1) cell growth You should look into chemotherapy and cancer
medicine in general. Because chemo is mostly effective because
it kills fast dividing cells, this has been worked out
reasonably well. the 7-10 year number is not really correct,
some cells are replaced a lot more slowly. This is why hair
often falls out in cancer treatment, because the follicle cells
are growing quickly. Neurons divide very slowly - if at all -
and often are never replaced. Fat cells are in between -
probably replaced in the 7-10 year range. Heart cells are
replaced albeit quite slowly - less than 1% per year, which
implies that many cells are with you your entire lifetime. 2)
atoms/molecules change The cell itself is in a continuous state
of flux, but different parts of the cell, like cells in the
body, change at different rates. Some proteins which make up the
cell matrix or the DNA in the nucleus are replaced very rarely
(through repair or rearrangement of the chromosome for instance)
and most of the chromosome DNA is with the ce