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Germ Theory & Viruses
+Before there were microscopes…
�People could not see microorganisms, so
they didn’t know they existed.
�People created explanations for disease:
� Witchcraft
� Evil spirits
� Bad air (“miasma”)
� Balance / Imbalance
�Eventually, people understood that there was
a link between dirt and disease, but they
could not explain the link.
+Old explanations for diseases/behaviors…
+Old explanations for diseases/behaviors…
Discovery of Micro-organisms
�Leeuwenhoek invented the first microscope.
�Saw small, living organisms in everything he looked at (food, poop, plaque, water, etc)
�He wasn’t a biologist, so didn’t understand what role they played in disease.
+Competing theories of disease
�Old Theory: spontaneous generation
� Said that micro-organisms come from rotting matter.
� In other words, said that diseases came from non-
living things.
� AKA abiogenesis
�New Theory: germ theory
� Says micro-organisms cause rotting matter.
� In other words, says that diseases come from living
things.
� AKA biogenesis
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Improved microscopes
�1800s – purer glass
produced � better
lenses for microscopes.
�1830 – Joseph Lister
developed a
microscope which could
magnify 1,000x
+Disproving spontaneous generation
�People who believed in spontaneous generation
basically believed that maggots came from
rotting meat
� (rather than adult flies laying eggs on rotting meat)
+Disproving spontaneous generation
�Francesco Redi disproved the theory of
spontaneous generation through an experiment
using meat in 3 jars
� 1 jar had no lid
� 1 jar had a mesh lid
� 1 jar had a solid lid
+Disproving spontaneous generation
� (What was the I.V.? What was the D.V.?)
http://www.phschool.com/atschool/phsciexp/active_art/redi_pasteur_experiment/index.html
+Linking micro-organisms to disease
�Louis Pasteur was the man that made the breakthrough and linked germs to disease.
�Did an experiment that proved microorganisms can be killed with heat
�Anything that can be killed must first be “alive”!
�This process is now called Pasteurization
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+Linking micro-organisms to disease
http://bcs.whfreeman.com/thelifewire/content/chp03/0302003.html
+Linking bacteria with disease
�Pasteur never showed the link
between bacteria and human
disease.
�This was left to Robert Koch
�Discovered microbes that cause
Anthrax, Tuberculosis, and
Cholera
+What is a pathogen?
�Pathogen = a microorganism
that causes disease
�Bacteria
�Virus
�Fungus
�Worm
+What are bacteria?
�Bacteria
�Single-celled
�Prokaryotic
+Types of Bacteria
+What are viruses?
�Viruses
� Considered non-living
� Not made of cells
� Do not grow, develop, or carry out
respiration
� Cannot reproduce on their own (need
host cell)
� Take over living cells in order to
reproduce
� Are like pirate robots
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+What are viruses?
�Viruses are made of:
� Crunchy protein coat
� Gooey Nucleic Acid (DNA/RNA) core
+What are viruses?
�How do viruses reproduce?
� Inserts its DNA / RNA into the host
cell
� The host cell copies the virus’ DNA
/ RNA along with its own DNA / RNA
� The cell explodes and new viruses
are released
+What are micro-organisms?
+Types of Viruses
+Now that we understand…
�We have changed our health practices
�Modern health practices emphasize:
� sanitation
� the safe handling of food and water
� techniques to keep germs out of the body
� the development of vaccinations, antibiotics, etc. that
destroy microorganisms
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