What is the smallest structural and functional unit of a living organism?

What is typically used to study the structure of a plant cell?

"Omnis-cellula-e-cellula" was given by

Which of the following is the first level of biological organization that can be considered a living entity?

$A.$ Mycoplasma, the smallest cells, are only $0.3 \mu m$ in length.
$B.$ Size of bacteria could be $3$ to $5 \mu m$.
$C.$ Human red blood cells are about $7.0 \mu m$ in radius.

Which statement is inconsistent with the Cell Theory?