Seed plants display several evolutionary advances over non-seed plants. 1) In seed plants, the gametophyte is much reduced. The gametophytes are not free-living but are retained within the reproductive tissues of the sporophyte. 2) Pollination replaces the sperm cell swimming to the egg. Drought-resistant pollen is carried to the female tissues by wind or animals. 3) The zygote is protected in a seed. The seed is the mature ovule which has food for the developing zygote and a protective seed coat. The seed can be dispersed, unlike the zygote of non-seed plants.