According to the biological species concept, what should biologists do when two similar organisms that were originally thought to be separate species are found to interbreed freely and produce viable, fertile offspring?

the answer is :

answer; both surfaces of the membrane are nonpermeable

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.