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Module " The cell "
Biology (Age 11 - 14 years)
It is t he goal of this module to introduce the cell step by step in order to avoid misconceptions.I have llustrated 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 high er scientific level. The more difficult terms are introduced gradually . In doing so it is particularly planned to address many different senses.
The pure ly lexical information is kept short, in order to on the one hand make pupils remember the facts more easily and on the other hand also to avoid too much content. Y oung 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 mak ing 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
Dimensions
Onion cell
Human cells
Diversity cell 1a-1d cell 2a-2c cell 3a-3b cell 4a-4b cell 5a-5c
Saturday, 30. October 2004 Mag. Peter Holub

Eyepiece tube
Body tube
Objective lenses
Stage
Condenser
Base
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Microscope
At the beginning of our modules you will get a short overview concerning basic microscope use and the most important parts of a light-microscope
Eyepiece and
Ocular lens
Coarse focus
Coarse adjustment
Fine focus
Fine adjustment
Arm
Micromanipulator
Aperture
Iris diaphragm
Condenser screw
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 be two clips to hold the specimen. The Fine and Coarse focus can be on one axe. They can lift either the 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 magnify
4X, 10X and 40X. Sometimes there is also an objective which magnifies 100X, and which can only be used with a special oil to be placed between the specimen and the objective.

Use of the m icroscope
Handling 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 were training for sports activities. Be certain to read every part of the sheet properly before you start to work with the microscope!
Most of the objects you can observe with the microscope have to be prepared in a way that makes them transparent b ecause 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 in to a liquid, mostly water, and to cover them with a very thin cover slip. This happens for optical reasons.
Slide Cover slip Prepared specimen
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 source or 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.

Use of the M icroscope
Second 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 and stop turning the coarse adjustment as soon as the object is in focus. Now use the fine focus to get a better view. It will probably be necessary to turn the fine adjustment wheel only part of a turn to focus the image accurately. 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 vi sion 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 opposite direction 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 any details. 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 slowly turning the fine course just a little bit to one or the other side. Again improve your view with the diaphragm.

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Microscope use
Third 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 the high-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 touches the 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 through the 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 is much less than the diameter of the low power field. So you might have to move the slide very carefully to center your specimen.
Make any adjustments of the light intensity and of the iris diaphragm that is necessary to regulate the illumination so as to give the clearest possible image.
For professionals:
You should get accustomed to us ing the diaphragm 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-power objective to the start ing position above the hole in the stage. This helps to avoid damages.

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Dimensions 1
To find out more about the size of objects you see when using the microscope you 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´s diameter 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:
4X objective
8 cells across
10 x objective (8 cells across)
Field of view = ? mm
8 cells = ? mm
1 cell = ? mm
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Most usual correlation between original size and magnification:
Objective Diameter Of Field Of View Magnification (10X Ocular)
4X
10X
40X
4,0 mm
2,0 mm
0,4 mm
40X
100X
400X
Dimensions of different living and not living structures
Length, Width, Diameter Micrometers water molecule 0,000385 width of DNA
AIDS-virus staphylococcus bacterium human cheek cell nucleus head of a human sperm human red blood cell human hair human cheek cell pollen grain grain of table salt (NaCl) onionskin cell confetti eucalyptus regnans planet earth (diameter)
0,025
0,1
1,0
5,0
5,0
7,5
50
60
100
300
400
5000
100000000
1,3 x 10
13
Millimeters
0,000000385
0,000025
0,0001
0,001
0,005
0,005
0,0075
0,05
0,06
0,1
0,3
0,4
5
100000
1,3 x 10
10
Millimeters
3,85 x 10
-7
2,5 x 10
-5
1 x 10
-4
1 x 10
-3
5 x 10
-3
5 x 10
-3
7,5 x 10
-3
5 x 10
-2
6 x 10
-2
1 x 10
-1
3 x 10
-1
4 x 10
-1
5 x 10
0
1 x 10
5
1,3 x 10
10
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?

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Dimensions 3
As 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 i s a cell. How big would the nucleus of an HIV-Virus, a bacterium or a water molecule be in this classroom?
6m
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 one square 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-dimensional enormous ly big body!

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Onion 1
The inner skin of onion leaves is very thin, so that it should be possible to look through with 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 microscop e 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 in to 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 similar ly shaped "rooms" in the membrane. Some may have formed folds so that they are not very transparent. Try to find a part which shows a clear view similar to the picture on top of this page!

