Why should the exine be hard?

The exine is hard to protect pollen grains from drying, heat, UV light, and enzymes so they can safely reach the stigma. The exine is the tough outer wall of a pollen grain. It contains a very resistant material called sporopollenin. This makes the exine extremely hard and durable. Because pollen must travel through air, insects, or water, a hard exine shields the male gametophyte (the pollen’s living part) until it lands on a compatible stigma for fertilization.

Main reasons the exine is hard

• Prevents desiccation: reduces water loss so the pollen does not dry out.
• Blocks UV and heat damage: sporopollenin absorbs/deflects harmful radiation and heat.
• Resists enzymes and microbes: avoids being digested or spoiled during travel.
• Mechanical strength: protects against physical shocks during transport by wind, insects, or animals.
• Longevity and fossil record: hard exine makes pollen durable; that is why pollen grains are found as fossils.

Structure and functions (at a glance)