf asked which plant organ is essential in absorbing compounds for a plant,most people would say it is the root. But roots are not the only plant organsinvolved in absorbing important compounds_. "Leaves absorb and releasegases, such as oxygen, carbon dioxide, and water vapor. As you might guess,gas exchange in a leaf affects the process of photosynthesis.

Prelab PreparationThink about the functions of gas exchange between a leaf and the atmosphere.Consider the roles of oxygen, carbon dioxide, and water in photosymhesisand in aerobic respiration within the cells of the leaf.

1. During what part of the 24-hour day would maxim~Jm ex-change of gases be most likely to occur? Why?

2. Under what environmental conditions would a plant benefitfrom reducing loss of water vapor through the leaves? Why?

3. What mechanism would you design to allow gas exchangebetween a leaf and the atmosphere?

4. How could your mechanism control the flow of gases into andout of the leaf, opening to increase the rate of gas exchange,and closing to reduce water loss?

Structures, perhaps similar to the one you would design, are present in theepidermis (outer cell layer) of the leaves of many plants. These structuresconsist of openings called stomata (singular, stoma), that allow water.vaporand gases to enter and exit the leaf. Two guard cells surrounding each stomaregulate its opening and closing. Review the functioning of stomata andguard cells in Section 26.4 of your textbook. In this investigation, you willexamine the epidermis of a leaf under a microscope to observe leaf stomata.

ProcedureA. Place a drop of water on a microscope slide. Obtain a healthy, nonwihed

leaf from one of the available plants. Holding the bottom surface of theleaf toward you, fold the leaf in half toward you so that the bottom sur-faces are together. (See the illustration on page 158.) Unfold the leaf andtear it along the crease by holding the left section of the leaf and pullingthe right section down at an angle. A clear, colorless outer layer shouldbe visible along the tprn edge. This layer is the lower epidermis.

B. Carefully cut off a small fragment of the transparent epidermal layer witha razor blade or pull it off carefully with forceps. Immediately place thefragment in the drop of water on your microscope slide and position acoverslip over it. Do not allow the fragment to dry out.

Investigation 26 157

Strategy for ObservingDraw the guard c~lls as soon as youmake yo~g obs~wadons of the epi-dermis.

3

Strategy for HypothesizingYour h~pothesis should be testable.As you generate hypotheses, think ofexperiments you could design to test

Strategy for PredictingList several predictions. Select theprediction most likely to be accuratebased on your hypothesis (see Ques-

tion 12).

C. F_,xandne the ~pidvrmis through the low-power objective of your micro.scope. Observ~ the sizes and shapes of the living ceils in the epidermis.The small bean-shaped cells occurring in pairs arc guaxd cells.5. Make an outline drawing of a pair of guard cells and the sur-

rounding epidermal ceils.D. Examin~hhepairofguardcellsund~rthchlgh.pow~robjecfive. The

opening or pore visible between the guard cells is the stoma.6. How does the wall of a guard cell vary in thickness? Add this

detail to Your drawing.£. Return the microscope objective to low power.

7. HOW many stornata are visible in one low power field?8. Compare your data with those of other students. What con-

clusions can you draw about the density of stomata?F. Repeat Steps A through E with another ]eaf from the plant you have been

using, but this time examine the upper epidermis. Holding the top sur-face of the leaf toward you, fold the leaf in half toward you so that the topsurfaces are together. Theu, tear the leaf along the crease, as you did inStep A, to obtain a fragment of the upper epidermis.

9. How many stomata are visible in your 1ragment of upper epi-dermis under low power?

10. What conclusion can you draw about the ~ocati0ns and densi-ties of stomata on leaves from your species of plant? Whatadvantage wou~d this have for the p~ant?

11. Where would you expect to find stomata on a water lily leaf?Why would you expect to find them there?

G, Guard cells conu’ol the movement of water raper and gases beween theleaf and the aUnospbere by opening and closing the stomata.12. State a hypothesis describing guard cell response to water

loss and the effect of this response on a stoma.

Make a flesh wet mount of the lower epidermis of a leaf. Observe astoma under high power. Place a drop of 5% NaCI solution at the edge ofthe coverslip. Take a piece of paper towel and touch it to the oppositeedge of the coverslip. The paper towel should draw out the water thatbathes the epidermis, and the NaCt solution should replace the water.This will create a concenla’ation gradient between the cells and their envi-ronment. Water will move out of the guard cells by osmosis until the saltconcentration inside the cells is the same as it is outside. Allow 5 min-utes for osmosis to be completed, then observe the guard cells and stomaagain.13. What has happened to the guard cells and to the s~oma?14. What property of guard cells permits such a change?15. Do your experimental results support your hypothesis?

Postlab Analysis16. In what way would the normal pattern of gas exchange be-

tween a leaf and the atmosphere be altered by coating bothsides of the leaf with petroleum jetty or wax?

17. Predict what would happen to guard ceils and stomata on ahot, dry day. How might this affect photosynthesis? Why?

Further Investigation1. Compare stomata on leaves from well-watered plants kept in dark with

stomata on leaves from well-watered plants kept in light.

