AP Biology

Definitions of Life

• Defining Life: Identifying a specimen as alive can be challenging due to various defining attributes that may not be uniformly applicable.

Challenges in Defining Life

• Case Study 1: Mammalian Red Blood Cells

  • Location of Production: Made in the red bone marrow of large bones.

  • Specialization: Specialized for gas transportation.

  • Characteristics of Maturity:

    • Lacks nucleus

    • Lacks mitochondria

  • Life Span: Approximately 120 days.

• Case Study 2: Viruses

  • Composition: Contains genetic material (RNA or DNA) and a protein coat.

  • Life Status: Considered an "obligate intracellular parasite", meaning they depend on a host's metabolic processes for reproduction.

  • Evolution: Capable of evolving, which is why a flu vaccine from a previous year might not be effective.

  • Host Range: Can jump between different species.

Virus Infection Process**

1. Entry: A virus enters a host cell.

2. Disassembly: Substances inside the cell begin to strip off the virus's outer protein coat.

3. Nucleic Acid Release: The nucleic acid of the virus is released into the cell.

4. Cell Reaction: The cell "ignores" its own chemical needs.

5. Manufacturing New Viruses: The cell begins to shift its manufacturing processes towards creating new viral particles.

6. Release of New Viruses: Many new viruses are produced and released, which can then go on to infect other cells.