ObservingCells
aI
06.03.F1
Name
LabPartner
The cell is the basicunit of all living things.All
organismsare madeup ofat leastonecell Large
suchashumans,aremadeup oftrillions of
organismso
cells.
Hour
ClassMicroscopeStandards:
Cork Cells-Cork cells hold a specialplace in the history
ofbiology. It was cork cellsthat RobertHookewas
lookingat in 1665whenhe coinedtlre name"c€lls."
Commercialcork is obtainedfromthe Cork Oaktee,
which is nativeto the Mediterraneanarea.The outerbark
ofthe tree producesthesecells.This bark may be
removedwithout damagingthe fiee.
To examinecork cellsoyou will needto cut a thin slice
from a pieceof cork. Caution:Cut the cork on a hard sudace.Always cut in a
direclion awalzfrom yotn body.-With a single-edgerazor blade,cut a thin
wedgefromthe endofthe cork.Then,cut offthe thick pieceofthe wedge.The
remaining pieceshould be thin enoughfor light to passthrough.If you find
it difficult to cut a very thin piece,scrapethe cork with the sharpedgeofthe
razor blade.The small dust-likepiecesshouldbe suitablefor viewing. Most
beginningbiology studentsusespecimensthat aretoo large--remember,in
microscopy,o'lessis mors" wtrenyou want to producequality slides.
Firstcut, as thin as Possible
i -,g'o:".*,-i
Secondcut
P i e c ef o r s l i d e
Placethe cork tissueon a slidewith a drop of water. Carefully position a coverslipon the slide so that the cork
is in the center. Examinethe stideunderthe cornpoundmicroscope.Begin your viewing at low power,then (if
your specimenis of adequatequality) switchto highpower for makingyour drawings. Look forthe boxlike
structruesthat Hooke calledcells.Note the thickenedcell walls of the cork cells.
The drawing of cork tissueshownbelow, asseenundera simplemicroscope,appearedin RobertHooke's166?
boolq Mcroscopy. Hooke narnedthe coryartrnents "cells." Yorn imagpshouldhavea'l^rhiteo'background
with dark cell walls.
Drawseveralcork cellsard estimatetheirsize.Showthe
thicknessof thecell walls.Labelthecell walls. You instructor
will needto venfywhatyouseeundertbescopeby initialing
bElow.
Verification
magnification
cell size
OnionCells
The bulb of an onion is really an undergroundstem. The stem is completely
coveredby leaves,which take the form of succulent(full ofjuice) scales.
Obtain a piece of scale of an onion bulb. You will use the outer layer (the
epidermalcells) from the scale.Bend the scaleuntil it cracks,then gently pull the
two piecesapaxt;the outer layer of epidermaltissue should peel off easily. This
tiszueurill be aboutasthin and flexible asplastic wrap.
Now put a drop of
Epidermal
tissue
waterinthe centerof
a cleanslide. Cut off
a smallpieceof the
epidermaltissueandplaceit in the drop of water.
E
l"To'" onc or tt.
lvlakesurethat the tissueis flat. If it is folded,
straightenit with a dissectingprobeor needle.Put
one drop of methylerreblue staindirectly on top of
the onion tiszue.Wait one minute,then placea
" :Jjii;1J:t::"t,"?",lffi
""". coverslipover tle tissue.
"ii1iii","#tii{f:
b
A Cut rn onion
butb
n!lny
!catr'.
tlav.!
Next, removethe stain from underthe coverslipandreplaceit with clear
water. To do this, placea papertowel at the edgeof one sideof
coverslip. Placea drop of water at the edgeof the coverslipon the other
side. The stainedwater underthe coverslipwill be absorbedby the paper
towel. As the stainis removed,the clearwater nextto the coverslipwill be
drawnunderthe coverslipto replacethe stainedwater.
