Why are there no gram-positive archaea species, but there are gram-positive
bacteria species?

There are no gram positive archaea because archaea lack peptidoglycan in their cell walls, meaning that the archaeic cell walls are more similar to gram negative bacterial walls, although they do show a greater variety of cell wall types.

EXPLANATION

Bacteria can be divided into gram-positive bacteria and gram-negative bacteria because of their cell wall composition.   The cell wall of gram-positive bacteria is made up of peptidoglycan which retains crystal violet stain and appears purple in color under microscope. The cell wall of gram-negative bacteria has an outer layer of lipopolysaccharide which do not retain crystal violet color and appear pink.   The cell wall of archaea is not made up of peptidoglycan but is made up of pseudo-peptidoglycan, therefore, no gram-positive archaea species is present on the earth.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.

examples of nucleic acids are deoxyribonucleic acid (dna) and ribonucleic acid (rna).