Penicillin inhibits peptidoglycan cross-linking in bacterial cell walls. Streptomycin targets ribosomes, tetracycline inhibits protein synthesis, and chloramphenicol inhibits 70S ribosomes.

Flagella enable bacterial movement in response to chemical gradients (chemotaxis). Chemoreceptors detect signals, but flagella provide the locomotion. The other options are not functions of flagella.

Viruses lack their own metabolic machinery and depend on host cell machinery for replication. Options A, C, and D are all characteristics of viruses.

Influenza viruses (types A, B, and C) belong to the family Orthomyxoviridae. They are enveloped, negative-sense RNA viruses with segmented genomes.

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.

Bacteriophages replicate through either the lytic cycle (destroying the host cell) or lysogenic cycle (integrating DNA into host chromosome). Binary fission is bacterial reproduction.

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.

Bacillus subtilis is a gram-positive, rod-shaped bacterium capable of forming endospores. E. coli is gram-negative, V. cholerae is gram-negative curved rod, and P. aeruginosa is gram-negative.