LESSON M

The WOWBu,Closer Look

;: Getting a

A compound light microscope

estimated to be 40-50 years old

INTRODUCTIONMany of the organisms pictured on the organ-ism photo cards in Lesson 1 cannot be seenvery well, or at all, with the naked eye. Thosephotos were made with the aid of magnifica-tion. To view the organisms yourself, you woulduse a microscope. In this lesson, you will learnhow to prepare a dry-mount slide and how touse a compound light microscope to observeorganisms. You will also learn how to preparescientific drawings according to a specific set ofguidelines, which you will use throughout themodule. You will learn these skills while observ-ing and learning about an interesting organismcalled the "WOWBug," a tiny wasp that isharmless to humans.

OBJECTIVES FOR THIS LESSON

Learn the parts of a microscope, andpractice manipulating them to obtain thebest image of slide-mounted specimens.

Measure the diameter of the field of

view under different magnifications ofthe compound microscope.

Learn how to handle, manipulate, andrecapture WOWBugs.

Prepare dry-mount slides of liveWOWBugs.

Observe WOWBug grooming behavior.

Draw, label, and measure a WOWBug,following specific guidelines forscientific drawings.

Update your organism photo card forWOWBugs.

12 ST(VMH I M O R G A N I S M S — F R O M M A C R O TO M I C R O

THROUGH THE COMPOUND EYEFor thousands of years, humanbeings have used tools. For abiologist, one of the most impor-tant tools is the microscope.Since its invention in the early1600s, the microscope has beentransformed into a relativelyinexpensive, yet efficient, wayfor scientists such as yourself toview a world invisible to thenaked eye.

You probably will use a com-pound light microscope duringthis module. In this type ofmicroscope, light is providedeither by a mirror or a small,built-in lightbulb. The word"compound" refers to the twolenses—one in the eyepieceand one in an objective—thattogether magnify the image.You can calculate the totalmagnification by multiplying themagnification of the lens of theeyepiece by that of the lens inthe objective.

The drawing on page 14shows the parts of a compoundmicroscope and explains thefunction of each part.

As you use your microscopeduring this module, you will gaina working knowledge of its partsand their functions and becomemuch more proficient at usingthis important tool of science.

(continued)

Since the eyepiece is lOx and the objective is 4x, the total magnification of these

two lenses used together is 40x.

13

LESSON 2 THE WOWBuG: G E T T I N G A CLOS ER LOOK

(continued from pg. 13)

The compound light microscope

Eyepiece—Usually contains a lOx lens

Nosepiece—Holds theobjective lenses;rotates to enablechanging magnification

Objective Lenses—Usedin combination with theeyepiece; provide a rangeof magnifications, usuallyfrom 40x to 400x

Arm—Supports the upper part ofthe microscope; serves as a handle

Stage Clip—Usually one oneach side of hole in stage;helps to hold slides in place

Stage—Supports the slides

Diaphragm—Wheel or lever thatadjusts amount of light thatpasses through hole in stage;provides proper contrast

Coarse Adjustment Knob—Raises and lowers thestage or objective lenses

Light—Sends light through thehole in the stage to illuminatespecimen on slide

Base—Supports the microscope;serves as a handle

Fine Adjustment Knob—Raises and lowers the stageor objective lenses a tinydistance for exact focusing

14 STCA1S'

LESSON2 THE WOWBuc,: G E T T I N G A C L O S E R LOOK

Getting Started

•I Working in groups, observe your handlens. Notice the shape of each lens. Theyare called "convex lensevs" because theybulge in the middle and taper toward theedge. Stand at your desk and hold a handlens about 1 centimeter (cm) above a lineof text in your Student Guide.

O Iii your science notebook, make n quicksketch of the hand lens, showing theappearance of the text through each of itslenses. Record your estimates of the mag-nifications directly on the correspondinglenses in your sketch. For example, if youestimated that one of the lenses magnifiedthe text to two times its normal size, youwould write 2x on that part of yoursketch.

