$$ extbf{Solution:}$$ $$ullet$$ Sporopollenin is present in the outer layer of pollen grains, called exine. $$ullet$$ Sporopollenin is the hard and one of the most resistant organic materials known. $$ullet$$ Significance of sporopollenin: Due to the presence of this sporopollenin, the microscopic pollen grains of the past are obtained as fossils.