Biology Lab-Mr.Willets
Microscope Lab #1
The microscope is the basic tool of the biologist. By means of lenses, the microscope magnifies objects and organisms too small to be seen by the unaided eye.
Two principles involved in using the microscope are:
a) magnification-the enlargement of an image
b) resolution-the clearness of an enlarged image
As magnification increases, the resolution or clearness of the image decreases. Also, as the microscope magnifies more, we see a smaller portion of the object.
PARTS OF THE MICROSCOPE
The microscopes we usually use are called compound light microscopes. Compound means they have more than one lens. Light means they use light rays. Therefore, we need only our eyes to use it.
Electron microscopes use beams of electrons instead of light. In order to see an image with an electron microscope, the beam of electrons must hit a cathode ray tube (CRT) which is basically what your TV screen or computer monitor is.
As you read about each part and its function, examine your scope and find the part and then label the diagram.
The parts of the scope can be divided into three groups: the optical parts, the mechanical parts and the illumination parts.
OPTICAL PARTS
a) An eyepiece or ocular lens- this is the combination of lenses you look through. On our scopes, the eyepiece magnifies 10 times (10X). The eyepiece assembly can be rotated to make it easier for you to look through the lens. Do not play with this feature. It will break.
b) Objective lenses-The objective lenses are located at the lower end of the scope. These lenses are placed very close to the object (hence the name) being magnified. Your scopes have three objective lenses. The one pointing straight down is the one in use at any given time. The scanning objective lens is the smallest of the three. It has red printing on it. Its magnification is 4X. The low power objective lens is mid sized, has a yellow stripe and magnifies 10X. The high power objective lens is the longest, has a blue stripe and magnifies 40X. The scanning objective lens should always be in place when you leave the lab.
NOTE- To calculate total magnification of the scope, simply multiply the magnifications of the lenses being used. For example, the eyepiece is 10X and the objective lens were 40X, the total magnification would be:
10 times 40 = 400X. Your eyepiece is always 10X. It is the objective lens that you can change. Your total magnification is calculated by multiplying 10 times the power of the objective lens being used at the time.
*Answer Questions 1-9 on the Data Sheet #Ques1-9
a) A stand that is made of a heavy base and a supporting an arm . These are the parts you should use when carrying the scope
b) A body tube which holds the lenses at either end. In older scopes, this part was actually shaped like a tube, hence the name. Your scope has a "bent tube" to make it easier to use. A mirror in the fat part of the tube changes the direction of the light. The top part of the tube holds the eyepiece and as mentioned earlier, this can be rotated to move the eyepiece into a more convenient position for you.
c) A nosepiece where the three objective lenses are attached. The nosepiece can be rotated to bring any of the objective lens into position. Rotate the nosepiece to bring the low power lens into place. (a lens is "in place" when it is positioned straight up and down). You will feel and hear the lens "click" into place. Rotate the nosepiece to put the high power lens into place. Make sure that whichever lens you are using is locked in position (listen for the "click"). Put the scanning lens back into position.
d) A horizontal stage or platform. Light passes through a hole in the stage. A slide is positioned on the stage with the specimen over the hole.
e) Focusing knobs- The knobs move the objective lens closer to the specimen on the stage. They are used to focus the image. They are located on both sides of the scope but only one side has to be used.
1) The larger knob is the coarse adjustment. It changes the position of the stage quickly. This is used to bring the image into general focus. The coarse adjustment is used only with scanning or low power. If it is used with high power, there is the danger that the lens will hit the slide and damage both. Try using the coarse adjustment to move the stage up and down.
2) The smaller knob is the fine adjustment. It changes the position of the stage very slowly such that you might not notice it moving. It enables you to make slight changes and focus as clearly as possible. You only use this after you have the specimen in view. It is only turned a half turn or so in either direction.
f) Metal clips to hold the slide on the stage. Please do not play with them.
#Answer Questions 10-12 on the Data Sheet #ques10-12
a) A substage light sends light through the hole in the stage and through the specimen on the slide. The specimen must be thin enough to let sufficient light pass through. Specimens that are too thick to be used are sliced with a special machine called a microtome. The power switch is on the base near the power cord.
b) A diaphragm which regulates the amount of light sent through the hole in the stage. It is a disc with different size holes in it. Rotating the disc (which "clicks" into place) will allow you to regulate the amount of light you use. The edge of the disc sticks out near the front of the stage. Look under the stage to see which size hole is in place. Do not lift the scope- simply look under the stage. Rotate the diaphragm so that the largest hole is in position. Look at the part of the diaphragm that sticks out beyond the edge of the stage. What number tells you that the largest opening is being used? This position gives you the most light.
**Answer Questions 13-14 on the Data Sheet #ques13-14
Make sure your scope is plugged in. Turn on the light. Look through the eyepiece. What you see is a circle of light called the "field of view" or just the field. There is a "pointer" that is visible in the field. Its use will be discussed in a later lab.
When using the scope, it is best to keep both eyes open. This will seem annoying at first but if you continually keep one eye closed, you will get a headache. Most right-handed people use their left eye to look through the scope - lefties use their right eye.
Get a slide of "Housefly Wings" from the front desk. Make sure that the scanning objective lens is in place and the diaphragm is set for the most light (#5). Place the slide on the stage with the specimen over the hole.
