Many Japanese people consume a diet rich in seaweed, including the edible red alga Porphyra, which is used for preparing sushi. Although humans cannot digest the seaweed polysaccharides (porphyran and agarose), certain marine Bacteroidetes do possess the necessary CAZymes. Curiously, Japanese individuals frequently harbor seaweed-digesting Bacteroides plebeius in their gut microbiomes, while individuals from North America do not. Bacteroides plebeius is not a marine bacterium, and its close relatives cannot digest seaweed. What is the mostly likely explanation for how B. plebeius acquired functional porphyranase and agarase genes?

Bacteroides plebeius which is present in the gut humans have the same genes to marine bacterium Zobellia galactanivorans.

Explanation:

many researchers findout that bacteroides plebeius acquired functional porphyranase and agarase genes from a marine bacterium called Zobellia galactanivorans. Zobellia galactanivorans is a marine bacterium which has the ability to digest complex polysaccharides such as agarose and porphyran. so due to similar genes, Bacteroides plebeius also digest polysaccharides such as agarose and porphyran present in sea weed.

d. organisms have cells with different shapes and functions.

i would think a oil tanker that has leaked in a bay