what are factors that induce cells to divide in plant and animal cells?

Answer 1

Cell division (think CELL CYCLE) is regulated by an incredibly complicated series of genes/proteins and signaling. But in the simplest terms, cells have genes called "oncogenes" and "tumor supressor genes", of which the former causes cell division, and the latter stops cell division.

In all cells, both of these kinds of genes are functioning all the time, but are regulated by various pathways (by extracellular signaling, and even factors from within the cell).

An oncogene we know a lot about is called RAS, and a tumor suppressor we know a lot about is p53. Basically in cancer, and this is just two examples: (1) RAS (an oncogene) activity is unregulated, thus the cell loses control of the cell cycle and divides uncontrollably. (2) p53 activity is lost, and thus we lose "tumor suppressor" function, and the cell divides uncontrollably.

The problems with cancers are not always these genes themselves, but the pathways that regulate them (regulate their transcription for example). There are many many many different things that can upset these pathways, and thats why cancer is so so difficult to fight/prevent.

Answer 2

chemical signals from other cells, DNA production, size (surface area to volume ration) and the amount of diffusion it can handle to keep the cell running