Egg cell

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"Ovum" redirects here. It is not to be confused with Ovule.
egg cell
A human ovum with corona radiata surrounding it
Anatomical terminology

The egg cell, or ovum, is the female reproductive cell (gamete) in oogamous organisms. The egg cell is typically not capable of active movement, and it is much larger (visible to the naked eye) than the motile sperm cells. When egg and sperm fuse, a diploid cell (the zygote) is formed, which rapidly grows into a new organism.


In animals, egg cells are also known as ova (singular ovum, from the Latin word ovum meaning egg or egg cell). The term ovule is used for the young ovum of an animal. In vertebrates, ova are produced by female gonads (sexual glands) called ovaries and all of them are present at birth in mammals and mature via oogenesis.

Human and mammal ova[edit]

Diagram of a human egg cell
Ovum and sperm fusing together
The process of fertilizing an ovum (Top to bottom)

In all mammals the ovum is fertilized inside the female body.







Ova development in oviparous animals[edit]







In flowering plants, the female gametophyte (sometimes referred to as the embryo sac) has been reduced to just eight cells inside the ovule. The gametophyte cell closest to the micropyle opening of the ovule develops into the egg cell. Upon pollination, a pollen tube delivers sperm into the gametophyte and one sperm nucleus fuses with the egg nucleus. The resulting zygote develops into an embryo inside the ovule. The ovule in turn develops into a seed and in many cases the plant ovary develops into a fruit to facilitate the dispersal of the seeds. Upon germination, the embryo grows into a seedling.[4]



Other organisms[edit]

In algae, the egg cell is often called oosphere.[citation needed] Drosophila oocytes develop in individual egg chambers that are supported by nurse cells and surrounded by somatic follicle cells. The nurse cells are large polyploid cells that synthesize and transfer RNA, proteins and organelles to the oocytes. This transfer is followed by the programmed cell death (apoptosis) of the nurse cells. During the course of oogenesis, 15 nurse cells die for every oocyte that is produced.[6] In addition to this developmentally regulated cell death, egg cells may also undergo apoptosis in response to starvation and other insults.[6]


While the non-mammalian animal egg was obvious, the doctrine ex ova omne vivum ("every living [animal comes from] an egg"), associated with William Harvey (1578-1657), was a rejection of spontaneous generation and preformationism as well as a bold assumption that mammals also reproduced via eggs. Karl Ernst von Baer discovered the mammalian ovum in 1827, and Edgar Allen discovered the human ovum in 1928. The fusion of spermatozoa with ova (of a starfish) was observed by Oskar Hertwig in 1876.[7][8]

See also[edit]


  4. ^ a b Esau, K. (1977). Anatomy of seed plants (second ed.). New York: John Wiley and Sons. ISBN 978-0-471-24520-9. 
  5. ^ Mosquna, Assaf; Katz, Aviva; Decker, Eva L.; Rensing, Stefan A.; Reski, Ralf; Ohad, Nir (2009). "Regulation of stem cell maintenance by the Polycomb protein FIE has been conserved during land plant evolution". Development. 136: 2433–2444. doi:10.1242/10.1242/dev.035048. 
  6. ^ a b McCall K (October 2004). "Eggs over easy: cell death in the Drosophila ovary". Dev. Biol. 274 (1): 3–14. doi:10.1016/j.ydbio.2004.07.017. PMID 15355784. 
  7. ^ Needham, Joseph (1959). A History of Embryology (2d revised ed.). Cambridge: Cambridge University Press. 
  8. ^ Lopata, Alex (April 2009). "History of the Egg in Embryology". Journal of Mammalian Ova Research. 26 (1): 2–9. doi:10.1274/jmor.26.2. 

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