What is formed by the integration of organelles?

In terms of size, which category do atoms fall into?

The phase-contrast microscope is ..........

$A.$ 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.

What is meant by cell theory? Who presented its principles? Which improvements were done in it? Describe them.

................examined a large number of .................and observed that all are composed of different kinds of cells which form the tissues.