Use the coarse adjustment to raise the stage all the way up. The slide will not hit the lens. Look through the eyepiece as you lower the stage. When the wing comes into view, focus as best you can using the coarse adjustment and then use the fine adjustment to get the clearest image. Remember, the fine adjustment is turned just a little. Try different diaphragm settings to get the best lighting- not too bright nor too dim.
While looking through the eyepiece, move the slide to the right. In what direction does the image move? Move the slide away from you. In what direction does the image move? This can be annoying but you will get used to it.
Take note of what part of the wing is in the middle of the field of view. Now put the low power objective lens into position. Bring the image into clear focus. You will notice two things- 1) you do not see as much of the wing as before- only the part that was in the center of the field. 2) the part that you do see looks bigger.
##Answer Questions 15-17 on the Data Sheet #ques15-17
TO USE HIGH POWER- FOLLOW THIS PROCEDURE
1) Focus on the housefly wings using low power to get the clearest image
2) The part of the wing that you are going to see using high power is in the center of the field.
3) Do not move the slide- Do not touch the focusing knobs!! Rotate the nosepiece so that the high power lens clicks into place. It will look like the lens might hit the slide but it shouldn't.
4) Observe through the eyepiece. Use the fine adjustment to get the clearest image. Do not use the coarse adjustment while the high power lens is in place.
5) Adjust the diaphragm to get the best lighting.
+Answer Questions 18-19 on the data sheet. #ques18-19
Slides like the one of the housefly wings are permanent slides. The specimen is preserved and glued to a slide with a smaller piece of glass (cover glass) glued on top.
Temporary slides can be made in class. These are called "wet mounts" because we use water to prepare them. We will make a wet mount using a piece of newspaper that contains a lower case letter "e".
In the container marked "Slide Materials" you will find a box of clean slides, a box of cover glasses, a dropper bottle with water in it, a pair of scissors and a piece of newspaper. At the end of the lab, all these materials should be put back into this container.
1) Cut a word from a classified ad that contains a lower case "e". It should be in the smallest print on the page.
2) Place 2-3 drops of water in the middle of a clean dry slide.
3) Place the paper with the letter "e" in the water. Use forceps (tweezers) to hold the paper while you do this.
4) Add a cover glass- methods to do this will be discussed in class. If the cover glass is put on sloppily you will get air bubbles which can get in the way of seeing the specimen.
Put the scanning lens in place. Place the slide you just made on the stage and center the letter"e" over the hole in the stage. Follow the directions from before to get a clear image. Observe the ink and the paper fibers.
Change to the low power lens. Can you see the entire letter "e"?
Following the directions from before, examine the letter using high power. How much of the letter do you see now? What part of the letter do you see now? Which image was clearest- using scanning, low or high power? Try all three again to compare.
Answer Questions 20-22 on the Data Sheet #ques20-22
Clean the slide you just made. Carefully remove the cover glass and put it into the jar marked "Used Cover Glasses" Remove the piece of newspaper and rinse and dry the slide. Put the slide back into its case and put everything back into the container the way you found it.
Diagram to be labelled.
Biology Lab-Microscope Lab #1
Data Sheet
2 Define resolution-
3) What is the relationship between magnification and resolution?
4) What is the magnification of the eyepiece on your scope?
5) What is the magnification of the scanning objective on your scope?
What is the magnification of the low power objective on your scope?
What is the magnification of the high power objective on your scope?
6) What is the total magnification when using the scanning objective lens?.
What is the total magnification when using the low power objective?.
What is the total magnification when using the high power objective?_
7) What color is the print on the scanning lens?.
What color is the print on the low power objective lens?
What color is the print on the high power objective?
8) Which objective lens is longest? __________________ Which is shortest? ________________
9) Fill in the blanks in this table-
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* Return to the directions #*Return
10) Which focusing knob moves stage quickly? .
11) The coarse adjustment is used only with which 2 objective lens? ..
12) What might happen if you used the coarse adjustment with the high power objective lens in place?
# Return to the directions ##Return
13) What do you think the word "substage" means in the term "substage light"?
14) Which number on the diaphragm indicates the dimmest light setting? .
**Return the directions #**Return
15) What is the name of the circle of light seen through the scope?
16) In what direction does the image move when the slide is moved to the right?.
In what direction does the image move when the slide is moved away from you?.
What general statement can you make about how the image moves compared to how you move the slide?
17) Draw a circle to represent the field of view using low power. Inside of it, draw the wing as seen through the scope. Fill in the total magnification.
##Return the directions ###Return
18) Before switching to high power, you should place the part of the slide you want to see in the ____________________ of the field.
19) High power magnifies more than low power. With which power do you see a larger portion of the specimen? _______________________________ In your diagram above left, circle the part of the wing that was seen when you switched to high power. Draw a circle below to represent the high power field and draw the part of the wing as seen using high power. Fill in the total magnification.
+Return to the directions #+Return
20) If you put the cover glass on sloppily, what might happen that could make it more difficult to see the specimen?
21) Draw a circle below to represent the low power field. Inside of it, draw the letter "e" as seen using low power. Just draw the basic outline without the paper fibers. Fill in the total magnification.
Draw another circle to represent the high power field. Draw the part of the letter "e" seen using high power. Again, just the basic outline- no details. Fill in the total magnification.
22) Explain this statement-"With high power, you see more of less".