topic 2.1 – size of cells & magnification 2.1.1 - 2.1.10 text pg 7-21
TRANSCRIPT
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Topic 2.1 – Size of Cells & Magnification
2.1.1 - 2.1.10
Text pg 7-21
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Size of Cells
• Typically use
m and nm
1 m = 1,000 mm1 mm = 1,000 µm (10-6)1 µm = 1,000 nm (10-9)
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Average Sizes:
Eukaryotic cells (8-100 µm)
Organelles (2-10 µm)
Bacteria (1-5 µm)
Viruses (100 nm)
Cell Membranes (10 nm)
Molecules (1-2 nm)
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12
3
1 cm 10 cm 100 cm
Assume we have 3 cubes:
With sizes:
What will happen to ratio between Volume and Surface Area as their size increases?
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Surface Area/Volume
• Surface area determines the rate of exchange (how quickly nutrients are absorbed and wastes removed.)
• Volume determines the rate of resource use and waste production.
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V= lwh= x3 SA= 6lw = 6x2
Cube Side Length (cm)
Volume (x3)
(cm3)
S.A. (6x2)(cm2)
Ratio (S.A./V)
1 1 1
6 6
2 10 1000
600 0.6
3 100 1 000 000
60 000 0.06
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Cube Side Length (cm)
Volume (x3)
(cm3)
S.A. (6x2)(cm2)
Ratio (S.A./V)
1 1 1
6 6
2 10 1000
600 0.6
3 100 1 000 000
60 000 0.06
Volume increases faster than surface area
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Surface Area/Volume
• Volume increases faster than SA• Resources are used and waste produced
faster than it can be removed– Eg. Heat not lost fast enough
• Does not support the cell’s function• Keeps cell size small
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The Light Microscope
This is the microscope that we will be using.
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The Scanning Electron Microscope
Used in research labs and universities.
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The Transmission Electron Microscope
Used in research labs and universities.
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How are they DIFFERENT?
Light microscopes use a beam of visible light!
Can magnify images up to 2000 X (but are
really clear only up to 600 X)
Are small, fairly inexpensive, and
portable
Electron microscopes use a beam of
electrons!
Can magnify images up to 500 000 X
Are large, very expensive and not
portable
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Light Microscopes
Easy and fast to prepare specimens for viewing; uses water and a slide.
Electron Microscopes
Specimen preparation can take days and
many procedures; uses toxic chemicals
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Light Microscopes
Can view living materials. Less
danger of artificial structures appearing
due to specimen processing.
Electron Microscopes
Specimens are killed during preparation;
changes may occur during processing.
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Light Microscopes
Movement can be observed both
inside and outside of cells.
Electron Microscopes
No movement as specimens are dead.
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Light Microscopes
Colors can be seen -- both natural and
with staining
Electron Microscopes
Only black and white images; some
people do “colorize”images.
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Magnification
• Microscopes magnify images, but it is important to know the actual size of the specimen
• Remember:
1 m = 1,000 mm1 mm = 1,000 µm1 µm = 1,000 nm
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Determining size or magnification
• Magnification = image size specimen size• Example: A
– Note that resizing an image changes magnification
x4000 x4000
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Example calculation 1
• A mitochondrion has a length of 12 m. • It is drawn 8.4 cm long. • What is the magnification?
Mag. = image size / specimen size
= 8.4 cm / 12 m= 84,000 m / 12 m= 7,000 x
8.4 cm
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Example calculation 2
• An image of a nucleus is 122 mm wide• The image has a magnification of 1500x• How wide in the nucleus?
Mag = image size / actual specimen size
Actual specimen size = image size / magnification
Actual specimen size = 122 mm / 1500
Actual specimen size = .081 mm = 81 m
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Example calculations: Microscopes
• Given: The microscope has a field of view (FOV) of 500 m at 400x
• What is the size of the specimen?
Image / FOV in image = Specimen / FOV
3.4 cm / 9.8 cm = x / 500 mx = 170 m
3.4 cm
9.8 cm
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Example calculations: scale bar
• Scale bar must represent a reasonable, appropriate value (1, 5, 10, 20, etc.)
• An image is magnified 4000 x. • How long would a scale bar of 10 um be?
Magnification = Image size / actual specimen size
4000 x = image size / 10 mScale bar image = 40000 m = 40 mm
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• Determine the magnification of the image• Determine the size of the viral head.
Mag = Image / actual specimen size
= 20 cm / 100 nm
= 200 000 000 nm / 100 nm
= 2,000,000 x
Actual specimen size = Image / Mag
X = 16 cm / 20,000x
X = .000008 cm = 0.008 m = 80 nm
20 cm
16 cm
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Biological DrawingsWhat makes this a good biological drawing? What
are the rules?
See page 7.
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Homework
• Pg 13 # 1-4