O Center the smaller lens on top of the word"of" in this sentence. Close one eye, butcontinue to stare at the word "of." Slowlyraise the lens from the page toward youropen eye. Answer the following questionin your science notebook:

A. How does the image of the word "of"change as you raise the lens?

A Repeat Step 3, but stop raising the lenswhen the word "of" appears upside downand backward, while still remaining infocus. Pick up the second hand lens.Center its larger lens directly over thesmall lens of the first hand lens, whichshould still be focused on the word "of."Look through the large lens while youraise it slowly. Keep your head up. If youput your eye down to the lens you will not

MATERIALS FORLESSON 2

For you1 copy of Student

Sheet 2.3A:Guidelines forScientificDrawings

1 copy of StudentSheet 2.3B:Drawing YourWOWBug

For your group2 compound light

microscopes2 depression slides2 plastic slides4 hand lenses5 WOWBugs2 pipe cleaners1 piece of notebook

paper2 pieces of

transparent tape2 transparent rulers2 metric rulers,

30 cm (12")1 plastic cup with

lid, 4 oz1 plastic cup of flour4 No. 2 pencils2 toothpicks1 box of colored

pencils

STG/MS1 15

LESSON 2 T H E WOWBuG: G E T T I N G A C L O S E R LOOK

see the intended effect. Answer the fol-lowing question in your science notebook:

B. What happens to the image of the word"of" in the larger lens as you raise it awayfrom the smaller lens?

C With a partner, take a close look at yourmicroscope. Refer to the reading selection"Through the Compound Eye," which youread for homework, to identify the micro-scope's main parts and to find out how to

calculate the magnifications you wouldget using its different lenses. Discuss withyour group how two lenses work togetherin a microscope to produce an image.

Inquiry 2.1Corralling Your WOWBugs

PROCEDURE

Place a piece of notebook paper infront of your group. Your teacher willput about five female WOWBugs on thepaper.

Have one member of the group verygently corral the WOWBugs into thecenter of the paper using the tip of the

pipe cleaner, as seen in Figure 2.1. Agentle nudge of the pipe cleaner willstimulate the WOWBugs to changedirection. After about 30 seconds,quickly pass the pipe cleaner toanother group member. Have this

member continue to corral theWOWBugs into the center of thepaper. Continue until all group mem-bers have had a turn.

O While the last groupmember is practicinghandling the WOWBugs,

have another groupmember carefully invertthe plastic cup overeach WOWBug, one at atime, until they have all

crawled up on its insidesurface. Save forInquiry 2.2.

Figure 2.1 Move the pipe cleaner

quickly to keep up with the WOWBugs!

16 STCAIS™ O R G A N I S M S — F U O M M A C R O TO M I C R O

LESSON 2 T H E W O W B U G : G E T T I N G A C l . O S E R LOOK

Inquiry 2.2Preparing a Dry-Mount SlideTo View WOWBug GroomingBehavior

PROCEDURE

•1 Working with a partner, take the followingsteps to prepare a dry-mount slide of aWOWBug:

A. Plaee a depression slide on the notebookpaper. Keep handy a flat, plastic slide andtwo 2-cni pieces of transparent tape.

B. Dip a toothpick into the container of floursupplied by your teacher. Then tap a fewspecks of the flour into the well of thedepression slide. Stir the flour with thetip of the toothpick to scatter it aroundthe depression. Use just enough flour dustso that the WOWBug becomes slightly"dirty." Too much flour could harm theWOWBug.

C. Use the pipe cleaner to remove oneWOWBug from the cup and transfer itinto the slide's depression. Quickly placethe flat, plastic slide on top of it, trappingthe WOWBug in the depression.

D. Use the two pieces of transparent tape tofasten the ends of the slides together toprevent the WOWBug from escaping.Your slide should look like the one inFigure 2.2.

2 Take the following steps to view the dry-mount slide:

A. Place the dry-mount slide on the micro-scope stage and focus on the WOWBugunder the lowest magnification. If theWOWBug is moving around, practicekeeping it in the field of view by movingthe slide slowly and smoothly with yourfingers while you observe it through theeyepiece. If you are lucky, you may get tosee the WOWBug standing still to cleanthe flour from its legs or antennae. Note

Figure 2.2 Fasten the tape securely or the WOWBug might escape!

