Influenza A virus has 8 RNA segments, enabling antigenic reassortment. This segmentation allows rapid evolution and pandemic potential through genetic exchange with other influenza strains.

Bacillus and Clostridium are the primary gram-positive bacteria capable of forming endospores. These structures are highly resistant to heat, chemicals, and radiation.

Pili (sex pili) mediate bacterial conjugation, enabling direct DNA transfer between cells. Flagella aid motility, capsules provide protection, and teichoic acids are cell wall components.

Prokaryotes (bacteria and archaea) lack a membrane-bound nucleus and organelles, with circular DNA. Eukaryotes (animals, plants, fungi) have a true nucleus and membrane-bound organelles with linear chromosomes.

Varicella-zoster virus (VZV) causes varicella (chickenpox) in primary infection. The virus remains dormant in nerve tissue and reactivates as herpes zoster (shingles) later in life.

HIV is a retrovirus that carries reverse transcriptase enzyme to convert RNA to DNA. It causes acquired immunodeficiency syndrome (AIDS). Hepatitis B is a hepadnavirus, HSV is a herpesvirus.

Flagella are whip-like appendages that enable bacterial motility. Pili are used for attachment and DNA transfer, capsule provides protection, and mesosomes are infoldings of cell membrane.

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB). M. leprae causes leprosy, C. diphtheriae causes diphtheria, and S. aureus causes various infections.

SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) is the virus responsible for the COVID-19 pandemic that emerged in late 2019. SARS-CoV-1 caused the 2003 outbreak.

Peptidoglycan is the major structural component of bacterial cell walls, forming a rigid framework. It contains N-acetylglucosamine and N-acetylmuramic acid linked by peptide bridges.