Joe Student is looking through a microscope at a sample of planktonic life filtered from the Gulf of Mexico. He discovers a single-celled organism with no pigmentation, but with a glassy-looking and porous shell or skeleton. Through the pores, tiny extensions of cytoplasm extend out in all directions, stiffened by thin rods. Joe is correct in thinking he is observing a member of the .

4

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.