"The cell"

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Module " The cell "

Biology (Age 11 - 14 years)

It is the goal of this module to introduce the cell step by step in order to avoid misconceptions.I havellustrated instructions to take pupils to the lab where they must observe, make drawings and label the different parts of a cell .The module is partly designed in a playful way, partly, especially as far as practical experimental work is concerned, on a higher scientific level. The more difficult terms are introduced gradually. In doing so it isparticularly planned to address many different senses.The purely lexical information is kept short, in order to on the one hand make pupils remember the factsmore easily and on the other hand also to avoid too much content. Young people are often crushed by masses of material. I think that sometimes less can be more efficient. It also means that genuine learning by experience and making experiments shall replace stereotyped learning by heart. The experiments selected are partly well known and often used, but also partly completely new and designed by the author. Each part of the module has been and will continuously be tested with different pupils. Everything will be also evaluated by the teachers using the worksheets

Modules

Microscope usage cell 1a-1d

Dimensions cell 2a-2c

Onion cell cell 3a-3b

Human cells cell 4a-4b

Diversity cell 5a-5c

.

Saturday, 30. October 2004 Mag. Peter Holub

"The cell".

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Microscope

At the beginning of our modules you will get a short overview concerning basic microscopeuse and the most important parts of a light-microscope

Eyepiece andOcular lens

Coarse focusCoarse adjustment

Fine focusFine adjustment

Micromanipulator

ApertureIris diaphragm

Objective lenses

Stage

Condenser

Body tube

Condenser screw

Eyepiece tube

Base

Arm

Note, that there are many different types of microscopes. Some of them get their light by a mirror under the condenser, others use lamps. Instead of the micromanipulator there can betwo clips to hold the specimen. The Fine and Coarse focus can be on one axe. They can lift eitherthe tube or the stage. There can also be two eye pieces and photo tubes or other divergences.Usually the ocular lense in the eye piece provides a 10X magnification. The objectives magnify4X, 10X and 40X. Sometimes there is also an objective which magnifies 100X, and which can onlybe used with a special oil to be placed between the specimen and the objective.

"The cell"

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Most of the objects you can observe with the microscope have to be prepared in a way that makes themtransparent because usually you can see the details only if the light passes through the specimen. It is also necessary to put most of the samples on a glass slide and into a liquid, mostly water, and to cover them with a very thin cover slip. This happens for optical reasons.

First you will use prepared specimens which are embedded in a special liquid.

1. Magnification 10X (ocular) x 4X (shortest objective)

Place the slide on the stage of your microscope with the cover slip side of the slide up. Move the slide till the object that you are going to examine is in the centre of the hole in the stage. Turn on the light sourceor focus the mirror to make sure the light goes through your sample. Make sure that the low power objective is the one in position. Lower the tube by turning the coarse focus until the objective is about one quarter inch from the slide, but be careful to keep the objective from touching the glass.

Cover slipSlide Prepared specimen

Use of the microscopeHandling a microscope correctly is not too difficult, but especially in the beginning it is very important to learn how to use it correctly to train your movements as if you weretraining for sports activities. Be certain to read every part of the sheet properly beforeyou start to work with the microscope!

"The cell"

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Use of the MicroscopeSecond Part

Attention!

Lower the head to the level of the stage, to be able to see the front of the objective as you are doing this.The objective is now in a position which is lower than the position it will occupy when it is finally in focus.Look through the eyepiece and slowly elevate by the coarse focus. Watch carefully through the ocular andstop turning the coarse adjustment as soon as the object is in focus. Now use the fine focus to get a betterview. It will probably be necessary to turn the fine adjustment wheel only part of a turn to focus the imageaccurately. You should now have a clear image of the object that you are examining.

Centering:

If it is not in the centre of the field of vision you will have to move the slide carefully, till it is centered. Since the image as you see it in the microscope is reversed, it will be necessary to move the slide in the oppositedirection from that which would appear necessary.

Aperture:

Adjust the aperture. If the opening in the diaphragm is too large, the light might be too bright to see anydetails. Turn the lever which controls the aperture until the diameter of the opening is correct. Observe the effect through the microscope while you are adjusting the diaphragm.

