2. Overview
Homeostasis: stability of the internal environment and the mechanisms that maintain the stability
Homeostasis is constantly threatened
If an organism doesn’t respond to these threats it can result in disease or death
Viruses, bacteria, fungi, and other parasites may infect organisms and disrupt homeostasis  impacts on life functions

3. Germ Theory for Disease
Germ Theory: Disease is caused by the presence of pathogenic microorganisms
Many scientists contributed to this understanding, but Pasteur and Koch are the two most recognized for their contributions
Louis Pasteur:
Chemist
Discovered fermentation and decay were caused by living microorganisms  pasteurization process
Robert Koch:
Microbiologist who built on Pasteur’s finding
Discovered a universal method for determining whether a specific bacterium causes a certain disease
PAUSE before this slide and show this video about Pasteur’s experiments, just 0-3:43!

4. Causes Presence of disease-causing bacteria, viruses, or fungi
Remember viruses are not living things – they are intracellular parasites that can only reproduce using another cell
Hereditary factors
Genes you inherit from your parents
Environmental factors
Ex. Toxic substances, poor nutrition, unhealthy habits, exposure to mutagens, etc.
These can show up right away or have effects years down the road
Gene mutations  uncontrolled cell division = cancer
It is important to emphasize that exposure to environmental factors that cause disease can have immediate impacts on our health and ability to maintain homeostasis and prevent disease, but they can also not show to have any effects until years down the road.
YES, this is a unit specifically about pathogens – aka microorganisms or biological entities that cause disease – BUT we would be remiss NOT to address other disease causing factors, such as inherited genes that cause genetic disorders, genes that give us genetic predispositions to certain diseases, and of course environmental influences.
This is a topic that is still being HIGHLY researched and the wealth of knowledge available and understanding is still vastly growing and developing. This concept is designed to give students an overview of this broad topic and some points of clarification.

5. Why are they such threats?
Bacteria and Viruses
Specifically in this unit, we are going to focus on how bacteria and viruses cause disease.
Why are they such threats?
They can live in a variety of environments.
We can’t see them.
They reproduce SO FAST!
This allows them to evolve adaptations in populations quickly
Very quick video clip about rapid bacteria growth and reproduction:

6. How do bacteria cause disease?
Bacterial Diseases
How do bacteria cause disease?
Invade the organism
Challenge the immune system
Use cells for food  a breakdown of healthy cells and tissues
Release toxins that can travel to different tissues throughout the body, once in the bloodstream
These next two slides are simplified overviews of how bacterial and viral diseases work. Students will get a more in-depth understanding through the disease research project.
Make sure students know that research is constantly being done on disease and new discoveries are impacting how we understand and treat disease.
HOW THE ON EARTH DO THESE TINY MICROORGANISMS DOMINATE MASSIVE ORGANISMS LIKE US?  A fascinating TED Talk can be seen at the following link which talks about the discovery of how bacteria communicate and facilitate group behaviors to work together to take over massive hosts:

7. How do viruses cause disease?
Viral Diseases
How do viruses cause disease?
Viruses target specific tissues
Ex. Influenza virus targets the respiratory tract
Ex. Hepatitis targets the liver
Invade target cells
Hijack their protein expression mechanisms
Copy themselves
This slide and the previous one are simply overviews of how bacterial and viral diseases work. Students will get a more in-depth understanding through the disease research project.
Great video about how the flu virus invades our bodies: