Practice question

Land plant spores possess complex wall stratification including innermost intine cellulosic, middle exine rich in chemically inert sporopollenin highly resistant polymer derived from lipid metabolism, and outer perispore. Primary adaptive value involves preventing desiccation during prolonged airborne dispersal across dry air, fluctuating humidity and high temperatures, maintaining protoplast viability until germination on moist substrate. While sporopollenin confers resistance against pathogens, chemical degradation and UV, desiccation resistance drives major selection. Herbivory and mechanical damage affect larger vegetative organs, but microscopic spores chiefly face abiotic drying stress during colonization.