2. Magnification 10X (ocular) x 10X (medium objective)

Now change to the next higher magnification, but not 40X or 100x, and try to get a good view by slowlyturning the fine course just a little bit to one or the other side. Again improve your view with the diaphragm.

"The cell"

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Microscope useThird Part

3. Magnification 10X (ocular) x 40X (longest objective, if there are three)

After you have examined the object with the lower power objectives, lift the objectives and shift to thehigh-power objective and look at it under greater magnification.After the high-power objective is in position, lower the tube until the objective front lens almost touchesthe cover glass on, but be very careful to keep the objective from actually touching the glass.Lower the head to the level of the stage, to be able to see the front of the objective as you are doing this.

Attention:

Look through the eyepiece and slowly elevate by the coarse adjustment. Watch very carefully throughthe ocular and stop turning the coarse adjustment as soon as the object is in approximate focus.Bring the object into final accurate focus by using the fine adjustment.

Problem:

You may have a problem to find the chosen part of the object, as the diameter of the high power field ismuch less than the diameter of the low power field. So you might have to move the slide very carefully tocenter your specimen.Make any adjustments of the light intensity and of the iris diaphragm that is necessary to regulate theillumination so as to give the clearest possible image.

For professionals:

You should get accustomed to using thediaphragm and the fine focus with both hands at the same time to get a good view as soon as possible

After finishing your observations elevate the objective carefully, remove the slide and bring the low-powerobjective to the starting position above the hole in the stage. This helps to avoid damages.

"The cell"

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Dimensions 1

To find out more about the size of objects you see when using the microscopeyou can use a simple confetti disk:

1. Take a confetti disk. Try to draw four parallel lines, which divide the disk into 5 slices of almost equal width. Add a small symbol or geometric object. Measure the disk´sdiameter and have a look at it in the microscope using a 40X (objective 4X, ocular 10X) magnification :

How would you describe the relation between the size of the disk and the diameter of the field of vision? Write your answer down before you continue with part two!

2. Prepare a simple onion skin for the microscope. Look at the cells using a 40X magnification.Do you now know the length of the diameter of the field of vision?How many cells fit in it (one after the other)?How long approximately is one cell?You can use the following graph as an example:

have

10 x objective (8 cells across)

8 cells = ? mm 1 cell = ? mm

4X objective

Field of view = ? mm

8 cells across

*

"The cell"

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Try to find examples for other structures in a book, journal or using the internet.At which part of the table would your body length be placed correctly?

Most usual correlation between original size and magnification:

Objective Diameter Of Field Of View Magnification (10X Ocular)

4X 4,0 mm 40X

10X 2,0 mm 100X

40X 0,4 mm 400X

Dimensions of different living and not living structures

Length, Width, Diameter Micrometers Millimeters Millimeters

water molecule 0,000385 0,000000385 3,85 x 10-7

width of DNA 0,025 0,000025 2,5 x 10-5

AIDS-virus 0,1 0,0001 1 x 10-4

staphylococcus bacterium 1,0 0,001 1 x 10-3

human cheek cell nucleus 5,0 0,005 5 x 10-3

head of a human sperm 5,0 0,005 5 x 10-3

human red blood cell 7,5 0,0075 7,5 x 10-3

human hair 50 0,05 5 x 10-2

human cheek cell 60 0,06 6 x 10-2

pollen grain 100 0,1 1 x 10-1

grain of table salt (NaCl) 300 0,3 3 x 10-1

onionskin cell 400 0,4 4 x 10-1

confetti 5000 5 5 x 10 0

eucalyptus regnans 100000000 100000 1 x 105

planet earth (diameter) 1,3 x 1013 1,3 x 1010 1,3 x 1010

"The cell"

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Dimensions 3As you have learned, a human cheek cell is about 60 Micrometers in diameter.If it was 100000 times bigger, it would have the length of an average classroom (6 m).Try to imagine that your classroom is a cell. How big would the nucleus of an HIV-Virus, a bacterium or a water molecule be in this classroom?

Classroom

cheek-cell = 60 Micrometers X 100000 = 6000000 Micrometers = 6m

bacterium = 1 Micrometer X 100000 = ?

HIV virus = 0,1 Micrometers X 100000 = ?

width of DNA = 0,025 Micrometers X 100000 = ?

Find objects with a suitable size and place them in the classroom

Something special:.

