Chapter 7

The Size Range of Cells

A Tour of the CellProkaryote

• No membrane bound nucleus or organelles

• DNA is concentrated in a region called the nucleoid

• 1 – 10 μm in diameter

• Include bacteria and archaea

Eukaryote• Membrane-bound

organelles • True nucleus

(w/DNA) enclosed in a nuclear envelope

• 10 – 100 μm in diameter

• Include protists, plants, fungi and animal cells

A Tour of the Cell

Animal Cell

Plant Cell

Animal CellHave:

MitochondriaNucleusCell MembraneRough & Smooth ERRibosomesGolgi ApparatusCytoplasmCytoskeletonPeroxisomes

Also:LysosomesCentriolesFlagella and Cilia

Plant CellHave:

MitochondriaNucleusCell MembraneRough & Smooth ERRibosomesGolgi ApparatusCytoplasmCytoskeletonPeroxisomes

Also:ChloroplastsVacuolesCell WallPlasmodesmata

Microscopes

Transmission Electron Microscope (TEM)

Scanning Electron Microscope (SEM)

The Compound Light Microscope

• Magnifies up to 1500x

• Living and non-living specimens

• 3-D image

• Image produced using 2 lenses

• Light must be able to pass through specimen

Parts of the Microscope

Objectives

• Left- Scanning- 4x

• Middle-Low power-10x

• Right-High power-40x

Magnification - the ratio of an object’s image to its real size

Total magnification = eyepiece x objective

X

Resolving Power

 The ability of a microscope to distinguish clearly between objects close together under a

microscope

Low resolution High resolution

Field of Vision

Amount of area visible under each objective Field of vision diameter

Measuring the field of vision

1 millimeter (mm) = 1000 micrometer (μm)

• How large is the field of vision pictured in mm? In μm?

• Suppose you estimate 13 microorganisms could fit across this field of vision? How large is one microorganism in μm?

Field of Vision

Observe the next three slides. What is happening to the field of vision as the magnification increases?

Field of Vision

Field of Vision

• What happened to the field of vision as you change from scanning to low to high power objective?

• How would the object’s apparent size change?

The Stereoscope

• Also called dissecting microscope

• Can view large opaque objects

• Living and non-living specimens

• Magnifies up to 100x

• 3-D image

Electron MicroscopesElectron Microscopes – Electron beam

focused through the specimen or onto its surface (electron beams have wavelengths much shorter than visible light)

• Two types–Transmission Electron Microscope (TEM)

– internal or ultrastructure–Scanning Electron Microscope (SEM) –

surface of the specimen–Scanning Tunneling Microscope (STM) -

views molecules at atom level

TEM

• Transmission Electron Microscope

TEM• Beam of electrons pass through specimen

• Magnifies up to 500,000x

• 2-D image• Non-living

specimens only

TEM

Collagen Fibrils in the cornea

TEM• Plant Cell-22,500X

• C = ChloroplastER = Endoplasmic ReticulumG = Granum M = Mitochondrion S = Starch GrainT = Thylakoids V = Vacuole W = Wall

SEM

• Scanning Electron Microscope

• Electrons bounce off surface

• Specimen placed in vacuum chamber

SEM•

• Non-living specimens

• 3-D image• Magnifies up to

60,000x

SEM

• Technician monitors image on screen

SEM

Pollen Grain

Scanning Tunneling Microscope

• Developed in 1980’s

• Can view atoms on surface of objects

• Non-living• 3-D image• Magnifies up to

100 million x

STM

• Barium, Copper, and Oxygen atoms

STM• Silica atoms

• A nanometer (nm) is one millionth of a millimeter