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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