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Microscopes
&
Cells
What is a Microscope?
•Most microscopes consist of either a single
lens (simple microscope) or multiple lenses
(compound microscope) that allows us to
magnify something to a size greater than we
could see with the naked eye.
•Not all microscopes have lenses, the
electron microscope uses a beam of
electrons to create a detailed image of a
specimen.
A Little Microscope History
•It is difficult to trace the origins of the first lenses, but rock
crystals found in northern Iraq in the 8th century B.C. may
have been used as lenses.
•The word ‘microscope’ was first coined by members of the
first “Academia dei Lincei” - which was a scientific society that
included Galileo.
•The seventeenth century was a period of great interest in the
microscope. But back then the microscope was not only
engaged as a scientific tool, but also as a recreational toy used
by upper-class citizens to look at things close up, such as the
legs and wings of insects. Many of these citizens thought this
was very interesting, but most could not imagine that a tool
like this could make too many new scientific discoveries.
Early Microscopes
•The first microscope was reported in use in 1590. It was
invented by two Dutchmen named Hans and Janssen and had two
ground lenses - this made it a compound microscope.
•In 1660 Marcello Malpighi used the microscope to see capillaries.
•The drawing below shows an early microscope used by Robert
Hooke. The eye views from point A. The 3 lens system remains
the standard configuration in microscopes today, except that each
lens may be made out of a combination of close lenses.
Early Microscopes
• Robert Hooke was an
English microscopist who
made this microscope in
1665.
• The magnifying power
was from about 10x to
40x.
• Can you pick the light
source, condenser and
eyepiece?
Early Microscopes
•In 1665 Hooke published his book of drawings - ‘Micrographia’ where he showed micrographs of cork with small pockets of air.
•This reminded him of cells in a monastery and so the name
“cell” was first used. Hooke didn’t understand though that these
hollow spaces of air were once living.
Early Microscopes
•By the 1670s Antoni van
Leeuwenhoek started making
drawings of bacteria and
spermatozoa which he called
“animalicules”. He also made
detailed descriptions of the red
blood cell.
•He used a microscope that he
made himself at home (his actual
profession was draper) that could
magnify up to 200X compared to
only 50X of the previously built
microscopes. His trick was to use
one very good quality lens that
didn’t give a blurred image.
The lens of this simple microscope
sat between two metal plates
Brownian motion
•In 1827 Robert Brown was studying pollen down the microscope and
noticed that it moved around in the water.
•He then looked at dust and found it did the same thing so he
concluded that particles did not have to be alive to move.
•He could not explain this observation as Einstein had not yet
published his work on kinetic energy - which would have provided the
theory to do so.
•Browne called this phenomenon Brownian motion.
Magnification & Resolution
•Magnification: the number
of times larger an image is
than the actual specimen.
By adding stronger lenses a
microscope can magnify an
image many thousands of
time, but resolution may be
limited.
•Resolution: the degree of
detail which can be
achieved. An electron
microscope has greater
resolution than a light
microscope.
All of these dots have the same
magnification, but a different resolution
Early Microscopes
•In the USA, the first compound microscope appeared
at Harvard College in 1732 - although simple
microscopes would have been used before this.
•By 1831 there were about a dozen microscopes in
the US. Instructors were using them by 1850 and
some students by 1875.
•They were in general use in 1890.
Early Microscopes
Light source
Condenser
Specimen
Focus adjustment
Eye
piece
Bonannus 1691
The Light Microscope & Cells
•The most common microscope
in use today is the light
microscope.
•This is similar to the one we
use in our laboratory at school.
•With the advent of the light
microscope, scientists were able
to study cells with the kind of
detail never known before.
The Light Microscope
Eye piece
Coarse focus knob
Fine focus knob
Arm
Stage adjustment
Stage clip
Condenser
knob
Body tube
Rotating nose piece
High power
objective lens
Low power
objective lens
Stage
Diaphragm
Condenser
Mirror
Base
Cells -
what can we see with the Light Microscope?
•Before we discuss cells in any detail, first we must consider
a cell and the cell theory
•The cell theory states that:
•All living things are made up of one or
more cells or of products of cells
•The cell is the simplest unit of life
•All cells are produced from existing cell
Cells -
what can we see with the Light Microscope?
•Here are 3 light
micrographs of onion
skin (epidermis) at
different magnifications
•You can just about
make out the nucleus
in the middle of the cell
•There is a rigid cell
wall, which helps to
identify it as a plant
Nucleus
•You could also label
the cytoplasm
Rigid cell wall
Cytoplasm
Cells -
what can we see with the Light Microscope?
