History of microscopy
Introduction Structure of microscope Care of microscope Use of microscope Magnification
As we already know cells are microscopic. What does this mean? Scientists were able to see and study the cells because of a discovery of microscopes. Initially botanist and zoologist were only able to study, describe, draw and label only the external structure of macroscopic organism. This is referred to as the macroscopic view. What are macroscopic organisms?
Microscopic: refers to organisms that are so small that they are not visible to the naked. Macroscopic: refers to organisms that are visible to the naked eye.
Robert Hooke, an English scientists looked at cork tissue under a very simple microscope as shown below. He observed these cells in 1665. As shown in the insert he saw many box like compartments. He called these compartments cells.
The cork tissue comes from the cork plant. However all he managed to see were the cell walls of the cells. The cork cells were dead, therefore there was nothing inside these cells.
He was a Dutch scientist. He observed the bacteria under a simple microscope in 1674 as shown below ( little animals in rain water).
Three scientist, Oken in 1805, Lamarck in 1809 and Dutrochet in 1824, independently stated that plants and animals were made up of cells. In 1838 Mathias Schleidan, a German scientist, was first to regard the cell as a structural unit of plants. Then in 1839, Theodor Schwann was the first to regard the cell as the structural unit of animals.
A German scientist, Purkinje, was the first to use the term protoplasm to describe the living contents of the cell. This was in 1839. Then 1859, another German scientist, Schultz, was the first to describe the protoplasm as the physical basis of life. Finally, Rudolf Virchow, put forward the idea that new cells formed when existing cells divided. These scientist were able to make these discoveries as a result of advancement in the development of the microscope.
These ideas mentioned in the previous two slides developed into what is known as the cell theory. According to this theory: 1. Every living organism is made up of cells (cells are the basic unit of life). 2. Every living cell comes from another. 3. All cells are basically similar. 4. Cells consist of a substance called protoplasm.
Compound light microscope (use 2 lenses) With your microscope at school you are able to see objects magnified 600 times, by using the 40X objective and 15X ocular lens. The nucleus, cell membrane, cytoplasm and chloroplast were observed and named using the light microscope. However the details of these structures were not visible because the microscope is not powerful enough.
However in the 1930s a more powerful microscope was invented by Zworykin. This was called the electron microscope There are 2 types of electron microscopes. They are the scanning electron microscope (SEM) and the transmission electron microscope (TEM) The SEM is used to scan and view the surface of objects. The TEM is used to see inside the objects by allowing light to pass through them.
With the electron microscope we are able to view objects 50 000 to 100 000 times. The image is clear and not blurred. They are able to provide such good images because they use electron beams instead of light
1. Base: supports the microscope. Always place your hand under the base when transporting the microscope. 2. Mirror: provides source of natural light. The mirror must be focused to reflect light. 3. Illuminator/lamp: it provides an electric source of light, it is much easier to use. 4. The condenser: it is found below the stage. Its function is to concentrate the light through the slide and specimen. 5. Iris diaphragm: this is an opening in the condenser, it controls the amount of light falling on the specimen.
6. Stage: this is the platform on which the slide is placed. 7. Stage/slide clips: these are metal clips that are used to hold the slide in position so that is does not move around when it is being focused. 8. Mechanical stage: this is found in only some microscopes, it allows easy movement of the slide.
9. Objectives: these are a combination of lenses used to magnify the specimen. There are 3 different types of objectives. 10. 4X objectives: this is the short objectives. It magnifies the objectives 4X 11. 10X objectives: this is the medium objective. It magnifies the specimen 10X. 12. 40X objective: this is the long objective. It magnifies the specimen 40X 13. The revolving nose piece: the objectives are attached to this nose piece. Ensures the objective is in position when viewing the specimen.
14. Body tube: the eye piece and objectives are found on it. It also links the eye piece and objectives. In other words it links and supports the optical parts. 15. Coarse adjustment screw: used to make adjustments to focus the image. It moves the body tube up and down quickly, it provides quick focus. Used mainly at low magnification.
