Sperm cell in the context of "Bacterial flagella"

An embryo (/ˈɛmbrioʊ/ EM-bree-oh) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres are arranged as a solid ball that when reaching a certain size, called a morula, takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals.

The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis. Gastrulation is the formation of the three germ layers that will form all of the different parts of the body. Neurulation forms the nervous system, and organogenesis is the development of all the various tissues and organs of the body.

Anisogamy is a form of sexual reproduction that involves the union or fusion of two gametes that differ in size and/or form. The smaller gamete is male, a microgamete or sperm cell, whereas the larger gamete is female, a larger macrogamete or typically an egg cell. Anisogamy is predominant among multicellular organisms. In both plants and animals, gamete size difference is the fundamental difference between females and males.

Anisogamy most likely evolved from isogamy. Since the biological definition of male and female is based on gamete size, the evolution of anisogamy is viewed as the evolutionary origin of male and female sexes. Anisogamy is an outcome ofboth natural selection and sexual selection, and led the sexes to evolve different primary and secondary sex characteristics including sex differences in behavior.

The cilium (pl.: cilia; from Latin cilium 'eyelash'; in Medieval Latin and in anatomy, cilium) is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body. Eukaryotic flagella found on sperm cells and many protozoans have a similar structure to motile cilia that enables swimming through liquids; they are longer than cilia and have a different undulating motion.

The cilium (pl.: cilia; from Latin cilium 'eyelash'; in Medieval Latin and in anatomy, cilium) is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike projection that extends from the surface of the much larger cell body. Eukaryotic flagella found on sperm cells and many protozoans have a similar structure to motile cilia that enables swimming through liquids, but they are longer than cilia and have a different undulating motion.