Gram-positive bacteria appear purple because they contain:

A. Periplasmic flagella: Spirochetes have flagella located within the periplasmic space between the inner and outer membranes. These internal flagella, also called axial filaments, rotate to produce a corkscrew-like motion, allowing the bacterium to move efficiently through viscous environments such as mucus or connective tissue. This unique mechanism is characteristic of genera like Treponema and Borrelia.

B. Pili: Pili are hair-like appendages on the surface of many bacteria used primarily for attachment to surfaces and for conjugation (gene transfer). Pili do not contribute to the corkscrew motility seen in spirochetes.

C. Capsules: Capsules are extracellular polysaccharide layers that protect bacteria from phagocytosis and desiccation. While important for virulence and immune evasion, capsules do not play a role in bacterial motility or the corkscrew movement of spirochetes.

A. log phase: The log phase, or exponential phase, is characterized by rapid, logarithmic growth of bacteria. During this period, the rate of cell division exceeds the rate of cell death, resulting in a steep increase in population size. Nutrients are abundant, and waste products have not yet accumulated to inhibitory levels.

B. lag phase: The lag phase is the initial period after bacteria are introduced into a new environment. During this phase, cells are metabolically active but not dividing, as they adapt to the new conditions, synthesize necessary enzymes, and prepare for active growth.

C. telophase: Telophase is a stage of eukaryotic mitosis, not a bacterial growth phase. Bacteria reproduce via binary fission, so this term does not apply to the bacterial growth curve.

D. stationary phase: The stationary phase occurs when nutrient depletion and waste accumulation slow microbial growth. During this phase, the rate of cell division equals the rate of cell death, resulting in a plateau in population size. This phase reflects environmental stress and triggers survival mechanisms in bacteria.

E. death phase: The death phase follows the stationary phase when the rate of cell death exceeds the rate of new cell formation. The bacterial population declines due to exhaustion of nutrients and accumulation of toxic byproducts.