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Onion cell 2
Here you can see some of the details the microscope shows. The puzzle like parts of the membrane are the cells, which contain a center called nucleus and a lot of other biological units of which only few are visible at light microscop e magnification.
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
This region, which borders the plant cell is called cell wall
The large, fluid-filled space inside the onion cell is the sap vacuole.
The compact round part of the cell is the nucleus, containing hereditary information. It seems to be in the vacuole. But it is in the cytoplasm (In the picture below the transparent cytoplasm is in front and behind the nucleus)
The cell wall allows the plant cells to be more rigid
The shimmering part is called cytoplasm. It borders the cell membrane which is so small that you cannot see it properly
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 !
Wh at could be the main function of these onion cells?

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Human cells 1
Animal 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 easy ly be observe d and should also show some details: Squamosal epithelial cells from the cheek.
Place a drop of water on a microscop e 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 a cover 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 lowest magnification. Scan for some individual cells and look for cells that are separated from the other and not folded at the edges. Change to a higher magnification. If you can see a small, dark structure which looks like a small, round egg or circle, you found the nucleus. Draw one of these cells in your notebook, including details, like the shape of the cell and nucleus and the structure of the surrounding cytoplasm. Finally, move on to the high-power lens and draw the cell again in the appropriate way.
The nucleus
The cell membrane which is not bordered by a cell wall like the onion cell
The nuclear membrane
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?

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Human cells 2
If 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 microscop e slide, marked with your name.
Place small drop of methylene blue or Wright`s reagens on the center of the slide. L eave it there for one minute, then carefully rinse the colored slide with distilled water. Now you can watch the slide with the microscope. Start with the lowest magnification, where you should see something like this:
If you see lots of circles in multiple layers, switch to the borders of the slide, where the blood looks 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 last image on this page:
Be sure to make drawings of each magnification and try to change the contrast at the microscop e aperture. You will get a better view especially at the last magnification.
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 wer e living structures, could you suspect differences concerning their life-span s ? Write down any reason you can imagine!

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Diversity 1 - Collecting of Plankton
A 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 cell organisms you will learn how to find, watch and identify protists. In the beginning it does not matter if they were animals or plants, l ater on you will learn that some of them can be both!!!
First of all you need some pond water which should be taken from the surface using a self made plankton net.
Primitive self
made plankton net thick wire, twisted to fix the stocking on the tape and to form the holder nylon stocking (folded to include the plastic tape) part of a plastic bottle inside the stocking to catch the plankton about 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 old badminton racket!
The plankton should be taken from the surface by plugging some seconds through the water. Afterwards you can 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, you should 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 o f the dynamic changes.
During the next lessons you will learn how to identify different species with the microscope and how to watch them properly to see details.

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Diversity 2 - Different species 1
The following worksheets contain pictures of some of the most frequent protists in ponds, lakes or small rivers. If the water is too clear , there are fewer species.
If the water is bad ly polluted, there are other populations.
Yo u 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.
First of all you have to put a drop of water containing the protists on a microscop e slide and cover it with a cover glass. Then you can start watching the probe using the microscope.
Chlamydomonas and Scenedesmus are very common green algae. Scenedesmus consists of 4 single cells. This is one of nature`s the first trials to form complex organisms
Closterium and Micrasterias are conjugating green algae.
Euplotes and Stylonychia, two common ciliates Vorticella, a Ciliate that is connected with the ground (plants, stones.....)
If you want to watch the protists at "slow motion" you can use some quince seed. You put 5 or 6 of them in to 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 , t he organisms can hardly move because of the now very high viscosity of the liquid.

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Diversity 3 - Different species 2
On this sheet you can find some other protists. Most species have not yet been 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.
This is a Heliozoon (helios= sun).
The radial thin parts of its body can change its shape ( in Austria we call such species "morphing animals") and go right through small holes in the skeleton of this protist.
A diatom, which belongs to the unicellular algae.
The stripes on its skeleton are typical and can be parallel or radial. They have got a skeleton consisting of two parts like the upper and lower part of a box.
Euglena, in Austria called
"green beautiful eye" can switch from animal to plant. Once showing a light red eye and chasing other protists, then getting more and more green and performing photosynthesis. Because it moves using its flagellum, it is member of the so called flagellates.
Ceratium has got horns on the skeleton.
It also moves using a flagellum. That makes it distantly related to Euglena.
If you find other species during your microscop e work, ask your teacher or try to find their names in a book or using the i nternet. Many tiny ones seem to be protists, but they are bacteria. As they have no proper cells, they will not be discussed during this course.