Top View
After the stain is replaced with
clear water, you will see that
certain portions of the cell
absorbed the stain well, while
othersdid not. The stainedparts of
the cell are more visible under the
microscope.
Side View
Stain
Obseryethe slide under the microscope.Try to identifr the parts of the onion cell. Look for the nucleus,
cytoplasrn,and cell wall.
Drawthe onion epidermis. Label the cytoplasmand cell wall.
Magnification
Cell width
Verified
Human CheekCells
You will now observesome of your own cells. The epithelial cells lining yorn mouth axeconstantlybeing
replaced"The old cells that me readyto sloughoffcan easilybe collected.
Put a drop of water on a cleanslide. Using the end of a toothpick, gently scrapethe inside of your cheek.Stir
the water on the slide with the end of the toothpick to mix the cells with the water. If this doesnot produceany
cells, scrapearoundyour teeth at the gumline.Epithelial cells that have sloughedoffthe cheekoften mix in the
salivaand get lodgedin the tee,th"
Apply one drop of methyleneblue stain to the cells. Wait one minute and place a coverslipon tle slide. Clear
the slide of stain,usingthe tecbniquedescribedearlier.
Observethe slide underthe microscope.Try to idertifr the partsof the cheekcell. Look fot the cell membraneo
the nucleus,andthe cytoplasm.
Draw seneralcheek epithelial cells and estimatetheir size. Label the cell membrane,the nucleus, and the
cytoplasnr
A . G e n t l ys c r a p et h e i n s i d eo f y o u r
c h e e kw i t h t h e b r o a d e n d o f a
toolhoick.
Epithelial(cheek)cells
B . S t i r t h e s c r a p i n g si n t o a d r o p
o f w a t e ro n a s l i d e .
Ivlagnification
CellSize
FrG.2-7
Procedure
for studyinghumanepidermal
cells.
Verified
Prepareanotherslideofthe onion epidermaltissue. Repeatthe stainingprocessusinga different stain,acetodye will stainthe cytoplasmand nucleusof your cells pirtk or red. Attempt to
carmine. 45Yoaceto-carmine
distinguishbetweenthe vacuolesandthe cytoplasm. The cytoplasmis within the cell membraneand is
"livin!," whereasthe contentsofthe vacuolesare often iRertstoredmaterials. Locatethe nucleuswhich should
now be red. Draw severalcells showingthe nucleusin red/pink sincethis is the color impartedby the stain.
Specimen
Stain
Magnification
Width of a cell
Verified
In the onion cell, it is possibleto observemitochondria-thosecell organellesinvolved in cellular respiration-To
do this, selectanotherpieceof onion epidermaltissueandcut it with a sharprazor sothat it is approximately1
X I cm in size.On a cieanslide, mountthe tissuein a drop of 5% sucrosesolution. Add fromthree to five
dropsof the stainJanusGreenB. Add a coverslip,view at high power, anddraw what you observe.
of a nearlytransparentbrrickwall
If yots preparationis truly onecell in thickness,it will havethe appearance
when ui.*"6 underthe low power of your microscope.Using the high-powerobjective,locatemitochondria,
which look like very small rods or spheresat the peripheryofthe cell. They shouldbe blue in color whenyou
fust view your prepaxationIfthey are not stained,placea strip of filter paperor other absorbentpaperat the
edgeof the courtrlip. Add a few dropsof JanusGreenstainat the oppositeedgeof the coverslip,anddraw it
thrbughyour prepaxationby absorbentp4per.Stainedmitochondrialosetheir color in about5 minutesasa
enzymelocatedon their surface.
result of the actionof a dehydrogenase
Specimen
Stain
Magnification
Verified
(.{
ElodeaCells
In this exercise,you will examinecells &om the leaf
of an aquaticplant comrnonlycalledElodea.These
cells are greenbecausethey containa pigmentcalled
chlorophyll. In photosynthesis,
this pigrnentabsorbs
light energyand convertsit into chemicalenergy.
