Ovum facts for kids
An ovum (Latin: "egg", plural: ova) is the name for the haploid female reproductive cell, or gamete. Both animals and land plants (embryophytes) produce ova.
Mammals
Humans
Ova are made and released by a female's ovaries. At birth, a female has all of her eggs, and from puberty, she releases an egg once a month until none are left. This is called oogenesis.
When the ovum is fertilised by a male's sperm, it becomes a zygote, which develops into a new organism. The ovum is fertilized inside the female body, and the embryo then develops inside the uterus, being fed by the mothers placenta.
The ovum is the largest cell in the human body. You can see it without a microscope. The human ovum is between 100 and 200 µm long. They are nevertheless much smaller than the cleidoic eggs laid externally by reptiles and birds, which is why they need a long period of internal development in the womb.
Other mammals
The sexual cycle is quite different in other mammals, whose females are only receptive during their 'heat', which triggers the release of eggs from the ovary.
Plants
In many plants, ova are made inside archegonia through meiosis. The archegonium has a long 'neck' with the egg cell inside. When the egg is mature, the neck opens and sperm swims in to fertilize the egg.
In flowering plants, the female gametes are made of only eight cells, called the embryo sac, inside the ovule. The cell closest to the opening of the embryo sac becomes the egg cell. When pollinated, sperm swims into the embryo sac and fertilizes the egg. The zygote then develops into an embryo inside the ovule.
Gallery
-
A human ovum
-
Sperm cells trying to fertilize an ovum
-
A sperm cell fusing with an ovum
Related pages
Images for kids
-
Gene expression pattern determined by histochemical GUS assays in Physcomitrella patens. The Polycomb gene FIE is expressed (blue) in unfertilized egg cells of the moss Physcomitrella patens (right) and expression ceases after fertilization in the developing diploid sporophyte (left). In situ GUS staining of two female sex organs (archegonia) of a transgenic plant expressing a translational fusion of FIE-uidA under control of the native FIE promoter
See also
In Spanish: Óvulo para niños
