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The smaller, usually motile male reproductive cell of most organisms that reproduce sexually. Sperm cells are haploid (they have half the number of chromosomes as the other cells in the organism's body). Sperm often have at least one flagellum. During fertilization, the nucleus of a sperm fuses with the nucleus of the much larger egg cell (the female reproductive cell) to form a new organism. In male animals, sperm are normally produced by the testes in extremely large numbers in order to increase the chances of fertilizing an egg. Motile sperm cells produced by some multicellular protist groups (such as the algae), the bryophyte plants, and the seedless vascular plants, require water to swim to the egg cell. In gymnosperms and angiosperms, sperm do not need water for mobility but are carried to the female reproductive organs in the pollen grain. In the cycads and the gingko (both gymnosperms), the sperm are motile and propel themselves down the pollen tube to reach the egg cell. In the conifers and angiosperms, the sperm are not themselves motile but are conveyed to the ovule by the growing pollen tube.