Information AboutOvum |
| CATEGORIES ABOUT OVUM | |
| reproductive system | |
| germ cells | |
| gynecology | |
| cloning | |
| female reproductive system | |
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An ovum (plural '''ova''') is a Haploid Female reproductive cell or Gamete . The word is derived from Latin , meaning Egg or Egg Cell . Both Animal s and Embryophyte s have ova. The term '''ovule''' is used for the young ovum of an animal, as well as the plant structure that carries the female Gametophyte and egg cell and develops into a seed after fertilization. In some Plant s, such as Algae , it is also called '''oosphere'''. MATERIAL CONTRIBUTION TO OFFSPRING The egg is the sole provider of such Endosymbiotic Organelle s, including mitochondria and chloroplasts within the cytoplasm. These cannot be produced with nuclear DNA alone and must be manufactured from DNA within existing organelles of their type (such as Mitochondrial DNA ) — this is important in Human Mitochondrial Genetics and can be used to trace maternal and paternal Ancestry , especially as plants contain chloroplasts as well. Sperm are often too small to contribute anything physical except DNA and its own mitochondria gets destroyed by the egg. OVA PRODUCTION In higher animals, ova are produced by female Gonad s (sexual glands) called Ovaries and all of them are present at birth in Mammal s, and mature via Oogenesis . Human and mammal ova In the Viviparous animals (which include Human s and all other Placental Mammal s), the ovum is fertilized inside the female body, and the Embryo then develops inside the Uterus , receiving nutrition directly from the mother. The ovum is the largest Cell in the human body, typically visible to the naked eye without the aid of a Microscope or other magnification device. The human ovum measures on average, 145 µm in diameter. Protist and plant ova In Protist s, Fungi and many plants, such as Bryophyte s, Fern s, and Gymnosperm s, ova are produced inside Archegonia . Since the archegonium is a Haploid structure, egg cells are produced via Mitosis . The typical bryophyte archegonium consists of a long neck with a wider base containing the egg cell. Upon maturation, the neck opens to allow sperm cells to swim into the archegonium and fertilize the egg. The resulting zygote then gives rise to an embryo, which will grow out of the archegonium as a Sporeling (young Sporophyte ). In the Flowering Plant s, the female Gametophyte , which usually gives rise to the archegonium, has been reduced to just eight cells referred to as the Embryo Sac inside the Ovule . The gametophyte cell closest to the Micropyle opening of the embryo sac develops into the egg cell. Upon Pollination , a pollen tube delivers Sperm into the embryo sac 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 . OVA DEVELOPMENT IN OVIPAROUS ANIMALS In the Oviparous animals (all Bird s, most Fish es, Amphibia ns and Reptile s) the ova develop protective layers and pass through the Oviduct to the outside of the body. They are Fertilized by male Sperm either inside the female body (as in birds), or outside (as in many fishes). After fertilization, an Embryo develops, nourished by nutrients contained in the egg. It then hatches from the egg, outside the mother's body. See Egg (biology) for a discussion of eggs of oviparous animals. The egg cell's Cytoplasm and Mitochondria (and Chloroplast s in plants) are the sole means of the egg being able to reproduce by Mitosis and eventually form a Blastocyst after fertilization. OVOVIVIPARITY There is an intermediate form, the s use this technique. SEE ALSO
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