100000000 bacteria could be on onesquare centimeter of skin,only 1 of 10000 takes the chance.

Measure your length from the top of your head down to your feet.If one of your cells on top of your head was as big as your classroom, how far away(in kilometers or meters) would a cell of your toes be.Imagine, how difficult it would be to find an object as small as a virus in this 3-dimensionalenormously big body!

6m

"The cell"

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Onion 1

The inner skin of onion leaves is very thin, so that it should be possible to look throughwith the light microscope. We will try to find out which details can be found.

1. Split an onion bulb into its almost transparent leaves

2. Isolate one of them

3. Remove the skin from the inner side of the leaf

4. Place a flat piece of this membrane in a drop of water on a microscope slide

5. Cover it with a cover glass

6. Be careful to keep the membrane from folding and wrinkling

7. Throw your remaining piece of onion into the trash can

8. Observe the slide using the 4X objective lens and the 10X ocular (magnification = 40X)

9. Now change to 10X and 10X (magnification = 100X) with the diaphragm wide open.Slowly reduce the light intensity by closing the diaphragm, and observe the image.

10. Again change, but now to 40X and 10X (magnification = 400X) with the diaphragm wide open.Be careful not to use the macrometer screw in order not to destroy the glass!

11. Which light intensity revealed the greatest detail?

You can see a lot of similarly shaped "rooms" in the membrane. Some may have formed folds so that they are not very transparent. Try to find a part whichshows a clear view similar to the picture on top of this page!

"The cell"

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Onion cell 2

Here you can see some of the details the microscope shows. The puzzle-like partsof the membrane are the cells, which contain a center called nucleus and a lot ofother biological units of which only few are visible at light microscope magnification.

These are some of the most important parts in a plant cell.Of course there are many differences depending on the type of plant and on their function.Think about the part of the onion these cells have been taken from!What could be the main function of these onion cells?

The cell wall allows the plantcells to be more rigid

This region, which bordersthe plant cell is called cell wall

The large, fluid-filledspace inside the onioncell is the sap vacuole.

The compact round part of the cell is the nucleus, containinghereditary information. It seems to be in the vacuole. But itis in the cytoplasm (In the picture below the transparentcytoplasm is in front and behind the nucleus)

1. Draw a group of 5 neighboring cells and try to label all the parts you see

2. Switch to magnification 400X and have a look at the details

The shimmering partis called cytoplasm. Itborders the cellmembrane which isso small that you cannot see it properly

"The cell"

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What is the shape of the individual cheek cells?Was the nucleus centrally or peripherally located?Why do you think, was it so easy to separate cheek cells?Did you find differences to the plant cell of the onion bulb? Describe them!Think about the function of these cells: Do you think that they have a long or a short life?

Place a drop of water on a microscope slide. Gently scrape the inner surface of your cheek with the flat part of a toothpick. Transfer the cells from the toothpick to water and cover the slide with acover slip. Place one edge of the cover slip next to one edge of the smear,then lower it slowly into the smear. By lowering it slowly you will avoid forming air bubbles.Place the cheek smear slide onto the stage of your microscope. Focus first with the lowestmagnification. Scan for some individual cells and look for cells that are separated from the otherand not folded at the edges. Change to a higher magnification. If you can see a small, darkstructure which looks like a small, round egg or circle, you found the nucleus. Draw one of thesecells in your notebook, including details, like the shape of the cell and nucleus and the structureof the surrounding cytoplasm. Finally, move on to the high-power lens and draw the cell again inthe appropriate way.

The cell membrane which isnot bordered by a cell walllike the onion cell

The nucleus

The nuclear membrane

Human cells 1Animal and human cells are different to plant cells. In addition, most of them do not show very exact structures. One human cell type can farely easyly be observedand should also show some details: Squamosal epithelial cells from the cheek.

"The cell"

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What do you think are the light red circles?What could be the bigger objects with the violet structures be?What are the violet structures?Think about the difference! If these were living structures, could you suspect differencesconcerning their life-spans? Write down any reason you can imagine!