17

LESSON 2 T U G WOWB0G: G E T T I N G A C l . O S G K LOOK

whether it cleans away the specks of flourin any particular order or manner.

B. Repeat Procedure Step 2A with each ofthe other objective lenses until you haveviewed the WOWBug under all magnifi-cations.

C. Have your partner repeat Procedure steps2A and 2B.

•O Save the slide for Inquiry 2.3.

Inquiry 2.3Preparing ScientificDrawings of the WOWBugPROCEDURE

1 Listen while your teacher reviews theinformation on Student Sheet 2.3A:Guidelines for Scientific Drawings.

2 Have one student in your pair place yourWOWBug dry-mount slide on the micro-scope stage.

O Draw the WOWBug in the top circle on" Student Sheet 2.3B, following the guide-

lines on Student Sheet 2.3A. Include asmuch detail as you can. Take turns withyour partner at the microscope. TheWOWBug should stand relatively stillwhile cleaning itself, so you can pay closeattention to details like the number ofparts in the antennae or legs. Use thehighest magnification through which youcan see the entire WOWBug in greatestdetail. This should be the one in whichthe WOWBug nearly fills the field of view.Since the WOWBug is three dimensional,you may find that you have to adjust thefine focus at times to sec the variousstructures more clearly.

A Normally, as you view the WOWBugthrough the microscope, it will be rightside up so that you would be looking at itsback, which scientists call its dorsum. Ifthe WOWBug is walking upside down onthe top cover, you will see its underside,which is called its venter. If this happens,flip the slide over on the stage andobserve it from the other side. Title yourdrawing, "WOWBug—Dorsal View."

C If the WOWBug is too active and repeat-edly crawls out of the field of view, tryviewing the slide prepared by the otherpair in your group. If you still can't seethe WOWBug, ask your teacher for assis-tance.

C Label at least five structures. Refer to the" illustration of the WOWBug in the reading

selection "Intriguing Insects" for names ofits structures.

7 To complete your drawing, it is necessaryto give the viewer or reader some idea ofthe size of the WOWBug. After followingthe steps below, you will better under-stand the relative sizes of different kindsof organisms when given a drawing ofthem.

A. Remove the slide from the microscopestage, and switeh the magnification to thelowest power.

B. Center the transparent ruler on the stageand count the number of millimeter (mm)lines you can see across the widest part ofthe field of view. Record this number onStudent Sheet 2.3B on the line next tothis label: Diameter of Field of View (mm)at Low Magnification.

C. Switch the magnification to mediumpower, and repeat your measurement.

18 STG/MS™ O R G A N I S M S — K R O M M A C R O TO M I C R O

LESSON 2 T H E WOWBuo: G E T T I N G A C L O S E R L O O K

Record this number next to the label:Diameter of the Field of View (mm) atMedium Magnification.

D. Switch the magnification to the highestpower, and repeat this process once more.Record this number on your studentsheet next to this label: Diameter of theField of View (mm) at High Magnification(400x, 430x, or whichever is greatest onyour microscope.)

E. Remove the ruler. Switch the magnifica-tion to the lowest power, put the slideback on the stage, and focus on theWOWBug. Based 011 the number of rulerlines you counted under the lowest mag-nification, estimate the length of the

WOWBug in mm. Record this number onyour student sheet next to this label:Estimated WOWBug Body Length (mm) atLow Magnification.

F. Now place the ruler underneath the slideuntil the tip of one end of the WOWBug isright in the center of one of the mmmarks, as shown in Figure 2.3.

G. Measure the actual body length of theWOWBug in mm, and record that lengthon your student sheet next to the label:Actual WOWBug Body Length (mm) atLow Magnification. Also record the lengthon Student Sheet 2.3B, just to the right ofthe drawing's title. Check the actual mea-surement against your estimate.

Figure 2.3 You can only measure the length of the WOWBug accurately when it is

positioned correctly against a mm mark of the ruler.

