CELLULAR HISTORY

&

MICROSCOPES

• Knowledge of cells originated from English scientist Robert Hooke in 1665→ Studied thin sections of cork and saw

boxlike cavities he called “cells”

Robert Hooke

A. Cellular Scientists

• Dutch scientist Antony van Leeuwenhoek examined pond water in 1676→observed “animalcules” or tiny animals

oWere single-celled amoeba, paramecium, and other water-borne pathogens

Anton van Leeuwenhoek

Water flea daphnia found in pond

water

• Matthias Schleiden in 1838 studied plants→cells make up every part of plant – stems,

roots, leaves, flowers

Matthias Schleiden

• Theodor Schwann in 1839 viewed cartilage tissue cells→animals are also made out of cells

oPublished theory that cells are basic unit of life

Theodor Schwann

• Rudolf Virchow used work of Schwann and Schleiden to advance cell theory in 1858

Virchow1821-1902

→Cell theoryo All living things are made of one or more

cellsoCells are basic units of structure and

function in organismso All cells arise from pre-existing cells

Apple cells

• living organisms may consist of one cell (bacteria) or many cells (plants and animals) that act as a unit or in coordination with each other

Staphylococcus aureus Elodea plant

B. MICROSCOPE STRUCTURE• Microscope: instrument used to

magnify very small objects

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Microscope Parts FunctionArm Connects to base and supports microscope

head, also used to carry the microscope.

Base Bottom of microscope, supports it and houses light source

Body tube Holds eyepieces in place above objective lens

Course adjustment Focuses microscope by moving stage up and down in large movements

Diaphragm Controls amount of light reaching specimen, located above light source and below stage

Fine adjustment Sharpens focus of microscope by moving stage up and down in slight increments

Light source Low voltage, halogen bulb for microscope, typically located in base

Microscope Parts FunctionObjectives Primary optical lenses on a microscope that

magnify imageScanning 4X – used to locate specimenLow power 10X – used to locate specific area on specimenHigh power 40X – used to magnify specific area on specimen

Ocular lens (eyepiece) 10X

Lens at top of microscope that eye looks through

Revolving nosepiece Houses objectives mounted on a rotating turret so different objectives can be conveniently selected

Stage Where specimen to be viewed is placed

Stage clips Holds the slide in place

Accessories Function

Cover slip Square piece of glass or plastic to hold specimen on slide

Forceps Type of tweezers used to grasp specimen

Slide Piece of rectangular glass on which specimen is placed; held by stage clips

Wet mount Setting specimen on slide, covering with a drop of water to stabilize specimen

QUIZ – can you name all the parts?

C. MAGNIFICATION• Magnification of objective is not total

magnification – must consider power of ocular lens, too– Multiply ocular lens by objective lens for

correct magnification• Ex: ocular lens has magnification of 4X. If

objective lens is 40X, what is total magnification?

– 4 x 40 = 160X

• Ex: ocular lens has magnification of 10X. If objective lens is 100X, what is total magnification?

– 10 x 100 = 1000X

Three types of microscopes, depending on what scientists want to look at:o Light microscopeo Electron microscopeo Scanning tunneling microscope

Simple Compound

Light Microscopeo light microscope: a microscope that

uses a beam of visible light passing through one or more lenses to magnify an object up to 1,500 times¨ Two types:

- Simple light microscope (1 lens)- Compound light microscope (2 lenses)

¨ compound light microscope: uses two lenses and a light bulb to shine light up and through object being studied- it contains the following parts:

>ocular lens: lens viewer looks through, usually has magnification of 10X

>objective lens: lens closest to specimen through which light travels; can have magnification of 20 X, 40X, 100X, up to 200X

>specimen: object being studied, usually put on glass slide resting on stage

> stage: area specimen rests on, can move up or down to bring object into better focus

> focus knob: knob that moves stage up and down to bring object into focus; may have fine focus knob which moves stage at microscopic rate for better resolution

> light source: usually a light bulb which shines up through specimen, through objective lens, through ocular lens; may also be a mirror that reflects overhead light

Parts of Compound Microscope

MEMORIZE!

- to obtain actual magnification, must multiply magnification of ocular lens and objective lens together> if ocular is 10x, and objective is 40x, 10 x 40

= total magnification of 400x10x

40x

(10x)(40x) = 400x

> PRACTICE: If the ocular is 10x and the objective you

are using is 10x, what is your total magnification?100x

If the ocular is 5x and the objective you are using is 100x, what is your total magnification?500x

If the ocular is 2x and the objective you are using is 40x, what is your total magnification?80x

Electron Microscopeo electron microscope (EM): a microscope

that focuses a beam of electrons to magnify objects up to 200,000 times actual size¨ two types of EM:

- transmission electron microscope (TEM)- scanning electron microscope (SEM)

- transmission electron microscope (TEM): electron beam is directed at a very thin slice of specimen stained with metal ions. Heavily stained parts absorb the electrons, while those parts with less stain allow electrons to pass through, and strike a fluorescent screen> these micrographs can reveal cell’s internal

structure in fine detail, but are not in color~scientists have to add artificial color to

make certain structures more visible

TEM

Transmission electron micrograph of myelinated neurons.

SEM

This colorized scanning electron micrograph shows pollens—Bermuda

grass in green, maple in red, and ragweed in yellow—at roughly 3,000

times their itchy, sneezy life size.

- scanning electron microscope (SEM): electron beam is focused on specimen coated with very thin layer of metal. Electrons that bounce off specimen form an image on fluorescent screen.> Shows three-dimensional (3-D) images of

cell surface, but are black and white~scientists have to add artificial color to

make certain structures more visible

o scanning tunneling microscope (STM): uses a needle-like probe to measure differences in voltage caused by electrons that leak, or tunnel, from the surface of the object being viewed¨ computer tracks movement of probe across

object, enabling very small objects the size of an atom to be viewed

¨ computer generates 3-D image of specimen’s surface

¨ can be used for living organisms

STM

A scanning microscope (micrograph of the foot of the jumping spider E. arcuata. (Image courtesy Institute Of Physics)

Cell Size• All substances that enter or leave a cell

must cross that cell’s surface.• Small cells function more efficiently than

larger cells.– About 100 trillion cells in human body– From 5µm-20µm in diameter

• Small cells can exchange substances more readily than larger cells because small object have a higher surface area-to volume ratio than larger objects.

Relationship Between Surface Area and Volume

Slide length Surface area Volume Surface area/Volume ratio

1 mm6:1

2 mm 3:1

4 mm 3:2

26mm

224mm

296mm

31mm

38mm

364mm

If the cell’s surface area-to volume ratio is low, substances can not enter and leave the cell in numbers large enough to meet the cell’s needs.