The Cell TheoryThe Cell Theory

And how it And how it developeddeveloped

Problem: Cells are Problem: Cells are smallsmall

Most cells are too small to be Most cells are too small to be seen without magnification.seen without magnification.– Look at your hand? Do you see Look at your hand? Do you see

cells?cells?

Sizes of cellular Sizes of cellular componentscomponents

Solution: MagnificationSolution: Magnification

Simple magnifiers: drop of water or Simple magnifiers: drop of water or glass bead.glass bead.

Compound magnificationCompound magnification

First microscope invented by First microscope invented by Zacharias and Hans Janssen in Zacharias and Hans Janssen in

the 1590'sthe 1590's – Uses a series of lenses to make Uses a series of lenses to make

larger imageslarger images

MicroscopesMicroscopes

Various styles Various styles ofof

microscopemicroscope

were developedwere developed

by mid 1600’s,by mid 1600’s,

mostly tomostly to

examine clothexamine cloth

Robert Hooke - 1665Robert Hooke - 1665

First First recordedrecorded examination of biological examination of biological material with microscopematerial with microscope

Looked at slices of corkLooked at slices of cork Described structure as Described structure as “ “cells”cells”

Hooke’s observationHooke’s observation

Hooke’s observationsHooke’s observations

Cork was long-dead Cork was long-dead

material – saw remains ofmaterial – saw remains of

cell walls only.cell walls only. Later examined fresh plant Later examined fresh plant

tissue – saw fluids inside.tissue – saw fluids inside.

Impact:Impact:

Cells are the basic structural Cells are the basic structural unit of living things.unit of living things.

Anton Von Anton Von LeeuwenhoekLeeuwenhoek

Good amateur microscope Good amateur microscope maker.maker.

1668 - Examined pond water 1668 - Examined pond water with microscope: with microscope:

saw freely moving “beasties” saw freely moving “beasties” or “animalcules”.or “animalcules”.

Von LeeuwenhoekVon Leeuwenhoek

Also examined Also examined blood.blood.

First to observe First to observe single-celled single-celled organisms in organisms in tooth debris.tooth debris.

Von LeeuwenhoekVon Leeuwenhoek

Considered Considered

the fatherthe father

ofof

microbiologymicrobiology

Impact:Impact:

A single cell can perform all A single cell can perform all life life

functions.functions.

Henri Dutrochet - 1824Henri Dutrochet - 1824

Proposed that all living things Proposed that all living things were made of cells.were made of cells.– based on observations of many based on observations of many

organisms.organisms.

Technology – 1820’s Technology – 1820’s on:on:

Development of staining Development of staining techniques improves visibility of techniques improves visibility of cellular structure.cellular structure.– unstained tissue mostly clear.unstained tissue mostly clear.– Special chemical reactions can Special chemical reactions can

show structures, enzymes, whole show structures, enzymes, whole cell shape, etc.cell shape, etc.

Staining makes Staining makes bacterial cells bacterial cells stand out.stand out.

Robert Robert BrownBrown - 1831 - 1831

Realizes that all Realizes that all cells have a cells have a dense region in dense region in the center.the center.

Calls it a Calls it a nucleusnucleus.. Function Function

unknown.unknown.

Matthias SchleidenMatthias Schleiden - - 18381838

Observed many Observed many plant samplesplant samples

ConcludedConcluded that that

all plants areall plants are

made of cellsmade of cells

Theodor Schwann - Theodor Schwann - 18391839

Observed manyObserved many

animal samplesanimal samples ConcludedConcluded that all that all

animals are made animals are made of cells.of cells.

JohannesJohannes PurkinjePurkinje - - 18391839

Reported that all cells he Reported that all cells he observed were filled with jelly-observed were filled with jelly-like substance.like substance.

Named this substance Named this substance protoplasmprotoplasm..– assumed to have special life-assumed to have special life-

giving chracteristics.giving chracteristics.

Impact:Impact:

All living things are made of All living things are made of cellscells

Rudolph Virchow - Rudolph Virchow - 18551855

Observed Observed cells dividing.cells dividing.

True in plants True in plants and animalsand animals

Impact:Impact:

All cells come from pre-existing All cells come from pre-existing cellscells

Cell Theory – late Cell Theory – late 1800’s1800’s

1.1. All living things are made of cells All living things are made of cells and cell products.and cell products.

2.2. All cells carry on life activities. Life All cells carry on life activities. Life activities of multicelled organisms activities of multicelled organisms are combined product of all cells.are combined product of all cells.

