Re: How do diatoms get chemicals like water though there glass cell wall?

The shells or "frustrules" of all diatoms are full of tiny holes (pores), 
which number in the hundreds of thousands on a single cell.  (These pores 
have lovely geometric patterns, for which diatoms are justly famous)
When seen with high power SEM (scanning electron microscopes), these pores 
turn out to be rather complex; if you see one pore on the outside of a 
diatom, it often is connected to a tiny chamber which has a seive-like inner 
surface perforated by dozens of really tiny pores.  Even slender diatom 
spines, like tbose on Chaetoceros (which are hollow), are perforated by 
orderly rows of rectangular pores.

Diatom frustules offer protection, but only against the really small enemies 
of diatom-kind.  (I have seen a large naked dinoflagellate swallow a large 
round diatom whole, and then spit out the empty frustule.)  Some small 
diatom-loving grazers like dinoflagellates can jam a feeding tube into the 
tiny gap between the two halves of the frustule and suck out chloroplasts 
and everything, while certain other non-photosynthetic marine  
dinoflagellates that I once studied (called Protoperidinium) can wrap a 
giant pseudopod around the entire diatom (even long spiney chains of 
diatoms) and digest it "extracellulary", allowing their digestive enzymes to 
diffuse into through the diatom pores, and the liquified diatom cytoplasm to 
then diffuse back out, leaving the frustules clean and intact.  

Cheers,
Dean Jacobson