Which is a part of the cell theory? cells come from pre-existing cells cells have a nucleus organisms with one cell must be seen with a microscope organisms must have more than one cell to live

Cells come from pre-existing cells.

The correct answer is option A, cells come from pre-existing cells.

There are three major concepts of the cell theory and these are as follows:

1) There are numerous cells in an organism. Thus, it can be stated that all organisms  are made of one or more cells.  

2) Each cell has a specific job or function.

3) All cells evolve from their parent cell ( or already existing cells)

.

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!