STC/MS™ ORGANISMS—FROM M A C H O TO M I C R O 19

LESSON 2 THE WOWHuc.: G E T T I N G A CLOSER LOOK

O When you and your partner have com-pleted your drawings, review the 10guidelines on Student Sheet 2.3A. Whenyou are satisfied that you have correctlyfollowed these guidelines, trade drawingswith your partner. Notice that the num-bers 1-10 are listed below the Title line ofyour drawing. These represent the draw-ing guidelines. Circle, in pencil, the num-ber of each guideline that your partnerdid not follow. Then, assign each other'sdrawing a score of 1 to 10, based on thenumber of guidelines that were followedcorrectly. When you are both finished,return each other's drawings. Revise yourdrawing and give it back to your partnerto review again. Erase the circle aroundeach number of a guideline that wasrevised correctly. Continue until you both

earn 10 points. This process is called peerevaluation. It is an important part of sci-entific inquiry.

C| Focus the microscope on one structure ofthe WOWBug (an antenna, a wing, or aleg, for example) using the highest magni-fication possible. Draw that structure inthe second circle on Student Sheet 2.3B.Give it an appropriate title, and label any-thing on this structure that you found inthe illustration of a WOWBug in the read-ing selection "Intriguing Insects," whichyou read for homework. Peer-evaluatethis drawing before turning it in, if youwish.

1 O Update your organism photo card for the" WOWBug.

20 STCAIS™ O H C I A X I K M S — F U O M M A C R O TO M I C R O

LESSON 2 THE WOWBUG: G E T T I N G A C L O H E R LOOK

REFLECTING ON WHAT YOU'VE DONE

On the basis of what you have learned in thislesson, answer the following questions onStudent Sheet 2.3B. Be prepared to discussyour answers with the class.

A. Explain two ways in which the com-pound light microscope is an improve-ment over the microscope developed byAntony van Leeuwenhoek.

B. List three ways in which lenses areused as tools of science, in addition totheir use in compound microscopes.

G. How did the diameter of the field ofview change when you changed themicroscope's objective lenses?

D. What characteristics of the WOWBugdid you observe that suggest it is aninsect?

E. In what ways did your WOWBugremove the flour dust from its body? Listtwo reasons why you think groomingwould be important to a WOWBug. (Hint:Why is grooming important for you?)

F. According to the reading selection"Intriguing Insects," how arc parasiticwasps, such as WOWBugs, important tohumans?

STC/M8 O R G A N I S M S — F R O M M A C R O TO M I C R O 21

LESSON2 Tiii< WO\VBu(.i: GKTTINC A C L O R K K LOOK

When you thinkabout insects, whichcome to mind first?Butterflies? Ants?Bees? In fact, beetlesare the most com-mon insect. If youlined up every kind ofplant mid animal in arow, every fourthorganism would likelybe a beetle. And bee-tles are only one kindof insect!

There are hun-dreds of types ofinsects on Earth,ranging from thecommon to the exot-ic. You're probablyquite familiar withwasps, flies, mosqui-toes, moths, crick-ets, fireflies, anddragonflies. Haveyou ever heard of acicada known as the"buffalo head"because its headresembles a buffalo's,complete with a setof horns? Or thewhirligig beetle,which uses its twosets of eyes in aclever way when it goes swimming? One setlooks above the water's surface, while theother checks out the action below. Anddon't forget the fruit fly, Drosophila. Thescientific study of the brief life cycle of thistiny fly laid the groundwork for moderngenetics.

What do all of these insects have in com-mon? They all have three distinct body

These are just a few of the thousands of varieties of beetles found all over the world.

parts—a head, a thorax, and an abdomen.They also have six legs, four wings, and anouter covering called mi "exoskeleton."

When you think about it, insects are justabout everywhere. They live in our houses, inour gardens, on our pets, and sometimes evenon us. You find them in lakes, ponds, andstreams. They survive on the coldest mountainsand in the hottest deserts.

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LESSON 2 T H E WOWBtIG: G E T T I N G A C L O S E R LOOK

Good Guys andBad GuysSome people don'tlike insects at all.However, each kindof insect has a role toplay in the world, andeach affects our livesin a different way.

