Approximately how many atoms are in a human ovum?

Ok. Here is the approach I took. In the chart in the first link, human ova mass (weigh is listed as 3.6 micrograms. (0.0000036 g). For some chemistry, Avogadro's number (6.022 x 10^23) can be used to interconvert mass and molecular count via molecular formula weights. For instance formula weight of a mole of pure water is 18 g/mol. So a gram of water has Avogadro's number of molecules. You asked for atoms though so a gram of water (2H + O) would have 3 times that many atoms. Unfortunately the number I arrive at below will not be very exact because the physiology of an ovum is very complex. I mention water because that is the primary constituent of cytoplasm...the jelly like filler material inside the egg. However there is the cell wall, nucleus (predominantly genetic material) and even protein strings within the cytoplasm. Rather than get too granular with estimates of percent weight of hundreds of different constituents. For a rough estimate somewhere in the region of the true number I treated it as if the egg was comprised of 60% water and 40% glycine (formula weight 75 g/mol, 10 atoms per molecule), a very common amino acid in proteins.

from there it is (mass of ovum ÷ molecular formula weight) × Avogadro's number × number of atoms per molecule.

Can calculate the water and glycine portions seperately or do a weighted average.

I come out to 3.08 ×10^17 or
300,800,000,000,000,000
Three hundred quadrillion plus change

https://en.m.wikipedia.org/wiki/Glycine
https://en.m.wikipedia.org/wiki/Orders_of_magnitude_(mass)
http://www.britannica.com/science/ovum
http://www.britannica.com/science/Avogadros-number

Sorry, second sentence should refer to the second link not the first. Glycine link got added out of intended order.
Should also read "18 grams of water have a mole of molecules"