Let's explore the wonderful kingdom Protista! (even though it's not actually a natural category... <_<)

(Keeling et al. 2005 Trends Ecol Evol)
Protist = all of the above - land plants, animals, fungi
Can I jgo through single forum without whipping out the Keeling Tree at some random occasion?

Ok, first one will likely be familiar:

Diatom. Important for marine photosynthesis.
The shell consists of two parts -- one bigger than the other. When they divide, both halves become the top (bigger) part of the new cell, with a brand new bottom half forming. This means that with each division, one of the cells actually gets smaller! This results in a population of smaller and smaller diatoms... so how do they get around that?
Well, the ultimate solution to all life's problems: SEX.
They fuck, and make a brand new shell with proper-sized halves. And then the process repeats...
