topic 2.1 – size of cells & magnification 2.1.1 - 2.1.10 text pg 7-21

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