16. Fine adjustment screw: is used to make fine adjustments to focus the image. Used with higher magnification. Prevents damage to slide if any sudden movements are made during focusing. 17. Eye piece/ocular: combination of lenses that are used to magnify the specimen. There are 3 oculars 5X, 10X and 15X
Use your notes and diagram of the microscope to label the diagram and provide the functions of the following parts: 1. A 2. C 3. E 4. I 5. M
A. Eyepiece B. Coarse adjustment screw C. Body tube D. Fine adjustment screw E. Nose piece F. Medium objective/10x G. Arm H. Long objective/40x I. Stage J. clip
K. Diaphragm L. Base M. Light source N. Short objective/4x 1. Eye piece-magnifies image 2. Body tube- supports and links optical parts 3. Nose piece- attachment of objectives 4. Stage- platform on which slide is place 5. Light source- provides electrical light
Follow these guidelines when handling a microscope: 1. Transport the microscope by placing one hand under the base and the other holding the arm, 2. Work one hand width away from the edge of the work bench. 3. Use only soft tissue to clean the lens. 4. Always ask for help if you are unsure of anything
Setting the light and condenser 1. Open the diaphragm fully. 2. Look at the mirror. Notice that it has two surfaces: a plane one and a concave one. If the microscope has a built in condenser then have the plane surface of the mirror facing up. If the there is no condenser then the concave surface must face up. 3. Adjust the mirror so that it faces a source of natural light. E.g. A window, open door.
Setting the light and condenser 4. Select the lowest power objective by turning the nose piece until you hear or feel the object click into position. 5. Place a sharp pencil on the mirror and focus until you obtain a sharp image of the pencil tip.
Focusing at low magnification 1. Place the slide on the stage. 2. Secure it using the clips. 3. Look through the eyepiece and slowly turn the coarse adjustment screw to focus the specimen. 4. Slowly turn the fine power objective to focus a clearer image of the specimen. 5. The slide may need to be moved to ensure the part of the specimen under examination is what you are seeing.
Focusing at higher magnification 1. Move the next objective into position by carefully moving the nose piece until the objective clicks into position. 2. If the specimen is not clearly visible then use the fine adjustment screw to obtain a clearer image. 3. You may repeat the process using the next high power object if more detail is required.
Changing the eyepiece 1. The magnification can be increased by using higher power eyepieces. 2. Simply remove the existing eyepiece and replace it with one that has higher magnification power.
Record what you see 1. Draw a diagram of what you see. 2. Draw and label exactly what you see, even if many aspects are missing. 3. In many cases you do not have to draw the entire image, only a portion of it. 4. Do not forget to indicate the scale of your drawing. For example if you used the medium power objective and the 5X eyepiece then your scale is 150 times(5x10) 5. Use a sharp pencil.
1. Remove the slide. 2. The 4x objective must be in position. 3. Replace the dust cover 4. Place the microscope in the correct box. 5. Store away.
Magnification of the microscope when viewing an objective: In order to determine how many times the specimen viewed is magnified by we need to calculate the magnification of the microscope. We can do this by using the following formula: Magnification power of = magnification of eyepiece X magnification of microscope lens
For example if you use the 10X eyepiece and the 40X objective then Magnification = 10 X 40 = 400X It is usually expressed as viewed under the microscope at 400X. To determine the actual size of an object viewed under the microscope using the field of view approach.
To determine the actual size of an object viewed under the microscope using the field of view approach. The field of view is the circle of light that you see when looking through the eyepiece. The diameter maybe measured by viewing a ruler under the microscope. The diameter for the field of view and the lens on your microscope is about 4.5 mm or 4500μm.
To calculate the length of the object you must determine the portion/fraction of the field it covers. This can only be done by determining the number of objects that can fit in the field of view.
For example look at the two field of views below. X X X X X In the one on the right 4 of the object can fit in the field of view. Therefore one object occupies ¼ of the field diameter.