A. Elodea plant
Removea youngleaf fromthe tip ofthe plant.Place
the leaf in a drop of water on a slide,and add a
coverslip.E)taminethe preparationwith the lowpower
objectivein position. Locatethe nucleus,cytoplasrn,
andcell wall.
Examinea groupof cells nearthe centerof the leaf. Careftlly switch to high power.
Eachof the small,regularly shapedunits you seeis a cell and is delimited by cell walls madeof cellulose.
Celluloseis a complexcarbohydrateforrred of glucosemoleculesattaplredend-to-end.The cell membranelies
just insidethe cell wall.
Chloroplastsare suspendedin cytoplasna,which makesup most ofthe cell. Stareat an individual cell for a few
seconds.If you arepatient,you canseethat the contentsofthe cells are moving. This phenomenonis called
cytoplasmicstreamingor cyclosis.
A centrally locatedvacuoleoccupiesapproximately90%ofthe volume of eachElodeacell though it is difficutt
to makeout for the beginningbiologist. Focusup anddown throughthe cell andnote that mostcellular
componentsarepressedagainstttre cell wall. Fromthis, you infer that the middle ofthe cell is a "hollow"
causedby the vacuole.
Draw severalof the cells. Use greento showthe individual
chloroplasts.Labelthe cell walf cytoplasm,andchloroplast
in oneofthe cells.
SpecimenName
Magnification
Cell Length
Whv areElodealeavesereen?
Namethe processby which a plant absorbslight energyand covertsit to chemicalenergy.
Namethe processby which organellesmove aroundinsidesomecells.
What is the purposeof a vacuole?
What are cell walls madeofl
Verified
5
organellesuniqueto plants.You bave
Plastids are membrane-bound
(containing
alreadybeenintroducedto onetypes-chloroplasts
types
several
of pigmentincluding
chlorophyll).Chromoplastscontain
carotenoids,which give plantsan otangeor yellow color.
Use a razorbladeto slice a pieceof tissue,asthin aspossible,fromthe
outer portion of a peeledcarrot.Preparea wet-mountslide.
Draw a sampleofthe tissue(to the righ$ anduseorangeto showthe
carotenoid-filled chromoplasts.
Obtaina scalefromthe'ted" onion Usethe epidermal
tissuefromthe sideWITH the pigmentedcells. Make
a wet-mountslideand draw a sampleof the tissuein the
spaceto the left below. Use color to showthe
chromoplasts.
SpecimenName
Magnification
Verified
plastkts),makea thin slice &om a potatotuhr. Placethe section
To examineleucoplasts(starch-containing
on a slideand stainit for a few sepondswith iodine, a stainspecific for starch. Move the stainedsectionto B
drop of water on a cleanslide,add a coverslip,andview Tlre intenselystainedstrupturesin the cells are
leucoplasts(often called amyloplasts).Draw severalof the cells.
SpecimenName
SpecimenName
Magnification
Magnification
Verified
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t
Bacteria(ProkaryoticCells)
Use a toothpick to placea tiny dab of yogurt on a slide. Add a drop of tap
water and stir the toothpick aroundto spreadout the cells. Add a coverslip
and view. First uselow power,then switch to high power. The swarmsof
rod-shapedorganismsthat you seeshinrmeringare cells ofthe yogurt
bacteriumlactobacillus. Thesebacteriaare adaptedto live on milk sugar
(lactose)andareusedby humansto convertordinarymilk to yogurt.
Yogurt is acidic andkeepsmuch longerthan milk. Draw severalbacteria
in the spaceto the right. Estimatetheir size.
SpecimenName
Magnification
Cell Size
Verified
'Phceadrop+f tap+rra*er
en-aoleansliCe. Use a cleantoothpick to scrapebetweenyour teethandaroturdyour
gum-line. Swirl tHootffiindhedrop-of
water-spread the specimenso that it is very thin. The water
shouldturn milky with tartar from your teeth" Severalspeciesof bacteriamakeup the "normal florao'of your
mouth.
