cellular history & microscopes. knowledge of cells originated from english scientist robert...
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CELLULAR HISTORY
&
MICROSCOPES
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• 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
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• 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
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• Matthias Schleiden in 1838 studied plants→cells make up every part of plant – stems,
roots, leaves, flowers
Matthias Schleiden
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• 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
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• Rudolf Virchow used work of Schwann and Schleiden to advance cell theory in 1858
Virchow1821-1902
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→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
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• 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
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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
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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
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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
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QUIZ – can you name all the parts?
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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
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Three types of microscopes, depending on what scientists want to look at:o Light microscopeo Electron microscopeo Scanning tunneling microscope
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Simple Compound
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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)
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¨ 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
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> 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
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Parts of Compound Microscope
MEMORIZE!
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- 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
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> 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
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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)
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- 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
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TEM
Transmission electron micrograph of myelinated neurons.
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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.
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- 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
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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
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STM
A scanning microscope (micrograph of the foot of the jumping spider E. arcuata. (Image courtesy Institute Of Physics)
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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
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• Small cells can exchange substances more readily than larger cells because small object have a higher surface area-to volume ratio than larger objects.
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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.
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