  We consider a general growth mechanism, which acts at cellular level and
above (organs, systems and whole organisms). Using its mathematical
representation, the growth equation, we study the growth and division
mechanisms of amoeba and fission yeast Schizosaccharomyces pombe. We show how
this mechanism, together with biomolecular machinery, governs growth and
reproduction of cells, and these organisms in particular. This mechanism
provides revealing answers to fundamental questions of biology, like why cells
grow and divide, why and when cells' growth stops. It also sheds light on
questions like why and how life originated and developed. Solving the growth
equation, we obtain analytical expression for the growth curve of fission yeast
as a function of geometrical characteristics and nutrient influxes for RNA and
protein synthesis, and compare the computed growth curves with 85 experiments.
Statistical evaluation shows that these growth curves correspond to
experimental data significantly better than all previous approximations. Also,
using the general growth mechanism, we show how metabolic characteristics of
cells, their size and evolutionary traits relate, considering fission yeast. In
particular, we found that fission yeast S. pombe consumes about 16-18 times
more nutrients for maintenance needs than for biomass synthesis.
