¿Por qué se dice que la célula es la unidad funcional de todos los seres vivos?

answer; ///i believe that the correct answer is (a) specialized cells)

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs

for a different answer set the answer would be because the oxygen in the water had depleted (apex)