You Are Looking at a Sample from the Top Green

Multiple Choice

You are looking at a sample from the top green layer of a colorful bacterial mat. Using phase contrast and fluorescence microscopy, you see evenly spaced cells in the middle of a filament that are slightly smaller than the others. The smaller cells are not fluorescent, indicating they lack photosystem II, but the rest of the filament is fluorescent. What is the most likely function of the smaller cells in the filament?

A) survival in the dark
B) nitrogen fixation
C) sulfur storage
D) nitrate storage