Light micrograph of plant
cells with large vacuoles
around the central nucleus
Light micrograph of blood
showing red blood cells
(stained pink) and white
blood cells (purple stained
nucleus)
Cells -
what can we see with the Light Microscope?
Light micrograph of bacteria
(bacillus) shown with a
purple stain. Only the outline
of the cells can be seen
Human egg cell injected with a
fine needle. The cell is held in
place with the delicate suction
from the pipette on the left.
The Phase Contrast Microscope
•The Phase contrast microscope looks like a light
microscope but works on the principle of creating a
type of shadow of the specimen.
•This sort of microscope has limited use for looking
at specimens in great detail, but can be used in
tissue culture where the general growth of cells is
monitored.
•The beauty is that slides do not need to be
prepared and specimens can be viewed actually in
the dished they are growing in.
Cells -
what can we see with the Phase Contrast Microscope?
This is an oocyte taken under a
phase contrast microscope, again
the detail is not as good as with
an ordinary light microscope
Here we can see the bacteria similar
to the bacteria under the light
micrograph but with less detail
The Electron Microscope
•In the 1930s the electron microscope was
developed. Instead of using light, it applied a
beam of electrons to view the specimens at
around 100,000x magnification.
•There are two kinds of electron microscopes
in use today, the Scanning Electron
Microscope (SEM) which gives an image of
the surface of a specimen, and the
Transmission Electron Microscope (TEM)
which sends electrons through the specimen.
The Electron Microscope
Cells -
what can we see with the Electron Microscope?
These Electron micrographs show the
surface of the female egg cell (oocyte).
Compare the detail in these to the light
and contrast photomicrographs!
This EM micrograph shows the 3D state of
these red blood cells (concave shape) and
the single white blood cell. The photo has
been colour enhanced as EM micrographs
can be seen only in black and white.
Cells -
what can we see with the Electron Microscope?
Electron Microscopes allowed Scientists to identify new and different structures
within cells. This enabled them to classify cells into three basic types.
All Cells
Prokaryotes:
Eukaryotes:
No true nucleus such
as in bacteria
True nucleus
Plant Cells:
Animal Cells:
Cell wall
No cell wall
Chloroplasts
No Chloroplast
Large central vacuole
Small vaculoes
Cells -
what can we see with the Electron Microscope?
Prokaryotic cell - Bacteria
•Much greater detail is
evident on the surface
of this bacteria.
•Two cell membranes
can be seen.
Cells -
what can we see with the Electron Microscope?
Prokaryotic cell - Bacteria
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Animal cell
•As with the bacteria,
the electron microscope
can pick up much
greater detail.
•Here we can even see
some of the organelles
inside the cell.
•Let’s have a closer
look...
Cells -
what can we see with the Electron Microscope?
Pinocytosis
vesicle
Lysosome
Golgi vesicles
Rough endoplasmic
reticulum - RER
Smooth endoplasmic
reticulum -SER
Eukaryotic cell - Animal cell
Mitochondria
Golgi body
Nucleolus
Nucleus
Centrioles
Microtubules
Cell
membrane
Cytoplasm
Ribosome
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Animal cell
Mitochondria
Mitochondria
Golgi body
Nucleus
Nucleolus
Nuclear
pore
Rough ER
Cell Membrane
•Here is a 3D
diagram of a
plant cell with all
its membrane
bound
organelles.
•See how many
of these you can
recognise...
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Rough ER
Rough ER with
many ribosomes
Nucleus
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Mitochondria
Mitochondria
Inner folded
membrane
Outer membrane
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Mitochondria
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Golgi Body
Golgi body
Golgi vesicle
Cells RER
what can we see with the Electron Microscope?
Nucleus
Centrioles
Eukaryotic cell - Centrioles
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Plant cell
•What other structures
can you identify in a
plant cell?
•Can you find the cell
wall, the chloroplasts
and the large vacuoles?
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Plant cell
Golgi vesicles
Ribosomes
Smooth ER
Nucleolus
Nucleus
Rough ER
Cell wall
Cell membrane
Golgi body
Chloroplast
Vacuole membrane
Vacuole
Starch granule
Mitochondria
Cytoplasm
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Plant cell
Chloroplast
Vacuole
•This is the 3D
view of a typical
plant cell; note
the rigid shape
that is typical of
plant cells
•Can you
recognise the
typical plant cell
organelles?
Cell wall
Cells -
what can we see with the Electron Microscope?
Eukaryotic cell - Plant cell - Chloroplast
Grana stacks
Thylakoid
membrane
Cells -
what can we see with the ELectron Microscope?
Eukaryotic cell - Plant cell - Chloroplast
The End