158 lnvesdgation 26

¯ Prepare a wet mount of the onion epidermisusing a law drops of water.

¯ View the wet motmt under low, then high powermagnification.

If the epidermis is not clearly visible, there isprobably still part of the soft celluL~ materi~ o~the leaf present. If so, repe~t the scraping of the leafwith a new g~een onion section. It may ta~ke severaltries to obtain only the epidermis.

¯ Under high power magnification, identify struc-tures using Figure 52-3 and the following descrip-

In) epidermis cells--long, diamond-shapedcells

[b) guard cells--half circle-shaped cells(cJ stomata--small spaces or openings between

two guard cells{dJ clzloroplasts--green dotlike parts within the

guard cells"

leaf epidermis

¯ Use the space provided to diagram what you seeunder high power. Label guard cell, stomata,chloroplasts, epidermal cell.

Analysis1. What is the major function of leaves?

2. [a] What pigment is present m certain leaf tissues that allows a lea~ to carry on its major ~unction?

(b) What color is this pigment? _~_3. List all tissues or cells obscrved or described in this investigation that allow a leaf to carry on its major

fu ,notion.

What is the Ktnction of each of the following tissues or structures? [See Part A.)

(a} epidermis"

(c] guard ceils

(d~ stomate_

ie) palisade lnyer _ "

FiGUR~ 52-1

Observing Stomata

¯ place a .~�~ion ~f g~een onion lsaf on amicroscope slide,

¯ With a razor blade, slice the lea~ section so it liesflat on the slide as shown in Fi~zre 52-2.CAUTION: Blade is shaw. Cu: away fromlingers, Make sure the ori~ns!, outside smface ofthe lea~ xs d~wn.

FIGURE 52-2

onion leaf

¯ Scraping in one d~reetion only, use a single edgerazor blade to gently scrape away the soft cellularm~tenal ~rom the in~de of the leaf. Use Figure51-2 as a ~aide.

¯ Continue scraping the le~E until o~ly the outer,transparent epidermis remams,

~ 1-6-./---- s’~

fhe in and out of stomata Page 6 of 8

Suggested Photoperiod Procedure:

Three sample slides were made every hour, over a 24-hour period, using the same tree. Each samplewas taken from three different areas of the tree. Humidity, light intensity, and temperature wererecorded with each sample.

To analyze the data, images were captured using a flex-cam attached to a compound microscope (400x).A "Snappy-cam" (video capturing device) was used to photograph the imprints on the slide. Theseimages were then transferred to "_S_C_ IONI.M_A_ GE" for total area measurement of stomatal pore openings(at 400x, the entire stomata has a length of 20microns). Scionlmage can be downloaded free from theintemet!

This procedure can be altered to fit any student-generated hypotheses mentioned in the summary sectionabove.

If you do not have access to a flex-cam, snappy-cam and scionlmage, an alternative way to assess thearea of the open pores is to compare them to the following images, photographed using a compoundmicroscope (400x).

100% 75% 50%

open open

open

25% 15% 0-5%

open

For sample results of this photoperiod lab~ click here - RESULTS.

Return to the

EVALUATION / ASSESSMENT:

Students demonstrate mastery of science concepts by completing the imprinting, data collection,

ht~p ://www.woodrow.org/teachers/bi/1998/stomataJ 12/19/2005

Leaf Stomata ( 75. points)

Scientific approach (13 points)Prelab questions: 1-4 - Answer in complete sentences(8 points)

I. During what part of the 24 -hour day would maximum exchange ofgases be most likely to occur? Why?

Procedure: Write out what you did? (5 points)

Materials: List materials used(5 points)Questions page 158 5-17 (26 points)

Relabel figure 52-1 (4 points)

Diagram of leaf epidermis(5 points)

Analysis#I 1 ptso#2 a and b 1 point each#3 ! points#4 a-f (6 points)

SAFARI Montage: Quiz Page 1 ofl

SAFARI

Quiz Questions For Photosynthesis

Use your browser’s Print page function to print this quiz.

1, Chloroplasts are found in the of a leaf.

A, epidermis6. chlorophyllC. palisade layerD. guard cells

2. What role does chlorophyll play in photosynthesis?

A. It produces starch from sugar molecules.B. It releases energy that plants use for growth.C. It absorbs light and transforms it into chemical energy.D. It controls the amount of oxygen that is released by the plant into the

atmosphere.

3. During the Calvin Cycle, carbon is linked with hydrogen and oxygen tomake:

A. pigment.B. sugars.C. ATP.D. starch.

4. Respiration is:

A. the opposite of photosynthesis.B. the process a plant goes through to release water vapor through the

stomata.C. the evolution of plants over 3.5 billion years.D. how plants produce their own food out of carbon dioxide and water.

5. According to this show, how could artificial photosynthesis help infuture space flights?

A. Plants would be able to grow on Mars.B. Plants would keep the air breaLhable on-board space ships.C. Plants would produce enough food for space crews to survive over a long

period of time.D. All of the above,

Back to Search Results View Answers to Quiz

http ://sa~ari/S AFA£J/montage/displayquiz.php?S earchPage=tme&keyindex= 1014&locati... 10/23/2009

NAME

Photosynthesis

Section Review 4.2The Big Idea!

