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Topic 2.1 – Size of Cells & Magnification
2.1.1 - 2.1.10
Text pg 7-21
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)
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)
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?
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.
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
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
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
The Light Microscope
This is the microscope that we will be using.
The Scanning Electron Microscope
Used in research labs and universities.
The Transmission Electron Microscope
Used in research labs and universities.
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
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
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.
Light Microscopes
Movement can be observed both
inside and outside of cells.
Electron Microscopes
No movement as specimens are dead.
Light Microscopes
Colors can be seen -- both natural and
with staining
Electron Microscopes
Only black and white images; some
people do “colorize”images.
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
Determining size or magnification
• Magnification = image size specimen size• Example: A
– Note that resizing an image changes magnification
x4000 x4000
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
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
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
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
• 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
Biological DrawingsWhat makes this a good biological drawing? What
are the rules?
See page 7.
Homework
• Pg 13 # 1-4