Place small drop of methylene blue or Wright`s reagens on the center of the slide. Leave it therefor one minute, then carefully rinse the colored slide with distilled water. Now you can watch theslide with the microscope. Start with the lowest magnification, where you should see somethinglike this:

If you see lots of circles in multiple layers, switch to the borders of the slide, where the bloodlooks more transparent. Then take magnification 100X. You will get a picture like this one:

If you only see light red circles, try to find a place where also violet-centered, bigger objects can be seen. Now change to magnification 400X. You should see something similar to the lastimage on this page:

Be sure to make drawings of each magnification and try to change the contrast at themicroscope aperture. You will get a better view especially at the last magnification.

Human cells 2If you want to have a look at another type of human cells that can easily be observed,you need the help of a doctor. She or he will get some blood from the tip of your finger and put it on a microscope slide, marked with your name.

"The cell"

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First of all you need some pond water which should be taken from the surface using a self-madeplankton net.

Primitive self-made plankton net

The plankton should be taken from the surface by plugging some seconds through the water. Afterwards youcan place the water including the plankton in a capped glass.This glass should be labeled: name and location of the water source, date and name of the collector.It may also be important to add a description of the weather (rainy, sunny...) and to protocol the time of day.The probe should be analyzed under the microscope as soon as possible. If this cannot be managed, youshould add some clear water and leave the glass open at room temperature.The later you watch your result, the more changes within the population of microorganisms can be expected.So one possibility might be to watch the same probe after 1 2, 6.....days to get an overview of the dynamic changes.

During the next lessons you will learn how to identify different species with the microscope and how towatch them properly to see details.

part of a plastic bottle inside the stocking to catch the planktonabout twenty layers of a broad sticky tape

or any other stiff ring (diameter about 5 inches)

Instead of the stiff tape and the wire you can also use the ring of an old colander or an oldbadminton racket!

thick wire, twisted to fix the stocking on the tape and to form the holder

nylon stocking (folded to include the plastic tape)

Diversity 1 - Collecting of PlanktonA drop of pond water can show you more living things than any lexicon if you observe it using the microscope. In the "diversity lessons" dealing with single-cellorganisms you will learn how to find, watch and identify protists. In the beginning it does not matter if they were animals or plants, later on you will learn that some of them can be both!!!

"The cell"

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First of all you have to put a drop of water containing the protists on a microscope slide and cover it witha cover glass. Then you can start watching the probe using the microscope.

If you want to watch the protists at "slow motion" you can use some quince seed. You put 5 or 6 of theminto a little glass of water and leave them there for some hours. This makes the water get a structure like liquid honey. If you add a drop of this jelly to the drop of water which contains the plankton, the organisms can hardly move because of the now very high viscosity of the liquid.

Euplotes and Stylonychia, two common ciliates Vorticella, a Ciliate that is connectedwith the ground (plants, stones.....)

Chlamydomonas and Scenedesmus are very commongreen algae. Scenedesmus consists of 4 single cells. Thisis one of nature`s the first trials to form complex organisms

Closterium and Micrasteriasare conjugating green algae.

Diversity 2 - Different species 1The following worksheets contain pictures of some of the most frequentprotists in ponds, lakes or small rivers. If the water is too clear, there are fewer species.If the water is badly polluted, there are other populations.You can find some of them when using magnification 40 x, others become visible using m 100x. In order to see details you need stronger magnification, but this difficult because some of them are very fast.

"The cell"

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Diversity 3 - Different species 2On this sheet you can find some other protists. Most species have not yetbeen described by anyone, but we know there have to be many unknown ones. Therefore only the most common of them have got a place in our lessons.

If you find other species during your microscope work, ask your teacher or try to find their names in a bookor using the internet. Many tiny ones seem to be protists, but they are bacteria. As they have noproper cells, they will not be discussed during this course.

Euglena, in Austria called"green beautiful eye" can switch fromanimal to plant. Once showing a light redeye and chasing other protists, then gettingmore and more green and performingphotosynthesis. Because it moves usingits flagellum, it is member of the so calledflagellates.

This is a Heliozoon (helios= sun).The radial thin parts of its body canchange its shape (in Austria we call suchspecies "morphing animals") and goright through small holes in the skeletonof this protist.

A diatom, which belongs to the unicellular algae.The stripes on its skeleton are typical andcan be parallel or radial. They have got askeleton consisting of two parts like the upperand lower part of a box.

Ceratium has got horns on the skeleton.It also moves using a flagellum. Thatmakes it distantly related to Euglena.