Therefore the approximate length of the object can be calculated as follows: 4500 μm X ¼ = 1125 μm The approximate length maybe calculated using the formula: Approximate length of object = fraction X diameter of field
To determine the magnification of a drawing. 1. You need the actual size of the object drawn and the actual size of the drawing. 2. Magnification of the drawing can be calculated using the formula: Magnification of drawing = drawing size object size
3. For example if your object has an actual length of 1115 μm, and your drawing of that object has a length of 5 cm, then you,can calculate magnification of drawing as follows: First the 5cm must be converted into μm that is Then: 5 X 10 000 = 50 000 μm Magnification of drawing = drawing size object size = 50 000/ 1115 = 45 μm
To determine the actual size of the object whose image or micrograph is viewed using a scale line. 1. Determine what the scale line measures. 2. Assume it represents 1 μm. 3. Measure the scale line given in the drawing or micrograph. ( lets say its 15mm) 4. Measure the length of the image in ;the drawing or micrograph. ( lets say its 50mm) 5. Now we can use the following formula
Actual size = measured length of object (mm) X length of scale line (μm) measured length of scale line (mm)) = 50mm X 1 μm 15mm = 3.3 μm
Macroscopic: refers to organisms that are visible to the naked eye. Microscopic: refers to organisms that are so small that they are not visible to the naked. Field of view is the circle of light that you see when looking through the eyepiece
1. The platform on which the slide sits is called the A. Base B. Stage C. Condenser D. diaphragm
2. Opening that controls the amount of light entering the microscope A. Base B. Stage C. Condenser D. diaphragm
3. It concentrates light through the slide and specimen A. Base B. Stage C. Condenser D. diaphragm
4. The combination of lens to magnify the image from objectives and specimen A. Eyepiece B. Body tube C. Illuminator D. Mirror
5. It supports and links the optical parts. A. Eyepiece B. Body tube C. Illuminator D. Mirror
6. Provides support for the microscope A. Base B. Stage C. Condenser D. diaphragm
7. Provides electrical light when switched on. A. Eyepiece B. Body tube C. Illuminator D. Mirror
8. Provides a source of natural light. A. Eyepiece B. Body tube C. Illuminator D. Mirror
9. Attachment of objectives. A. Nose piece B. Mechanical stage C. Stage clips D. Fine adjustment screw
10. Holds the slide in position on stage. A. Nose piece B. Mechanical stage C. Stage clips D. Fine adjustment screw
11. Allows for easy movement of slide A. Nose piece B. Mechanical stage C. Stage clips D. Fine adjustment screw
12. The picture below shows the microscope used by A. Robert Hooke B. Van Leeuwenhoek C. Oken D. Lamarck
13. The scientist who viewed cork cells under a simple microscope. A. Robert Hooke B. Van Leeuwenhoek C. Oken D. Lamarck
14. The scientist that observed and described single celled organisms. A. Robert Hooke B. Van Leeuwenhoek C. Oken D. Lamarck
15. The electron microscope was invented by A. Robert Hooke B. Van Leeuwenhoek C. Zworykin D. Lamarck
16. Calculate the magnification power of a microscope if you use the medium power objective and the 15X eyepiece. A. 150X B. 75X C. 25X D. 20X
17. Calculate the length of an object if it covers ½ of the field of view, assume that the diameter of the field of view is 4500μm A. 2250 μm B. 2000 μm C. 4500 μm D. None of the above
18. Calculate the magnification of a drawing you have done if your drawing of the organism is 2500 μm and your drawing of it is 7 cm long. A. 2507 μm B. 28X C. 0,0028 D. 28 μm
19. If you wanted to scan and view the surfaces of objects, you must use the A. Electron microscope B. SEM C. TEM D. Light microscope
20. If you wanted to see the inside of objects you would use the A. Electron microscope B. SEM C. TEM D. Light microscope
1. B 2. D 3. C 4. A 5. B 6. A 7. C 8. D 9. A 10. C
11. B 12. B 13. A 14. B 15. C 16. A 17. A 18. B 19. B 20. C