10) The fertiliensation in frogs as called external-
fertilisation.
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Answer:
Typically, frogs lay eggs. This process usually occurs through external fertilization, where the female releases her eggs from her body into water. Then, the male releases his sperm to fertilize them.
Typically, frogs lay eggs. This process usually occurs through external fertilization, where the female releases her eggs from her body into water. Then, the male releases his sperm to fertilize them. However, a few species of frog use internal fertilization.
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External fertilization.
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.[2] External fertilization typically occurs in water or a moist area to facilitate the movement of sperm to the egg.[3] The release of eggs and sperm into the water is known as spawning.[4] In motile species, spawning females often travel to a suitable location to release their eggs. However, sessile species are less able to move to spawning locations and must release gametes locally.[4] Among vertebrates, external fertilization is most common in amphibians and fish.[5] Invertebrates utilizing external fertilization are mostly benthic, sessile, or both, including animals such as coral, sea anemones, and tube-dwelling polychaetes.[3] Benthic marine plants also use external fertilization to reproduce.[3] Environmental factors and timing are key challenges to the success of external fertilization. While in the water, the male and female must both release gametes at similar times in order to fertilize the egg.[3] Gametes spawned into the water may also be washed away, eaten, or damaged by external factors.
Sexual selection .
Sexual selection may not seem to occur during external fertilization, but there are ways it actually can. The two types of external fertilizers are nest builders and broadcast spawners. For female nest builders, the main choice is the location of where to lay her eggs. A female can choose a nest close to the male she wants to fertilize her eggs, but there is no guarantee that the preferred male will fertilize any of the eggs. Broadcast spawners have a very weak selection, due to the randomness of releasing gametes.[4] To look into the effect of female choice on external fertilization, an in vitro sperm competition experiment was performed. The results concluded that there was a decreased importance of sperm number, but increased the importance of the sperm velocity, thus changing the outcome of sperm competition. The ovarian fluid also increased the paternity for the preferred male because they release fewer and faster sperm.[1] The success of a male fertilizing an egg relies on the ability of a male's sperm to outcompete other sperm that is looking to fertilize the same egg. Sperm chemotaxis is the use of chemical signals to give sperm the ability to navigate an egg and is a huge contributor to reproductive success.[6]
Invertebrates .
Benthic sessile animals that make up the majority of invertebrates using external fertilization rely on ambient water motion to bring the sperm and eggs together. Other invertebrates that externally fertilize are organisms like the sea urchin, are confined to shallow burrows on exposed shores. Turbulent flows in the surf zone also create a transport of gametes.[3] Hydrodynamic conditions and gamete properties control the efficiency of fertilization because they influence the rate at which the water mixes.[7] The only dilemma with turbulence is the possibility of dilution of sperm and egg because of over mixing. Rapid mixing can cause a lower probability to fertilize.[3] Sessile adult staged animals commonly produce gametes at the same times, also known as a synchronized release of gametes, for external fertilization in the water column. This is helpful because of the lack of mobility these organisms share.[8] They also can rely on turbulent mixing and sperm mobility to enhance the chances of fertilization.[3]