Download IGCSE Microscope lab with cells 2016

Microscope and Cell Observation Lab
PURPOSE: To learn how to use the microscope, and to observe some plant and animal cells.
Rules for Biological Drawings
1. Draw what you see, not what you think should be there.
2. A lead pencil, preferably a 2H, is to be used for drawings, titles, and labels.
3. Drawings (or diagrams) should be as simple as possible with clean cut lines (do not sketch) showing what has
been observed. All drawings should be done on unlined (blank) paper and should be also neatly labelled.
4. Drawings must be large enough to show all parts without crowding. The greater the number of parts to be
included, the larger the drawing should be. Drawings must be about half a page in size.
5. Keep your drawing to the left of the center of the page. (Save the right-hand side of the page for labels)
6. All labels should be in a column to the right of the drawing and printed. Lines to the labelled parts should be
drawn with a ruler and parallel to each other. The lettering of the words should be horizontal.
7. Use a ruler for label lines.
8. Do not shade your drawing. If you wish to indicate a darker area use dots(stipple).
9. Indicate the thickness of a plant cell wall by using 2 lines.
10. Most plant and animal tissues are made up of individual cells. When one representative cell of such a tissue
is to be drawn, make sure you include the cell boundaries of the other cells that border it. This will indicate the
general appearance of the tissue without the necessity of drawing every cell.
11. All drawings are titled. The printed and underlined title appears immediately above the drawing, against the
left-hand margin. The magnification of the object drawn follows the title and is in parentheses. Example: Blood
Cell (300X).
12. Name and date are printed in the top right hand corner.
INTRODUCTION:
Because biological objects can be very small, a microscope is often used to view them. Light
microscopes use light rays that are magnified and focused by means of lenses. The compound light
microscope is used for examining small or thinly sliced sections of objects under magnification.
Illumination is from below, and the light passes through clear sections but does not pass through
opaque sections. To improve contrast, the scientist uses stains or dyes that bind to cellular structures
and absorb light.
THE COMPOUND LIGHT MICROSCOPE
Total Magnification
Total magnification = magnification of the ocular lens (eyepiece) X magnification of the objective lens
Record the magnification powers of your microscope, using a table like this.
Eyepiece magnifying power:
Low objective power:
Medium-power objective power:
High-power objective power:
Total magnification:
Total magnification:
Total magnification:
Focusing the Microscope
Lowest Power
1.
2.
3.
4.
Turn the nosepiece so that the lowest power lens is in straight alignment over the stage.
Always begin focusing with the lowest power objective lens.
With the coarse-adjustment knob, lower the stage until it stops.
Cut out a word from a newspaper. Place it on a slide or use a prepared slide and stabilize it
with the clips.
5. Again, be sure that the lowest power objective is in place. Then, as you look from the side,
decrease the distance between the stage and the tip of the objective lens until the lens comes to
an automatic stop or is no closer than 3 mm above the slide.
6. While looking into the eyepiece, rotate the diaphragm (or diaphragm lever) to give the
maximum amount of light.
7. Slowly increase the distance between the stage and the objective lens, using the coarseadjustment knob, until the object comes into view, or focus.
8. Once the object is seen, you may need to adjust the amount of light. To increase or decrease
the contrast, rotate the diaphragm slightly.
9. Use the fine-adjustment knob to sharpen the focus if necessary.
10. Practice having both eyes open when looking through the eyepieces, as it greatly reduces
eyestrain.
Exercise 1
1. Draw the slide’s “field of view” as it appears when you look through the eyepieces on the
lowest power. Remember to draw this on separate paper. Make the
2. Move the slide to the right. Which way does the image appear to move? _______________________
This phenomenon is known as inversion.
Higher Powers
Compound microscopes are parfocal; once the object is in focus with lowest power, it should also be
almost in focus with the higher power.
1. Bring the object into focus under the lowest power by following the instructions in the
previous section.
2. Make sure that the image on the slide is centered in the field of view of the lowest objective.
3. Move to the next higher objective (low power, 10x) by turning the nosepiece until you hear or
feel it click into place. Do not change the focus; parfocal microscope objectives will not hit
normal slides when changing the focus if the lowest objective is initially in focus.
4. If any adjustment is needed use only the fine-adjustment knob. Always use only the fineadjustment knob with higher powers.
Repeat steps 2-4 with the 40x power objective lens.
5. When you have finished your observations of this slide (or any slide), rotate the nosepiece
until the lowest power objective clicks into place, and then remove the slide.
Exercise 2
1. Choose 1 other prepared slide and make small drawings of what you observe using low,
medium, and high power objective lenses. Each on a different side of the paper.
Microscopic Observations
When a specimen must be prepared for observation, the object should always be viewed as a wet
mount. A wet mount is prepared by placing a drop of liquid on a slide or, if the material is dry, by
placing it directly on the slide and adding a drop of water or stain. The mount is then covered with a
cover slip.
Exercise 3:
PLANT CELLS
1. With a knife or your fingers, strip a thin, transparent layer of
cells from a piece of onion.
2. Place it gently on a clean, dry slide.
3. Add a drop of methylene blue stain and cover with a cover slip.
4. Observe under the microscope and draw what you see. Be sure to
label your drawing with what it is, and what power you were using.
5. Locate the cell wall. Is a nucleus visible?
Exercise 4:
HUMAN EPITHELIAL CELLS
Epithelial cells cover the body's surface and line its cavities.
1.
2.
3.
4.
5.
Obtain toothpick.
Gently scrape the inside of your cheek with the toothpick.
Place the scrapings on a clean, dry slide.
Add a drop of very weak methylene blue stain and cover with a cover slip.
Observe under the microscope, using the directions for focusing given before. Start with the
low power objective to find some cells, then observe under both low and high power.
6. Locate the cell membrane, the cytoplasm, and the nucleus.
7. Make a drawing of what you see. Be sure to label the drawing with what it is, and what power
you were using when you made your drawing.
8. Record some obvious differences between the human cheek cells and the onion cells.
9. Record any similarities between the two types of cells.
10. If there is time you may practice using other plant leaves provided.
To finish the lab each day, please put your microscope back in order by:
1. Putting the lowest power objective towards the stage.
2. Taking out any slide that may still be on the stage
3. Turning off the light
4. Putting the microscope cover back on.