Cells and Microscopy

History of Cell Theory• 1665 Robert Hooke view cork

piece and creates the term “cell”– 1) Cell is smallest unit of life

• 1838 Schleiden says all plant are made of cells and Schwann says all animals are made of cells– 2) All living things made of cells

• 1855 Virchow theory states all cells come from pre-existing cells– 3) Cells only come from pre-

existing cells• Cell theory is finally complete

Why Cells?• Cells are the smallest unit of

life. Why?– Cells control chemical reactions

by creating an “inside” and an “outside”; plasma membrane

– Compartmentalize by dividing jobs between specialized organelles (tiny organs)

• Similar to society?– Form a group; inside vs. outside– Divide labor as we all get

specialized jobs

Limits of Light• 1800’s birth of cytology (study of cells)• Human eye 100 μm• Light microscopes show us:

– Plasma membranes, cytoplasm, mitochondria, cell walls, nucleus, etc…

– But we hit a limit; 0.2 μm (200nm)• Magnification number of times larger

an image is to the real size of the object– Mag= size of image / real size of object– X1500 for light microscopes

• Resolution ability to distinguish between two points; clarity– ½ the wavelength of radiation used– Light is 400nm – 700 nm

Eye Piece Mag Objective Mag

10x 4x

10x

40x

100x (oil emmersion)

Question 1.2 and 1.31.2 a) Calculate the mag. of the drawing of the animal cell

in fig. 1.2.

b) Calculate the actual length of the chloroplast in fig. 1.23.

1.3 Explain why ribosomes are not visible using a light microscope.

20 μm average animal cell6mm (60,000 μm) diagram60,000/20 = x3000

x20,000 Mag65mm (65000 μm) diagram65000/20,000= 3.25 μm

Max res. Of light microscope is 200nm and ribosomes are only 22nm in diameter

Mag/Res Practice1) What is the max. resolution possible for an image made

using infrared?

2) Based on the image of HIV shown, what is the actual size of the virus?

3) What wavelength would be needed to take this image?

700nm line between VL/Infrared Resolution = ½ radiation used0.5 * 700nm 350nm

9mm 9000μm 9000 μm / 75,000 = 0.12 μm (120nm)

120nm = 0.5 x wavelength of radiationWavelength= 240 nm (UV light)

Measuring Cells• Light microscope good for 40μm–0.2μm• Eye-piece graticule scale in eye-piece of

microscope– 100 units; but what does 1 unit mean?– Needs to be calibrated

• Stage micrometer slide that can show the scale of our graticule divisions– 0.1 and 0.01 mm units

• Match up the scales and do simple calculations– Calibrated units= # of stage units / 100– X 1000 to change to μm

• Cell size = # graticule units x calibrated units

Electromagnetic Spectrum• What other forms of radiation

exist?– Gamma– X-ray– Ultra violet

• Higher energy radiation has shorter waves; lower has longer waves

• What limits resolution?– ½ wavelength of radiation used– 400nm only get down to 200nm

• How can we see smaller than 200nm?– Use higher energy radiation!

-Infrared-Microwave-Radio

Electron Microscopes• UV, X-Ray, Gamma powerful and

hard to focus• Electrons act like X-rays but are

easy to control. Why?– e- , can control them with magnets – More energized the electrons the

smaller they can see• What are negative parts to an

electron microscope?– No color images; False-color– No air; must use a vacuum– No H2O; must be dehydrated– No living specimen

Types of Electron Microscopes1) TEM Transmission Electron

Microscope– Electrons pass through thin object– Detailed interior (up to x500,000)– 2D image

2) SEM Scanning Electron Microscope– Electrons scan surface– Detailed external (up to x100,000)– 3D image

• What situations would you need an SEM or a TEM?

Did you do the reading?You have 3 mins to explain

to each other TEM and SEM…

Homework• Read p 7-16• Vocabulary lists• Questions 1.3 and 1.4• Cell labeling worksheet• Visit electron

microscope in school museum–Take a photo next to it

and get a bonus point