2. Overview Pathogens = disease-causing agents
Can be bacteria, viruses, or other microorganism
Only 1% of all bacteria are actually pathogens!!
Bacteria and viruses are often confused. We are going to differentiate between the two in terms of structure, reproduction, and other characteristics!
This concept is an important overview and introduction before we can really jump in to bacteria and viruses as pathogens! We really want to steer clear of having students really focus on bacteria and viruses solely in relationship to disease in this concept. Let’s give students an appreciation for them as biological entities prior to jumping into the disease content!

3. BACTERIA Prokaryotic unicellular organisms Characteristics
10x smaller than eukaryotic cells
Organisms means they are LIVING! They meet all the characteristics of life.
This is a great time to the review those! If you haven’t previously covered characteristics of life, check out my free inquiry activity on them:

4. BACTERIA Structure Cell wall made of peptidoglycan Cell membrane
Cytoplasm
Nucleoid region with 1 circular DNA chromosome and plasmids
Ribosomes
SOME have a capsule on the outside
Flagella and pilli can be used for movement
Plasmids = small ring of DNA that carries a few genes, separate from the circular bacterial chromosome that even replicates separately from the singular chromosome. Often where genes for antibiotic resistance are carried.

5. Classification by Shape
BACTERIA
Classification by Shape
Bacteria can have many different shapes and are often classified by their shape. A few of the most common shapes are:
Coccus
Ex. Streptococcus
Bacillus
Ex. E. coli
Spiral
Ex. Treponema pallidum
Coccus = singular, Cocci = plural
Streptococcus causes strep throat, meningitis, pink eye, and bacterial pneumonia
Bacillus = singular, Bacilli = plural
Treponema pallidum causes syphillus

6. Classification by Gram Stain
BACTERIA
Classification by Gram Stain
Bacteria can also be classified by differences in cell wall structure:
Gram-positive: cell wall is high in peptidoglycan  shows purple dye
Gram-negative: cell wall has a thin layer of peptidoglycan with a polysaccharide layer on the outside instead  doesn’t show purple dye, appearing red
G-P Photo Credit: CDC -
G-N Photo Credit: CDC -

7. BACTERIA Uses Foods like yogurt, cheese and pickles Decomposing matter
Every step of the nitrogen cycle
Arguably most importantly converting atmospheric nitrogen into a usable form for plants!
In humans:
Bacteria on our skin help to prevent infections
Bacteria in our gut help us digest our food
Biotechnology:
Making antibodies, insulin, HGH, vitamins and other drugs
BACTERIA DO SO MUCH MORE THAN JUST CAUSE DISEASE!! This should be the anthem of this slide!!
Prior to going through this slide, ask students what they know bacteria do. If you have used my full year biology curriculum, they should DEFINITELY know about the role of bacteria in decomposition (carbon and nitrogen cycles) and every step of the nitrogen cycle! Only 1% of bacteria actually cause disease!

8. BACTERIA Reproduction Asexual reproducers that do binary fission
Nucleoid region is copied
Unicellular organism splits in half  2 identical bacteria
How is genetic variation introduced?
Mutation: random change in genetic material
Conjugation: DNA transfer between two cells
Transformation: uptake of foreign DNA from the organism’s surroundings
Transduction: when a virus transfers genes between prokaryotic organisms
Discuss when lecturing this slide the evolutionary disadvantages of asexual reproducers  identical offspring, which is the lack of genetic variation!
How then are bacteria able to evolve via natural selection? Due to MUTATION! (They should be able to come up with this with proper prior knowledge of evolution!) They will not be able to come up with conjugation, transformation, and transduction.