• Microbes are beneficial in different ways.
• Microbes that possess virulence factors are pathogens.
• Epidemiology is the study of factors that influence transmission and distribution of diseases in a population.

1. How do microbes directly benefit you?
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2. What makes some microbes virulent?
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3. What are the different ways you can catch an infectious disease?
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• Viruses are not cellular and have to reproduce inside a living host.
• Viruses cause many human diseases such as influenza, the common cold, and measles.
• Prions are infectious proteins that can cause disease.

1. Are viruses alive? How can they replicate?
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2. Why aren't you always immune to influenza once you've had it before?
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3. What diseases are caused by herpes viruses?
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4. What does chickenpox have to do with shingles?
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Essential Study Partner

• Characteristics of Viruses
• Viral Replication

Concept Quiz

• Viruses

Bioethical Focus

• Testing of HIV Vaccines

• Bacteria are single-celled organisms that lack a nuclear membrane and other membranous organelles.
• Bacteria can be categorized as gram-positive or gram-negative.
• Bacteria cause many humans diseases including strep infections, food poisoning, and tuberculosis.

1. What is the structure of a bacterium, and how do the cell walls of Gram-positive and Gram-negative bacteria differ?
   Answer
2. What complications are possible after a strep infection?
   Answer
3. Why is tuberculosis on the rise today?
   Answer
4. What are the two major types of food poisoning?
   Answer

Essential Study Partner

• Characteristics of Bacteria
• Diversity of Bacteria

Art Labeling Activity

• Bacterium Cell

• Fungi, protozoans, and worms can also cause disease.

1. What types of diseases are caused by fungi?
   Answer
2. What is the most widespread and dangerous protozoan disease?
   Answer
3. Why isn't schistosomiasis prevalent in this country?
   Answer