Allow the water to dry. You rnight want to placethe slide on the light sourcebelowthe stage. The heatwill
speedthe process.WhenreadS passthe slide (specimenside up) slowly throughthe flame of a Bunsenburner
threetimes. Thls process"fixes" the bacteriato the slide.
Add one drop of crystal violet stainand allow it to standfor one minute.
Gently washthe slide andusea papertowel to blot it dry-DO NOT
RIJB, just blot. DO NOT adda drop of water or cover slip for viewing
this slide. Instead,placeit directly on the stageof the microscopeand
view it at low, then higtg power. Draw a portion of what you seeand
estimatethe averagesizeofthe cells.
SpecimenName
Stain
Magnification
Cell Size
Verified
7
Plasmolysisof Living Cells
The plant cell is enclosedby a nonliving sell wall anda cell membranethat is difficult to observebecauseit is
pushedtightly againstttrc insideof the cell wall. You can makethis membraneeasierto see,however,by
thanthe cytoplasm).
placingthe cell in a hypertonicsalinesotution(i.e., a solutionthat is moreconcentrated
Berrg hypertonicto the cytoplasnl the salinecauseswaterto moveout of the cell andthe cell protoplastto
which covers
slrink awayfrom the cell wall. Under theseconditions,you canreadily seethe cell memb,rane,
protoplast.
the surfaceof the
SelectanotheryoungElodealeaf, mount it in a drop of water, and adda coverslip.Examinethe preparation
with the low-powerobjectiveas you did earlier in the lab. Locatea sectionof the leaf nearthe tip. Switchto
high power and studythe cell.
Add oneor two dropsof a"l,0o/o
NaCl (saline)solutionto oneedgeof the coverslip.Thentouchthe liquid on the
oppositesideof the coverslipwith a pieceof papertoweling so that the paperdrawsup the liquid. Repeatthis
steptwo moretimesto be surethat the original water hasbeenreplacedby the saline. Onceagain,exarninethe
cellsclosely.Whathashappened
to the cells?
Re-readthe first paragraph(above). Explain your observations:
Draw severalof the plasmolyzedcellsin the spacebelow. Labelthe cell wall, c.ellmembrane.andg*oplapru.
Name
Specirnen
Magnification
Verified
1. Add I to 2 drops ot 10% salt solutionto one edge
of cover glass.
2. Touch the fluid at opposite edge with a piece oi
paper toweling.
Procedureto draw salt solution under a cover glass.
t
The Centrifuge,a Tool of Science
The centrifugeis usedto "spin" a sampleat very high rpm (revolutionsper minute). Centrifugalforce--the
force on an object awayfrom the centerwhen slung in a circle--causesmaterialmoredensethan water to go to
the bottomof the tube andmateriallessdensethan waterto rise to the top.
Obtain a 16mmX 125mmculturetube (this tube is shorterandfits the centrifuge). Gently stir you Pondin a Jar
so the water becomescloudy. Fill the culturetubo approximatelytwo-thirds full of water from your Pondin a
Jar. Placethe sampleinone of the centrifugebaysmaking surethe sampleis balancedwith a secondtube in a
slot acrossfrom yours. NOTE TIIE NUMBER NEXT TO YOUR BAY so you canretrievethe correcttube
when done. Startthe centrifugeand spin the sampleat high speedfor five minutes.
In the spacebelow, useshadingto showthe arrangementof any layersthat formedin the centrifugedtube.
Using a dropper,obtaina samplefromthe surfaceofthe culture tube. Placeit on a slideand view at low, then
high, powers.
Use your dropperto obtaina samplefrom the bottom of the tube. Repeatthe processof viewing. Draw what
you observedfrom ONE of the view in the spaceprovided.
Name
Specirnen
Magnification
Verified
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