Microscopy Study Materials

Microscopy Microscopes create magnified images of objects, such as cells, so they can be seen in more detail. Light Microscope The light microscope uses light waves and lenses to magnify objects. Eyepiece lens Coarse adjustment knob Nosepiece Fine adjustment knob Objective lenses: x4, x10, x40 lenses Specimen Stage Light/mirror Onion cell biological drawing (Magnification × 100) Nucleus Cell wall Cytoplasm Cell membrane Total magnification = Magnification of eyepiece lens Magnification of objective lens Magnification is how much larger an image is compared to the real object. Actual Size = Image size Magnification AM Microscopic objects are measured using these units: Millimetres mm μπ nm pm 1x 10m Micrometres 1 x 10m Nanometres 1x10m Picometres 1x10m Example The image of a cell viewed at x40 magnification has a diameter of 1 mm. What is the cell's real diameter? Substitute the numbers into the formula: Actual size= 40 2 Solve: Actual size = 0.025 mm or 25 µm Electron Microscope The electron microscope uses a beam of electrons to magnify objects. The light microscope was invented in the 16th century, but a major advance in microscopy came in the 1930s with the invention of the electron microscope. An electron microscope has a much higher magnification and resolution than a light microscope so smaller things can be seen in more detail. Resolution is the ability to distinguish between two separate points. A typical light microscope has a resolving power of 200 nm. This means it can distinguish between points 200 nm apart. The resolving power of an electron microscope is up to 0.2 nm. The development of electron microscopes has enabled scientists to see structures more clearly and in more detail, which has increased our understanding of microscopic objects such as cells. Light Microscope Electron Microscope Bacteria viewed on a light microscope and an electron microscope Microscope Practical Activity Use a light microscope to observe, draw and label a selection of plant and animal cells. To view a specimen under a light microscope, it must be mounted correctly on a slide, a strip of clear glass or plastic used with microscopes. 2 Follow these steps to mount a specimen. -Cover slip 1 Place a drop of water on the centre of the slide. Position the specimen on the liquid. At an angle, place a cover slip against the slide, and gently lower it to avoid air bubbles. Remove excess water with a paper towel. You may also need to add a stain, such as iodine solution, to help highlight the different parts of the specimen. Once the slide is prepared, clip it on the microscope stage. Turn the nose piece to select the lowest power objective lens. 5 6 9 10 Turn the coarse adjustment knob to position the lens just above the slide. Look through the eyepiece, and slowly turn the coarse adjustment knob to move the slide away from the lens until the cells come into focus. 7Slightly turn the fine adjustment knob to bring the cells into clear focus. 8 When you have found some cells, turn the nose piece to switch to a higher power lens. Bring the cells back into focus by using the fine adjustment knob. Using a pencil, make a labelled drawing of some of the cells. Do not add any colour or shading. Write the magnification underneath your drawing. Remember to multiply the objective magnification by the eyepiece magnification. Human cheek cell viewed at 400 x magnification Cytoplasm Nuoleus Cell membrane 3 40 um