Biology - Microscopy
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How were cells first discovered?
Using a microscope.
What is the purpose of using a microscope?
To magnify things through lenses, such as cells.
How do we study living cells?
Through using a light microscope.
What are the 2 main types of microscopes used to study cells?
Light microscopes and Electron Microscopes.
The electron microscope was invented first, before the light microscope. True or False.
False. The light microscope was invented first.
Explain the main differences between a light microscope and an electron microscope.
LIGHT microscopes have: low magnification, low resolution and are used to STUDY LIVING CELLS. Uses BEAMS of LIGHT. Less expensive. ELECTRON microscopes have: higher magnification, high resolution but CAN NOT BE USED TO STUDY LIVING CELLS. Uses BEAMS of ELECTRONS. More expensive.
If you wanted to look at a nucleus and chloroplasts and other sub-cellular structures, what type of microscope could you use?
A light microscope.
If you wanted to look at sub-cellular structures in much finer detail such as mitochondria, ribosomes, what type of microscope could you use?
Electron microscope
Name 2 subcellular structures that can not be seen with a light microscope?
1) Ribosomes 2) Mitochondria
EXPLAIN how you would PREPARE your specimen using a light microscope? (5)
• Take THIN SLICE of specimen. • Take clean SLIDE and use a PIPETTE to put ONE DROP OF WATER in the MIDDLE if it. • Use TWEEZERS to place your specimen on the slide. • Add a drop of STAIN to make it easier to see your specimen. • Lower a COVER SLIP onto the slide using a MOUNTED NEEDLE, trying not to trap any BUBBLES under the cover slip.
EXPLAIN how you would VIEW your specimen using a light microscope? (6)
• CLIP the slide onto the STAGE • Select the OBJECTIVE LENS with the LOWEST MAGNIFICATION • Use the COURSE ADJUSTMENT KNOB to move the stage UP to JUST UNDERNEATH the objective lens. • LOOK down the EYEPIECE, then move the stage DOWN until the specimen is nearly in focus. • MOVE the FINE ADJUSTMENT KNOB until you get a clear image. • If you want the image bigger, use an OBJECTIVE LENS with a HIGHER MAGNIFICATION (and REFOCUS).
Explain how to do a SCIENTIFIC DRAWING of a SPECIMEN (5) so you are prepared if you are asked to do this in an exam.
• Sharp pencil to draw smooth outline of the main features. • Label the features with straight lines (don’t cross lines). • No colour or shading. • Drawing needs to take up at least half the space available. • Include the MAGNIFICATION and SCALE.
A student wants to look at a thin piece of onion skin under a light microscope. Describe the steps she could take to prepare the skin for viewing (3 marks).
• Take a clean slide and use a pipette to put one drop of water in the middle (1 mark) • Use the tweezers to place the onion skin on the slide and add a drop of stain (1 mark) • Carefully lower the cover slip onto the slide using a mounted needle (1 mark)
What is magnification or define magnification?
How many times larger the image is than the object.
What is the TOTAL MAGNIFICATION FORMULA?
Total Magnification = Eyepiece Lens Magnification x Objective Lens Magnification
Work out the following: What is the total magnification of an image viewed with an eyepiece lens magnification of x10 and an objective lens magnification x 40
Total magnification = 10 x 40 = 400
https://www.bing.com/videos/search?q=total+magnification+of+microscope+gcse+exam+questions&view=detail&mid=39495E4B9A022821A4E639495E4B9A022821A4E6&FORM=VIRE
watch re microscopes
If the image appeared 1000x larger than the object, what would the magnification be?
1000
Explain how you would work out the magnification of an image if you don’t know what lenses were used?
1). Measure the image. 2. Know the real size of the specimen. • Use the formula Magnification = Image Size divided by Real Size
Work out the following: The width of a specimen is 0.02mm. The width of the image under a microscope is 8mm. What magnification was used to view the specimen?
Magnification = 8mm divided by 0.02mm = x 400
Draw the formula triangle to include: image size; magnification and real size. Cover the part you want to find. The parts you can see are the formula you need to use.
Triangle Formula - write IMAGE SIZE at top of triangle, draw a line underneath to create the divide sign, then write MAGNIFICATION bottom left corner of triangle and write REAL SIZE bottom right corner of triangle. Remember to write the times sign in between magnification and real size. DRAW IT.
Work out the following using the Triangle Formula: The width of the specimens image underneath a microscope is x 100. What is the REAL width of the specimen?
Cover up the ‘REAL size’ on the triangle (bottom right of triangle). This leaves the formula IMAGE SIZE DIVIDED BY MAGNIFICATION. The REAL WIDTH = 3mm divided by 100 = 0.03mm (remember the units need to be the same, in this example it is mm).
Sometimes you might need to convert units. What is the abbreviation for these units: 1) millimetres 2) micrometres 3) nanometres
• mm • um (check how to write as inaccurate on PC) • nm
What are these units used to measure? 1) millimetres 2) micrometres 3) nanometres
Very small objects e.g. cells.