# Topic 2.1 – Size of Cells & Magnification 2.1.1 - 2.1.10 Text pg 7-21.

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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 mm 1 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)

1 2 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= x 3 SA= 6lw = 6x 2 Cube Side Length (cm) Volume (x 3 ) (cm 3 ) S.A. (6x 2 ) (cm 2 ) Ratio (S.A./V) 11 1 66 210 1000 6000.6 3100 1 000 000 60 000 0.06

Cube Side Length (cm) Volume (x 3 ) (cm 3 ) S.A. (6x 2 ) (cm 2 ) Ratio (S.A./V) 11 1 66 210 1000 6000.6 3100 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 mm 1 mm = 1,000 µm 1 µm = 1,000 nm

Determining size or magnification Magnification = image size  specimen size Example: A –Note that resizing an image changes magnification 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  m x = 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  m Scale 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 Drawings What makes this a good biological drawing? What are the rules? See page 7.

Homework Pg 13 # 1-4

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