Multiple choice Which of the following is the hardest plant product? Lignin Cutin Suberin Sporopollenin - Reveal answer Fill a bubble to check yourself D Correct answer Explanation Sporopollenin is one of the most chemically inert biological polymers. It is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well preserved in soil.