3.3. New cells arise only from other New cells arise only from other cells by the process of cell division.cells by the process of cell division.

Technology improvesTechnology improves

1939 – Electron microscope allows 1939 – Electron microscope allows much greater magnification.much greater magnification.– Uses electrons, rather than light.Uses electrons, rather than light.– Allows much greater Allows much greater resolutionresolution, too., too.– Specimens must be exposed to Specimens must be exposed to

vacuum, so not good for living things.vacuum, so not good for living things.

Getting information from an Getting information from an image:image:

MagnificationMagnification tells how many times tells how many times bigger the object appears. Bigger is bigger the object appears. Bigger is easier to see.easier to see.

ResolutionResolution tells how much detail is tells how much detail is available in the image.available in the image.– A bigger image with poor resolution is A bigger image with poor resolution is

useless!useless!

Electron MicroscopeElectron Microscope

Scanning Electron Scanning Electron MicroscopeMicroscope

Bounces electrons Bounces electrons off surfaces off surfaces without without penetrating.penetrating.

Produces very Produces very detailed 3-D view detailed 3-D view of of surfacesurface..– No internal No internal

structure!structure!

SEM ImagesSEM Images

Transmission Electron Transmission Electron MicroscopeMicroscope

Maximum magnification – can see Maximum magnification – can see large molecules!large molecules!

Electrons pass through very thin Electrons pass through very thin (0.2(0.2m) slices of an object and are m) slices of an object and are detected on a screen. detected on a screen.

Allows examination of structures Allows examination of structures withinwithin cells. cells.

TEM ImageTEM Image

Compound Light MicroscopeCompound Light Microscope

Light passes up from the Light passes up from the base and is focused base and is focused through a through a diaphragmdiaphragm. It . It passes through the passes through the specimen, and a series specimen, and a series of lenses in the of lenses in the objectiveobjective magnify the magnify the specimen.specimen.

Lenses in Lenses in eyepieceeyepiece provide a magnified provide a magnified view of the first image. view of the first image.

The specimenThe specimen The object to be The object to be

observed is placed on observed is placed on a glass slide. a glass slide. – Must be thin and clear Must be thin and clear

enough for light to pass enough for light to pass through.through.

It must be covered It must be covered with water or another with water or another clear liquid.clear liquid.

A thin cover glass is A thin cover glass is placed over the object placed over the object and liquid.and liquid.

IlluminationIllumination

Different types of illumination can Different types of illumination can emphasize different features of the emphasize different features of the specimen.specimen.

Can be combined with special stains Can be combined with special stains – UV light with fluroescent stains or – UV light with fluroescent stains or labels for particular types of labels for particular types of materials.materials.

Types of Light Types of Light MicroscopyMicroscopy

StereomicroscopeStereomicroscope

A A stereostereo or or dissection microscopedissection microscope is a low is a low power light microscope. Good for magnifying power light microscope. Good for magnifying objects and getting a three dimensional view objects and getting a three dimensional view of surfaces. of surfaces.

Light can bounce off the surface of the Light can bounce off the surface of the specimen, be transmitted through it, or both. specimen, be transmitted through it, or both.

You cannot typically see individual cells You cannot typically see individual cells because of the low magnification, and because of the low magnification, and because the objects are too thick for good because the objects are too thick for good resolution.resolution.

A stereo A stereo microscopemicroscope

Note the 2 light Note the 2 light sources:sources:

1.1. From above, or From above, or epi-illuminationepi-illumination

2.2. From below, or From below, or transilluminatiotransilluminationn

StereomicroscopeStereomicroscope

Also called a dissecting microscope, Also called a dissecting microscope, it is most useful for magnifying it is most useful for magnifying objects while they are being objects while they are being manipulated.manipulated.

What to use?What to use?

What type of microscope you use What type of microscope you use depends on what information you depends on what information you need.need.

May use a stereomicroscope to May use a stereomicroscope to obtain a tissue sample, a light obtain a tissue sample, a light microscope to look at the tissue, and microscope to look at the tissue, and transmission electron microscope to transmission electron microscope to learn about the details within the learn about the details within the cells.cells.