A pollen grain is a tiny structure produced by seed plants, including flowering plants and conifers. It contains the male gametes necessary for fertilization. Pollen grains are typically carried by wind, water, or animals to reach the female reproductive parts of flowers, where fertilization can occur. Each pollen grain has a protective outer layer called the exine, which helps it survive harsh environmental conditions. The size, shape, and surface texture of pollen grains can vary widely among different plant species, making them useful for palynology, the study of pollen, in understanding plant evolution and ecology.