Some insects seemto cause more thantheir share of trouble.According to Dr.Robert Matthews, aprofessor at theUniversity of Georgia,insects have causedan enormous amountof human suffering. Some mosquitoes transmitdiseases, like malaria and yellow fever, whichare major threats to human health in much ofthe world. Flying grasshoppers called migratorylocusts destroy entire fields of crops.

We consider other insects to be good guys.Honeybees pollinate the flowers of many of ourfavorite food crops. Anyone who has enjoyed abiscuit with honey also appreciates their efforts.

Less familiar insects, such as parasitic wasps,lay their eggs in or on other insects. A parasiteis an organism that obtains its nutrients fromanother organism, generally damaging the otherorganism in the process.

A World Without WaspsParasites may sound destructive, but they alsoplay an important role. For example, a worldwithout parasitic wasps would be a very differ-ent place. These insects help lower Earth's pestpopulation. In fact, scientists have calculatedthat a single pair of houseflies, if left alone,could potentially produce enough descendantsin a year to cover the surface of the earth sev-eral centimeters deep. Fortunately, this doesn'thappen, thanks to natural enemies such as par-asitic wasps, which kill large numbers of flieseverv vear. D

Few crops can stand up to a swarm of insects such as this.

As you can see, grasshoppers can do considerable

damage to a field of com.

STC/MS1 O K G A N I . S M S — F R O M M A C R O T O M I C K O 2 3

LESSON 2 THE WOWBUG: GETTING A Cl.USEK LOOK

Dr. Matthews and the WOWBug

Dr. Matthews, second from left, sharing a butterfly collection with

members of the WOWBugs team.

These WOWBugs are only 1.5 millimeters long, but they play a very

large role in helping to control bee and fly populations. Female (left);

male (right). Note the male's unusual antennae.

Dr. Robert Matthews is an ento-mologist, a scientist who studiesinsects. He has studied insectsfor many years and in manyparts of the world.

One of Dr. Matthews's favoriteinsects is a small parasitic waspcalled Melittobict digitata. That'squite a mouthful, which is whyDr. Matthews nicknamed it the"WOWBug." He and his studentshave learned much about thestrange habits of this intriguinginsect. Through their efforts, theWOWBug has become one ofthe newest organisms studied inthe science classroom.

What's so special aboutWOWBugsV And how did theymake their way into the class-room? It was an unlikely begin-ning. Dr. Matthews did not findthe bugs—they found him!While he was a graduate student,Dr. Matthews decided to exam-ine the nests of some little wildbees he found outdoors. lie tookthe nests inside and put them ona shelf in his laboratory. Later,he got the nests clown to studythem. To his surprise, he foundnot little bees, but WOWBugs!Unnoticed, they had sneakedinto the nests, fed, and multi-plied. They had destroyed nearlyall of his bees, and Dr. Matthewswas pretty angry.

Many years later, while think-ing about new ways to teach biol-ogy, Dr. Matthews rememberedthe WOWBug. He realized thatthe same WOWBug behaviors

24 STCA1S"'

LESSON 2 T H E W O W B l I G : ( J E T T I N G A C L O S E R L O O K

Wings

Eye

Hindle§

Female, lateral view

Female, dorsal view

that nearly ruined his early research would makethese little parasites wonderful in the seienceclassroom. WOWBugs breed easily in large num-bers, they have a very short life cycle, and theydon't take up much spaee. Best of all, they can'thurt humans with their stingers.

As he worked with WOWBugs, Dr. Matthewscontinued to learn new and fascinating thingsabout their biology and behavior. He wanted toshare what he was learning. With the help ofother scientists and teachers, Dr. Matthews

developed a set of teaching activities to helpstudents learn science concepts and skills byworking with WOWBugs.

Scientists on the WOWBugs team at theUniversity of Georgia continue to make newdiscoveries every day. They write a newsletter,give workshops for teachers, and develop newlab investigations. If you'd like to learn aboutthe latest developments on WOWBugs, visit theNSRC Web site (http://www.si.edu/nsrc) to finda link to the WOWBugs Web site. D

25

LESSON2 T H E WOWBuc: GETTING A CLOSER LOOK

MICROSCOPE PIONEERSYou can't study organisms thoroughly without agood microscope. This tool, which today's sci-entists take for granted, has played a major rolein helping scientists understand more about Hy-ing things.

