5b) Gram-positive bacteria: • Have a thick peptidoglycan layer in their cell wall. • Lack an outer membrane. • Retain the crystal violet stain and appear purple after Gram staining. • Examples: Staphylococcus aureus, Streptococcus pyogenes. Gram-negative bacteria: • Have a thin peptidoglycan layer in their cell wall. • Possess an outer membrane containing lipopolysaccharides (LPS). • Do not retain the crystal violet stain and appear pink or red after Gram staining. • Examples: Escherichia coli, Salmonella typhi. 5c) Koch's Postulates: 1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms. 2. The microorganism must be isolated from a diseased organism and grown in pure culture. 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 specific causative agent. 5d) Four examples of culture media: 1. Nutrient Agar (general purpose) 2. Blood Agar (enriched, differential) 3. MacConkey Agar (selective, differential) 4. Mannitol Salt Agar (selective, differential) 5e) A bacterial growth curve illustrates the change in the number of viable bacterial cells in a population over time when grown in a batch culture. It typically consists of four phases: 1. Lag phase: Bacteria adapt to the new environment; little to no cell division occurs. 2. Log (exponential) phase: Cells divide rapidly at a constant rate, leading to exponential increase in population size. 3. Stationary phase: The rate of cell division equals the rate of cell death due to nutrient depletion and waste accumulation, resulting in a plateau in population size. 4. Death (decline) phase: The rate of cell death exceeds the rate of cell division, leading to a decrease in the number of viable cells. 6a) Bacteriophages are viruses that infect and replicate within bacteria and archaea. They are composed of genetic material (DNA or RNA) enclosed in a protein shell called a capsid. 6b) Step 1: Determine the number of generations ($n$). The formula for bacterial growth is $N_t = N_0 \times 2^n$, where $N_t$ is the final number of cells, $N_0$ is the initial number of cells, and $n$ is the number of generations. Given: $N_0 = 1000$ cells, $N_t = 1,000,000$ cells. $$1,000,000 = 1000 \times 2^n$$ Divide both sides by 1000: $$1000 = 2^n$$ To solve for $n$, take the logarithm base 2 of both sides, or use common logarithms: $$n = \frac{\log_{10}(1000)}{\log_{10}(2)}$$ $$n = \frac{3}{0.30103}$$ $$n \approx 9.966 \text{ generations}$$ Step 2: Calculate the generation time ($g$). Generation time is the time it takes for a population to double, calculated as $g = \frac{t}{n}$, where $t$ is the total time. Given: $t = 24$ minutes. $$g = \frac{24 \text{ minutes}}{9.966}$$ $$g \approx 2.408 \text{ minutes}$$ The generation time is approximately $\boxed{\text{2.41 minutes}}$. 6c) Four differences between lytic and lysogenic cycles: 1. Fate of Host Cell: In the lytic cycle, the host cell is lysed (destroyed) to release new virions. In the lysogenic cycle, the host cell is not immediately destroyed; the viral DNA integrates into the host genome. 2. Viral DNA Integration: In the lytic cycle, the viral DNA remains separate from the host genome. In the lysogenic cycle, the viral DNA (prophage) integrates into the host bacterial chromosome. 3. Replication: In the lytic cycle, the viral genome replicates independently and produces new viral particles. In the lysogenic cycle, the integrated prophage replicates along with the host chromosome during cell division. 4. Prophage/Provirus State: The lytic cycle does not involve a prophage stage. The lysogenic cycle is characterized by the presence of a prophage, which can remain dormant for many generations. 6d) One function for each: i. Capsid: Protects the viral genetic material (DNA or RNA) and aids in the delivery of the viral genome into the host cell. ii. Plasmid: Carries non-essential but often beneficial genes (e.g., antibiotic resistance, virulence factors) that can be transferred between bacteria. iii. Ribosomes: Sites of protein synthesis (translation) in both prokaryotic and eukaryotic cells. iv. Pili: Involved in bacterial conjugation (transfer of genetic material between bacteria) and attachment to surfaces. v. Capsules: Provide protection against phagocytosis by host immune cells and aid in adhesion to surfaces. vi. Flagella: Provide motility, allowing bacteria to move through liquid environments. vii. Fimbriae: Short, hair-like appendages primarily involved in attachment to host cells and surfaces. viii. Autoclave: Uses high-pressure steam to sterilize equipment and media, killing microorganisms including spores.