What is the main reason that viruses are not considered to be living
organisms?
A They are too small to be living.
B They do not have DNA.
C They need the host cell to replicate.
D
They kill the host cells.

C. They need a host cell to replicate.

Explanation:

In order for an organism to be considered living it must be able to reproduce on with its own species or on its own, (sexually and asexually) which is why we consider viruses not to be living.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.