Robert Hooke and Antony van Leeuwenhoek(Lay-ven-IiOKE) were important pioneers inthe development of this important scientificinstrument. Hooke was born in England in1635. A member of the Royal Society ofEngland, he was one of the most famous scien-tists of his time. Leeuwenhoek was born in theDutch town of Delft in 1632.

Cork cells as seen by Robert Hooke

Hooke: Discovering the Mysteries of CorkToday, Robert Hooke is remembered more as amathematician than as a biologist. But like allscientists of his day, he had broad interests. Hemade many contributions to biology. In hisbook, Micrographici, Hooke described and illus-trated the discoveries he had made using acompound microscope that he'd built. Hookeused the microscope to observe familiar objectssuch as insects, sponges, and feathers. "When heput a thin slice of cork under the lens of hismicroscope, Hooke made a very important dis-cover)'. He saw the cell walls in the cork tissue.Hooke had discovered plant cells.

Even though his discoveries were amazing inhis day, Hooke's microscope was quite crude. Itdidn't look that different from today's micro-scopes, but it had poorly ground lenses, whichcaused Hooke's view of the objects to be blurredor distorted. YiTiat's more, early microscopescould not magnify objects more than 20 or 30times their actual size. By contrast, most micro-scopes found in middle schools today can mag-nify objects up to 430 times.

Leeuwenhoek Perfects the LensLeeuwenhoek's major contribution to the devel-opment of the microscope was to make lensesthat were much more finely ground than thoseused by Hooke and others. He never went tocollege, and he earned a living by selling fabricin a small shop. For him, making microscopeswas a hobby that became a lifelong obsession.

Leeuwenhoek learned to grind lenses byobserving the craftsmen who made eyeglassesin Delft. Leeuwenhoek's lenses, often no morethan 0.3 centimeters across, were so even andperfect they provided clear images that werefree of distortion. They could magnify objects tobetween 50 and 300 times their actual size. Hemounted the tiny lenses in frames of gold andsilver that he also crafted himself.

26 STC/MS™ O K G A N M S M S — F R O M MACRO TO MICRO

LESSON2 Tin-: \YOWBiu; : G E T T I N G A C I . O S K R LOOK

i a

I I

Hooka's microscope was called a "compound micro-

scope " because it had two lenses.

Unlike Hooka's compound microscope,Leeuwenhoek's device had only one lens. It wasmounted in a tiny hole in a brass plate.Leeuwenhoek placed the object lie wanted toexamine on a sharp point in front of the lens.He adjusted the position with the screws. Theentire device was less than 10 centimeters long.

For a scientist, good tools are just the start.Scientists also need the ability to observe care-fully and to record theirfindings accurately. Theyneed patience.Leeuwenhoek had all thesequalities; in addition, hewas very curious. He wroteabout everything he saw,from algae on pond waterto mineral crystals andfossils. He discoveredmicroscopic organisms inrainwater. He discoveredblood cells and was thefirst to see living sperm inan insect. He is creditedwith publishing the firstdrawing of bacteria.

Leeuwenhoek stuck justabout everything under hislens—including plaque from

Leeuwenhoek's microscope

his own teeth! What did he see? Something thatwouldn't surprise your dentist at all. "I saw . . .many very little living animalcules," he wrote."Very prettily a-moving. The biggest . . . had avery strong and swift motion . . . and shotthrough the water. The second . . . spun aroundlike a top."

Hooke passed away in 1703, and Leeuwenhoekdied in 1723, at the age of 91. Both had become

world famous.Leeuwenhoek was sofamous that Peter theGreat, czar of Russia,once came to Delft tovisit him at his home.

The science ofmicroscopy has madegreat progress since thetime of Ilooke andLeeuwenhoek. To get anidea of how muchprogress, take a look atthe image of a mite. Itwas taken through a

This mite, which measures 150-200 microns

in length (Yiooo mm), is magnified 850 times

its actual size.

scanning electronmicroscope that has amagnification range offrom 15 to 200,000times! D

STCVMS1 27