All organisms get energy by breaking down the chemical compounds in food and making ATPand other molecules, 4,

Concepts¯ During photosynthesis, sunlight is converted into chemical energy, which is stored in

food.¯ Photosynthetic pigments such as chlorophyll are contained in chloroplasts.¯ The first stage of photosynthesis consists of light-dependent reactions in which light

energy is used to split water into oxygen, hydrogen ions, and electrons.¯ In the second stage of photosynthesis, called the Calvin cycle, carbon d~oxide is converted

into glucose.

Wordsphotosynthesis pigment chlorophyll chloroplast Calvin cycle

PART A Match each term in the Data Bank with its description below. Write the letter of the correctterm on the line provided.

Data Bank

a. grana b. chlorophyll c. stroma d. chloroplasts

e. photosynthesis f. pigment g. photosystems

1. process by which autotrophs convert sunlight to a usable form of energy

2. molecule that absorbs certain wavelengths of light and reflects or transmits others

3. most common and most important photosynthetic pigment in plants and algae

4. organelles that contain chlorophyll

$. gel-like matetial that surrounds the thylakoids ’

a. stacks of disk-shaped si:cUcrures that contain chlorophyll

7, light-coLlecting units of the chloroplast

PART B

1. What wavelengths of light are absorbed by chlorophyll? What wavelengths are reflected?

2, Why is light energy Important to the photosynthetic process?

Copyright © Addison Wesley Longman, Inc. All rights reserved. Unit 1 Review Module

NAME CLASS ,

In which stage of the photosynthetic process is oxygen produced? What happens tothis oxygen?

4.What chemicals are necessary for the Calvin cycle to occur? Where do these chemicalscome from?

$. What compound is formed from carbon dioxide in the Calvin cycle?

6. How do plants store energy they do not need immediately?

PART C Complete the following sentences by choosing the correct term from the Data Bank andwriting it on the line provided. Some terms may be used more than once.

Data ~ank

glucose carbon dioxide hydrogen ions concentration gradient

starches water ATP Calvin cycle

stroma ADP r, electrons

1. Plants use energy from sunlight to split molecules of

oxygen, , and

of photosynthesis.

, releasing

in the light dependent reactions

Using the energy of electrons produced in Photosystem II,

transported ~rom the stroma to the thylakoid space.

are actively

3. This movement of hydrogen ions into the thylakoid space creates a(n)

which provides energy for the conversion of __ into

4. The process in which carbohydrates are formed from carbondioxide is called the

, which takes place in the of the chloroplast.

$. For every six molecules ofis produced.

that enter the Calvin cycle, one molecule of

Both autotrophs and heterotrophs convert the produced by

photosynthesis into to power life functions.

Most piants store energy in the form of , which are long strings of

molecules.

Unit 1 Review Module Copyright © Addison Wesley Longman, inc. All right~ reserved.

NAM£ __ CLASS DATE

Photosynthesis

PART A Answer the Following questions on the lines laro~ded.

1. W’nat is photos.~mthesis?

¯ 2. Vv2aa~ molecules, pzoduced b.v photosy~I.hesis, are used to store energy from the stm?

PART 8 Use ".he diagram of photosymthesis below to answer the following;

A ~ Light-DependentUg~t Reactions

~l C and D

E _I Carbon fixation(Calvin cycle)

¯ F

I. Iden~i~ ~e compound each letter represents.

b.

d.

f.

How do plants obtain the carbon cLiox~de they need for photos.~rt~thesis?

NAME

Work~heet 10

CLASS DATE

Hg~t-D, ependent P|avLight-Dependent Reactions "

Uses light ene.z~" to split

Uses light ener~" to re-energi_zeelec-~ons.

¢. electron ca2Tier protein

d. ATP sy~thase

Transfers elecl:rons between Light-collecting molecules.

$. __i__ Re,on where hydrogen ionsaccumulate when water is split

e. thylakoid space (2umen)

PART B Answer the following questions on the lines provided.

1. Explain the role o~f hght ener~" m t_he hght-dep, endent rea~-Xions. ,

P.~-~.,~..~- ~ -~ _,~ ~_ ~ ....

:2. Describe the location of photosystems I and II inside the chloroplast.

B. lVhat two high-ener~~ compounds are created by the light-dependent reaCtions?

Copyright © Acid son Vves ey Longrnan, Inc. All rlgnts reserved, Anirnared .Biological Concepzs I $

Online Activity 8.2( closer look) and Activity 8.3

1 .Water (H20) is split in photosystem II to form two protons(H+), two electrons(E-) andoxygen (O). What role do each of these products play in photosynthesis?

2. How man 3 - PGA molecules are produced from each reaction RuBP and CO2?

3. What type of molecule is mbisco?

4. Name the high-energy molecule that is required for the regeneration of RuBP/

5. What is the primary function of the Calvin cycle?

6. A plant used 18 ATP molecules in the formation of two G3P molecules that combineto form glucose. When you eat a marshmallow containing sugar, how many ATPmolecules ~vill you make from one molecule of glucose?