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Microscope

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  • 1. THE MICROSCOPE
  • 2. Parts of the light microscope
  • 3. Objective lenses HP objective lens is close to slide
  • 4. Total magnification: Magnification = Objective lens X Eyepiece lens e.g. What is the total magnification if the objective lens is twenty times (X20) and the eyepiece lens five times (X5)? Magnification = 20 X 5 = X100
  • 5. As magnification increases, detail increases but: Onion cell 40x Onion cell 100x Onion cell 400x less of the cell is seen
  • 6. Caring for the microscope: 1. Do not let any liquids to come in contact with the microscope. 2. Always store the microscope inside a box after use. 3. Return the objective lens onto low power after use. 4. Carry the microscope by the arm. 5. Use a soft clean tissue to wipe the lenses
  • 7. Microscope slides Coverslips
  • 8. Fig. 2 Preparing a slide as a wet mount.
  • 9. Use of stains:  some parts of a plant cell can be clearly seen when the cell is mounted in water  E.g. an Elodea leaf cell:  cell wall  several chloroplasts are seen
  • 10.  other cell structures which are not so obvious can often be shown up more clearly by the addition of dyes called STAINS METHYLENE BLUE To stain animal cells IODINE SOLUTION To stain plant cells
  • 11. A thin inner layer of epidermis is peeled off. An onion is cut into quarters. One of the fleshy scale leaves is removed. Snapping leaf backwards exposes the epidermis. Epidermis is placed on slide & covered with 2-3 drops of distilled water . Coverslip is lowered. A drop of stain is put at one end of slide. 1 2 3 5 4 6 7 Stain is drawn over specimen using a small piece of filter paper.
  • 12. Questions 1. A pupil prepared a microscope slide of onion cells using water. Diagram A shows how the cells looked when first seen with the microscope. Diagram B shows their appearance after the addition of another liquid. What name is given to a liquid used to make cell structures easier to see? Stain
  • 13. 2. The drawing shows the appearance of a prepared slide. What causes the ring shapes? (1) Air bubbles trapped beneath the coverslip.
  • 14. 3. This diagram shows the main parts of a typical light microscope. a) How is a glass slide held in position on the stage? By the clips.
  • 15. b) Why must the specimen on the slide be in the centre of the hole in the stage? To allow light pass through the specimen. c) Why does the nosepiece rotate? To clip in position the required objective lens.
  • 16. d) What is the mirror for? To reflect light onto the specimen. e) How can you control the amount of light coming through the microscope? By moving the diaphragm.
  • 17. f) Explain how you would use the microscope to look at a specimen under the low power. 1. Clipping slide by clips. 2. Placing the low power objective in position. 3. Moving the tube downwards while looking from the side until objective lens is close to the slide. 4. Using the coarse adjustment knob, the tube is racked upwards until image is focused.
  • 18. g) If you had a specimen in focus under the low power, how would you go on to look at it under high power? By using the fine adjustment knob.
  • 19. h) Why should you never rack downwards with the coarse focusing knob while you are looking down the microscope? Not to break the slide.
  • 20. i) If the magnifying power of the eyepiece lens is ten times (X10), and that of the low power objective lens is four times (X4), what is the total magnification of a specimen under low power? 10 x 4 = x40
  • 21. T H E E N D