melphalan, a bifunctional alkylating agent frequently employed in chemotherapy, induces DNA lesions during meiosis that may persist in an unrepaired state as germ cells progress through DNA repair-competent phases of spermatogenic development. Such unrepaired DNA damages in spermatozoa, after fertilization, can lead to offspring with various abnormalities. Sea urchins such as Arbacia punctulata are ideal organisms to use in sperm research, they spawn large numbers of sperm into the sea, making them well-suited as model organisms for experiments. The spermatozoa of marsupials are usually longer than those of placental mammals. Plants, algae and fungi The gametophytes of bryophytes, ferns and some gymnosperms produce motile sperm cells, contrary to pollen grains employed in most gymnosperms and all angiosperms. This renders sexual reproduction in the absence of water impossible, since water is a necessary medium for sperm and egg to meet. Algae and lower plant sperm cells are often multi-flagellated (see image) and thus morphologically different from animal spermatozoa. Some algae and fungi produce non-motile sperm cells, called spermatia. In higher plants and some algae and fungi, fertilization involves the migration of the sperm nucleus through a fertilization tube (e.g. pollen tube in higher plants) to reach the egg cell. Spermatozoa production in mammals Spermatozoa are produced in the seminiferous tubules of the testes in a process called spermatogenesis. Round cells called spermatogonia divide and differentiate eventually to become spermatozoa. During copulation the cloaca or vagina gets inseminated, and then the spermatozoa move through chemotaxis to the ovum inside a Fallopian tube. In assisted reproductive technology, normozoospermia is referred to a total amount of >39 mill ejaculated, >32% with progressive motility and >4% normal morphology. Also, a normal ejaculation in humans must have a volume over 1.5 ml, being an excessive volume 6 ml per ejaculation (hyperspermia). An insufficient volume is called hypospermia. These problems are related to several complications in spermatozoa production, for example: Hyperspermia: usually provoked because of prostate inflammation. Hypospermia: an incomplete ejaculation, usually referred to an androgen deficit (hypoandrogenism) or obstruction in some part of the ejaculatory duct. In laboratory conditions, is also due to a partial loss of the sample. Aspermia: there is no ejaculation. It could happen due to retrograde ejaculation, anatomical or neurological diseases or anti-hypertensive drugs. Spermatozoa activation Approaching the egg cell is a rather complex, multistep process of chemotaxis guided by different chemical substances/stimuli on individual levels of phylogeny. One of the most