Which structure or structures shown in figure 20-1 have key differences in bacteria and archaea?
a. a and c
b. a and b
c. d only
d. a only

A and B

The label A here represents cell wall and the label B represents cell membrane. Through archaea and bacteria belongs to the same phylum but still there are some differences in their characteristics, such as differences in their cell walls and cell membranes.

The cell wall of archaea is made up of pseudo-peptidoglycan layer, while the cell wall of bacteria is made of the peptidoglycan .

The cell membrane of bacteria is made of lipid membrane with ester bond with fatty acid, while the cell membrane of archaea have ether bonds with the branching of the aliphatic acids.

i'm thinking 600 feet deep in one of the finger lakes.