Viroids are naked RNA molecules that infect plants.

Smallpox, caused by the Variolavirus, is the only human disease that has been completely eradicated globally through vaccination efforts. The World Health Organization (WHO) launched an intensive smallpox eradication campaign in 1967, using the vaccinia virus to immunize populations worldwide. Vaccination created herd immunity, interrupting transmission of the virus between humans, as humans were the only reservoir for smallpox. The last naturally occurring case was reported in 1977, and in 1980, WHO officially declared smallpox eradicated.

A. Nucleus: The nucleus contains the cell’s genetic material and controls transcription and replication. While nuclear damage can affect gene expression and cell survival, it does not directly explain the acute loss of ion gradients and cellular lysis caused by disruption of membrane integrity.

B. Cell membrane: The cell membrane, composed of a phospholipid bilayer with embedded proteins, maintains selective permeability, ion gradients, and cellular homeostasis. Disruption of the membrane compromises the barrier between intracellular and extracellular environments, causing uncontrolled ion flux, osmotic imbalance, and eventual cell lysis.

C. Ribosome: Ribosomes are responsible for protein synthesis, translating mRNA into polypeptides. Impaired ribosomal function affects protein production but does not immediately cause loss of ion gradients or membrane rupture.

D. Cytoskeleton: The cytoskeleton provides structural support, intracellular transport, and shape maintenance. While damage to cytoskeletal elements can affect cell morphology and motility, it does not directly cause ion imbalance or lysis due to phospholipid bilayer disruption.

E. Golgi apparatus: The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or intracellular use. Dysfunction here affects protein processing and trafficking but does not directly compromise membrane integrity or lead to immediate lysis.