1. Unit 3: It's a Small World
Microorganisms and
Disease

2. What Do You Think?
When you “catch a cold,” what is it
that infects your body?

3. Germ Theory
 Idea that microorganisms can and
are the cause of many diseases
 Originally proposed back in 1020
A.D. and built upon by many
different scientists
 Microorganisms were first observed
by Anton van Leeuwenhoek
 Louis Pasteur, a French
chemist, helped to disprove another
competing theory and his

4. Germ Theory
 Joseph Lister, an English
surgeon, was one of the 1st to
realize the importance of germ
theory
 He used chemicals on wounds to
kill germs
 Also made sure that everything that
touched his patients was washed in
a chemical solution so that it was
free of germs

5. Antiseptics = Disinfectants?
 Antiseptics are for use on people
 Disinfectants are for use on objects
and surfaces.

6. Robert Koch
 1st to actually demonstrate that
microorganisms do cause disease
 Studied anthrax
 While investigating the disease, he
developed a set of rules for proving
that a microorganism is the cause
of a specific disease.
 These rules are called Koch’s
postulates and they are a good
example of the scientific method.

7. Koch’s postulates
1. The microorganism must be found
in abundance in all organisms
suffering from the disease, but not
in healthy organisms.
2. The microorganism must be
isolated from a diseased organism
and grown in pure culture.

8. Koch’s postulates
3. The cultured microorganism
should cause disease when
introduced into a healthy organism.
4. The microorganism must be
reisolated from the
inoculated, diseased experimental
host and identified as being
identical to the original agent.

9.  List as many different diseases as
you can.

10. Diseases
 2 types of disease
 Noninfectious diseases: diseases
that are not spread from one person
to another
 Infectious diseases: diseases that
can be passed from one living thing
to another

11. What causes disease?
 Noninfectious diseases can be
caused by many different factors.
Smoking, lack of physical
activity, and a high-fat diet can
greatly increase a person’s chances
of getting many noninfectious
diseases.
 Infectious diseases are caused by
pathogens

12. Think, Pair, Share
 How is an infectious disease
different from a noninfectious
disease?

13. Did You Know?
 Before the mid-1800’s, doctors and
surgeons rarely washed their hands
before surgery.
 This was because pathogens were not
known about
 Many people believed that if someone
got a disease it was because they were
being punished

14. Pathways to Pathogens
 Look at p.S68 in your textbook.
What are two ways that infectious
diseases are spread?

15. Pathways to Pathogens
 There are many ways pathogens
can be passed from one person to
another. Being aware of them can
help you stay healthy.
1. Through the air: a single sneeze
releases thousands of tiny droplets
of moisture that can carry
pathogens

17. Pathways to Pathogens
2. Contaminated objects: person who
is sick may leave bacteria or
viruses on objects such as
doorknobs, keyboards, drinking
glasses, towels, or combs.
3. Person to Person: may become
infected with some illnesses by
kissing, shaking hands, or touching
the sores of an infected person

18. Pathways to Pathogens
4. Animals: some pathogens are
carried by animals; humans can get
ringworm from handling an infected
dog or cat. Also, ticks can carry
bacteria that cause Lyme disease.
5. Food and water: water lines can
break or treatment plants can
become flooded allowing
microorganisms to enter the public

19. Brain Food
 In developing countries, 80% of
diseases are related to
contaminated drinking water.

20. Inferring Relationships
 Why might the risk of infectious
disease be high in a community that
has no water treatment facility?

21. Checkpoint
 Jackie cut up raw meat on her
kitchen counter. If her brother
makes a sandwich on the same
counter later, how could he come in
contact with a pathogen?

22. Causes of Infectious Disease
 Bacteria are one kind of
microorganism that can cause an
infectious disease.
Can affect the human body in different
ways
 Bacteria can kill cells and tissues
 Other bacteria do damage by
releasing toxins

23. Causes of Infectious Disease
Viruses
 Smallest of disease-causing
microorganisms
 Even the largest virus can just
barely be seen with a light
microscope
 Common
cold, influenza, warts, rabies, AIDS,
Ebola

24. Causes of Infectious Disease
Protozoans
 Malaria and sleeping sickness
Fungi
 Cells of the fungus enter the body
through the digestive or respiratory
system
 Athlete’s foot and ringworm

25. Think, Pair, Share
 What are the four causes of
infectious disease?
 Which cause involves toxins?
 Which cause is at fault when you
have the flu?