Download Microscopes

Cytology
Technology and Discoveries
Timeline
Microscopes allowed discoveries
about cells to be made
• Light microscopes
– use beams of light and lenses to
create magnified images
– can be used to view dead or
living organisms
Early light microscopes
• Simple Light
Microscope – uses
ONE lens and light
• Basically just a
magnifying glass
• These were in use by
the early 1600’s.
First view of cells
• Robert Hooke used a sharp knife
to slice a thin layer from a piece
of cork, and looked at it under a
microscope.
• He called the small chambers he
saw “cells” because they
reminded him of the small rooms
(cells) in monasteries.
• This first use of the word cells
occurred in 1665.
• They were actually cell walls.
First knowledge that there are organisms
too small to see with the naked eye
• Anton von
Leeuwenhoek used a
simple light microscope
to look at a sample of
pond water.
• He was the first to
realize, in 1674, that
there are living things
to small to see with the
naked eye.
First effort to prove that life does not
appear by “Spontaneous Generation”
• People had noted that maggots
often appeared on rotting meat.
• They though meat produced
maggots.
• This (incorrect) idea is called
“spontaneous generation.”
• Francisco Redi did an
experiment in which he showed
that maggots only appear if
flies are allowed to lay eggs on
the meat.
• This happened in 1668.
Modern Compound Light
Microscopes Become Available
• Compound light
microscopes use two lenses
and light to produce a
magnified image.
• The total magnification =
eyepiece magnification x
objective magnification
All plants are made of cells
• Mathias Schleiden used
a compound microscope
to examine many, many
plants.
• In 1838, he concluded
that all plants are made
of cells.
All animals are made of cells
• Theodore Schwann used a compound microscope
to look at many, many animals.
• In 1839, he concluded all animals are made of
cells.
All cells come from pre-existing cells
• Rudolf Virchow
studied cells from
embryos and from
adult human tissue.
• In 1855, he helped
spread the knowledge
that all cells come
from pre-existing
cells.
The Cell Theory 1864–
Summarized findings about cells
1. All living things are composed of
cells.
2. Cells are the basic units of structure
and function in living things.
3. New cells are produced from
existing cells.
Cell Theory has been UPDATED
to also include:
4. The activity of an organism depends on the
total activity of independent cells.
5. Energy flow (metabolism and biochemistry)
occurs within cells.
6. Cells contain hereditary information (DNA)
which is passed from cell to cell.
7. All cells are basically the same in chemical
composition in organisms of similar species.
Spontaneous Generation does NOT
occur
• Two hundred years
after Redi’s
experiment, some
argued that the only
reason spontaneous
generation didn’t occur
in his jars was because
there was no air for
organisms to breathe.
Definitive proof that life does not
arise by spontaneous generation
• An experiment by
Louis Pasteur in
1864, involving a
goose-neck flask,
finally proved
there is NO
spontaneous
generation.
Pasteur’s experiment disproving
spontaneous generation
Disease and infections are caused by
germs
• Louis Pasteur, who
disproved spontaneous
generation, also
proposed the Germ
Theory of Disease in
the 1860’s.
• Specific diseases are
caused by specific
microorganisms.
Robert Koch – 1876; developed a method to
prove whether a certain germ caused a certain
disease.
Penicillin – the first antibiotic (kills
bacteria) is discovered
• 1928 – Alexander
Fleming was studying the
bacteria that cause staph
infections.
• He found that if mold
grew in the bacteria
dishes, it killed the
bacteria.
• The mold produced
penicillin.
Electron Microscopes – 1940’s
• Use a beam of electrons, instead of
light, to produce magnified images
• Preparing the object for magnification
involves coating it with metal, so it
can’t be used to view organisms while
they are alive.
Scanning Electron Microscope
• Magnifies 100,000
times or more
• Observes surface
detail
• Specimen coated
with thin metal
coating
• 3-D Effect
Transmission Electron
Microscope
• Observes fine
detail
• Requires thin sections
of a specimen
• Magnifies up to one
million times
• This microscope allowed
discovery of organelles!
Origin of Life – Miller and Urey
Experiment
• Designed to test
hypothesis that life in
Earth’s primitive
oceans began when
simple compounds
combined to form the
organic compounds
needed for life.
• Experiment was
performed in the
1950’s.
Amino acids
appeared in the
collecting trap.
Endosymbiotic Theory –
Margulis
• Billions of years ago, complex cells with
organelles arose when several types of simple
cells developed a symbiotic relationship.