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External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. [1] It is contrasted with internal fertilization, in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism.
Many protists reproduce sexually, as do many multicellular plants, animals, and fungi. In the eukaryotic fossil record, sexual reproduction first appeared about 2.0 billion years ago in the Proterozoic Eon, [64] [65] although a later date, 1.2 billion years ago, has also been presented.
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual. In asexual reproduction, an organism can reproduce without the involvement of another organism.
An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems.Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment.
The omasum's main function is to absorb water and nutrients from the digestible feed. The abomasum has a similar function to the human stomach. [14] Cattle regurgitate and re-chew their food in the process of chewing the cud, like most ruminants. While feeding, cows swallow their food without chewing; it goes into the rumen for storage.
A form of asexual reproduction related to parthenogenesis is gynogenesis. Here, offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg merely be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring.
Manatees (/ ˈ m æ n ə t iː z /, family Trichechidae, genus Trichechus) are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows.There are three accepted living species of Trichechidae, representing three of the four living species in the order Sirenia: the Amazonian manatee (Trichechus inunguis), the West Indian manatee (Trichechus manatus), and the West ...
The recently extinct Steller's sea cow was the largest known sirenian to have lived, reaching lengths of 10 metres (33 feet) and weights of 5 to 10 tonnes (5.5 to 11.0 short tons). [2] Sirenians have a large, fusiform body which reduces drag through the water and heavy bones that act as ballast to counteract the buoyancy of their blubber. They ...